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post #1 of Old 12-04-2007, 09:28 PM Thread Starter
sasquachYJ
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1999 XJ Cherokee 
 
Join Date: Oct 2007
Location: New Lenox, Illinois
Posts: 180
Crash Course In Brain Surgery Replacing Capacitors On ECU

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
http://i259.photobucket.com/albums/h...l/S7301732.jpg

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.
http://i259.photobucket.com/albums/h...l/S7301729.jpg
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.
http://i259.photobucket.com/albums/h...l/S7301731.jpg
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)
http://i259.photobucket.com/albums/h...l/S7301732.jpg
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.
http://i259.photobucket.com/albums/h...l/S7301734.jpg
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.
http://i259.photobucket.com/albums/h...l/S7301740.jpg

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post #2 of Old 12-04-2007, 09:34 PM
Tomb Raider
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Join Date: Aug 2005
Location: Jefferson City
Posts: 4,995
Quote:
Originally Posted by sasquachYJ
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
http://i259.photobucket.com/albums/h...l/S7301732.jpg

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.
http://i259.photobucket.com/albums/h...l/S7301729.jpg
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.
http://i259.photobucket.com/albums/h...l/S7301731.jpg
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)
http://i259.photobucket.com/albums/h...l/S7301732.jpg
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.
http://i259.photobucket.com/albums/h...l/S7301734.jpg
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.
http://i259.photobucket.com/albums/h...l/S7301740.jpg


You my friend.....





Are ALOT smarter than me.


Strong work.

I like to build stuff. Want to know what I build, you can google it HERE
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post #3 of Old 12-04-2007, 09:37 PM Thread Starter
sasquachYJ
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1999 XJ Cherokee 
 
Join Date: Oct 2007
Location: New Lenox, Illinois
Posts: 180
it isnt as hard as it seems, its just really hard to under stand how all it works and kind of nervous in tearin apart a somewhat good ECU!
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post #4 of Old 12-04-2007, 09:39 PM
BlackRhino
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1991 YJ Wrangler 
 
Join Date: May 2007
Location: Prescott
Posts: 921
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.






Click Free. Looks good, definitely cheaper than replacing the thing.

Black '91 YJ, pretty much stock for now. Finished engine rebuild. Runs beautifully.
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post #5 of Old 12-04-2007, 09:59 PM
SonofSam02
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1994 YJ Wrangler 
 
Join Date: Oct 2006
Location: Odenton, Md
Posts: 476
i vote sticky or something like a
"THIS IS THE PLACE FOR THE GOOD WRITEUPS"
so that they are all in one place
cause for as often as this comes up
especially with it getting colder
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post #6 of Old 12-05-2007, 01:34 AM
YJ_
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Join Date: Dec 2005
Location: Cincinnati, OH
Posts: 344
This is awesome, I had a 94 ECU do the EXACT same thing. Its sitting in my basement and I had no idea what to do with it... Think I'll try this out and either sell it or sell the one in there now... props on the writeup

I second on the sticky (or add it to the FAQ)

94 YJ_

"if ya can't duct it **** it"
[] IIIII []
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post #7 of Old 12-05-2007, 04:26 PM Thread Starter
sasquachYJ
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Join Date: Oct 2007
Location: New Lenox, Illinois
Posts: 180
when you solder the capacitors, make sure and double check the connection, because if it is bad the it will not work correctly. Just to let everyone know, me and my buddy are not very good with wiring, so dont be afraid to attempt this! It isn't as hard as it seems.
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post #8 of Old 12-05-2007, 06:33 PM
votedean
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2001 TJ Wrangler 
 
Join Date: Nov 2006
Location: Longmont, Colorado
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yeah, I just did this a few weeks ago. Worked awesome. I'm not that great with soldering either. In fact, I didn't need to use any solder on this job. I was just very careful not to pull too much of the old solder out with the crappy capacitors. Then I just heated up the old solder points and slid in the new caps. Took me about twenty minutes.
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post #9 of Old 09-23-2008, 08:54 PM
green95rcjeep
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1995 YJ Wrangler 
 
Join Date: Aug 2008
Location: Down South
Posts: 17
The clicking relay monster

I think I try this. I have traced the fuel pump wires. I changed both battery cables. I changed the battery. I changed the ignition switch. I changed the relays. I looked at and dismantled the fuse and relay box. I bought a new fuel pump. I changed the fuel filter. I check for ohm resistant in the crank position sensor. AND DO NOT FORGET I PRICED A NEW PCM. WOW! I'm still not broken. I once read some where that a man that owns a jeep is always ready to work on it. I think it went some thing like that

If you chase 2 birds, they both will get away. StAy FoCuSeD
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post #10 of Old 10-18-2008, 04:22 PM
hsdsashs
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Worked awesome. Jeep Fired right up on the 1st Try. Thanks for the posting !!!!
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post #11 of Old 10-18-2008, 05:06 PM
jay-h
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Why did you assume the problem to be capacitors, as opposed to the many other electronic components on the board?
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post #12 of Old 10-18-2008, 07:37 PM
foggybottombob
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1984 CJ7 
 
Join Date: May 2008
Location: Monument Colorado
Posts: 5,840
Being an electronics engineer for the last 30 years I had the same question as jay-h. How in the world would you know to change some electrolytic caps instead of any one of a hundred other parts? I suppose electrolytics are bad about the electrolyte drying out after a long term exposure to heat but I would think it was pure luck for changing those to fix the whole circuit board.
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post #13 of Old 10-23-2008, 02:21 PM
jws1961
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what are the capacitors needed for the 4.0 engine? Are they the same?
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post #14 of Old 10-23-2008, 03:42 PM
HalfShaft
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1994 YJ Wrangler 
 
Join Date: Dec 2007
Location: Northern Illinois
Posts: 85
I am an Idiot

4.0 caps are 22Uf and 32 volt. Radio Shack 1.29 each.

I will provide this information provided you do not let another soul know.

Be carefull with what kind of sealant is used to re-seal the caps/ solder points and the circuit board to the case. Make sure there is no water or water based solvent in it what so ever. "a guy I know" used caulk, didn't check that it was latex based. Bad for everything including solder, circuit boards and traces on them.

Everything is better now, "he" got real good at fixing circuit board traces.

Just a little humble advice.

"Quitters only get stuck in the same place once"

1993 Grand Cherokee Limited - "Rose"
1994 Wrangler - "White Whale"
2000 Ford F250 Diesel - "Bigfoot"
2000 Ford Excursion V10 - "Hungry"
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post #15 of Old 10-23-2008, 07:07 PM Thread Starter
sasquachYJ
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Join Date: Oct 2007
Location: New Lenox, Illinois
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the way i was told of the capacitors could be the problem is my friends 94 started doing acting up when it was cold out and the elecrolite fluid or whatever its called freezed up and messed up the capacitor. my friends brother works on sound and circuit boards for a living and he told us that could be the problem and we tried it and it worked. it was pretty much hit or miss you just have to get the right capacitor.

stock 99 for now
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