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Old 10-28-2011, 07:34 AM   #1
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Cold Weather Problem

For the last few days my 1991 Jeep Wrangler Sahara has refused to start in the morning. The mornings have been appx 30 degrees. After it warms up a little outside the Jeep starts immediately. Searching the internet, it looks like the problem mght be the ECM. Any other ideas that might be a little cheaper???
Thanks!

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Old 10-28-2011, 07:52 AM   #2
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try turning it on to accessory for about 10 seconds before trying to start it...i have roughly the same problem and that works for me each time.

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Old 10-28-2011, 08:58 AM   #3
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Thanks!
We'll try it tomorrow morning!
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Old 10-28-2011, 09:22 AM   #4
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I noticed exactly the same thing this morning, and this morning being the coldest morning so far. Tomorrow I will try that too.
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Old 10-28-2011, 09:46 AM   #5
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mine did that in 2009. On cold mornings I would turn the key to on and nothing... 5-20 minutes of sitting and the check engine light came on with the fuel pump growling at the same time. Then it runs ok... I replaced the PCM, no problems since.

Turning the key to on and not hearing the fuel pump growl and having to wait anywhere from 1-20 minutes (with the key to ON) is a classic sign it has failed.

I had great luck with autocomputerexchange out of FL. They sent a new one pre-programmed to my VIN. Powdercoated black, new labels, very nice.
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Old 10-29-2011, 08:03 AM   #6
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Thanks, I was afraid of that. It's cold again this morning and nothing worked. We'll check with autocomputerexchange today about the PCM.
Thanks again!
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Old 10-29-2011, 08:52 AM   #7
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Autocomputerexchange folks were great and we have a PCM on order. It's odd, but the Haynes Manual doesn't show where the PCM is located or how to replace it. Any ideas where to find this info for a 1991 Wrangler? Thanks for all the help!
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Old 10-29-2011, 09:50 AM   #8
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Just a short update. In trying to get the necessary part number by VIN from a dealer, we were told he could not locate a part # for our 1991 Jeep Wrangler so we cancelled the order for the PCM/ECM. Dealer suggested 2 sensors but could not get more specific until next Monday. Anyone else heard of such a thing?
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Old 10-30-2011, 02:27 PM   #9
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Hi, all! This is downtownoffice1's hubby. We still, can't get the Jeep to start! It was suggested to me that I replace the oxygen sensor. I drove the 40-miles to the nearest AutoZone. I took the old sensor with me to match it with a new one. The sensor they sold me is a Bosch and doesn't resemble the old one. The guy at Autozone insisted it was the right one. Still, no start! I replaced the coil, also. This is a real head-scratcher.

Question: Can an old oxygen sensor be cleaned and re-used?


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Old 10-30-2011, 02:43 PM   #10
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Chuck,

I don't believe you can, once they have gone the way of the Dodo you just have to put a new one in.

It is getting fuel at all? You can try starting it, if it does not start then pull one of the spark plugs and see if it is wet.
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Old 10-30-2011, 04:40 PM   #11
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Thanks, for your response! The fuel-pump and filter were changed this past March. As it turned-out, I went ahead and put the new Oxygen sensor in. My wife asked if she could try starting it... why not! It started! I'm curious if, it might be the manifold intake air temperature sensor??? The MAP sensor was replaced in June of this year. Our Jeep won'tstart on mornings below 40-deg.


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Old 10-31-2011, 05:22 AM   #12
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After messing with our Jeep, all week-end, I tried turning the ignition to 'accessory', let it set that way for 10 - 12 seconds and tried to start it. I barely bumped the starter and it fired right up. After starting, the Jeep idles and runs like it should.
The outside temperature at the time I started it this morning was: 37-deg.
I'm curious... could it be that, letting the ignition switch set in thaccessory position, allows the ECM to 'warm-up' and get things going?


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Old 10-31-2011, 03:34 PM   #13
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after a short time, the ECM will kick the fuel pump on and you should hear it growl when it comes up (for a second)

Yes, you could live with it but personally I was tired of sitting in the driveway every morning for 10-20 minutes waiting for the darned thing.

You also should not need a part number from a dealer, Auto computer exchange programmed mine off from my VIN. They should only need make, model, year, trans type and VIN number.

Sounds like confusion somewhere??? Personally, I feel everything you do besides getting the PCM rebuilt or replaced is waisting your time. I only say this because I've seen this issue so many times, and time and time again, its the computer causing the delay. Specifically three capacitors on the main system board that get all cooroded over time.
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Old 10-31-2011, 06:36 PM   #14
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do you hear a clicking noise? if so recently i had the same problem. my father said its the starter. he experienced it with many of his old cars, all he would do, he would take a crow bar and hit/tap the starter, and it would work. ive done it last night and this morning it worked. he says it shakes of any frost that could be on the starter itself
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Old 11-01-2011, 05:21 AM   #15
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The past two mornings, I've been turning the key to 'accessory', holding it there for 10-seconds then try to start it. It fires right up, idles and runs just great.


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Old 11-01-2011, 08:44 AM   #16
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The past two mornings, I've been turning the key to 'accessory', holding it there for 10-seconds then try to start it. It fires right up, idles and runs just great.


Chuck
good deal, work it while it still works!!! let us know what it does when it gets down to about 25-27 degrees.
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Old 11-01-2011, 11:57 AM   #17
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good deal, work it while it still works!!! let us know what it does when it gets down to about 25-27 degrees.
That's kinda what we've been thinking... work it while it works. I'll be sure to post the results when it gets that cold.


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Old 11-01-2011, 02:26 PM   #18
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If, it gets colder than 25 - 27 degrees... I'm not gonna start!


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Old 11-03-2011, 08:15 AM   #19
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good deal, work it while it still works!!! let us know what it does when it gets down to about 25-27 degrees.
This morning, at 7:00, the temperature was 26-deg. I tried starting our Jeep by holding the ignition at accessory, counting 10-seconds and no start. It sounds like when I'm trying to start it, there's no spark. I'm really thinking, the ECM needs to be replaced!? I'm stumped. I'm calling our repair shop and see what he says.


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Old 11-03-2011, 09:46 AM   #20
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This morning, at 7:00, the temperature was 26-deg. I tried starting our Jeep by holding the ignition at accessory, counting 10-seconds and no start. It sounds like when I'm trying to start it, there's no spark. I'm really thinking, the ECM needs to be replaced!? I'm stumped. I'm calling our repair shop and see what he says.


Chuck
If you really want to know for sure, pull your ECM off the firewall. Its easy, first remove your washer fluid res. (drivers side) then remove the cable off the front (lay it somewhere clean) and there are only three screws holding the computer to the firewall. Pull it out, bring it in the house and open up the shell. You should find a few capacitors in there that are toast. Either burnt, leaking or otherwise cooroded. Unless its an experienced jeep mechanic you are contacting he's gonna tell you to replace everything you already did. We've seen your symptoms time and time again, each time, its the computer.

Let us know if you attempt to pull it open... or, if the mechanic wants to start throwing more hardware at the jeep that really won't make a difference.

...just trying to help a fellow jeeper experiencing the same headaches I've already fixed. You story brings back bad memories, I was pretty pissed at my jeep when it was doing that. 2009, new computer, never had a prob since. Even down to -18 degrees last winter. Its so common that Im considering adding rebuilding these to the list of things my wifes computer store takes care of. If I can identify the bad capacitors theres no reason I can't solder new ones in.
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Old 11-03-2011, 10:04 AM   #21
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here is a good write up of how to replace the capacitors, not suggesting to try it but the pics may show you where they are on the board.

Crash Course In Brain Surgery Replacing Capacitors On ECU - JeepForum.com
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Old 11-03-2011, 10:07 AM   #22
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oh, and if you do pull the ECU, disco the battery first and do not hook it back up until the UCE is wired back into the jeep.
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Old 11-03-2011, 10:37 AM   #23
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If you really want to know for sure, pull your ECM off the firewall. Its easy, first remove your washer fluid res. (drivers side) then remove the cable off the front (lay it somewhere clean) and there are only three screws holding the computer to the firewall. Pull it out, bring it in the house and open up the shell. You should find a few capacitors in there that are toast. Either burnt, leaking or otherwise cooroded. Unless its an experienced jeep mechanic you are contacting he's gonna tell you to replace everything you already did. We've seen your symptoms time and time again, each time, its the computer.

Let us know if you attempt to pull it open... or, if the mechanic wants to start throwing more hardware at the jeep that really won't make a difference.

...just trying to help a fellow jeeper experiencing the same headaches I've already fixed. You story brings back bad memories, I was pretty pissed at my jeep when it was doing that. 2009, new computer, never had a prob since. Even down to -18 degrees last winter. Its so common that Im considering adding rebuilding these to the list of things my wifes computer store takes care of. If I can identify the bad capacitors theres no reason I can't solder new ones in.
What great help and information! Thank you! I've checked-out the cost of a Mopar ECM and the average cost is $636.00... Yikes! Have you ever done business with or know of: Automotive Electronics Solutions? They rebuild ECM/PCM's. I want to solve the problem but I'm not made of money, either. I'm tired of throwing new parts at it, too.
I did hold a hair dryer on the ECM, this morning (26-deg.) and the dang thing started! Thanks again, for all your help.


Chuck
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Old 11-03-2011, 11:24 PM   #24
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mine did that in 2009. On cold mornings I would turn the key to on and nothing... 5-20 minutes of sitting and the check engine light came on with the fuel pump growling at the same time. Then it runs ok... I replaced the PCM, no problems since.

Turning the key to on and not hearing the fuel pump growl and having to wait anywhere from 1-20 minutes (with the key to ON) is a classic sign it has failed.

I had great luck with autocomputerexchange out of FL. They sent a new one pre-programmed to my VIN. Powdercoated black, new labels, very nice.
a pcm like unichip could fix the problem?
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Old 11-04-2011, 07:53 AM   #25
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^ not sure...
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Old 11-04-2011, 04:21 PM   #26
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^ not sure...
I've got our mechanic trying to locate one. What I don't understand is, why they are so hard to find? Do you know of a good source for ECM's? Also, I was told that dealers in my area can only get re-builts. That's fine, as long as they are re-built good.


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Old 11-05-2011, 07:47 PM   #27
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^ not sure...
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a pcm like unichip could fix the problem?
We were going to go through Auto Computer Exchange and checked up on them to see what their reputation was like. According to all the complaints... not good. I read somewhere that the original owners sold the business awhile back!?


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Old 11-05-2011, 08:00 PM   #28
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^ not sure...
I guess, our luck is running out. My wife has been driving the Jeep to work, the last couple days (20-miles, both ways) with no problem. Hold the key on 'Accessory' 10-seconds and it fires right up. Tonight, on her way home, it stalled twice and she told me the needle on the amp gauge was bouncing irratically. I'm assuming, this is related to a bad ECM!?
Thanks in advance, for your help.


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Old 11-05-2011, 08:35 PM   #29
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my cherokee did this exact same thing if it was below 40 degrees. Just wait till the engine light comes on and it fired right up.
I ended up swapping out the ECM and PCM, I was able to get the ECM from the junkyard for like $20 and luckily it worked.
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Old 11-05-2011, 08:39 PM   #30
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my cherokee did this exact same thing if it was below 40 degrees. Just wait till the engine light comes on and it fired right up.
I ended up swapping out the ECM and PCM, I was able to get the ECM from the junkyard for like $20 and luckily it worked.
We've been talking mostly ECM, here. The PCM is new to me. What is the difference?


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