[npgraves]

I have a 1987 GT that has mismatched parts from a 1991, the computer and engine are both 91. The car was running very rich and would not go to wide open throttle if I mashed the pedal to the floor but would if I very slowly pressed the pedal to build up to wide open throttle, it also seemed to idle well just rich as I had said. I tried to pull codes from under the hood using the test light method but got only a solid light (no flashes). With the help of some of these threads I was able to trace the problem straight back to the EEC and found that the trace wire for pin 46 was burnt. I had an electrical technician at work solder a jumper wire between the posts and replace the caps with all 16v 47 microfarrad (one original was leaking). So now the problem:

I put the EEC back in and now the car won't start. The fuel pump primes and the engine cranks but doesn't seem to fire it just cranks. So now that the EEC is fixed the car won't start does anyone have any suggestions? Or can someone point me to the right thread to start testing pins at the EEC/connector? Also, what may be related, are there certain wiring looms between the 87 and 91 that don't mesh? I am going to try and pull codes using the test light method again now that the SIGRTN wire is fixed and will update with the results from that.

Thanks everyone.

 

[Decipha]

splice in to the signal return wire and throw it to ground

 

[npgraves]

I'll try that Decipha, but what exactly will putting the signal return wire straight to ground solve? Have you had this issue also?

 

[thenemesis]

I'll try that Decipha, but what exactly will putting the signal return wire straight to ground solve? Have you had this issue also?

Sounds like you have a lack of ground/continuity.

 

[Decipha]

signal return is the ground reference, by throwing it to ground it ties the ground reference and chassis ground together to 'repair' it if it has issues

usually, when signal return goes to crap the tps voltage will read 5v on the ecu input and thus enable flood clear mode shutting off the injectors so the engine will not start

if grounding sig return doesn't allow it to start then unplug the tps and try again, its a long shot but about your only hope

without a quarterhorse from moates to actually diagnose the ecu you have no other option

 

[indy2000]

I have a 1987 GT that has mismatched parts from a 1991, the computer and engine are both 91. The car was running very rich and would not go to wide open throttle if I mashed the pedal to the floor but would if I very slowly pressed the pedal to build up to wide open throttle, it also seemed to idle well just rich as I had said. I tried to pull codes from under the hood using the test light method but got only a solid light (no flashes). With the help of some of these threads I was able to trace the problem straight back to the EEC and found that the trace wire for pin 46 was burnt. I had an electrical technician at work solder a jumper wire between the posts and replace the caps with all 16v 47 microfarrad (one original was leaking). So now the problem:

I put the EEC back in and now the car won't start. The fuel pump primes and the engine cranks but doesn't seem to fire it just cranks. So now that the EEC is fixed the car won't start does anyone have any suggestions? Or can someone point me to the right thread to start testing pins at the EEC/connector? Also, what may be related, are there certain wiring looms between the 87 and 91 that don't mesh? I am going to try and pull codes using the test light method again now that the SIGRTN wire is fixed and will update with the results from that.

Thanks everyone.

did you address why the trace burned up before throwing the repaired ECM back in?

 

[npgraves]

did you address why the trace burned up before throwing the repaired ECM back in?

indy2000, I did not address why the signal wire initially burnt up before putting the repaired EEC back in. I'm guessing there could be a lot of possible reasons why it would burn up but is there a common fault to cause this? I bought the car years ago from a guy that was using the 91 as a parts car since the rear axle broke loose from it, I just started working on the car again and can't remember/don't know what all the other guy had done to the car.

My plan so far is to try and get the codes off it in the key on engine off state, if I still can't get the test light to flash then that leads to a ground issue with the signal wire and I will splice into the wire as Decipha suggested.

 

[npgraves]

So don't call me stupid but Indy was right, I should have figured out why the signal return wire burnt up in the first place. I just opened up the EEC and the new jumper wire is burnt up now too after previously trying to start it.

What causes this!?

 

[theYman]

Research when a car is converted from AOD to a T5. If the A9L computer is used you must also change the Oxygen sensor harness. They are different between the A9P and A9L. Not changing the harness will burn the trace.

 

[indy2000]

So don't call me stupid but Indy was right, I should have figured out why the signal return wire burnt up in the first place. I just opened up the EEC and the new jumper wire is burnt up now too after previously trying to start it.

What causes this!?

what causes it??

mix matched parts as you said

if you have 12volts at pin 46 in crank without a load, it will burn out, its called a short to power

46 is a sig ground

its all pretty easy to see in the diagrams

different years have different pins

they do NOT plug and play

 

[npgraves]

And I'm getting .98k ohms from pin 46 at the connector to the body ground.

 

[npgraves]

So don't call me stupid but Indy was right, I should have figured out why the signal return wire burnt up in the first place. I just opened up the EEC and the new jumper wire is burnt up now too after previously trying to start it.

What causes this!?

what causes it??

mix matched parts as you said

if you have 12volts at pin 46 in crank without a load, it will burn out, its called a short to power

46 is a sig ground

its all pretty easy to see in the diagrams

different years have different pins

they do NOT plug and play

I'm sorry I'm new to the whole EEC differences and switching them around. Like I said when I bought the car I thought the guy knew what he was doing so I didn't back track his stuff. I'm not entirely certain what wiring looks are installed. Is there a way to check which O2 sensor wiring loom I have?

 

[npgraves]

Research when a car is converted from AOD to a T5. If the A9L computer is used you must also change the Oxygen sensor harness. They are different between the A9P and A9L. Not changing the harness will burn the trace.

Meant to respond to you (see previous post). Is there a way to tell what O2 sensor wirring loom I have installed?

But why are you bringing up the AOD, both the 91 and 87 were manuals.

 

[indy2000]

And I'm getting .98k ohms from pin 46 at the connector to the body ground.

okay this is a classic example, so lets play.........



is that reading what you expect to see?

 

[npgraves]

And I'm getting .98k ohms from pin 46 at the connector to the body ground.

okay this is a classic example, so lets play.........



is that reading what you expect to see?

What I expected, but not what it should be.

 

[indy2000]

you back probed, with the ecm connected?

 

[npgraves]

you back probed, with the ecm connected?

No I left the ecm disconnect and probed just the connector.

 

[indy2000]

what is the correct ohm value?

 

[npgraves]

I assume a low resistance something less than 1 ohm

 

[indy2000]

if the ground path is in the ecm, and its not connected, how would that be possible?