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i have a 1998 dodge ram 1500 4x4 that is bucking when i put

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my foot into the gas...
i have a 1998 dodge ram 1500 4x4 that is bucking when i put my foot into the gas. it originally started as backfiring but after all the parts changed, it is now just bucking only when im driving over 2000 rpm. it does not start doing it until the engine gets to operating temp. if im parked, it will run fine and i can give it gas and it does not seem to have any problems. before the problem started it was really easy to start it too, but now i have to turn the key on and off a couple times then crank it for like 10 seconds then it will finally start rough but eventually even out to a smooth idle. i have already changed out the plugs, wires, distributor cap, rotor button, pick up coil, fuel injectors, map sensor, throttle position sensor, engine temp sensor, and catalytic converter and none of that has seemed to help it at all. i also made sure that the plug wires were properly installed as per the service bulletin for dodge trucks. i was thinking about changing the idle air control valve next but before i do that, what do you think i should do?
Submitted: 7 years ago.Category: Dodge
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2/24/2010
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
Dodgerench
Dodgerench, ASE Certified Technician
Category: Dodge
Satisfied Customers: 3,409
Experience: 30+ years Dodge/Chrysler exp., ASE Master with L1 certification. Driveability/ combustion specialist
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HiCustomer welcome to Just Answer!.

Replacing the IAC motor wouldn't have any effect on your problem. What the idle motor does is meter airflow to control your lift-throttle engine speed, which isn't anything close to what you're fighting right now. The two things I'm most concerned with at this point would be with harness wiring (for shorting) and your distributor index position.

Problems that happen only during events such as acceleration can sometimes be traced to the reaction that the powertrain has when asked to provide power. It's going to twist to the passenger side of the vehicle, carrying pretty much everything attached to it with it. Some things like wiring harnesses are connected to the body at certain points and can't move fully with the engine... so there may be abrasion or rubbing going on.

I'd be interested to know if the wiring in the driver's side-rear-top of the engine is in good shape. The place I'm describing is just to the (vehicle) left of the distributor and between the intake manifold and inner valve cover area where the upturned edges of the valve cover tend to have a sawing effect on the harness.

The wiring in this area is heavy with important stuff like MAP, TPS and the 5v feed that supplies both. You also have the cam and crank sensor wiring coming up from below in the same general area, things that can surely cause you some running problems if shorted to ground.

After that, I'd have to wonder when the last time the distributor was indexed. With ignition reference no longer being produced within the distributor, the positioning of the distributor has a great deal of importance concerning cross-fire and cam-crank sync. A window of 10 degrees (advanced or retarded) checks OK with the PCM but if you're right on the edge of being out of bounds... you might be having either crossfiring or un-sync events under acceleration.

Distributor index is something that's set accurately by the factory when the engine is new but time and miles of use will tend to let that adjustment slip a bit. If it's over 100K miles and hasn't been reset yet (or the distributor has been turned without using a sync procedure), it may be time to do the adjustment if for no reason other than simple maintenance.

It can be done either manually or with the use of a compatible scan tool... something like the factory DRB3. The scan tool method is easier, faster and a bit more accurate, but requires a trip to the dealer. The manual method is completely acceptable but will take up to an hour of your time to complete. I'll be happy to describe the process if you'd like to give it a go. It requires a digital voltmeter, a tool to loosen the distributor base (for turning) and hand tools to manually rotate the engine.

Check out your wiring first, using some "wiggle testing" in the area I described (and anyplace else you care to check) and then we'll move on to the distributor index procedure if you'd like to pursue it.

Good luck!
Ed
Dodgerench
Dodgerench, ASE Certified Technician
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Customer reply replied 7 years ago
earlier this evening i had the throttle body taken off and i cleaned it and put it all back in and fired it up. it still had the long cranking issue and rough idle at the beginning like i said before but it smoothed out. all of this started right after a hard snow here. one night it was running fine and then the next morning it was doing this and has been like this for about three weeks now. one other thing is after i have driven it around a little bit, when i give it a little gas at idle, it starts to act like it is going to die but doesnt. does all this sound like the indexing thing you mentioned before?
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
That's interesting!
Do you ever see a CHECK ENGINE lamp illumination while driving?
Did you put fuel in the truck the night before the snow by chance?

Ed
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Customer reply replied 7 years ago
i dont get a check engine light at all, but the fuel thing, yea i did the night before. i have taken it to advance auto and used there scan tool and it reads a code for multiple cylinder misfires even after all the parts ive changed out. that tank of gas has since ran out and i have put in 93 octane the last time i filled it up like two days ago.
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
It's just a hunch, but I'd sure take a fuel sample at this point. Problems that happen that close to a fuel stop are often something associated with wrong fuel (diesel, ethanol) or water.

To get a fuel sample, I go to the injector rail. Your 98 should have a metal rail with a test port on the driver's side with a black plastic cap.

Do this on a cold engine if at all possible to reduce fuel spray and fire hazard. Have an extinguisher on hand at all times and a helper would be a good idea.

Remove the cap from the rail and then remove the pintle with a tire valve stem core removed (same-same). With the pintle removed, there will be nothing holding fuel pressure back at that point. Press a 3/8" section of fuel line onto the test port threads and direct the hose into a clean water bottle (or something similar). Have someone crank the engine as you monitor bottle filling, stopping after about half full... which should be enough.

If the fuel sample appears cloudy, let it sit for a few minutes. It's probably water, which will separate out to give you a better idea what's going on.

If the fuel sample is clear, dip a finger into the fuel and blow on it until it evaporates. If it doesn't evaporate after a full minute... and feels oily... it's probably diesel, which sometimes gets put in the wrong holding tank. When mixed with gasoline, it will burn fairly well until the engine cools off and then you'll have problems.

If the fuel sample evaporates completely and is clear, add about 25% more straight water to the bottle. If it disappears completely, it's being held in suspension by ethanol, another OOPS by the gas station operator. Not likely, but needs to be checked.

I'm mostly concerned with water at this point because I don't really anticipate bucking to be involved with diesel or ethanol issues... but it always pays to keep your eyes open as it does with wiring damage by critter chews in the wee hours of the night. Take a look around for signs of rodent damage (chewed hood pad, nesting, destroyed wiring... you know) and we'll go from there.

Ed
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Customer reply replied 7 years ago
well ill check the water in the fuel thing tomorrow once i get off work and have some time to look into it. as far as the critter chew thing, i have looked all over the truck since this started and i have not seen anything like that.
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
Sounds good, talk to you later.
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Customer reply replied 7 years ago
ok i checked the wire harness again and checked the fuel for water and there were no problems with either one. if im not getting the right pressure from the fuel pump, would a drop in pressure just happen like that over night to cause this sort of thing or no? next thing.......could the crank sensor be a possibility here?
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
Yep.
Low pressure or loss of pressure at rest can cause early startup problems like long crank time and idle roughness for a short period until vapor is pushed through the injectors. It's not normally a huge issue with cold engine start as much as hot restarts because the vapor "bubble" that forms in the fuel rail on a hot engine when pressure drops after key off will resist the efforts of the pump to resupply the rail.

Fuel works just like water when it comes to pressure... the more pressure, the higher the boiling point. Your fuel system operates at a 50 psi level, enough to keep fuel from boiling at almost any normal condition. But if the fuel pump module can't retain pressure at key-off, it will allow boiling as pressure drops off, producing a vapor bubble that pushes liquid fuel back in the supply lines all the way to the tank.

Refilling those lines will take some time, but is usually easier on a cold engine because the vapor bubble has collapsed and a small vacuum has replaced it. If at all possible, I'd like you to test the fuel system for its ability to retain pressure but that involves the use of a high pressure fuel system tester... something not everybody has lying around the garage.

No matter. If you have a big-chain auto parts store nearby (like Autozone), they offer free or low cost rental of fuel system pressure testers. Good stuff.

When connected and the engine is shut off, expect some loss of pressure... it just plain happens. But the rate of decay is important.

My preference is that it loses no more than 10 psi in the first 10 minutes and then settles down to a very slow loss at that point. Early loss allows violent boiling and fuel push-back, but if it happens gradually... we're OK.

By the following morning, most systems have lost all pressure but that's OK because the lines will still be populated with liquid gasoline... not vapor. Given a little extra time, the loss of engine heat will affect fuel boiling less and less, eventually becoming a non-event.

This scenario might explain the cold start problems, but not everything. It's always tempting to think that one problem is at play on something like what you've got, but you've gotta keep your eyes open and eliminate things as they come at you.

Hey... I'm really glad you don't have water problems for one thing! It's a nasty process getting rid of the stuff, so we're already in better shape. Thanks for your help in this.

Ed
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Customer reply replied 7 years ago

ok with the fuel system pressure thing, i have to leave it on the fuel rail overnight? is that right? if there is supposed to be pressure in the fuel lines still all the time, when i took the plastic cap off the fuel rail and pushed in the valve stem, should there have been some fuel spray out a little cause that did not happen. i had not started the truck since last night too if that affects the pressure thing.

Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
The test can be done overnight and is helpful if you can watch pressure build as you crank the engine. If it fires only after you've mostly restored the 50 psi cap on the system... it tells me that you've got pressure retention issues.

But it's just as useful for the early decay portion I described. ALL of our pumps have small amounts of decay over the course of 12 hours, so don't imagine that your fuel system will still have full pressure on tap as you roll out of the house in the morning. Doesn't happen.

But, YES.... having the pressure tester installed overnight would be a valuable tool, especially if you have a good view of the gauge as you attempt engine start. Seeing no pressure for the whole time until it fires definitely means you've got fuel supply issues if nothing else.

Ed
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Customer reply replied 7 years ago
well i can definitley tell that there is fuel there when i try to crank it cause after a few seconds, you can really smell the odor of gas in the engine. after a few more seconds, it fires off slowly then gradually builds to a steady idle. before all this started i could crank it and it would start right up. but after changing the distributor cap, rotor and pickup coil, it takes it a little bit to start but eventually does. that sounds more like it being mis-indexed right?
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
Ooooooooo... not necessarily.
If you aren't using accelerator pedal input, try using that next time.

A slow engine start with a slow engine ramp-up is often the result of a delayed IAC motor input, which can simply be caused by lost IAC position. While I told you at the start that the IAC wouldn't solve your surging problem... it may well have a bearing on your delayed start issue.

Try this for me for tomorrow morning.

Disconnect the battery and let it sit for about 30 seconds.
Reconnect and then just roll the key to the ON position without trying to start the engine.

This gives the PCM time to relearn IAC motor position without the complication of having to support combustion, so it will be done properly. Many cold start (or idle problems in general) are based in IAC motor step count retention, something that the PCM has to know in order to conduct business.

Low battery voltage during engine start can cause loss if IAC step count. Since the IAC motor is operated electrically, lower than normal voltage can make it sluggish and may cause it to miss commands altogether. When lost, those steps cannot be made back up.

Over time, your PCM will become more and more confused as to actual position of the IAC motor. Without an accurate count, it always assumes more airflow is present than actual... so idle or engine start problems are quite likely. The reset procedure will be effective in bringing the actual count back, which is what the PCM needs.

It won't affect driveability issues above an idle, but it's an important step in the diagnostic process. Fix one thing... move on.

If you feel that your battery is weak... it's time to replace the thing. Low voltage is just not a good thing on these units. If you see less than 10v with the starter engaged, it's marginal. If below 9.5v... it's a gonner.

Ed
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Customer reply replied 7 years ago
well even if i use accelerator input, it still takes a few seconds for it to start up. i can go do that right now and see how it goes. if that works for that part, then we can move on from there. ill let you know what happens in a few minutes
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
Sounds good!
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Customer reply replied 7 years ago
ok i did that and it fired right up without a problem. once it started to get to normal operating temp, if i put my foot into the gas really quick, it seemed like it wanted to die out for a second, but then came right back up to normal idle again.
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
A big improvement in crank time when actively pressing the throttle makes me believe you may be suffering from a lack of air when starting in a lift-throttle mode. Either that or you have a slight flooding issue going on after the engine shuts off due to a leaky injector.

It gets complicated sometimes.

The sag as you stab the throttle is almost certainly a mixture problem, but the cause isn't obvious right now.

It wouldn't be a distributor index problem although a fuel pressure issue is still possible... although unlikely. Our fuel systems seldom provide something between zero and the correct value... it's usually right or it doesn't run at all. But that's where a fuel system pressure test would put this to bed or not.

If you're about done for the night, do the battery disconnect-relearn procedure I mentioned earlier for tomorrow morning's cold start. If it makes a substantial difference, we may have an idea what to do for the long crank time issue.

I kinda hate to tell you to do that because it's going to erase your PCM memory, which includes any trouble codes stored as well as the fuel system adaptive values which may be involved in your other running problems. But without a capable scan tool, there simply isn't a way to access this data anyway, so if you would like to try it... go right ahead.

Pay close attention to how it runs tomorrow for the first ten minutes of driving, which will be largely without the influence of fuel system adaptive shift that has been stored up to now. As the engine reaches 170 degrees, long-term adaptives will combine with the short term adaptives and any odd shifts will have the capacity to double in size.

So go ahead and do the disconnect-reconnect-key on-wait 5 seconds thing. Drive it like you normally would tomorrow and let me know about any changes. I can go into much greater detail about what's going on but it's late and I know you'd rather sleep tonight lol!

Take great notes and let me know how it works out tomorrow!
Ed
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Customer reply replied 7 years ago
well i have not been driving it to and from work since this problem started. i have been driving my roommates car. and all the trouble codes that were there at one point have been erased when i went to advance and used there scan tool. i erased them after i replaced most of the parts. so i suppose what i can do is do that disconnect thing again and drive it to and from work tomorrow and take it to advance and get the scan codes from there before i come back home. that is if there are any in there. if there are any at that point, ill write them all down and let you know what they are as well as give you the details about how it runs tomorrow.
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
I like it. That's a plan!
Talk at ya tomorrow!

Ed
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Customer reply replied 7 years ago
ok here is what i have so far. i did what you said with the battery disconnect thing and when i tried starting it up, it cranked for a few seconds and then slowly built up to a steady idle. once it was idling, it was running ok. from a stop, once i start out it runs fine until it gets to the point where it will downshift to a steady idle. once at a steady idle no matter if i was driving through town or while i was driving on the highway, if i tried to put my foot on the gas to pick up speed it would buck. if i let the truck slow down to around 30 or 35 and i tried to put my foot on the gas, it would up shift and would be ok while it picked up speed again. once it got to around 55 or 60 and it downshifted again, it would buck if i was going up a hill or put my foot into the gas a little bit. ill go to advance and get the codes, if there are any, this afternoon on my way home. but that is our starting point as of right now.
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago

I don't like the slow ramping up in cold start idle speed. If the IAC was working right, you'd get a high idle immediately after it fired and then it would taper down from there. When the idle starts low and struggles to gain engine speed, it might mean the IAC is simply shot.

 

While you can't observe its actual operation with it installed, you can take some clues from the noise your engine makes as you start it. The air cleaner might have to come off for this.

 

Start the engine and listen to the induction noise made at the throttle body. This is normally pretty loud on a cold start because the IAC will be rolled open to allow a great deal of air to pass... which is needed for cold fast idle.

 

If you notice little to no change in sucking sound from the time the engine first starts... or it becomes louder as it runs a while... the IAC isn't opening the way it should be when it was originally asked to by the PCM. Do a few restarts and listen to the induction noise each time to see if it works the same each time or improves with a little heat and exercise. You should have a loud sucking noise and high idle speed immediately, fading off as the engine runs. I'm beginning to think you were right all along about the IAC... it sounds poopy.

 

Your bucking problem still makes me wonder about distributor index of course. With new plugs, wires, distributor cap, rotor and no obvious signs of harness shorting, it really doesn't leave much to go wrong in a situation where your problem is dependent upon a certain engine speed and load to produce. Erratic crank sensor output would likely afflict the engine in this way, but would be more engine speed dependent than load, since it doesn't know what load is... it just signals crank timing.

 

Ed

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Customer reply replied 7 years ago
ok i went to advance on the way home and checked for codes and there were none. all passed. as i drove home, i tried a couple of other things. if i take off from a stop, i can put my foot into the gas and i can pick up speed pretty quick. once it downshifts, i have to keep my foot at a steady spot. if i put my foot into it a little bit after it downshifts, it starts to buck. if i drop into 2nd and put my foot on the gas, it does not buck at all. it picks up speed and i can put my foot into the gas and it acts ok and then i can shift it back to drive and go from there. but like i said before, if i dont keep my foot steady after it down shifts and i press the gas a little, it will start start to buck. also i noticed that when i am at a stop, i looked closely at my rpm guage and the needle pulsates really slightly and i know it should not do that if it is at a steady idle. so thats what we have right now. what do you think?
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
(Still sorting this out)
By 'bucking', does that mean a very sharp transition between running and NOT running? It almost tosses the vehicle when I think of bucking...

Ed
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Customer reply replied 7 years ago
by bucking, i mean it like jerks the truck back and forth.
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
That's what I thought... the perfect definition of bucking!

That type of activity is sometimes more than simple misfire....it's crossfire or something equivalent to that. A misfire will just register to the driver as a loss of power but a bucking condition pretty much describes something that's trying to reverse vehicle direction.

Let me soak this in a bit and I'll be back shortly...

Thanks!
Ed
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Customer reply replied 7 years ago
ok. no problem. i did buy a new IAC to see if that would have any affect on any of this at all but i have not installed it yet.
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
I have a couple concerns at this point... maybe three.

Bucking from my experience is an ignition type thing, meaning spark finds the wrong path to the plugs. With all new secondary ignition already installed, that would leave only a distributor index as being the cause if it's being caused by cross-fire... as is usually the perp.

Since ignition reference signal now comes from the crank sensor... located in the upper right transmission bellhousing... not the distributor, proper positioning of the distributor housing has dual importance.

It houses the cam sensor, which must be synced to the crank sensor within 10 degrees of crank travel and it positions the distributor cap in relation to the distributor rotor for spark delivery.

Improper positioning can result in an un-sync event at the cam-crank department, as well as having the distributor rotor being in a position to deliver spark to an undeserving cylinder when spark happens. I'd TOTALLY like to do a distributor index procedure at this point... if for no reason other than to fulfill a maintenance requirement that happens from time to time.

This can be done either manually or with the use of a compatible scan tool... something your dealer can do quickly and efficiently. The manual method involves rotating the engine by hand to position it just so and tools to do the rotating, loosen the distributor hold-down and a digital voltmeter to monitor cam sensor voltage. The manual method is a bit time consuming (about an hour) but can yield results comparable to what the dealer can do... and saves you about a Benjamin.

Let me know if this is something you'd like to try.

Ed
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Customer reply replied 7 years ago
ok. well i changed out the IAC and it had no effect on the problems what so ever. while it was running, i reached under and grabbed the throttle and pressed it quickly and it made a loud sucking sound, like it was sucking in a lot of air, and died. as far as the indexing thing goes, yes i want to do that but the issue is that i really dont have the right tools here to be able to do that. i have a digital multimeter and the tools to loosen the distributor hold down, but i dont have a big enough socket for the crankshaft to be able to turn it. do you know how big the crankshaft bolt is so i can get a socket for it by chance?
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
A loud sucking noise with no improvement in engine speed means you have mixture issues. With the IAC rolling out and doing its job, the extra airflow should be matched with fuel... which appears to be an issue.

I've seen this problem often with the upstream oxygen sensor on a cold or warm engine as the sensor isn't able to heat up to operating temperature.

Cold engine operation is strictly open-loop... the mode where the PCM doesn't seek advice from the UP02. As the engine warms, the PCM sees a certain time frame expire and will compare this to engine temperature. When the lines cross, it will begin looking at UP02 signal for mixture advice... which might be very bad.

The JTEC engine controller your 98 truck uses supplies a super-weak 5v bias signal to the 02 sensor signal circuit for self diagnostics. When the sensor fails to heat and produce its own signal on time, the potential to set a code is present... but doesn't always happen.

This 5v bias hangs around on a weak sensor for far too long and will trick the PCM into thinking you have a rich mixture... which means it will take away fuel until it sees this problem fixed. It doesn't always happen.

In the meantime, your adaptives will be pushed heavily negative with fuel delivery at the injectors becoming less and less because the PCM believes what it's told. A weak UP02 will cause horrendous cold-to-warm engine driveability and beyond if it's in really sad shape. These problems should be caught by the OBD2 onboard diagnostics but it seldom happens.

While I can't say for sure that this will cure your bucking problem, enough evidence exists to focus attention on the UP02, which is located in the front of the catalytic converter, right between the two pipes that enter the unit.

Check to see if damage to the sensor or wiring has occurred because it's not uncommon on a forward-facing sensor line this to take a rock hit or something from time to time. Visible damage to the sensor is enough reason for replacement alone.

As for the distributor index thing.... I don't use the crank bolt! It's a PITA to reach the thing and the alternator is just SO much easier to get to.

The alternator uses a 7/8" and 10mm hex at the nut and shaft, either one of which will work to rotate the engine. Turning it clockwise means you'll have to add some pressure to the serpentine belt at the tensioner, but it's still way easier than reaching that freakin crank bolt.

I use a 15mm wrench on the tensioner bolt (at the pulley) and then a motorcycle tie-down to pull the belt taut to apply more pressure to the belt. Then you can turn the engine from the top.

The adjustment procedure will follow shortly if you're game!

Ed
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Customer reply replied 7 years ago
as far as the UP02, if this has gone bad, wouldnt it cause a check engine light? just so you know why i changed out the catalytic converter, about a week after all this started happening, the internal parts of the old cat crumbled and was rattleing around inside and sounded like rocks in a tin can. the upper O2 got changed out last year around may time frame cause i had a check engine light that called out an O2 sensor. after changing it out, the light still did not go out but it was not until october when i was finally able to get the rear one changed out cause it was rusted in place on the exhaust pipe and had to be cut out. after changing that out, the light went out. now after that long of a time frame between changing the upper and rear, would it be possible that the upper one went bad cause it was the only one that was working right and just got burned out?
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
Tough call, but with the UP02 being that new... it's not a likely problem. But the on-board diagnostics for (especially) upstream 02 sensors are just plain awful in the late 90s on our trucks. I see engine sag problems described constantly here (and in person) that are caused by weak UP02 sensor heater problems that don't get picked up by the onboard diagnostics.

Pay close attention to the timing of your engine performance problems the next time you drive. If it starts happening after 90 seconds all the way up to five minutes... then improves... it may be an UP02 that's messing with you. These things are really tough to diagnose without scan tool data at the time of the problem, so I can't say for sure just what's going on.

But what you saw with the cat was super-common.... they break up like that all the time. We had an extended warranty on those units but your truck is outside the period unfortunately.

Upstream oxygen sensor and downstream sensors work independently, so failure of one won't affect the other. Not to worry about that one at least!

Ed
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Customer reply replied 7 years ago
now here is the awful thing about when i had to change the cat. it was just changed out by the last owner in january of 2008 and i just had to do it again that fast. this truck was in very bad shape when i first got it last year and a lot of parts had to be replaced over the last year. just sayin. as far as the upper O2 that i put in, it has a one year warranty on it for free replacement if defective so what i can do is take it out tomorrow and get a new one for free and see what happens from there.
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
I'd have to go along with that if the warranty is still good. Aftermarket oxygen sensors work pretty well in this model, so I'd have no problem with using another one for sure!

Ed
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Customer reply replied 7 years ago
ok. ill change it out tomorrow and let you know what happens from there
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
Sounds good. Do another battery disconnect after the repair to clear any erroneous adaptives, with the normal 5-second pause between key-on and engine start.

Good luck!
Ed
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Customer reply replied 7 years ago
would the O2 sensor have anything to do with the truck being able to start? i wouldnt think so. i tried to crank her up this morning and all it would do was crank and every now and then it would fire in a couple cylinders but would not fully start. i'm really beginning to think that it is the distributor indexing that is messed up cause that would go right along with everything. its not getting the spark into the cylinders where it needs to be to fire it up on start and when im driving and step on the gas. please send me the instructions on how to do the indexing cause i want to check that before i move on to something else.
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago

An 02 sensor can cause hard starting problems, but only once it's completely corrupted your fuel system adaptives. You'd have some flooding issues if that was the case and the engine could probably be cleared and started using wide open throttle. Occasional combustion like what you're seeing might even be a weak coil, especially if it's a cold, damp day where you are. You might try checking spark length at the coil and again at the plugs to see if there's a sizable difference between the two.

 

If you happen to see a pound of white dust fall out of any of the plug wire or coil wire boots when disconnected, you can safely assume that the cable is burned out by the way. It's something that happens at the 90-degree boot ends at the coil and distributor cap connections pretty often and will seriously reduce spark available at the plugs.

 

I'm still in agreement about the indexing but won't have time to sit down and type the post out for a little bit (I'm at work). If you're really in a bind, let me know and I'll fake an injury or something.

 

Ed

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Customer reply replied 7 years ago
fake an injury. lol not in that big of a rush. anyway, i changed out the pick up coil, and the plug wires the day you and i started talking, and i checked the spark plugs for firing and everything seemed to be ok. i can check them again and see if by chance it is any different. i guess what i can also do is change out the O2 sensor and clear the computer with the battery disconnect thing and see what happens from there. when you get a chance, please send me the indexing procedure cause i would still like to do it to be sure about what is going on.
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago

Will do.

So you've already put a cam sensor in?

 

Ed

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Customer reply replied 7 years ago
no. should i change that one out? what does that effect? and what about the crank sensor? should i do that one as well as the UP02?
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago

If you replaced the sensor in the distributor... that would be the cam sensor. The crank sensor is a bear to get to on these trucks, living back on the trans bellhousing behind #8 cylinder. Ugh. It might have something to do with your no-start but I'd sure exhaust some other possibilities first.

 

Too bad we can't pull codes...

Ed

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Customer reply replied 7 years ago

Wiki answers says the crankshaft sensor symptoms are no spark and no fuel pulse at the injectors. the vehicle will stall when stopped, stall at highway speed but will start again cause of the speed you are going. sometimes it is hard to start with long cranks and will most likely start after a few tries of trying to start. does that sound right?

 

is the pick up coil what you are refering to as the cam sensor?

Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago

Yeah. We used to call the sensor in the distributor a pickup coil back in the old days of electronic ignition (the 70s and 80s) but the unit your Magnum engine has is actually a Hall switch and is called the cam sensor.

 

This particular fuel/ ignition system requires that you have both a cam and crank sensor available and that they be in sync before you'll get spark or injector pulse, so it's a little bit tougher to sort out without a scan tool.

 

Long crank time is more often a result of lost fuel pressure on this vehicle, but if you combine that with the bucking you had recently... it gets a bit confusing. See if you can locate any spark at the coil or plugs if you get a chance.

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Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
Morning! Shall we get started?

Since the engine isn't in running condition right now, let's check the cam sensor for proper operation before we break the distributor loose. You can't sync an engine with a poopy cam sensor.

Backprobe the tan/ yellow wire on your distributor cam sensor pigtail (with the meter set to 20v DC and the black test lead connected to battery negative) by inserting a paper clip (or your red test lead if long enough) until it makes contact with the circuit. Voltage seen will vary between something like 5v and almost zero volts... actually just a few hundredths of a volt. It depends which end of the engine cycle you're coming up on for which voltage you'll see.

Then bump the engine around a little with the starter while watching your meter for voltage state change. Expect good transitions between 0v and 5v with those actual voltages being pretty close to .1v and 5.1v. If good, leave the meter attached and we'll get started on engine positioning.

Locate the scribe marks on your crankshaft balancer that will be used for engine positioning. You'll find heavy cuts that indicate TDC for all 8 cylinders every 90 degrees, but those aren't the ones we'll be using. We need the V8 mark, which is cut pretty close to one of those heavy marks... about 10 degrees to the left... and might be hard to see thanks to the "scalpel" the factory used to make it. Another mark that will look similar (V6) is also on the balancer, so be careful to avoid using that one.

I mentioned using the alternator earlier for crankshaft turning. That works only if you apply extra tension to the serpentine belt tensioner pulley by putting a 15mm wrench on the pulley bolt and pushing it to the passenger side of the compartment. Since it will just spring back, I use a motorcycle tie strap (one of those friction buckle things) to pull the wrench and hold it, leaving both hands free for battle with the engine. You have a choice of using the 10mm hex on the alternator shaft itself or the 7/8" nut that holds the pulley on. Either one will work fine.

Rotate the engine until you align the V8 mark with the stationary TDC mark on the timing cover, which will be at about the 2 o'clock position as you stand in front of the truck. If you happen to go past the TDC mark or just want to try again, back the crankshaft up at least 20 degrees and do it again. This keeps all slack from engine timing mechanisms on the trailing sides of the gears and such, just as if the engine was running.

Now positioned, get the digital voltmeter turned on again, being careful to not hit the starter as the key is turned to the ON position.

Loosen the distributor enough that it can be turned easily by hand and then turn it clockwise as far as it will allow with the hold-down still in place.

Now turn the distributor counter clockwise until you see a transition in the cam sensor output voltage. It can go from 5v to 0v or the other way around, but what you're looking for is the transition point, where you stop and lock the distributor down. Done!

Just like at the crank, I prefer that you back the distributor up a great deal and start over if you're not happy with the adjustment to get everything operating in its normal relationship. With the distributor shaft moving CW during engine run times, you need to turn the housing CCW to maintain that same effect with the engine stationary.

It's not rocket science and you have a full 10 degrees of offset that the PCM will accept in either direction, but we might as well set it as close to center as possible. If nothing else, it extends the time between adjustments a bit!

Good luck and I'll see you in a bit!
Ed
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Customer reply replied 7 years ago
ok i did all that and i got the truck started. before it got to 170, i could gun it and it would react just fine. after it got to 170, i tried to gun it and it would shudder a little then react. it would still have that sucking sound after that. do you still think it is the upper O2 sensor since it is not reacting that way until after it gets to operating temp?
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
That's very possible!
170 is a magic number when it comes to engine temperature and adaptive values. That's because until it reaches that temperature, your only adaptive value that can be generated is the short-term stuff, which can reach a total of 33% either direction... additive or negative.

After hitting 170, the long-term adaptive function becomes active which means an additional 33% can be tacked on if sensor signal dictates. Long-term adaptive's job is to bring short-term back to about even (zero %), so an actual -33% that existed on short term would be almost immediately transferred to long term. And then the short term would continue to work as it always does with the capacity to add or subtract that same amount if needed, combining to a possible 66% of fuel shift.

So yes... it's quite possible. A quick battery disconnect should clear long-term again and if you were to disconnect the UP02, things might stay good for a lot longer. In theory, an open circuit on the oxygen sensor should produce a trouble code (and turn the CE light on), which should be enough to keep the PCM from using its signal for mixture control.

See if it makes any difference.
Ed
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Customer reply replied 7 years ago
ok i tried that and it did not make a difference. so where do we go from here?
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
Just to recap...

You did the index procedure...
The engine runs now...
It ran decent until it got to about 170...
Then you developed sag on hard acceleration...
And clearing memory and disconnecting the UP02 didn't help.

Does that sound about right?
Did the CE light come on after you disconnected the UP02?

Ed
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Customer reply replied 7 years ago
all that is right but no check engine light. i took a harder look at it and it shudders even before it gets to 170. i disconnected the O2 and cleared the PCM then started it. it ran for a few minutes with no check engine light so i reached in and stabbed the throttle and it still shuddered.
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
If it shudders like that right after a memory-clearing, I wouldn't expect it to be something to do with adaptive mixture then. That would be too fast for the 02 to crap things up, so we might just be looking at a bad plug wire or low spark output from the coil. Did we look at those things yet?
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Customer reply replied 7 years ago
well all the plug wires are brand new and i replaced them twice and it still does this. how do i check the spark output from the coil? by coil, do you mean the cam sensor or the actual coil itself on the motor that has the coil wire running from it to the distributor?
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
The coil itself... the unit over at the passenger side front of the engine.

I'd start by pulling any easy to reach plug wire off and then place it on top of the engine. Start it up and see if you can coax something close to 3/4" of spark out of the boot end of the plug wire. If you see less than that (or nothing at all) you might have to insert a paper clip into the open boot to bring spark out a bit.

Anything at or less than 1/2" isn't healthy and we might have to go back to the coil to check output right there. It makes me wonder if spark might be your problem now that you've indexed the distributor and got it to run again. A properly indexed distributor will possibly have less air gap to jump in the rotor to cap, so that may have helped.

Ed
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Customer reply replied 7 years ago
ok i checked that and i have right at about 1/2" spark there. do you think i have a bad coil now?
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
It might be. A half-inch has shown to be a bit marginal from experience here on JA, so with the new plug wires, coil wire (?) and cap-rotor... there ain't much left. You could check it right at the coil to see how much is being lost through the secondary ignition but I'd think it to be pretty good at this point.

Take a look at the coil itself first off. The center stamped steel core on these units tends to corrode and spread between the layers which can crack the coil body. Once a crack opens up to the outside world (or inside), spark can find another path to ground which will limit your total output somewhat. Wet weather can short it out completely, making it a common source of damp no-start complaints.

Lemme know!
Ed
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Customer reply replied 7 years ago
ok i took it off and its a little corroded on the center stamped core but not cracked at all. tell you what i am going to do, ill replace it and then check the spark at the spark plugs again to see if it has improved.
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
That would be great. You don't even have to install the new coil, which might make it easier to return if it doesn't change anything. Just make your connections and let it hang.

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Customer reply replied 7 years ago
ok i replaced it and started it up. it started quickly and once it got to 170, i stabbed the throttle and there was no shudder in the engine anymore. im going to drive it around and see how it runs now.
Customer reply replied 7 years ago
ok i just got back from driving it around and i gunned it in a straght away and there was no bucking or anything anymore. it has quick engine start response now and quick throttle response as well. i think that may have been the problem all along. at least now since all those parts have been replaced, it will be awhile (hopefully) before any of those will go bad again. thanks for all your help with this.
Dodge Mechanic: Dodgerench, ASE Certified Technician replied 7 years ago
Great news! I should've known better with all the weirdness you had going on that it might be spark related. Thanks for all your hard work, bud!

Ed
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