95 Wrangler wont start....

[jonzjeepyj]

This is for a '94 Yj 2.5 liter ECU repair,
Symptoms: turn key but no check engine light but after a few minutes of the key on, you hear clicking and then the check engine/shift light come on and you hear the fuel pump prime and it starts right up.

-I've been dealing with this for about 3 weeks now since the weather has gotten cold. when the problem first arose I thought it was a bad fuel pump so I replaced it and the strainer still same problem. I was really getting fed up with the problem of leaving it and coming back and having to wait 5 minutes before it would start, i searched all over jeepforum for an answer i found sentinel02's thread about checking all the plugs leading to the ECU very complex but informative but i didnt feel like checking all the electrical components. so I either had to send my ECU out to get rebuilt or rebuild it myself so I decided to take it step by step to show in detail how its done, due to the fact that i havn't seen a step by step version of this and also I noticed lots of '94 YJ owners having the same problem.

Tools/Equipment:
Small needle nose plyers
Soldering gun(including flux, wire)
x3 220 uf 35wvdc capacitor (radio shack) the stock spec is 25v but 35 seemed to work also.
utility knife
silicon/sealer
8mm socket

STEPS:
1. take ECU out of Jeep you'll need to remove the washer fluid container held on by one philips screw on the side and then it just slides right out.
2.now for taking off the ECU disconnect the main wiring harness leading into it using a 8mm socket, when loosen bolt and pull off gently being sure not so break any contacts.
3. once the harness is off there are 3,8mm bolts just undo them and the ECU will pop right off the firewall.
4.Take the cover off by prying at the prongs that hold the lid to the casing.
5.once cover is removed run a utility knife along the edge close too the plastic once you have cut alll the way around gently pull the ECU itself out of the casing.
6. now heres were it gets tricky. locate the 3 capacitors on the top of the ECU

7. After locating them you have to dig out on the underside of the ECU to expose the ballistics encased circuit board. Its a tidious task but it has to be done to get the capacitors out.

8. now that the contacts are exposed take a soldering gun and melt away the factory solder points, have a friend grab the contact on the top side and pull as you melt the solder.

9.After you get them out take the gun and put it were the contacts went through to make a hole for the new capacitors to go through.
10. now its time to put the capacitors in, make sure that the side with the stripe is facing the big metal tower (reference picture)

11.push them all the done and solder them on the other side back in the original place making sure the stripe is facing the correct way.

12. once they are soldered in place take nailclippers and clip the extra wire.
13. take putty or silicon to reseal the holes wait for it to dry and follow the take out procedure in reverse order.

 

[diforbes]

Excellent write up. Guess I know how I am spending my Sunday...

 

[superj]

wow, that is some serious water proofing on that mother board

 

[jfrabat]

Excellent write up; unfortunately, I do NOT have the skills to mess with electronics (other than selling them, that is!). But, on the bright side, I DO carry a spare ECU in my Jeep!

 

[markusgov]

Ok...so early this morning, I turned the key to the on position and let it sit for about 10-15 min. Dang thing started right up. I'm not that into rebuilding electronics either and I don't carry a spare with me, LOL, so I think I'll let some one do it for me. Thanks so much for the help guys. Mark

 

[diforbes]

Well, should have heeded the insights of others, but I figured since I know nothing about electronics, how hard could it be (same logic got me thru new transmission and clutch this summer, tho it did take a while)? Bottom line, I have a rebuilt ECU on order, no regrets, for $10 in parts, my kid and I got to break things together. Only insight to share is we managed to pull the capacitors out but leave the wires behind (then proceeded to mangle everything else trying to get the wires out), if we had left the old wires in I think we might have been able to solder the new capacitor wires to the old wires.

 

[superj]

ha ha ha. that is how i learned a lo when i was younger. the expensive way of learning though

 

[diforbes]

Well, got the ECU today, plugged it in, now jeep running like crap. Think it is missing two cylinders...any thoughts? Was the old ecu covering up the problem or is the new one the issue? Ran fine before, other than not starting when cold...does a new ECU need to "adapt?"

 

[jonzjeepyj]

One thing you must do is clear the presets on the rebuilt ECU. You must drain
the capacitors that hold the charge. The ones that went bad on your other
ECU. They will hold memory and where ever the last set points were in the Jeep
it used to be at is where it is at now. Take the + (POS) battery terminal off the
battery and ground it on the Neg battery terminal . This will drain all stored
power in the capacitors. It takes a minimum of 50 starts and run cycles for the
computer to learn and adjust to your Jeep. Remember, your ECU is smart and
slowly adjust to your ever changing set points in your Jeep. It needs time to
relearn your jeep. All sensors send back info to the ECM and it learns your set
points and slowly adjusts to gain maxim efficiency.

Keep Us Informed,
John

 

[diforbes]

Yeah, even tho the rebuilt ECU was supposed to be plug-n-play, I did run across what you suggest, and tried it. No difference. Called company I bought it from, they said it should work immediately, so they are sending out a new one, it comes reset to factory default settings. Btw, have been trying to drive it to go thru cycles just out of curiosity, but it keeps dying and I can't imagine running on 4 cylinders is particularly good for it. Should have a new one in a few days.

 

[Buzrd101]

John,
Thanks for awesome detailed fix on the ecu. I had the exact same symptoms. When it got cold, no start until I heard a clicking sound and then the engine light would flash until it fully lit. Only then would it start.
So, replaced the 3 capacitors, and the next day it was in the 20's guess what? Turn the key and a strong check engine light. Starts right up. For $5.00, 1.5 hrs. I fixed it and saved $over $200. I'm just a dumb toolmaker, so with a little patience and following this detailed guide, I really believe anyone can do it.First time poster.Thanks guys.
Frank

 

[cclsyj89]

My friend had to let his sit for over five minutes until it built up enough power.
He would literally turn it on in his garage and go back inside for five minutes. I
only said 30 sec because you said it took that long for your check engine light
to come on. Just sit in your Jeep and watch and wait for the check engine light,
up to 6-8 minutes long. it should be long enough. If not, I will send you a link
on how to rebuild your ECU if you want it.

I am having the same problem with my 89 YJ 2.5. I would like to have that link.

 

[jimbob2001]

It sounds Like an Electrical Issue.... But, when it won't start --- have you checked the Pressure on the FUEL RAIL? Also, Are you getting Spark at ANY of your Plugs? Codes? On the Issue of Rebuiling your ECM --- It can be done. BUT, ECM is an Electronic Device --- Certain Precautions MUST be observed. (Easy to damage this Part) Just a NOTE of Caution --- Good Luck! -- JB

 

[chesabill]

I had the same issues with my 4.0 in line 6 cylinder 1991 wrangler. After reading the fix for the 4 cylinder ECU I went at the one on my 6 cylinder. The only real difference was that instead of having 3 of the 220 uf capacitors, mine had two of the 220uf and one 470uf with the 470uf being located more to the middle of the board. All capacitors were easily seen without any removal of weather compound. Bought the capacitors at Radio shack and installed them. Everything now works as it should. Suggestion for cleaning out the rubberized compound on the front and back of the board is to use round wooden toothpicks after you get a little bit of it removed. The tooth picks do a nice job and you don't run the risk of scoring up the printed circuit board. Also as noted in the original directions, take note of the location of the band / stripe on the capacitor cover and make sure you install the new ones with the band / stripe in the same orientation. Thanks to all for the support offered by this site. Bill

 

[tims93yj]

I want to say thanks for this add, it has really helped me with my jeep. I just tryed this and finally this jeep of mine has started with a computer that would not start my jeep. Now i have a litte issue with my jeep. My jeep is now over charging due to this computer. Now i am just asking if you have come across this problem with the rebuild of the computer. Reason for me asking is that the computer that i used for this rebuild was outside in the weather elements. It has sat outside for a couple of weeks, so i am not sure if it just beacause of this reason for the over charge. I do have abother computer that i might just rebuild and try this again. So i am just wondering if this was an issue by someone else.........AGAIN THANKS FOR THIS ADD!!

 

[JPNinPA]

Verify all power and ground connections. And clean them. The PCM failing is not a normal item, throw it does occur. Use a voltmeter to measure the voltage on the battery when it is overcharging. What is the reading?

 

[tims93yj]

The meter was telling me at about a 18.6volts, i could hear it thru my radio badly. I took the computer out and put the other back and it went back to normal. I am thinking its that computer, i had it outside for a bit with no silicone covering it. I have 3 computers here so i am thinking i might try abother one to see if it cures my issue.