Codes? What codes...?

[Rawj]

Hello everyone.
Well title doesn't say much. To make a long story short, took the car out last week for a short ride and noticed that I was getting a check engine light at approx. 2800 rpm or 55 mph. Car would hesitate briefly and I would get a flick at the alternator.
Didn't think too much of it at the time but it would constantly do it everytime I would try to go over 55 mph. Torque converter trying to kick-in I thought. So once back home, I decided I would pull the trouble codes, if any. To my surprise, the minute I turned the ignition switch (no start) on, the check engine light would flick constantly and not give me the usual 1 - 2 starting codes.
Now, here is my question.
1. is my ECM gone south?
2. Could that be a faulty ground?
3. Loose connector somewhere? Or all 3 ?

I did do some work under the dash this past spring. Maybe I pulled on something without noticing it. Just wondering if someone had experienced something like this before.

Thanks for your help.
Roger

 

[Peer81]

Hello Roger,

Very strange! It doesn't sound like there is a logical problem that can give these kind of troubles. As you say the only thing I can think of at this moment is the ECM. As the ECM also controlles primairie fuel delivery to the engine I think it would be a good idea to start with the ECM.

Did you try for a longer time to get above 2800 rpm and is the SES light then constantly on?

Greetings Peter

 

[Sensei]

Have you tried re-setting the computer by disconnecting the battery for a couple of minutes? I would also look around in the area you worked on.

God bless, Sensei

 

[Rawj]

Peter, Sensei...thank you both for replying so fast. I agree, this problem doesn't make much sense. Right now, the ECM isn't controling anything. After the car is warmed up, I can't even hear the solenoids switching on and off anymore. Needless to say, it's running rich right now.

Sensei: yes, I've re-set the computer several times with no results. Well back to square one, I may have to take that dash apart again.

Peter: Who supplies a good ECM ? I may have to go in that direction.

Thank you all...
ROGER

 

[Hib Halverson]

If you can't hear the solenoids switching and, thus, the engine is rich, you can bet that, if the ECM's diagnostics are working properly, that is a reason for the engine light to come on.

My wild-assed-guess is that, the combination of:

1) appearant failure of the solenoids in the carb
2) MIL only flashes but does not send DTC12 when you ground the diagnostic pin of the DLC and turn on the key.
3) other than being rich, the engine controls still work.

means the first step is to check all wires and connections relating to the engine controls especially, wires going to the ECM and all grounds. My guess is that with a 30-year old car, you're more likely to have problems with wiring and connections. The second step is to obtain the Factory Service Manual and read it's troubleshooting info.

The last step, IMO, would be, if the diagnostic instructions lead you there, to replace the ECM.

 

[Sensei]

Who supplies a good ECM ?

They are available at most auto parts stores fairly cheap (about $100 if I recall correctly). But these computers are pretty reliable. I would not just go out and buy a new one without being sure that is the problem first.

You might start by checking continuity between the appropriate terminals of the computer's multi-pin connector and the various sensors etc. that they connect to. (i.e. check that the computer's MC output connects to the MC solenoid connector on the carb and is not shorted to ground). This should tell you if you disconnected/ shorted anything while you were under the dash. As you unplug things, put a drop of Caig Deoxit on the connections while you are at it.

God bless, Sensei

 

[Rawj]

If you can't hear the solenoids switching and, thus, the engine is rich, you can bet that, if the ECM's diagnostics are working properly, that is a reason for the engine light to come on.

My wild-assed-guess is that, the combination of:

1) appearant failure of the solenoids in the carb
2) MIL only flashes but does not send DTC12 when you ground the diagnostic pin of the DLC and turn on the key.
3) other than being rich, the engine controls still work.

means the first step is to check all wires and connections relating to the engine controls especially, wires going to the ECM and all grounds. My guess is that with a 30-year old car, you're more likely to have problems with wiring and connections. The second step is to obtain the Factory Service Manual and read it's troubleshooting info.

The last step, IMO, would be, if the diagnostic instructions lead you there, to replace the ECM.

Hib..,
That's exactly it. I will re-check all wires and connectors, including grounds. The Service Factory Manual I already have and will follow procedures.
By starting this thread I was kind of hoping somebody had experienced something similar in the past. Trying to save work and aggravation I guess. I must be getting lazy....

Thanks for your input.

 

[Rawj]

They are available at most auto parts stores fairly cheap (about $100 if I recall correctly). But these computers are pretty reliable. I would not just go out and buy a new one without being sure that is the problem first.

You might start by checking continuity between the appropriate terminals of the computer's multi-pin connector and the various sensors etc. that they connect to. (i.e. check that the computer's MC output connects to the MC solenoid connector on the carb and is not shorted to ground). This should tell you if you disconnected/ shorted anything while you were under the dash. As you unplug things, put a drop of Caig Deoxit on the connections while you are at it.

God bless, Sensei

Thanks Sensei..,
Good tips that I will surely put in practice.

 

[Peer81]

Hib..,
That's exactly it. I will re-check all wires and connectors, including grounds. The Service Factory Manual I already have and will follow procedures.
By starting this thread I was kind of hoping somebody had experienced something similar in the past. Trying to save work and aggravation I guess. I must be getting lazy....

Thanks for your input.

No not lazy, it the same thing I do! No need to invent something twice

If I recall correctly the wiring harness for the ECM is on the left side of the centre console then goes trough the wirewall somewhere above your gas pedal. And maybe you've done this already, check if the ECM connectors are not half lose.

Greetings Peter

 

[Rawj]

Thanks Peter..,
And that's exactly where I was, working on the air ducts last Fall. I remember having one heck of a time replacing all the wires on the driver's side.
Thanks again.
Regards..,
Roger