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sprinkles08
sprinkles08, Chrysler/Dodge/Jeep master tech
Category: Dodge
Satisfied Customers: 16614
Experience:  ASE Master and Advanced Certified, Chrysler/Dodge/Jeep Master Certified, Trans and Hybrid Specialist
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2001 Dodge Dakota: backfiring..I replaced the plug wires and rotor cap

Customer Question

I have a 2001 Dodge Dakota that is backfiring thru the carb (I know it's not a carb but not sure what it is called). It only does it within the first 2-3 miles while the truck is cold but it isn't as peppy as usual either. I replaced the plug wires and rotor cap but that didn't help. I keep hearing EGR valve but I find out that it doesn't have one. No codes are showing, we checked that. not sure what to do next, I suppose spark plugs but it doesn't appear to be missing and thus far the back firing is only when it is warming up.
Submitted: 3 years ago.
Category: Dodge
Expert:  sprinkles08 replied 3 years ago.

Hello and welcome to JustAnswer!

 

You're correct - your truck doesn't have an EGR valve. They went away on these engines after 1997.

 

Your problem sounds like a weak heater on the upstream oxygen sensor. The sensor has a built in heater because the exhaust doesn't heat the sensor enough to properly monitor oxygen content, and the heater helps it get into closed loop operation quicker from a cold start.

 

The sensor has a 5v pullup voltage on it for circuit diagnostics. When the key is first turned on the sensor reading will be at 5v. As the heater starts to work it bleeds off this voltage until the voltage is in the normal operating range.

 

When you start your engine it's in open loop mode. This means that the oxygen sensors are ignored and fuel control is managed basically by software alone. After it warms for a few minutes it will go into closed loop, when the oxygen sensor readings are then used. If you have a weak heater on your upstream oxygen sensor the pullup voltage will be bleeding off too slowly, and when the truck hits closed loop the sensor is still reading the higher pullup voltage instead of the actual sensor reading. The engine controller sees this and thinks its running rich and leans it out, giving you rough running, hesitation, and often some lean backfiring in the intake.

 

Also if it's already warm and you park it and let it idle for a few minutes the sensor will cool back off. The longer it sits and idles it may run worse and worse, usually you can hear the idle air control motor opening farther and farther to keep the engine running, giving a large sucking sound under the hood. This is worse in colder weather and happens more in the advanced stages of heater failure, you may not notice this symptom.

 

You would think this problem would set a code, but the software used in these engine controllers let this slip by without setting a code normally, because the voltage is still within normal operating range (not shorted to ground or an open circuit).

 

I'd recommend replacing the upstream oxygen sensor, the one on the front of the catalytic converter. After you do, disconnect the battery to clear the stored fuel control adaptives out that have been falsely learned by the bad sensor.

 

Customer: replied 3 years ago.
so I just ask for an upstream oxygen sensor at the auto store correct? Thanks, XXXXX XXXXX a load off my mind.
Expert:  sprinkles08 replied 3 years ago.
Yes, an upstream oxygen sensor would be what you want to ask for.
sprinkles08, Chrysler/Dodge/Jeep master tech
Category: Dodge
Satisfied Customers: 16614
Experience: ASE Master and Advanced Certified, Chrysler/Dodge/Jeep Master Certified, Trans and Hybrid Specialist
sprinkles08 and 5 other Dodge Specialists are ready to help you
Customer: replied 3 years ago.
does it matter right or left? autoparts online have both?
Expert:  sprinkles08 replied 3 years ago.
You probably don't have a right or left. You should have one upstream and one downstream, which means before and after the catalytic converter.

If you have a California emissions truck then you may have a left and right upstream sensor along with a catalytic converter on each exhaust pipe after the manifolds. If this is the case then you would either need to use a scan tool to look at the sensor's signals and see which one is the problem, or replace both sensors. They each have the same amount of age so it would make good sense to replace them both.

Slide underneath and take a look and see how your truck is set up. If you have a single catalytic converter on the right side after the Y pipe then you have a single upstream sensor. If you have a left and a right upstream then there will be catalytic converters on both sides with an oxygen sensor before and after each one. The ones before the converters are the upstreams.
Customer: replied 3 years ago.
I need some follow up, I'll gladly pay you for it. we replaced the upstream sensor, but took the truck out without remembering to disconnect the battery, and it ran just as it had been, with the backfiring, we quickly came home, disconnected the battery for 15 minutes, now it won't hardly run at all, unless we are in park, back firing and no power, help
Expert:  sprinkles08 replied 3 years ago.

Sounds like we have bigger issues than it just backfiring through warm up.

 

Does it seem rich, lean? Has the engine light come on?

 

 

Customer: replied 3 years ago.
no light, we even checked the codes again, smells richer to me when we finally got it back up the hill to home (was pretty sure that wasn't going to happen as we had not power, then revved up, put in drive and suddenly shot up the hill) we have the battery disconnected again, thought maybe 15 min wasn't long enough).
Expert:  sprinkles08 replied 3 years ago.

These new symptoms seem to have started as a result of replacing the oxygen sensor, correct?

 

Where did the new sensor come from/what brand was it?

 

 

Customer: replied 3 years ago.
It is a bosch sensor from Advanced Auto (supposedly their top of the line). The new symptoms actually started after we disconnected the battery. we did a short test before we remembered to disconnect the battery and we still had the initial backfiring, that stopped, we came home, disconnected the battery and let it sit for 15 min, then all heck happened.
Expert:  sprinkles08 replied 3 years ago.

Let's disconnect that new oxygen sensor, disconnect the battery again to clear the adaptives and see how the truck runs. If it runs ok then return that Bosch sensor and either get a Nippondenso or a Mopar sensor from your dealer. Bosch sensors are a pretty big source of problems.

 

 

Customer: replied 3 years ago.
how long should things be disconnected to clear everything
Expert:  sprinkles08 replied 3 years ago.

It doesn't take long at all, thirty seconds or a minute will be plenty.

 

 

Customer: replied 3 years ago.
well, raced to in town, the dealership sold me the wrong thing and is now closed. put things back together with the Bosch for the moment, we are still backfiring but better than earilier, more like before with the original sensor. Sucks. I'll get something else on Monday. The plug is exactly backwards on the one they sold me, not my day
Expert:  sprinkles08 replied 3 years ago.

Too bad about the wrong sensor. You have to watch them parts guys! Let me know what happens Monday when you get the right one in there!

 

 

Customer: replied 3 years ago.
well, what else could it be? we've replaced the O2 sensor and cleaned the IAC valve, but getting worse if anything.
Expert:  sprinkles08 replied 3 years ago.

Originally you said the problem was only for the first 2-3 miles after a cold start. Is this still the case or is it more than that?

 

Did you replace the upstream sensor with the Mopar now?

 

Has the engine light come on at all yet?

 

 

Customer: replied 3 years ago.
yes we replaced the upstream sensor, I'll admit, I did find out today the we were doing the wrong one on Saturday, laying on the ground, didn't even see the one further up the pipe, took it down and put in on a hoist today. At first after changing out the upper sensor I thought is was fine, then after about a mile it started backfiring again. the next run was after taking out and cleaning the IAC valve, and it ran even worse. I didn't get half a mile before I thought it was going to die, no power at all. I haven't gotten any further to see if it will even out. Still not one code though.
Expert:  sprinkles08 replied 3 years ago.

Did you disconnect the battery this last time after replacing the correct sensor?

 

Do you have four oxygen sensors on your truck or two?

 

 

Customer: replied 3 years ago.
yes we disconnected it for about 3 minutes (had to put the tire back on, getting to the front sensor was a bear). I didn't see any others around that catalytic converter or on further down the exhaust pipe. Would there be more up around the engine?
Expert:  sprinkles08 replied 3 years ago.

The first thing that needed to be done was determine if you had one or two upstream sensors. If you had two upstream sensors then either one of them could be causing the problem and they would have needed to both be replaced or monitored with a scan tool to see which one is bad.

 

Slide under the truck and see if there is a catalytic converter on each side of the engine. If there is a converter on both banks then each one will have an upstream and downstream sensor. Whichever bank you were just on, go to the other side of the truck and see if there is an upstream sensor there.

 

 

Customer: replied 3 years ago.
Shit, it's got them on both sides, damn, another $100. Well, know what I'm doing tomorrow night.
Expert:  sprinkles08 replied 3 years ago.

Let's unplug it first and see what happens. Unplug the sensor and make sure the wiring is out of the way so it won't get burnt on the manifold. Do yet another battery disconnect, take it for a ride and see how it does.

 

 

Customer: replied 3 years ago.
Well, thought we were good with the sensor unplugged, and it does run better so something is up with that sensor, but I'm still getting some backfiring. My husband got it disconnected while I was at work today and he took it out, heard if putt once then it ran fine for several miles. He had me take is out when I got home and I got 3 backfires while driving in the first mile, then it appears to smooth out. I have a check engine light on now, but I'm assuming it is since the sensor is unplugged, nobody had one for the left side in stock so I'll get that tomorrow. Any ideas about the continuing backfires?
Expert:  sprinkles08 replied 3 years ago.
Does it only backfire through the intake or is it exhaust too?

Does it only happen during warm up and then it's fine?

You mentioned a power problem. Is that only during warm up or is it low on power all the time?
Customer: replied 3 years ago.
I would say the power has been lower than normal since it started backfiring, I'm not hearing the louder crack as if it were backfiring out of the exhaust. The truck has a really jerky passing gear and that hasn't really been kicking in, except right after the battery is disconnected, it will kick in until it starts backfiring, then it is sluggish again, even after it warms up and is no longer backfiring. My husband is laid off at the moment so I'm really trying to avoid going to the dealer if possible, and we both know our way around a vehicle for basic maintenance, but I'm gettin way discouraged here.
Expert:  sprinkles08 replied 3 years ago.
Do you have access to a fuel pressure gauge or a scan tool?
Customer: replied 3 years ago.
I will have to ask my brother in law, his dad has some of things, maybe the fuel pressure gage, but otherwise, all I have is a code reader/reset computer.
Expert:  sprinkles08 replied 3 years ago.
You already ordered the other upstream sensor and plan on replacing it, correct? If so then see how it runs after that. If you still have problems after replacing the sensor and doing a battery disconnect then let's check fuel pressure if you can get a gauge. Fuel pressure should be 49.2 +/- 2 PSI. Hook the gauge up and monitor pressure at the time it's acting up to see if it's low.

Customer: replied 3 years ago.
okay, once again we had the wrong sensor on the drivers side this time, unplugged, but here in my next question, how in the hell do you get to the front plug to get the sensor unplugged. my hands and arms are torn to hell and back from trying to get my hands anywhere near the plug. what do I have to take off?
Expert:  sprinkles08 replied 3 years ago.

Nothing else has to be removed, but the upstream sensors can definitely be a pain to get to. I can't recall exactly where the connector is on this year/engine combination. Is the connector above the trans?

 

 

 

Customer: replied 3 years ago.
yes, and I have been unable to get my hands anywhere near it because of all the wiring that runs on that side of the transmission. I pulled the plastic wheelwell out but can't get between the transmission and the firewall to reach the end of sensor, my nephew finally spotted the end but couldn't figure out how to reach it.
Expert:  sprinkles08 replied 3 years ago.
If you wanted to you could drop the trans crossmember and lower the rear of the trans and that would probably give you more room to get your hand in there. That's alot of work though. Do you have a long screwdriver or better yet a long radiator hose pick? I often use a long radiator hose pick in situations like this to disengage the connector lock and then pull the connector apart.
Customer: replied 3 years ago.
if you use a pick, how do you get them back together? sorry for all the questions, this on has been a bit of a nightmare
Expert:  sprinkles08 replied 3 years ago.
To plug it back in you'd need to hold the connector on the wiring harness with another long pick, screwdriver or long needlenose, and then get the sensor's connector up there to it with a pick, screwdriver or needlenose.
Customer: replied 3 years ago.
I'll give it another try tomorrow, thanks, I'll let you know if we get it. (if you hear nothing we've died trying (just kidding))
Expert:  sprinkles08 replied 3 years ago.
Good luck with it!
Customer: replied 3 years ago.
Well, thanks to a friend we got the darn thing in. My husband said it did one small backfire after all that and disconnecting the battery and then ran fine. I'll try driving it in the morning. after the reset, should it have been able to do the one cough?
Expert:  sprinkles08 replied 3 years ago.
I wouldn't get too worried about it yet. See how it does for the next few days and go from there.
Customer: replied 3 years ago.
ran good yesterday, praying it's all better, thanks so much for your help.
Expert:  sprinkles08 replied 3 years ago.

That's great to hear!

 

 

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