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Old 03-03-2009, 06:12 PM   #1
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90 YJ - how do I get to the ECU?

Howdy,
I'm new to this forum and I'm new to Jeeps - but since my old mechanic and the Jeep dealer can't figure out the problem - without charging me more than I earn.....I guess I'm going to learn.
For numerous reasons which I won't get into, I'm going to change out the ECU. I see it back behind the glove box, but I can't get the glove box out. I took out the four screws that I can see....is there some trick to popping it out? Chilton and Haynes are no help. It's a 90 YJ
Many, many thanks.
Al

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Old 03-03-2009, 06:21 PM   #2
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well check page 12-2 the ecu isnt inside the tub at all its on the drivers side,inside the hood.you could probably take the ecu out with the litle space you have but,for more comfortably move everything out the way,like the antifreeze reservoir ,the wiper fluid bottle ,and if you still dont got enough space remove the fender.Good luck, and becareful with the electrical stuff.

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Old 03-03-2009, 06:21 PM   #3
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12-2 in the haynes manual
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Old 03-03-2009, 06:41 PM   #4
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Thanks YjMopower,
It's too cold and I'm too old to go crawling around in it right now. You're right, I see the diagram in the Haynes...it shows the Engine Controller right where you said......the Chilton says it's (the ECU) on the inside...I'm totally confused. The Chilton must be talking about a different year. But I see a box back up behind the glove box that looks like the ECU I bought. Maybe I'll just give up for the night and go drink. It'll be clearer in the morning.
Al
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Old 03-03-2009, 07:03 PM   #5
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No Problem-O
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Old 03-03-2009, 09:10 PM   #6
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his 90 might be a 4.2, i think that was the last year for it. the 4.2 ecu on my 87 was behind the glove box. i never remember if 90 was 4.2 or 4.0. 89 was 4.2 for sure. 90 was tbi 4 banger, and 4.2 six i think.
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Old 03-04-2009, 03:07 AM   #7
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Thanks jpdocdave,
So maybe I'm not going crazy. My mechanic was frustrated and said I had a morphrodite Jeep cause the ECU wasn't where he expected it to be either. I'm pretty sure it's behind the dash box. Any easy way to get the dash box out without taking the entire dash out? The diagrams show it as a separate component; I took the four screws out that I can see on the front, but can't seem to find the trick for popping it out.
And by the way, thank's for letting me on this forum!
This all started with the Jeep starting sometimes and not starting other times. No codes on the computer. Have replaced the CPS and the throttle IAC. The engine runs great, never stalls once it starts. My mechanic and the dealer can't figure it out and it's been going on for about a year. Thought I'd replace the ECU and see what happens.
Al
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Old 03-04-2009, 06:03 AM   #8
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Originally Posted by jpdocdave View Post
his 90 might be a 4.2, i think that was the last year for it. the 4.2 ecu on my 87 was behind the glove box. i never remember if 90 was 4.2 or 4.0. 89 was 4.2 for sure. 90 was tbi 4 banger, and 4.2 six i think.

89 was TB 4 banger.
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Old 03-04-2009, 09:02 AM   #9
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Quote:
Originally Posted by Bensjeep View Post
Thanks jpdocdave,
So maybe I'm not going crazy. My mechanic was frustrated and said I had a morphrodite Jeep cause the ECU wasn't where he expected it to be either. I'm pretty sure it's behind the dash box. Any easy way to get the dash box out without taking the entire dash out? The diagrams show it as a separate component; I took the four screws out that I can see on the front, but can't seem to find the trick for popping it out.
And by the way, thank's for letting me on this forum!
This all started with the Jeep starting sometimes and not starting other times. No codes on the computer. Have replaced the CPS and the throttle IAC. The engine runs great, never stalls once it starts. My mechanic and the dealer can't figure it out and it's been going on for about a year. Thought I'd replace the ECU and see what happens.
Al
Are you getting fuel when it won't start?
Are you getting spark?

I had/have a similar problem on a Grand cherokee, turned out to be an intermittent fuel pump problem.
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Old 03-04-2009, 11:21 AM   #10
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Hi all.
The ECU is definitely behind the dash and not in the engine compartment.
Sometimes I get spark and no fuel....it will fire up with starter fluid sometimes. And sometimes I don't have spark. My mechanic was not getting "pulse to the injector" and then he was. So I can't isolate it to spark or fuel. That's what got me thinking ECU.
My mechanic doesn't want to even see it anymore, and the dealer seems to be at a loss too; they'd be glad to keep replacing parts but I think I can replace everything a lot cheaper than they will. I'm absolutely not a mechanic but I can usually figure things out. Especially since I don't want to spend a fortune.
Al
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Old 03-04-2009, 12:02 PM   #11
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I have an 89 YJ with a 4.2. I replaced the Ignition Control Module which is under the anti-freeze overflow container under the hood. The Electronic Control Module (computer) is located behind the dash, behind the heater controls. I would replace the Ignition Module before replacing the computer. This part goes and is normally stocked at most auto part stores. It's held on with 3 10mm bolts and is easy to replace. I almost replaced the computer when I had a problem and was advised to replace the Ignition module first. I'm glad I did because that was the problem. Saved a lot of work.
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Old 03-04-2009, 12:07 PM   #12
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Just as a follow up, my 89 had the same symptoms. Sometimes it started, sometimes not. Sometimes after the engine was hot it started to stumble, backfire and not take gas. Replacing the Ignition Control Module solved the problem. The symptoms disappeared.
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Old 03-04-2009, 02:31 PM   #13
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Hi Kik,
I'm just about convinced to try the ignition control module. It's 150 bucks but it looks fairly easy to replace. Might as well go with the easier thing first.
Thanks for the input.
Al
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Old 03-04-2009, 06:01 PM   #14
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oh okay so there are two different things.This is good to know, i just removed my icm today, couldn't get to the bottom screw, it was a different head found that out after i yanked it out.
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Old 03-04-2009, 06:20 PM   #15
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I just picked up the ICM. It's supposed to be 60 degrees in Nebraska tomorrow and I'm working outside. What more could I ask for?
Thanks for the help, all. I'll let you know how it goes.
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Old 03-04-2009, 08:25 PM   #16
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Had the same problem with a friend's Suburban and it was the fuel pump in the tank had been replaced and installed improperly. The pump was loosing prime intermittently and driving him crazy. A failing one can do the same thing. If it won't start when it's hot, but will when cool the ICM could be the problem.

New to jeeps but that's where I'd start.

At least yours will move when it DOES start. Mine runs and won't go. Getting ready for surgery when the weather gets better or I drag it to my friends race car shop where there's a lift.

hope you find the problem without changing a bunch of unnecessary stuff.
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Old 03-05-2009, 06:22 AM   #17
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Well, I changed the ICM last night. It started about 8 times in a row last night and started first time this morning. I have high hopes that the ICM was the problem. Unfortunately, in the past, everytime the mechanic or dealer did something, the Jeep started okay for days or weeks and then the problem started up again. If it starts up again I'll probably do the fuel pump and the ECU. What the heck, by the time I'm done I'll have a new vehicle. BUT, I have a feeling, from the strong way it's starting, that the ICM was it. Thanks to everyone for your advice!
PS - I'd still like to know if it's possible to take out the glove box without removing the entire dash. Just out of curiosity and for future reference. Anyone know?
Thanks again! This is a Great website!
Al
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Old 03-05-2009, 05:50 PM   #18
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I'm glad that it's working. When I replaced mine I thought that it could be something else. 3 months later and everything is working fine. Give an update down the road. Can't help with the glove box. I don't know how many miles you have, but I decided to change the fuel pump after 94,000 even though the original one was still working. Why take a chance.
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Old 03-06-2009, 06:21 AM   #19
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Thanks kik - I'll let you know what happens. It worked all day yesterday. The real acid test will be when I'm 40 miles away from home, at night, and cold. You know how that goes. It's got about 120, 000 miles on it. I may very well go ahead and change out the fuel pump. Also, I read someplace that you should change the oxygen sensor at 80,000 miles.
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Old 03-06-2009, 10:32 AM   #20
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It should be changed. I replaced mine at 90,000. I also just replaced the coil and alternator.
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Old 01-02-2013, 10:50 PM   #21
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I know I'm really late, but if anyone is still wondering how to remove the dash... I just replaced the window cowl on my 90 yj and saw 5 screws that hold the dash in back, so to remove the dash you gotta take those out too. First, fold down the window, to do this you might need to get a little wd-40 on the t40 torx screws that hold to window in place as mine were rust locked. Also, take off the sun visors as lowering the window with those on will probably strip out the screws. Hope this helps somebody...
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Old 01-03-2013, 05:27 AM   #22
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You do not have to lower the windshield to remove the dash that is nonsense.
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Old 01-03-2013, 07:30 AM   #23
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You do not have to lower the windshield to remove the dash that is nonsense.
to remove the plastic cover and the gauges you don't but to remove the entire sheetmetal you do...
90 was still the 4.2..91 started the 4.0
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Old 01-03-2013, 07:11 PM   #24
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There are 4 nuts on the back side 2 on each handle end. You have to reach up behind the dash to get to them.

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