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Go Back JeepForum.com > Models > Jeep Grand Cherokee & Commander Forums > ZJ Grand Cherokee Forum > Fixing lazy PCM. New caps writeup.

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Unread 05-01-2013, 05:40 PM   #91
ijusgottajeep
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http://www.parts-express.com/pe/show...umber=020-1746
heres the better deal on capacitors. 43 cents a pop plus shipping but they are rated for 220 degrees/ 105 c

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Unread 08-02-2013, 10:41 AM   #92
diamondflaw
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Another happy camper here thanks to this post! Just finished this last night, and I am ecstatic! I think other people have said this, but the caps will not necessarily look domed, mine didn't (definitely looked sad, but not domed).

Over last couple of months my '93 4.0 had steadily needed more and more delay and cranks to start until about 4 days ago it just wouldn't start anymore, noticed CEL not tripping when turned to "on" and found this post.

After replacing these, no more need to wait before starting, starts on the first crank, and (could be my imagination just 'cause I'm excited to have her running again) the throttle seems more responsive on the road.

THANK YOU!
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Unread 09-07-2013, 04:38 PM   #93
stretchallen25
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Hi guys, I am new to this forum but I have read many threads about multiple things regarding stalling, dying, rough idles and have been searching endlessly trying to find a good relation to what my problem is. I have a 1994 Jeep Grand Cherokee V8 5.2L and I think it is a ZJ from doing some research. I am so frustrated with this issue. I have replaced fuel pump, fuel filter, did complete tune-up about 3 months ago. The problem is somewhat similar to others. I usually have no issues starting it when its cold only when it gets to normal temperature and then it usually starts my problem. My voltage starts out normal but as it warms up it slowly goes down while driving to around 12 volts. And when warm if I turn it off and then try to start it again, the volts will be low and it idles low and kinda rough and if I try to put it into reverse, it sometimes will die or at least, the RPMs will go really low and almost dies. Now this is only happening when it is warmed up. New battery in it also. Took it to get it tested at Autozone and battery passed, but he said my voltage regulator failed and I think he said diodes passed also. So I then asked him if the voltage regulator could just be replaced and he told me no that it was internally in the Alternator so I thought it was in the PCM. So I did buy the new alternator but it changed absolutley nothing so I took it back out and took it back for a refund. So if anybody can help me with this confirming that I need to replace my PCM. so as my jeep warms up, the problem starts so is the PCM getting too hot? Or could it be the IAC? Please help as I have 4 kids that I have to take back and forth to school everyday. Thanks a lot and I appreciate it very much.
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Unread 09-07-2013, 06:48 PM   #94
NJ2MDJim
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Very thorough write-up and clear pictures. I believe you have helped a lot of people today by showing them that they can do this themselves.
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Unread 09-08-2013, 12:34 AM   #95
moggie99
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Thank you to everyone who has contributed to this thread. I have just ordered the high temperature capacitors from partsexpress to tackle this job on my 1995 Cherokee which has a habit of cutting out in the desert (but which always restarts once cooled down a bit)

A thought: if, as it seems, the problem is that the PCM fails to power up the fuel pump, could we not just run a manually switched 12v supply to the pump?
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Unread 10-06-2013, 12:42 PM   #96
Rimfired
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Thanks for the writeup, I just fixed my pcm yesterday and confirmed a good fix this morning. At first I thought it was a bad check valve in the fuel pump assembly, but slowly the time it took from turning the key to on, the check engine light coming on and the fuel pump priming got longer and longer, and that confirmed the diagnosis of a "lazy pcm". This morning the check engine light came on immediately, the fuel pump primed immediately and the Jeep started right up.

As a tip, I got the high temp caps from Fry's Electronics, so if anyone has a store locally, that's the place to get them.
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Unread 10-06-2013, 02:41 PM   #97
ZeeJay1997
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Quote:
Originally Posted by moggie99 View Post
A thought: if, as it seems, the problem is that the PCM fails to power up the fuel pump, could we not just run a manually switched 12v supply to the pump?
PCM does not power the pump. the pcm supplies a ground to the fuel pump relay. i would never suggest that the fuel pump be manually operated, foremost for safety (auto shutdown is engineered safety) with practicality running a close second (forget to turn it off)
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Unread 10-07-2013, 05:31 AM   #98
moggie99
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I did the capacitor swap but am still getting the cutting out at high temperatures. I shall bite the bullet and buy a remanufactured PCM and a new CPS and (hopefully) that will cure the issue. I can't afford to have the car keep cutting out on me out in the desert.
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Unread 10-07-2013, 05:08 PM   #99
ZeeJay1997
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Quote:
Originally Posted by moggie99 View Post
I did the capacitor swap but am still getting the cutting out at high temperatures. I shall bite the bullet and buy a remanufactured PCM and a new CPS and (hopefully) that will cure the issue. I can't afford to have the car keep cutting out on me out in the desert.
define cutting out. is it a miss or does it shut off and wont start until it cools off?
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Unread 10-08-2013, 12:43 PM   #100
Tony
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Quote:
Originally Posted by moggie99 View Post
I did the capacitor swap but am still getting the cutting out at high temperatures. I shall bite the bullet and buy a remanufactured PCM and a new CPS and (hopefully) that will cure the issue. I can't afford to have the car keep cutting out on me out in the desert.
Keep us posted if you find the problem. My '95 does the same thing, runs great then just suddenly dies as if the ignition had been turned off, no hesitating or miss, just dies and will not start. Once it cools down it will start on the first try and runs great again, but I never know when it will randomly quit.
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Unread 10-09-2013, 02:58 PM   #101
moggie99
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Originally Posted by ZeeJay1997 View Post
define cutting out. is it a miss or does it shut off and wont start until it cools off?
The latter - it shuts down and I have to cool the PCM with ice cubes from my cool box and then it will start and run OK. It only happens when off-road due to the higher underbonnet temperatures from high power/low speed running, on road is fine (as are the stretches of off-road where I can crank up the speed).

I've bought a load of wire and solder and plan to extend the PCM wiring loom to bring it inside the car (which is MUCH cooler than the engine bay) and add a PC cooling fan to the box.
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Unread 10-09-2013, 05:52 PM   #102
ZeeJay1997
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Quote:
Originally Posted by moggie99 View Post
The latter - it shuts down and I have to cool the PCM with ice cubes from my cool box and then it will start and run OK. It only happens when off-road due to the higher underbonnet temperatures from high power/low speed running, on road is fine (as are the stretches of off-road where I can crank up the speed).
It may be the crank sensor. when it does it again, pull the connector from the TPS and check the outside contacts for 5v. sometimes the crank sensor shorts sensor reference circuit in PCM. you're measuring at the tps because it is on the same circuit and is easiest to access for testing.
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Unread 10-10-2013, 12:28 AM   #103
moggie99
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Quote:
Originally Posted by ZeeJay1997 View Post
It may be the crank sensor. when it does it again, pull the connector from the TPS and check the outside contacts for 5v. sometimes the crank sensor shorts sensor reference circuit in PCM. you're measuring at the tps because it is on the same circuit and is easiest to access for testing.
Thanks - I already have a new CPS on order and will be changing it on a "just in case" basis.
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Unread 10-30-2013, 10:49 AM   #104
Tony
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Just an FYI, I posted that I was having a similar problem earlier. I replaced the CPS and no more cutting off or no starts for almost 2 weeks. Seems to have been the CPS.
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Unread 11-07-2013, 12:26 AM   #105
moggie99
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I replaced the CPS about 2 weeks ago - no cutting out since. It has only had one offroad trip in the desert but it performed perfectly. Another guy in the group did have his XJ cut out a few times but throwing cold water on the CPS got him going again.

When mine was playing up before, what was noticeable before was that just before cutting out it would lose power, but no problems this time. Fingers crossed that this is fixed now.
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