Brew

1995 Jeep Grand Cherokee Laredo
4.0/6cyl | 4x4 | automatic

Last year, someone thought they were doing me a "favor" & without my knowledge or consent, sprayed degreaser over my engine & rinsed it off with a garden hose [in their driveway].

The first thing I found was a check engine light, due to the TPS [throttle position sensor] being corrupted, due to being saturated by water.

After replacing the TPS, the truck just didn't feel or appear to run correct, with rough idling, poor performance, etc..

Come several weeks later, the cold weather set in, beginning the onslaught of intermittent cold start issue. The intermittent portion is because it was occurring @ 40 degrees & below. Turning the key to start would result in nothing but cranking. Turn the key & leave it @ on position & waiting, resulted in hearing the Relay's in the Engine compartment clicking, and then the fuel pump priming.

After a lot of not knowing what was causing this, or how to fix it, it was finally suggested that is was the PCM / ECU, and the capacitors being bad.

I attempted to find an economically feasible PCM, and found one @ Ebay, with same part #, etc.. This was installed (tested) on the truck, and turning the key to "on", the PCM responded, but cranking it resulted in the truck starting, but not getting fuel = starts & shuts off immediately.

Put my original PCM back in, it starts. Try the new/used one, same thing, and giving it fuel when attempting to keep it running, provided same results.

I'm told that the new/used PCM from Ebay is no good.

The question is -
Is the New/Used PCM no good, or is 'programming' or some other adjustment(s) required ????

This issue has gone on way to long for me, and after an entire Winter of being out of work, and using whatever little funds I can muster to pay people 'not to fix' my Jeep, along with parts cost (the pcm being the most expensive), I am making desperate attempt to get this issue resolved asap, so I can get my vehicle back to being reliable (& back to work), like it was prior to the individual saturating my engine with the above mentioned.

If someone(s) with knowledge of PCM / ECU, can please advise, and or suggest legit solutions, or guidance, I'd greatly appreciate it, because all I've dealt with in the last 5 months are people that want to claim they're so great & knowledgeable about automotive, yet offer nothing to prove it - like, helping to resolve this truck issue, even though they were paid for their time.

- delayed relay(s) response & fuel pump prime @ 40 degrees & colder.
- rough idling
- poor engine performance (acceleration/ mileage)
- temperature gauge is erratic, moving up & down, in conjunction with acceleration or deceleration of the gas pedal (accelerating, the coolant temp goes up to what appears to be correct temp - (let off gas pedal, it drops/ bottoms out). The Coolant Temp. sensor was replaced when the erratic movement first began, yet was not solution.

Thank You.

dave1123

I would suggest you pull apart all your electrical connectors in the engine bay, clean them with electrical contact cleaner and reconnect. That engine solvent probably got contaminates into the plugs. Check carefully the CPS (crankshaft position sensor) wiring. The signal produced by this sensor is in the millivolt range and any bad contacts can interupt the signal. Look closely to see if there are bare wires near the plugs. BTW, dielectric grease is not a good thing where micro voltages are concerned.

You are right about the delay of the PCM being weak capacitors, but a trip to Radio Shack and a soldering pencil can fix them. Lower temps can cause them to charge slowly and in some cases, not charge at all. Some PCM's are "potted" as in having insulation poured into them to protect them from vibration. This needs to be removed around the caps carefully to avoid damaging the circuits. You'll have to know the values of the caps (there are 2) and if not labeled, you'll need a circuit diagram.

That's about all I've got. Hope it helps.