Fixing lazy PCM. New caps writeup.
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I'm guessing a voltage regulator for the 5V sensor output. All that extra voltage has to go somewhere.
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That looks familiar:
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thanks for the write up, mine sat for a few months then would not start, messing with it a while it did start, thats when i noticed it would only start when the check engine light came on and found this post.
something that might help others is i only have a 140 watt soldering gun. it really was to big to get in to the small pins on the caps. what i did was to use a pc. of solid coopper wire 12 ga.i think it was and bend up a tip for my soldering gum out of the wire. it gets hot in a instant
something that might help others is i only have a 140 watt soldering gun. it really was to big to get in to the small pins on the caps. what i did was to use a pc. of solid coopper wire 12 ga.i think it was and bend up a tip for my soldering gum out of the wire. it gets hot in a instant
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the other reason for capacitors fail is due to a counterfeit operation that was / is running. Had a load of computer power supplies and motherboards fail due to capacitor fail. I would guess that the 12v to 5v circuit is failing because of the caps (they form part of a regulator circuit) and then whatever the PCM does is not working.
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Just to insert
Hey I have the same ecm problem on a 93 jeep grand cherokee. However I noticed that the part number from radioshack on here matched as a 85 C rating. The capacitors you remove from the ecm the 105 C ratings. I read up about that on this post
http://www.jeepforum.com/forum/f9/anyone-ever-rebuild-their-pcm-628371/
That post said that radioshack didnt carry the 105 C rated ones. It does say you can get them from Digi-key. I checked with them and spoke with a tech and he said they did not carry the PL(W) series. He did say that these would be the same though
Digi-Key - 493-3277-ND (Manufacturer - UTT1E221MPD)
I posted because I saw everybody replacing theyres with the 85 C ones. Anyways thats my 2 cents worth after 3 days of thread combing. Props to all for the great info.
Hey I have the same ecm problem on a 93 jeep grand cherokee. However I noticed that the part number from radioshack on here matched as a 85 C rating. The capacitors you remove from the ecm the 105 C ratings. I read up about that on this post
http://www.jeepforum.com/forum/f9/anyone-ever-rebuild-their-pcm-628371/
That post said that radioshack didnt carry the 105 C rated ones. It does say you can get them from Digi-key. I checked with them and spoke with a tech and he said they did not carry the PL(W) series. He did say that these would be the same though
Digi-Key - 493-3277-ND (Manufacturer - UTT1E221MPD)
I posted because I saw everybody replacing theyres with the 85 C ones. Anyways thats my 2 cents worth after 3 days of thread combing. Props to all for the great info.
The PCM does not directly supply power to the coil. It supplies ground. However, the PCM does control the auto shutdown relay which in turn supplies power to the coil. Check the relay if you have no power on the coil.
You may have a fault that is keeping the PCM from closing the auto shutdown relay as it should.
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also, a no power to coil is the main symptom of a CKS fault(crankshaft position sensor), have you eliminated that as an option?
I replaced the CPS with a new one and no change also tested the auto shutdown relay and it seems to be working fine.
If the auto shutdown relay is working properly, and there is no power to the coil, that leaves the fuse, and the wiring from the auto sd relay to the coil.
The engine will not start unless there is constant power to the coil when the ignition switch is on. Nothing else really matters until the coil has power.
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So I take it this will work for both the 4 banger and the 5.2? I have just ordered a bloody fuel pump too. Ah well, lets see eh?
Nice write up though mate!
Nice write up though mate!
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no 4 banger in the ZJ's, you mean 4.0? and yes it should work in all of them
large writeup in wrangler forum. Did this repair on a 2.5 a couple of years ago. Used this thread to http://www.jeepforum.com/forum/f12/91-hard-no-start-long-cranks-cold-explained-490788/diagnois.
If memory is correct. If you hear the fuel pump the car will start. Another test is - turn the key to on -wait five minutes try to start the truck. Mine got so bad that i had to wait 15 minutes. I think the fuel pump sound was the tell tale sign that everything was ok but it could of been another relay sound. The waiting cuts down on draining the battery. First clue was the jeep started right up after being towed home from the airport after returning home on cold winter night. I had left the key on during the tow.
I potted with a two part urethane mold forming material with a durometer of 40. Work uses it to make fixtues to hold parts. Available at hobbie shops
The wrangler still start rights away with 198,000 miles. As the weather changes and it get colder the problem will get worse.
If memory is correct. If you hear the fuel pump the car will start. Another test is - turn the key to on -wait five minutes try to start the truck. Mine got so bad that i had to wait 15 minutes. I think the fuel pump sound was the tell tale sign that everything was ok but it could of been another relay sound. The waiting cuts down on draining the battery. First clue was the jeep started right up after being towed home from the airport after returning home on cold winter night. I had left the key on during the tow.
I potted with a two part urethane mold forming material with a durometer of 40. Work uses it to make fixtues to hold parts. Available at hobbie shops
The wrangler still start rights away with 198,000 miles. As the weather changes and it get colder the problem will get worse.
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Does this fix help with lazy starts? I dont have a no start issue, it just takes a few revolutions before it fires up... This sound like a cap problem?
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Do you hear your fuel pump prime when you first turn the key? If not then yes, you do have faulty capacitors.
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Im pretty sure I do hear it prime right off the bat. But if a wait a few seconds after I turn the key it will fire right up.
Thank you for all the good info guys. This is the only listing Google came up with that described my problem. I ordered my capacitors from mouser.com because they are rated for the correct temperature. It took me about an hour to do today and it worked like a charm!
I did not get the capacitors from Radio Shack as the ones they have are only rated to 85 degrees. The whole process took about an hour to do but you might be able to do it faster if your better with the soldering iron. I'm a novice at the iron so anyone can do this.
I used a razor blade and it came out very easily. A small toothbrush helps to clean things up a bit as well.
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I did not see anything obvious wrong with the capacitors that were in there. The tops were not domed and I could find no leaks. Possibly 2 of the 3 were a little domed on the bottom side.
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Once the new capacitors were in I siliconed everything up nicely, hooked it back up and she fired right up.
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I did not get the capacitors from Radio Shack as the ones they have are only rated to 85 degrees. The whole process took about an hour to do but you might be able to do it faster if your better with the soldering iron. I'm a novice at the iron so anyone can do this.
I used a razor blade and it came out very easily. A small toothbrush helps to clean things up a bit as well.
I did not see anything obvious wrong with the capacitors that were in there. The tops were not domed and I could find no leaks. Possibly 2 of the 3 were a little domed on the bottom side.
Once the new capacitors were in I siliconed everything up nicely, hooked it back up and she fired right up.
I just thought I'd share my experience with this. Also because if someone else hadn't taken the time to post their experience I'd be $200 shy in my wallet.
Recently my 4.0 from a 94GC stopped running. I hadn't changed any wiring but the fuel pump no longer primed when the ignition was turned on. I spent hours re-tracing wires and checking connections and came to the determination that the issue was in the PCM. Frustrated at not getting it to run as I needed to get antifreeze rather than water in the block before winter hits, I was sitting there thinking on it and the relay for the ASD starts to click. It progressively clicks faster and faster until it locks in and the fuel pump primes. huh?? Okay, crank and it starts up. I get the antifreeze in it let it warm up and shut it off. I come back an hour later and again no prime, no run. I let the key sit on for a few minutes and it does the click thing again and the pump primes.
Some searching around turned up a TSB on my model PCM
TSB
1993 - 1995 Jeep Grand Cherokee 4.0L
1993 - 1995 Jeep Grand Cherokee 5.2L
Symptom: Will not start immediately in cold ambient temperatures, no MIL immediately at key on, no communication with scanner, auto shut down (ASD) relay is clicking. Wait for awhile with key on and MIL comes and and then it will start.
System: Emissions/PCM/Fuel
Codes: N/A
Problem: When the ambient temperature drops below 40 degrees, the Powertrain Control Module (PCM) fails to power up until warmed up or key is left in the on position, the MIL comes on and the relays start clicking.
Test & Fix: If the problem cannot be duplicated, remove the Powertrain Control Module (PCM) and cool it in a freezer. Reinstall the PCM and check if symptoms are present. If symptoms are present and powers and grounds are OK, replace the PCM. "
This certainly sounded like my issue but I wasn't keen on replacing the PCM as Autozone wants $200 for a new one. Some more searching around Jeep forums turned up this post. :2thumbsup:
It was certainly worth a shot as I already have a soldering station and electrical parts are cheap.
All said and done, it absolutely works! No more lazy PCM and I saved myself a few hundred bucks and instead spent $6.00 on capacitors shipped from mouser.com.
I did not get the capacitors from Radio Shack as the ones they have are only rated to 85 degrees. The whole process took about an hour to do but you might be able to do it faster if your better with the soldering iron. I'm a novice at the iron so anyone can do this.
These are the capacitors in question. You have to dig out the gel pack from around them. I used a razor blade and it came out very easily. A small toothbrush helps to clean things up a bit as well.
![]()
I did not see anything obvious wrong with the capacitors that were in there. The tops were not domed and I could find no leaks. Possibly 2 of the 3 were a little domed on the bottom side.
![]()
![]()
![]()
Once the new capacitors were in I siliconed everything up nicely, hooked it back up and she fired right up.
![]()
Recently my 4.0 from a 94GC stopped running. I hadn't changed any wiring but the fuel pump no longer primed when the ignition was turned on. I spent hours re-tracing wires and checking connections and came to the determination that the issue was in the PCM. Frustrated at not getting it to run as I needed to get antifreeze rather than water in the block before winter hits, I was sitting there thinking on it and the relay for the ASD starts to click. It progressively clicks faster and faster until it locks in and the fuel pump primes. huh?? Okay, crank and it starts up. I get the antifreeze in it let it warm up and shut it off. I come back an hour later and again no prime, no run. I let the key sit on for a few minutes and it does the click thing again and the pump primes.
Some searching around turned up a TSB on my model PCM
TSB
1993 - 1995 Jeep Grand Cherokee 4.0L
1993 - 1995 Jeep Grand Cherokee 5.2L
Symptom: Will not start immediately in cold ambient temperatures, no MIL immediately at key on, no communication with scanner, auto shut down (ASD) relay is clicking. Wait for awhile with key on and MIL comes and and then it will start.
System: Emissions/PCM/Fuel
Codes: N/A
Problem: When the ambient temperature drops below 40 degrees, the Powertrain Control Module (PCM) fails to power up until warmed up or key is left in the on position, the MIL comes on and the relays start clicking.
Test & Fix: If the problem cannot be duplicated, remove the Powertrain Control Module (PCM) and cool it in a freezer. Reinstall the PCM and check if symptoms are present. If symptoms are present and powers and grounds are OK, replace the PCM. "
This certainly sounded like my issue but I wasn't keen on replacing the PCM as Autozone wants $200 for a new one. Some more searching around Jeep forums turned up this post. :2thumbsup:
It was certainly worth a shot as I already have a soldering station and electrical parts are cheap.
All said and done, it absolutely works! No more lazy PCM and I saved myself a few hundred bucks and instead spent $6.00 on capacitors shipped from mouser.com.
I did not get the capacitors from Radio Shack as the ones they have are only rated to 85 degrees. The whole process took about an hour to do but you might be able to do it faster if your better with the soldering iron. I'm a novice at the iron so anyone can do this.
These are the capacitors in question. You have to dig out the gel pack from around them. I used a razor blade and it came out very easily. A small toothbrush helps to clean things up a bit as well.
I did not see anything obvious wrong with the capacitors that were in there. The tops were not domed and I could find no leaks. Possibly 2 of the 3 were a little domed on the bottom side.
Once the new capacitors were in I siliconed everything up nicely, hooked it back up and she fired right up.
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