4.3L V6 4WD Vin Code "W". I have replaced spark plugs, wires, dist cap & rotor, coil, Crank Pos Sensor and cleaned all the grounds. I can only get around 500 miles before the ignition module goes and engine will not start. The ECM was replaced 6 years ago. I suspect that the ECM is now the culprit. Does this ECM have a problematic history? The replaced Ignition Modules are not Delco OEM, could this be a probem also?
Any ideas would be most helpful.

 

Had similar experience with ignition modules, finally got one that lasted....think it was a "Standard" brand...but not sure now...anyways it came with a 5 year warranty and I never needed to use it.

I too thought it was the ECM, but could never find one for a '95....tried one for a '96 just for the heck of it......but nope it did not work.

Suggest getting a "Standard" brand and be sure to put heat sink compound on the back of the module before installing onto the heat sink...available at Radio Shack for about $3 a tube....which is enough to do about 500 vehicles....does not take much...just a thin coating.

 

Is the check engine light on? Does it work? Are there any DTC's in memory, or pending?

If/when the crankshaft position sensor and/or timing cover are moved, removed, replaced, or disturbed in any way, the crankshaft position sensor relearn must be performed. Without performing it, the PCM uses the data from the last relearn, which is now incorrect. Calculations and adjustments that the PCM commands for ignition timing, injector timing, injector pulse width, EVAP, EGR, etc etc are all based on correct crankshaft sensor data. It requires a "high end" scan tool to initiate the relearn, and takes maybe 15 minutes to do it. The crank sensor has nothing to do with the ignition module failing.

If the distributor has been removed, camshaft retard must be checked and adjusted using a "high end" scan tool, (another 15 or 20 minute job). If cam retard is off significantly, it can cause the ignition coil and/or ignition module to fail prematurely, without ever setting a DTC or turning the check engine light on. There needs to be a thin coating of heat sink paste applied to the back side of the ignition module when it is replaced, (available at Radio Shack).

The PCM's in these things are darn near bulletproof and rarely fail. There are more PCM's replaced due to a misdiagnosis, than actually fail and need replacement.

 

Had one that did the same thing,stall and not restart,but no code.Ended up being the MAS airflow sensor intermittently going bonkers. Replaced with a cheapie from ebay and no probs since.

 

A faulty MAF sensor can cause stalling, but it will not affect the ignition module or coil, like the OP is experiencing.

 

I was throwing the MAF sensor out there because it it extremely hard to pin an intermittent problem down.When the engine quits without a hard code,it's mainly guesswork.Mine would restart after a while,sometimes after replacing a suspected part (TPS,EGR,coil etc) leading one to believe that we had found the problem. It took a buddy with a full scanner 20 minutes to nail the problem watching the maf output on his screen.

 

I ended up replacing the VCMA with a reman unit and installed a Delco D572 ignition module. Had the VCMA programmed at the local GM shop and they could not find any other items with the tech scan tool. I had two of the replaced ignition modules checked at the local OReilly parts store and each one of them showed failure modes either in frequency or rpm modes. Can only assume that the VCMA was faulty and affecting the ignition modules. I was getting the DTC 1351 code which led me to believe the problem was only the ignition modules. Never got any other codes or pending codes. Want to thank everyone for their input. Sometimes a person gets stuck on one item and forgets there may be something else that is causing the problem.

 

Did they check camshaft retard? It can be off as much as ~27 degrees and not set a DTC in memory. Spec is zero +or- 2 degrees. When camshaft retard is out of spec, the air gap between the rotor segment and the cap terminals increases when the coil fires. This causes added stress on the ignition module, ignition coil and the driver in the PCM. This could be the root cause of your problems.

 

Capt Hook, I am a little confused here by the camshaft retard phenomena. The camshaft has a timing chain and unless it is really worn would that cause the retard that you speak of? The distributor cannot be rotated due to the fingers on the base nesting over the dowel pin on the back of the engine. I was under the impression after reading the shop manual that programming the VCMA to the VIN number would control the timing of the spark firing to within the specs required. Am I missing something here? Thanks for your input. I looked at the old distributor cap and did not see any evidence of misfire.
Really appreciate your tech advice ~ thanks again.

 

Similar to the throttle position sensor, and the crankshaft position sensor needing to be aligned with their respective components, the camshaft position sensor needs to be aligned with the camshaft, hence the name of the sensor. The term "camshaft retard" is misleading and confusing: It implies that something with the timing chain or camshaft is not right. That's simply not the case.** As far as I'm concerned, it should be called "Camshaft Position Sensor Alignment". When the sensor is aligned correctly, the PCM uses the data for detecting, and accurately identifying, cylinder misfire. The adjustment also aligns the distributor cap so that the rotor segment is aligned with the cap terminals when the coil fires for each cylinder. This reduces/eliminates crossfire inside the cap.

When the distributor is installed, and the teeth are meshed with the camshaft correctly, P1345 will not be present when you start the engine. This is the "rough" adjustment for camshaft retard. To "fine tune" camshaft retard, you need to use a scan tool capable of viewing the streaming data. Desired spec is zero degrees, indicating that the sensor is perfectly aligned with the camshaft. The tolerance is + or - 2 degrees. The adjustment is done by loosening the distributor hold down bolt and slightly rotating the distributor. The inside diameter of the intake manifold is slightly larger than the outside diameter of the distributor. This "slop" is what allows the distributor to turn, more or less on an arc. From the factory, the total amount of camshaft retard adjustment is only ~11 degrees. If that's not enough, you need to remove and discard the original hold down bracket, and install one of these: http://www.summitracing.com/parts/mr...FYZaMgody1MARA This will make the distributor fully adjustable.

The distributor gear and the camshaft gear each have 13 teeth. Each tooth accounts for ~27 degrees of distributor shaft rotation. The PCM is programmed to set P1345 when camshaft retard meets or exceeds ~27 degrees. When this DTC sets, it's a dead giveaway that the distributor is not installed correctly.

When the PCM is flashed to the VIN, it will control the ignition timing correctly. However, crankshaft position sensor data is flashed to a default value. The engine will start and run using the default value. All calculations and adjustments that the PCM makes, (ignition timing, injector timing, injector pulse width, EGR, EVAP, etc etc.) are all based on correct data from the crank sensor. This is why the crankshaft position sensor relearn must be performed whenever the PCM is replaced, (even with a used one). If camshaft retard was set properly before the PCM replacement, no adjustment is necessary.

Tid bits:
Camshaft retard can be off up to ~26 degrees without setting a DTC or turning on the SES light. If it's off ~15 degrees, you might not notice a problem but, it will have crossfire in the cap, which will cause a misfire, shorten the life of the cap, and your fuel mileage will suffer. At 26 degrees, you'll have a boat load of crossfire going on in the cap, and P0300 will most likely set.

Once camshaft retard is set properly, you can unplug the camshaft position sensor. The SES light will be on, and if the engine misfires, the PCM won't be able to detect it. Other than that, the engine will start and run perfectly fine.

** Camshaft retard data can be used to help diagnose a jumped timing chain.

Hope this helps.