Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!

FIXED 95 Jeep Grand Cherokee Laredo 4.0L

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3 years 2 months ago #46028 by Jgpsvt
When I got the grand Cherokee it had a bad battery and alternator. Also it had a long crank and transmission would stay in 2nd gear unless you let the Ignition on for 2 min. I pulled out the engine and tranmission harness found areas that had issue made the proper Repairs. That solved the transmission stuck issue. I check the fuel pressure and the pump wasn’t keeping pressure after I would parked it. I replace the pump and filter. Problem solved it ran prefect for about a month. I was planing to take a road trip and it decided not to start it would crank but no start. I check for codes there was only 12 and 55 and I notice rpm wasn’t moving. So I replaced crank sensor and cam sensor. Still no start. So I left it home for two days. When I got back tried to start it and it started like nothing happen. Drove it for two week went outta town with it. It started to buck here and there every time it did that check engine would flash rpm gauge would jump some time it would turn off and I would turn back on. Then it wouldn’t start unless it sat for 20-30 mins and I was able to drive it the rest of the day. Now it won’t stay on long than 10-20 mins when it warm stay running for less time and wait time are long before restarts. Also notice when the check engine light is off at initial key on it would start. Only after it sit and I open key on and it shows for a few seconds at it normal state it starts. I cleaned all the ground in the engine by, and add new battery terminal. I check for 5v ref and had it when it ran but when it started to die it drop. So I unplug all the sensor on the 5v and 8v ref one at time checking didn’t change anything. So I jerry rig a external 5v ref started but was back to the same scenario but this time without the drop of the 5v or 8v ref. I bypass ASD relay, same. I read online about issue with the capacitor so I uncover the pcm and start to touch it start to hear clicking in the engine bay and it started it would still shut off but as soon as I moved it started back up. So I replace the pcm. Still same scenario but this time I don’t have a drop on my 5v and 8v ref. So it seem I’m making some progress. I did a voltage drop test on my battery,pcm,crank and cam sensor. Everything looks great. I ordered mopar crank sensor cause I put an aftermarket and I thought I mite be chasing my tail. Still same scenario starts but only runs for about the 10-20 mins. But I did notice if I cycle the key fast on and off to try to get the check engine light to appear once it does I’m able to start it. I also unplug the ignition switch and bypassed it still same. I’m out of ideas and where to look I have check everything I can possibly thing of and test and I’m just burn out and need help.
The following user(s) said Thank You: fall7rise8

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3 years 2 months ago - 3 years 2 months ago #46040 by fall7rise8
What fault codes remain after all your repairs, just 12 & 55? Can you monitor power and ground at PCM connecter when it fails? You stated that you replaced the crank sensor, some of them had a paper spacer to set the correct depth. Are you confident the sensor gap is correct? I have also heard a cracked or damaged flex plate can cause crank sensor to produce faulty signals.
Last edit: 3 years 2 months ago by fall7rise8.

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3 years 2 months ago #46053 by Jgpsvt
Thanks for the reply. When it didn’t want to run I replace crank and when I saw it didn’t start I went and bought the cam sensor but it still didn’t want to start. I left it for a few days without messing with it and it started with no problems. I live in miami and I drove it to Orlando 3hr away drove it all over Orlando and back home. Not one problem. Two days later I went to do Errands and started to buck and looks like I would lose power for split sec and it would come back on. It would do that here and there. Till now it doesn’t stay on for long. So the other day I order oem crank sensor cause I read a forum they had an issue with the aftermarket one. I look at some spacer online but don’t see were I can install it cause the crank sensor is bolted on the side so really you can’t bring it closer or farther.

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3 years 2 months ago #46054 by Jgpsvt
After I replace the pcm I have good 5v ref and 8v ref. Also when it died I have good power and ground also 5-8 v ref. Also those are the only codes I get, with the only pcm only code I would get was 12z

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3 years 2 months ago #46172 by Jasondo
With engine running, wiggle the connectors at the pcm and see if engine dies.

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3 years 2 months ago #46182 by Jgpsvt
Doesn’t do anything with the new pcm. With the old pcm you would pull or wiggle the capacitor on the pcm and the car would turn back on.
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3 years 2 months ago #46307 by Jgpsvt
New update. So yesterday I started unplugging as much as Eletronics I can get to. The Tcm, abs, Sam, chime, radio, ac, unplug fuse and relays that wasn’t needed for the engine to run. The jeep started ran about 20 mins died and key on and key to try to get the check engine light to come back on. No progress. I really can use help???

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3 years 1 month ago #47090 by Jgpsvt
Today’s New update. I had the auto parts warranty the new pcm I bought with another one. Plug it in problem solved . Doesn’t shit off after 20 mins and runs a drives good. Thanks for those who help.
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3 years 1 month ago #47108 by Noah
Glad you got it figured out, thanks for posting the fix

"Ground cannot be checked with a 10mm socket"

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