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Old 10-07-2011, 05:54 PM   #1
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So your engine cranks but wont start

I have been seeing a bunch of people having the same problem i have been having with a few jeeps, one jeep is mine and 2 are customers jeeps. People complain about the engine cranking but not starting. When its cranking and not starting you also dont have a Check Engine Light during cranking and when they put the key in position 2. Then all of a sudden when your cranking and about ready to quit your Check Engine Light comes on and the jeep starts.

People spend a good amount of money trying to fix this problem on stuff that is not the problem. The problem lies with the vehicles engine computer also known as the PCM, ECM and ECU.

I have had 3 fail in wranglers and one fail in a Cherokee. Each vehicle had the same symptoms and the symptoms seam to be worst in the cold. So if your jeep cranks but wont start with out a check engine light, then starts when once the Check Engine light comes on then replace your ECM.

I have only found this problem to be in the Multi Port Injection jeeps up to 1995.

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Old 10-07-2011, 06:04 PM   #2
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Sunday im going to take a video of the problem with the bad PCM and install the new PCM to show everything.

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Old 10-07-2011, 06:37 PM   #3
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Cool, will be looking forward to seeing it.
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Old 10-08-2011, 10:32 PM   #4
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i have a 94 yj and had the same problem. when the CE light is on it would start, but some times i would turn it off let it sit and come back to find the CE wouldnt come on when key is in run position, well hell i cranked her up and nothing, just crankin n crankin. my fuel pump wasnt responding ,no spark, nothing except acc. (radio ,heater,whatever). i replaced the ECU, it worked for about 4 days then the same problem arrised, no start. finially i gave up with lookin at it i took it to my local garage i been using for years, come to find out one of the red wires that goes to the ECU as well as the two other set of wires(above the ECU) was broken,worn out, loose. the wire was fixed and i havnt had a problem yet. so for people who changed an ECU and didnt get any affect to fix the problem check your connections to the computer as well as wires going into the computer ect. ect. in that area of the engine bay. that was what my problem was anyway hope this of some help
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Old 10-09-2011, 11:20 AM   #5
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I'm re-wiring my whole rig because of this... but so far, it wasn't the ECU, it was the fact that half my fuse block melted. I found that out after deciding to hell with it, I'd re-write the beast.

(the funny part is, I could get the jeep to 'pop start' with no problems. Just that half the gauges were out ).
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Old 10-10-2011, 12:02 AM   #6
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hmm mine was the same but not as bad as yours. i had a few in the fuse block melted but nothing important or serious enough to affect the rest of the equipment. wonder why? man these jeeps do some really stupid stuff at times but, gotta love it. for the buyer of a jeep who enjoys turning wrenches, this is a challange they wait for lol
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Old 10-10-2011, 05:49 AM   #7
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I just replaced my ECU this past weekend, and it solved almost all of my starting/electrical issues I have been experiencing.
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Old 10-10-2011, 08:53 AM   #8
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Replaced mine in 2009 after I'd have to wait 10-20 minutes for my fuel pump and CE light to come on (with the key to on)...
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Old 10-10-2011, 09:36 AM   #9
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I remember that was my key symptom. It would crank and crank w/o starting. Then the fuel pump would growl and the CE light came on, then it would be fine. Cold mornings were the worst. I would turn the key to on and wait... sometimes 1 minute, sometimes up to 20 minutes. Any cranking before the fuel pump kicked on was just a waste of time.
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Old 10-10-2011, 09:45 AM   #10
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I was having the same issues, so I replaced the ECM. Now it works, but after a few blocks of driving the CE light comes on? any suggestions?? the mechanic says its because the ECM is not from Florida,and something to do with the settings for emissions where the computer is from..not sure what to think of this.
I have not unplugged my battery yet, to see if it restarts the ECM and gets rid of the light? Any suggestions on this issue are welcomed...
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Old 10-16-2011, 11:43 PM   #11
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Quote:
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the mechanic says its because the ECM is not from Florida,and something to do with the settings for emissions where the computer is from..not sure what to think of this.
That's possible, though I've only heard of California being the odd-man-out for emissions rigging. there were also once early YJ models sold in Utah and Colorado being sold, with their carbs adjusted a bit lean for the higher altitudes (Salt Lake City sits roughly 4500' above sea level).

It's possible you may have gotten hold of a California-rigged ECU, which would definitely throw a monkey wrench in it when latched onto an emissions system that isn't similarly built.

You may want to check and see if an ECU can possibly be re-programmed...

('course, my solution to seeing that light on mine was to, umm, remove the bulb. I have 180k miles on the beast, and I intend to keep the thing until it finally cracks in half from either rust, off-roading, or both. Or if I win the lottery, in which case I'll just have it rebuilt. )
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Old 11-29-2011, 05:44 PM   #12
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Okay so I am having this problem with now power to my fuel pump. So I changed the pump and still nothing. Is there a test I can do to check if the computer is bad?
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Old 11-29-2011, 07:19 PM   #13
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Okay so I am having this problem with now power to my fuel pump. So I changed the pump and still nothing. Is there a test I can do to check if the computer is bad?
Have you checked the fuel pump relay?
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Old 11-30-2011, 01:06 PM   #14
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Yes, I checked the relay and it was fine. I know there is a lot of chatter on the ecu problem. I was just curious as to if there was a test I could run specifically for this to make sure that is my problem before I drop another 250 into it.
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Old 12-03-2011, 09:28 PM   #15
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Any ideas? I'm at my end with this.
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Old 12-03-2011, 10:08 PM   #16
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Is the check engine light coming on when you turn the key to crank it over?
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Old 12-05-2011, 08:16 PM   #17
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Yes the engine light comes on. I replaced the fuel pump a couple of days ago and it started right up and ran for 16.3 miles. Then as I turned a corner it died not to start again.
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Old 02-27-2012, 08:00 PM   #18
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mine has spark and fuel but no start and the ce light is also comin on do i need a new computer or wat. i changes cam and crank sensor as well im all out of ideas.
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Old 03-01-2012, 08:39 PM   #19
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mine has spark and fuel but no start and the ce light is also comin on do i need a new computer or wat. i changes cam and crank sensor as well im all out of ideas.
If you have fuel and spark then you DO NOT have a bad ECU. you need to check compression and the order of your spark plug wires.
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Old 03-01-2012, 08:42 PM   #20
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spark wires are in order and i dont know why i would loose compression its ran awesome and then one morning it just died after running like 2 seconds idk im diein here.
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Old 09-12-2012, 03:24 PM   #21
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I've read in another thread that this sympton is caused by a bad fuel pressure regulator and that what happens is the fuels drains back into the tank and then you have to turn the key ot the on position to get the CE light to come on and the fuel pump to kick in and push fuel to the imjectors. I never read anything about a bad ECM or computer.
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Old 05-25-2013, 07:52 PM   #22
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Would radio ACC have anything to do with ECU?

I have a 1992 6cyl man Wrangler. The radio / accessory fuse under the dash was blown. I replaced it. Turned the key to check if it was working - everything light as it should have and radio came on. Turned key off, 5 minutes later nothing. Ignition on and No check engine, no dash indicators at all. Strong crank. Checked relays manually, all working and checked the ECU fuse under hood - not blown. Does it make ANY sense that the radio fuse, or whatever blew that fuse, tripped up the ECU? I've had the key sitting in ON position for an hour, and no mystery CE lights have come back.
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Old 09-03-2013, 07:02 PM   #23
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I have a 1992 6cyl man Wrangler. The radio / accessory fuse under the dash was blown. I replaced it. Turned the key to check if it was working - everything light as it should have and radio came on. Turned key off, 5 minutes later nothing. Ignition on and No check engine, no dash indicators at all. Strong crank. Checked relays manually, all working and checked the ECU fuse under hood - not blown. Does it make ANY sense that the radio fuse, or whatever blew that fuse, tripped up the ECU? I've had the key sitting in ON position for an hour, and no mystery CE lights have come back.
Did you ever get your Jeep fixed?
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Old 09-04-2013, 02:18 PM   #24
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Each vehicle had the same symptoms and the symptoms seam to be worst in the cold. So if your jeep cranks but wont start with out a check engine light, then starts when once the Check Engine light comes on then replace your ECM.
I had these exact symptoms. I replaced the 3 capactors in the ECM and all is good. Complete job took less than an hour and under $5.

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