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Dodgerench
Dodgerench, ASE Certified Technician
Category: Dodge
Satisfied Customers: 3097
Experience:  30+ years Dodge/Chrysler exp., ASE Master with L1 certification. Driveability/ combustion specialist
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1996 Ram 1500: new cap, rotor, coil, wires - poor mileage..overdrive

Resolved Question:

1996 Ram 1500 318, new cap, rotor, coil, wires - poor mileage and at 1250 - 1500 rpm under normal driving appears to have a random misfire as identified by code reader and hesitancy while in this range. Have to turn overdrive off to keep rpm higher while at lower speeds. What could be causing the problem
Submitted: 6 years ago.
Category: Dodge
Expert:  Dodgerench replied 6 years ago.
Customer welcome to JustAnswer!.

It certainly helps that you've done a PCM scan and found only the P0300 code. While not eliminating other causes, it reduces the possibilities.

Since the misfire episodes are limited to a small RPM range, I think we can find the problem in one of two places.

  • Secondary ignition misfire. While the book on spark-related misfire is to expect increased incidence as the engine load is increased, electricity has a mind of its own. It always finds the easiest path to ground. Period. Sometimes that will happen at times when you don't expect it. A burned-out plug wire should affect engine performance disproportionately when under heavy throttle/ rpm loads, but it sometimes doesn't work out that way. Light loads allow additional spark timing advance, which might add to the travel the spark has to leap (in relation to the rotor tip and distributor cap). This could be more capacity than the ignition coil has, causing light-throttle misfire. A preferred check of the secondary ignition system would be to ohm out each plug wire. I use a 20K scale, as a go, no-go metering stick. If there is continuity (some reading other than infinity) between ends, I figure the wire is not burned out. You might also look for signs of abrasion of the cable or splits in the plug wire boot, allowing spark to find easy ground.
  • Distributor index. Your engine timing is no longer adjustable by means that might be familiar. Turning the distributor changes things, but it won't change base timing. The distributor now houses the camshaft position sensor (the only electrical lead from the housing). Turning the distributor varies the relationship between it and the crank sensor, which is located in the transmission bellhousing. Beside that, it varies the relationship between rotor tip position in the distributor and the distributor. If the spark happens to find another terminal in the distributor cap to be more attractive, it will take that path. Situations such as misfire or bucking in light-throttle top-gear operation are common to incorrect distributor indexing.

If you find nothing wrong with your plug wires, I would expect this to be the next-most logical spot to look.

The correct index procedure is a bit drawn-out and I hesitate to list the whole thing without knowing whether this is needed. While the index can be carried out with the use of the factory scan tool to within a single degree, the actual real-world adjustment for satisfactory operation is somewhat less demanding.

So, if you find this is the path you need to take, let me know and I'll send you information to allow an accurate method of index for your distributor.

I'll leave the light on.

Ed

Dodgerench, ASE Certified Technician
Category: Dodge
Satisfied Customers: 3097
Experience: 30+ years Dodge/Chrysler exp., ASE Master with L1 certification. Driveability/ combustion specialist
Dodgerench and other Dodge Specialists are ready to help you
Customer: replied 6 years ago.
Reply to Dodgerench's Post: I have reasonable confidence it is not the cap, rotor, wires, plugs or coil, granted they are all new (not necessarily guaranteeing performance) and I have inspected them several times with positive results. It sounds like I might have to index the distributor and if you can send me the instructions I will give it a try.
Expert:  Dodgerench replied 6 years ago.

Will do, J.

Off to work for now. Thanks.

Ed.

Expert:  Dodgerench replied 6 years ago.
Customer(can I call you J?), welcome back.

Long day, but it sure is beautiful this time of year. Hope your day was just as nice.

Distributor index goes something like this. I'll actually plagiarize an earlier Chrysler TSB and insert my own cautions as required. Remember that this procedure places the distributor (and the cam sensor within) to an operating medium with the crank sensor. The variance allowance is fairly large, something in the neighborhood of 12 degrees, either before or after the crank signal. That's pretty large. I hope we can put the index closer to the ideal zero degrees, but that can only be confirmed with a factory scan tool. I'll include my tips in italics.

  1. Connect a voltmeter to the distributor sensor (cam sensor) connector by removing the end seal and carefully backprobing the connector. Connect the positive lead to the sensor output pin (pin 3, a tan/ yellow wire). Connect the negative lead to the sensor ground pin (black/blue). I use neither. From experience, I noted the activation of both the ASD and fuel pump relays when the cam sensor changed states. I simply use their clicking as my signal to stop turning the distributor.
  2. Rotate the engine clockwise as viewed from the front, until the number one mark piston Top (TDC) compression on the vibration damper should line up with the zero degree (TDC) mark on the timing chain case cover. (Not identified in the TSB. You would need to take the distributor cap off to view the rotor coming around to the #1 cylinder firing position. It's a pain, because of the obstructed view. I take all plug wires from the engine left side off for this procedure. The firing order for the engine is 18436572. The distributor turns in a clockwise fashion. The #1 cylinder is at about the 9:00 position, often identified by a cast-in #1 number in the distributor cap.
  3. Continue to rotate the engine slowly clockwise until the V8 XXXXX XXXXXnes up with the zero degree mark n the timing chain case cover. The V8 mark is 17.5 degrees after TDC. It's important to continue to rotate the engine in the clockwise direction until you see the V8 mark. This keeps all mechanisms loaded in the normal direction of rotation. If you go past the V8 mark, back the engine up considerably and bring it back to the V8 mark. Timing chain slack starts at engine birth. This eliminates that slack.
  4. With the distributor clamp bolt loose and the ignition switch in the ON position, rotate the distributor slightly in either direction until the voltmeter switches between the sensor transition point of 0 and 5 volts. I mentioned earlier that I normally don't use the voltmeter for reference. For one thing, it might involve turning the distributor in a direction contrary to normal relation to rotation. My advice is to initially turn the distributor a great deal clockwise. This takes the cam sensor farther from the intended switch point. I position it so and then rotate it back (CCW) until I hear the relays click. This is the exact point of cam sensor state change. It matters not at all how slow the transistion happens, so take your time. ONE CAVEAT... The relay click will happen only once per ignition cycle. That means if you hear it once and you would like to check your work, you would need to turn the ignition key to the off position and then back on (no crank!). The distributor also needs to be rotated a sizable distance back to the clockwise position to prepare it for the next maneuver. Repeat it as described earlier. Using the Factory's method, you would encounter a defined "dead area", where the distributor can be turned with no change in cam sensor output state. My method always puts the distributor rotation against the normal direction of engine travel. The difference is no more than a few degrees, which will probably not matter. I just choose to improve on the spread and place my adjustments closer to zero.
  5. Adjust the distributor as close as possible to either side (split the difference using their method) of this transition point and tighten the distributor clamp bolt to 22 ft/ lbs torque.

Either way, you should be within a few degrees of perfection... easily enough to prove or disprove my theory.

Loosening the distributor may be the biggest obstacle. It's not easily accessed.

But be careful to first position the engine (no backing up!) to the V8 mark on the crank balancer. There is also a V6 mark, but it isn't anywhere near the TDC mark on your balancer. Don't be fooled. Clean the balancer marks if needed and set the engine position using the V8 mark at the timing cover TDC mark.

Then, you can either use the 5v-0v-5v transition point by turning the distributor (works) or my method of backing the distributor considerably past the switch point and then rotating the (CCW) back until the sensor switches (as identified by DVOM or relay click). Either works.

J, make sure and let me know how this comes out. I mean it. Distributor index problems aren't common anymore, but it can still happen. I use modeling for my diagnoses, where it might or might not pan out. If we need to go forward, it's all good.

I'll be here. Remember the light's on.

Ed.

One last thing. If you'd like to read the original TSB from which I paraphrased this post, type in Dodge TSB 18-08-93 into your search engine. The original TSB involved replacing parts your truck won't require.

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