90 Laser 2.0l ECU Q

[mattinthebox]

I have a 1990 laser 2.0l non-turbo automatic. No mods, just a daily driven street car.

The original ECU - MD128624 (E2T34472) failed.

I put another ECU - MD166255 (E2T36572) in it and it ran.
I think it's from an 93 2.0l non-turbo.

After the swap I noticed it took a few cranks more to get it started and it also started like it was starving for fuel or something.

It seems to idle okay and drives alright but the tach will peg "0" RPMs if you floor the accelerator. Then when you let off, the tach will bounce back to where it's supposed to be.

It will also pop out the exhaust if you drive it hard and downshift manually.

A few Questions:
1. Is this safe to leave like this or will I damage other components?

2. Can anyone tell me the specs and component pin outs of these two ECU"s?

3. Is there anything I can do to correct the symptoms I get from the swapped ECU?

4. I can't afford a new or rebuilt ECU so any advice on repairing my old ECU? I have already swapped out the caps. The problem with this ECU is that my injectors don't seem to be firing. Fuel pressure and spark are good.

5. Has anyone else experienced this?

Many Thanks in advance!!!

 

[bastarddsm]

on turbo cars the 90 ecu's are differn't ( 2 wires switched places) than the 91+... I would assume that the n/t are the same way. You need to check the vfaq.. VFAQ Site - Visual Frequently Answered Questions for this info. If you switch the wires it should be fine.

The two wires have to do with the tach signal, and the maf active reset, I have no idea what that its, but I'm sure the first is the cause of your tach problems.

Your lean sounding condition could indicate you might have a turbo ecu...check the p/n again.

 

[mattinthebox]

Ya I already checked the faq, there wasn't any info to help my problem.

I already had the pinout for the 1990 ECU (md128624) but I was hoping to find the same for the md166255 ECU.

I would really like to find a schematic for these two ECU's, that would be fantastic.
Is there any way I can find this information? If I had that I could cross reference the parts, find the specs, test and replace the failed components on my original ECU and save alot of $$$ all the way around!!!

I have 3 of the md166255 ECU's, that's why I am interested in finding out what may or may not be different between the two.

Just to clarify things BOTH of these ECU's are NON turbo with Federal emmisions, as is the car, 1990 plymouth laser 2.0l NON turbo, automatic.

I was thinking that the tach problem may be due to the design of the coil pack. I read an MSD article that required a tach adapter because the stock ignition blends 2 signals and sends a single signal back to the tach on the 1990. Can anyone confirm this and is there a workaround for this issue?

 

[bastarddsm]

Honestly I am not sure. There is a guy on here by the name of steve he knows all.

My buddy has a 90 that he got an ecu from jeffo KEYDIVER Chips - DSM ECU Tuning it was a 91, that was internally converted to be a 90 style....you might contact him as well.

 

[steve]

There are two issues. One is the pins that changed on the harness between 90 and 91 and the other is the change in the ignition detect signal and the ECU circuitry that causes tach problems on a 90 car.

On a NT there isn't the MAF reset signal like the turbo cars have so only the wire for the IPS (Idle Position Switch) needs to be moved on the car harness from pin 6 to pin 14. On the 90 ECUs the IPS is on pin 6 but on the 91+ cars it's on pin 14.

The board Keydiver sells converts the ECU to be compatible with the 90 Ignition Detect signal (pin 109) so that the stock tach works.

 

[mattinthebox]

Thanks sooo much for the replies!!!

I checked out the link and seen there is an inexpensive adapter, I'm gunna buy one!

So besides the adapter all I need to do is a 2 wire swap and the spare ECU's will work? Nice!

Now is there any other "known" issues with an ECU swap like this?

Does anyone know who manufactures the ECU's?
I would really like to contact the manufacturer and see if I could get a schematic and parts list so I can troubleshoot and repair the original ECU.

I'm only trying to repair my own ECU and not trying to steal any business from anyone. I really enjoy doing my own repairs like this, it's very satisfying knowing what the dealer wants for a new unit and what it may cost to repair it myself.

I guess I'll start tracing the pins back from each of the 4 injectors.
When I pulled the ECU everything was there (spark, compression, fuel) except I wasn't getting fuel from my injectors.
I tested the fuel pump, filter, regulator, MPI relay, fuses, and practically everything else.
I got it to kick over and stumble with starting fluid but never got the injectors firing.

What components in the ECU control the injector circuit?
Is there a faq or guide for something like this? I searched the forum but couldn't find anything.

I'd really like to hear the thoughts of anyone that has a deep understanding of the components within the ECU.

Thanks for the good info so far!

 

[steve]

Does anyone know who manufactures the ECU's?
I would really like to contact the manufacturer and see if I could get a schematic and parts list so I can troubleshoot and repair the original ECU.

Good luck with that. The rest of us had to trace the circuits to reverse engineer it.

I suggest you locate a copy of the 1G Technical Manual and read it first. It's the best reference on the ECU operation I've found.

 

[mattinthebox]

Steve,
I hear ya... I know the info is gunna be about as easy as finding kryptonite.
I wish I had another junk board to map out the components.

It sounds like you have done extensive research on these ECU's.

Do you know what parts of the ECU are in line with the 3 caps that usually fail?
I'm pretty sure it's safe to say that when a cap failed it took out something else further down the line.

I desoldered all 3 caps and tested them.
They all tested good with a meter, even tho that doesn't mean it won't fail under a load, but I remember 1 that really stunk like electrolytic fluid when I heated it with the iron.
The problem is that I don't remember which 1 it was... I think it was C106 or C108

Can you tell me what I may be overlooking?

Thanks...

 

[steve]

There are clues on the board, every part is marked. All the capacitors start with C, Diodes with a D, Resistors with an R, Transistors with TR, and IC's with U.

Sorry I can't answer any specific questions or help you fix it.

 

[mattinthebox]

Ya I'm familiar with the terminology on the boards, but none of my ECU's have a u representing an IC, they're all marked IC...

I've replaced the capacitors, all the diodes and resistors on the board tested good. I'm going to take a look at the transistors next. I don't want to mess with the IC's unless I have to.

I'm still stumped since all 4 injectors are dead, wouldn't they each have their own circuit and only one injector would quit if an IC or transistor went down? I still think its power supply related...

I was hoping more information was available... do you know how EASY these would be to fix if a schematic was available... This is comparable to finding a person's phone number in a phone directory but without any names listed...

Steve, you mentioned:
"I suggest you locate a copy of the 1G Technical Manual and read it first. It's the best reference on the ECU operation I've found."

I actually have that manual, 1990 Technical Manual Laser/Talon (does that sound like the right book?), along with the standard factory service manuals Vol. 1 and 2.
I read thru section 8 Electrical, which goes into great depth about ignition control, and section 14 Fuel System, 14-27 thru 14-39 which has given me a few more angles to work with so we'll see what happens...

I'm gunna try a few more things, I'll report back with my findings...

Thank you for the leads...