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Unread 08-05-2008, 11:43 PM   #1
AtzMaBoy
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1988 YJ Wrangler 
 
Join Date: Jun 2008
Location: W-PA
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"How-To" Repair your ECU

Someone great once said, “Necessity is the mother of all invention” (Plato). Well, I don’t claim to be Plato, but I do have the High Honors of possessing “Necessity”. That brings me to my point.

While Dad and I were working on this 1988 YJ project, we developed “necessity”. The Jeep was purchased with a suspect computer and wiring problem and in a non running condition. An eBay Wiring harness and ECU made short work of that “no run state” and the project rolled on. Until… The full description of that failure and symptoms can be found in this thread:

http://www.jeepforum.com/forum/f12/fuel-pump-symptoms-need-help-574745/

I would like to share what I found and what was done to REPAIR the ECU. If only one person can gain from this experience, I would feel like our blessing could be passed along to another in need.

First the basics: 1989 YJ, 2.5 4 Cylinder, Throttle Body Injection, Manual 5 speed.
Failure Symptoms: Fuel Pump Runs continuously with key turned from Off to ON position, No Spark, No Fuel Pulse at TB Injector.
ECU’s - common Part No. EF8953005023 (and the Renix 9-2099)
Renix (Remanufactured; original unit in Jeep, a non running purchase)
Bendix (eBay + Harness, worked when installed. Until…)
Siemens X2, (eBay purchase, seller sent two “just in case”. Both NOGO)

And I suppose a disclaimer is needed for those fool hearty enough not to realize if all goes well, they will be repairing a component that in not supposed to be repairable. Follow These Directions At your Own Risk; I am not responsible for what you do to your Jeep. …sorry

Early in the troubleshooting process I became fully convinced that the ECU was the point of failure. I eventually wound up having 4 ECU’s in hand and with nothing else to loose, coupled with the fact of being too stubborn to pay retail for a New Computer just to put it in and possibly toast it, (read no return on electrical parts) I had to go with my gut and crack them open.

Tools needed for the job:
TORX 10 & 20
Soldering Tool & Resin Core Solder (de-soldering may be necessary)
Patience


Here we are set up for the job…


The ECU is removed from the mounting bracket and the back cover is removed. The cover is held on by four Torx 10 screws. What I found in all cases was a heat damaged printed circuit board and or a diode.




This picture shows one board with a damaged Trace, the connection between Pin 3 on the main connector and the diode at position D35. Second picture marked for clarity.


A Multi-Meter set to Ohm’s can confirm no continuity resulting in an open trace.


This can also be performed easier from the bottom of the board.


To remove board from housing, remove the 4 - torx 10 at red circles and 1- Torx 20 at green circle. Lift board carefully from opposite side of main connector, do not bend PCB. (Poor picture sorry)


This is a picture of a damaged diode. Picture taken after de-soldering from ECU. This metered a value of .492 and was BAD, another was metered “open”, also bad.


This is a GOOD diode, meter value at 1.522 and another measured the same, these were the two boards I repaired.


The Renix remanufactured unit had a Heavy Duty looking diode installed when it was remanufactured, who knows when. I quickly realized that if the printed circuit was restored, it was highly likely that all would be good! Time to repair the open trace.


Carefully make a jumper wire from your choice stock, CAT5 in my case; this will be used to restore the open circuit.
Continued....

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1988 YJ, 2.5 4cyl TBI, 5 Speed, 4WD, 31's. Repaired ECU, Herculined. Wrenchin', scrapin', learnin', paintin', enjoy'n! - The "Work in Progress" …continues into '11! (althought she's been on the road since '08! Enjoy it Dad!)

Last edited by AtzMaBoy; 08-06-2008 at 12:13 AM..
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Unread 08-05-2008, 11:44 PM   #2
AtzMaBoy
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...Resumed

Lay it in and size it up to fit before soldering. Double check that you are making the correct connections!


Here is the Jumper after being soldered to correct pins.


A covering of Hot Glue provides both insulation and protection.


And lastly a quick check to verify operation. If you’ve made it this far, I hope you are as blessed as we were! Running Jeep, Priceless!
After testing, the unit was remounted into the outer case and reinstalled into the Jeep.


Final testing and “The Payoff”, Road Trip… (Ahh, life is good!) “Dad in his Jeep YJ”

Two ECU’s repaired - the fix; using the repaired Trace method. I will be looking for replacement diodes to mount into the two remaining ECU’s. I am confident that this will resolve their conditions as well.
I am also pretty certain that the weak connection or no connection at the starter relay main lug and the fusible links were the contributing factors in this particular failure. These were also completely redone while waiting for the mailman. Note: Pin 3 on the main ECU connector is identified in the FSM as Starter Switch.
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1988 YJ, 2.5 4cyl TBI, 5 Speed, 4WD, 31's. Repaired ECU, Herculined. Wrenchin', scrapin', learnin', paintin', enjoy'n! - The "Work in Progress" …continues into '11! (althought she's been on the road since '08! Enjoy it Dad!)

Last edited by AtzMaBoy; 08-06-2008 at 12:12 AM..
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Unread 08-06-2008, 01:26 AM   #3
BlackRhino
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Good job! Most electronics failures are caused by something simple like that.
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Unread 08-06-2008, 04:38 AM   #4
markr1001
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sweet.. go to know, i know quite a few people with those jeeps that have had that problem, and im sure they all still have the old ones too...
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Unread 08-06-2008, 05:08 AM   #5
havasu
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Thanks for the time consuming write up, and with pics, I now believe you! (JK)
Good Job!
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Unread 08-06-2008, 05:25 AM   #6
AtzMaBoy
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...there was a time when a man’s word was good enough.

Just kiddin'. I decided to do the "How-to" long before "that comment". The few hours it took to write up and prep the pictures were just a small portion of time compared to the many weeks of waiting around for useless parts and dealing with the frustration of the "unknown". It wasn’t all wasted time though, other things continued on the project build, (yeah we got pictures of those jobs too).

I'll say it again, if one person saves time, money or frustrated headaches, the whole jeep community has prospered.

Future users, post a reply if this helped you out. Enjoy!
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1988 YJ, 2.5 4cyl TBI, 5 Speed, 4WD, 31's. Repaired ECU, Herculined. Wrenchin', scrapin', learnin', paintin', enjoy'n! - The "Work in Progress" …continues into '11! (althought she's been on the road since '08! Enjoy it Dad!)
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Unread 08-06-2008, 05:37 AM   #7
havasu
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I agree 100%. Most believe this kind of stuff is impossible and just buy a new ECU. Either JF readers are extremely frugal, or just finatics. Either way, it's nice to know there are options out there!
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Unread 08-07-2008, 09:17 PM   #8
AtzMaBoy
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PASSED - Pennsylvania State Inspection & Emissions done today!
Fiirst stickers since 2005! Ahh, life is good.
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1988 YJ, 2.5 4cyl TBI, 5 Speed, 4WD, 31's. Repaired ECU, Herculined. Wrenchin', scrapin', learnin', paintin', enjoy'n! - The "Work in Progress" …continues into '11! (althought she's been on the road since '08! Enjoy it Dad!)
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Unread 11-11-2008, 12:16 PM   #9
Andy89YJ
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1989 YJ Wrangler 
 
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Same problem with '89 YJ 2.5L

Thanks for taking the time to post your solution to the fried ECU. I had the exact same problem you described, only difference was the fuel pump doesn't run at all (I think yours ran all the time). Problem appears to be caused when the electric terminal for the headlights, clock, etc. broke off of the post. No headlights with Jeep off, but Jeep started and ran, and headlights then worked for a second or two, then the engine stopped immediately. I think the power to the headlights must have found an alternate path through the computer and fried the same diode you showed in your picture.

Question - what is the spec. for the diode you replaced (if you remember), and where did you get it? My diode is a "BY 251", but Radio Shack doesn't carry those.

Thanks again for your post!
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Unread 11-14-2008, 01:13 PM   #10
Andy89YJ
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Success!

After my last post, I did some checking into the diode situation. My ECU was a Bendix (I think) and was made in France. The blown diode was a "BY251", which is a European designation for a 200 volt 3 amp diode. The nearest American equivalent as far as I can tell is a "1N5402", which Radio Shack supposeldy carries. What they actually had was a lot of "1N5404"s, which are 400 volt and 3.0 amp diodes. The guy at the local Radio Shack seemed to know what he was talking about, and he said the 1N5404 would be OK since the amp rating was the same, and the allowable voltage was higher. After some angst, and because I couldn't wait to see if I could actually fix the ECU, I replaced the diode with the 1N5404 and repaired three melted traces on the circuit board. I plugged it into the Jeep. After a heart stopping moment when nothing happened, I realized that I had removed the negative battery terminal while messing around with ECU. Reconnected that, turned the key, and heard the sweet sound of the engine starting.

I think this same thing happened to me three years ago when (as I realized just this weekend) the fuel pump terminal at the starter relay/main post must have broken off, and due to the same design flaw, it fried the computer. That time, the bill from the dealer was $1,000 +/- for diagnosis, new fuel pump (I think it was just the terminal), labor, and a new computer. This time my out of pocket was 85 cents for the diode and 25 cents or so for a new terminal end for the headlight circuit! Thanks again! I was starting to think it was time for the scrapyard!
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Unread 02-04-2009, 03:47 AM   #11
AtzMaBoy
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Sorry Andy89YJ, for the slow/no reply, I been away from the board awhile. Great news on your fix! I mentioned it before, the whole "ordeal" that dad and I went through, quickly fades away knowing that others are finding this "how-to" helpful.

I just love the sound of that... "the 85 cent solution"! (that has a nice ring to it)

How often do your hear the word "cents" during a Wrangler repair?
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1988 YJ, 2.5 4cyl TBI, 5 Speed, 4WD, 31's. Repaired ECU, Herculined. Wrenchin', scrapin', learnin', paintin', enjoy'n! - The "Work in Progress" …continues into '11! (althought she's been on the road since '08! Enjoy it Dad!)
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Unread 02-04-2009, 06:24 AM   #12
Que89YJ
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Diodes

The large diode is a transorb. Its purpose in life is to surpress transients caused by "load dumping". If it is blown then what has happened is a large device load was intermittantly connecting and disconnecting, usually the battery. The diode limits system transients to 30Vdc. All the electrical components are designed to survive up to 30Vdc.
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Unread 03-04-2009, 05:51 PM   #13
YJake
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My 91 2.5L is not sending the right info to my injectors resulting in the 1st one to not work. I swapped injectors to make sure it wa sthe wiring and it is. For some reason the computer just isn't sending what it's supposed to in order for the 1st injector to spray gas.

Is it possible that I have a similar issue with my ECU that could be repaired this way?
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Unread 03-06-2009, 05:52 PM   #14
DocArt
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Too bad there isn't a way to simply do away with all these intricate electronics once and for all !! Does anyone ever consider rewiring the harness to the ECU to completely bypass this part, altogether ? Would it work ?
I am seriously considering making the elctrical system as simplified as possible. Anyone done this yet for a 1988 YJ 4.2L with 5 Spd Man. Trans ? Had to ask...
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Unread 03-06-2009, 06:27 PM   #15
RIjon
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You can buy a stand-alone EFI system if you like. There are many.

Megasquirt would be one of the best...and the cheapest.
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