1G No output operation of ECU

[Nathan Jorgenson]

My 1990 Plymouth Laser RS had been parked all winter. Before parking it I removed and replaced the timing belt which it ran when it was parked. I was going to tear the engine down and inspect for wear and damage. When I go to start it I prime the fuel pump and turn the key, cranks but no start. Fun...

I start by verifying spark. No spark on cylinder 1, check cylinder 2 same thing. Verify coil primary and secondary resistance is good, everything checks out. I ended up removing the coil to test it. I removed the fuel rail out of its place and just have it sitting on the top of the intake with the wiring still connected. I thought I'd see if I have injection just for fun, don't have injection.

Go to test the crank angle sensor. I don't have a 5V reference.
Then I go with the limited service info I have on a 1990 Laser to test the ECU. I come to find that 12 on c-19 is supposed to be 12v power is grounded somehow? I check the 2 Grounds on pins 7 and 11. I don't have ground.
Then I sit back and start questioning the wiring diagram and the service info.

Factory ECU. There is no aftermarket items on the car.
What are your guys thoughts?
It would be greatly appreciated.

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[19Eclipse90]

Those pages you screenshot are for the theft alarm or security system ECU, not the engine ECU.

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I would suggest reviewing this, to start:
1G basic ECU MPI circuit relay function

 

[Nathan Jorgenson]

Thank you for pointing me in a better direction! I'll test this out tonight after I get home from work. Hopefully the ECU isn't damaged. If it is I'll cross that bridge soon enough!

 

[pauleyman]

Just a basic check, at key on check engine light should come on for 5 sec. If it doesn't I would suspect something with ECU circuit.

 

[steve]

Based on your descriptions the ECU is highly suspect here. It's what controls the MPI relay and sadly the 1990 ECU's are infamous for them burning up after sitting with the power removed. The capacitor that filters the incoming battery voltage drys out and shorts when you put power back on to the car.

I've got my fingers crossed that's not the problem but it's really common with ECU's that haven't had the capacitors changed. The other ECU failure that's common is the capacitors leaking and corroding away the circuit traces that control the MPI Relay (and others). This can happen with original as well as with poorly repaired replacement ECU's.

If you don't know what you're looking for you can post clear pictures of the circuit board here.

 

[Nathan Jorgenson]

I have now verified a few things. I started to with testing the mpi relay. To keep things short I have complete operation other than the mpi control unit output controls. Jumping the mpi relay pins 2-10 I have fuel pump operation. Jumping pins 8-10 I have fuel injection? I did not see the quality if the injection I just seen that there was fuel under the injectors.

So I looked up the power and grounds for the so called MPI control unit. ( I'm assuming they are calling the MPI control unit the ecu). On C-64 I have power on pin 103 and ground on pin 101 and 104.

Is there any other powers and grounds to check that I am missing? I'm ready to crack this ECU open and see the damage if any.

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[Nathan Jorgenson]

I cracked it open. I seen some damage. Any recommendations? Any budget friendly replacements? I've never been lucky with resoldering connections.

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[steve]

Good news that the C106 capacitor didn't torch itself but as you noted both it and C109 have leaked causing corrosion to the circuit traces.

1990 cars pretty much require 1990 ECUs due to differences in the ignition system from the later cars. There are also two pins that changed location on the connector between 90 and 91 but swapping them is easy where the ignition changes are not. So you either need another 1990 Federal Manual Turbo FWD ECU MD128625, the AWD version MD145903 or yours repaired. The best shop for that is ECMTuning in Frederick, MD.

 

[steve]

Did you get this fixed?

 

[Nathan Jorgenson]

Not yet. I wanted to diagnose the issue before I tore the engine apart. I'm doing a reseal. I will be measuring everything to see for example if the cylinder head is flat. I'm really just seeing what I can get away with. My budget isn't big and if it will cost to much to put back on the road I'll part it out.
There was lots of crank case pressure at idle. So we will see the cause of that issue.
I'd really like to daily the thing but again we will see if money allows.

 

[klipschaudio]

There was lots of crank case pressure at idle.

I've had the same issue, did leak down tests, compression tests, everything pointed to worn out piston rings, took it apart, checked everything, within specs fine, turned out bad valve stem seals!