Ward

iTrader: (1)

I replaced the SES bulb today, it was burned out. However, with a brand new bulb, it won't light up at all. I've verified that the new bulb is working. I've also verified that there's no power to the gauge cluster pin for the SES light. With the key forward and the engine off, it doesn't do anything, or with the ALDL pins jumpered, it doesn't do anything.

Also, when I was checking the TPS voltage yesterday, and I wasn't seeing the correct voltages. I got around .7V at closed position, but only about 1.3V at open position.

My question is, can the ECM be bad, or partially bad, and still run the engine? The car does run, although it runs very rich. The injectors are pulsing, and the ECM is advancing timing correctly. I'm running out of ideas to try, any help is appreciated.

Car is an 88 GTA, 5.0TPI, with the digital gauge cluster.

Supervisor42

The ECM turns on the SES light by providing a ground on the wire to the cluster. With the dash removed, there won't be any voltage on it.
You can test the light by removing the ECM and probing the pin A5 (brn/wht)with a grounded test light with the key on. The bulb in the dash will glow faintly.
If you decide to replace the ECM, don't go by the numbers on it as it may not be the correct one for your car.
I would verify the 5V source on the TPS first. The Gray wire should have +5 measured with the negative on the black wire.
If there is not 5V there, then there is something definately wrong.

Ward

iTrader: (1)

Thanks for the info, I'll have to try that tomorrow. Also, I read about using the ALDL pin "D" with a test light to pull the engine codes, but my ALDL plug doesn't have a D pin, just an empty hole. Is this normal?

Supervisor42

That must be some "generic" GM info. There is no pin "D" on the ALDL plug on any of the '88 engine setups (V6, TBI, or TPIs).
Edit: while you're at it, verify that the gray wire to the tps is not shorted (less than 1000 ohms to ground with key off).

Ward

iTrader: (1)

Well, that's good to know. I came across an old post where someone suggested using that pin, also shown in this diagram:
http://www.gmtips.com/3rd-degree/dox/tips/ecm/aldl.htm

Also, I went back oustide, and checked the voltage at the TPS plug. I tested at the connector from the ECM, across the black and gray wires, with the key in "on", and only got .05V.

Supervisor42

The diagram is probably correct for earlier (82-85) models.
With key off, check ohms to ground on the gray wire.
It may be some other output from the ecm that's shorted and killing the +5 power or it may be an ECM problem.
I bet it's been like this for a long time in search of someone to fix it...
EDIT: Or it could be one of the power feeds to the ECM is dead.

Ward

iTrader: (1)

Yeah the SES light must have been on for a long time for it to actually burn out. I will also check the TPS for a short tomorrow, I didn't think of that either. I did find out that someone directly wired the fuel pump power to switched 12V at the fuse panel, which could indicate that the ECM was having problems. I guess it's possible the ECM could be running in limp mode, but without a working SES light I don't really have a way of knowing. I think I remember reading that both fans come on and stay on in limp mode, well mine both come on as soon as the ignition is on. I haven't verified all of the fan wiring yet, so it's possible someone rewired them to do that. However, they are both still properly connected to the big relay on the PS fenderwell. I unplugged them for now, to keep the battery from going dead while testing without the engine running.

sofakingdom

iTrader: (1)

.

Nevermind; I was thinking this was a CC carb setup for some reason....

Supervisor42

I bet I know what's wrong!
The fuse that feeds the F/P relay and also feeds 1/2 of the ECM is blown.
It's not in the panel. It's by the cruise control/power steering pump. I like to have never found mine. It is in a little black box and looks like it is a relay.

Ward

iTrader: (1)

Did yours go bad? If so, did your SES light stop working when it was blown?

Supervisor42

No, my ECM is just unemployed.
I saw the fuse on the print and knew it wasn't in the fuse panel. What I didn't know, was where it was. So I had to find it. Someone had taken it out of it's little box, thrown the box away, and dropped it down between the steering sector and the frame.
I knew it was the one that fed the F/P relay and needed to secure it.
All the TPI wiring and ECM is still in the car in case I want to go back from carb to TPI...
You should find your fuse and get the F/P where it works without being hotwired.

Ward

iTrader: (1)

Well, good news. I found the ECM/FP fuse, and although it wasn't blown, the fusible link that feeds it was pretty melted. I bypassed the fuse and fusible link with a clip lead, and the SES light is working now. I even got a code 12 when the ALDL plug was jumpered. Looks like I'll be replacing the battery cable and fusible link tomorrow. Thanks for the info Supervisor42, I would have never known about that fuse otherwise.

Supervisor42

Woo HOO!!! I won one!
I bet your car will run much better with both power feeds to the ECM now.
Don't forget to remove the F/P relay bypass wiring.
...No telling how long that car has been waiting for you to show up .

Ward

iTrader: (1)

Well, it looks like that wasn't quite the problem. I rewired the ECM power wires today, and the SES light flickers on and off. Not like a trouble code or limp mode, but it's completely random. One of the factory fusible links had been replaced, but with a shoddy wiring job. I removed the fusible link, and now both ECM power wires have new 10A fuse holders inline, and are wired to the battery terminal with 12ga wire. All joints were soldered and shrink wrapped, so I'm positive it's not a power problem, at least not there. I also pulled off the plastic wire tubing from the wires, all the way back to where it meets the big wire pack at the firewall, and the wires don't look melted or burned.

I found 2 ground wires at the back of the DS head, and 2 more at the DS fender, by the booster. I checked ohms at both locations to the battery and both were fine. After studying the wiring diagram, it pretty much has to be either bad wiring to the ECM, or a bad ECM.

I went ahead and pulled the ECM out tonight, and noticed that it's a remanufactured unit. I pulled the cover off it, and couldn't find any burned spots, but I found a dealer service sticker on the inside of it. There was no date, but that tells me that it's had ECM trouble before. I'm going to get another ECM from the junkyard tomorrow, and see of the SES light still flickers randomly. If it does, then I think it's gotta be a wiring issue somewhere.

Supervisor42

A couple more things to consider: You may have to hunt down what shorted to burn the fuse link originally. It sounds like it may still be grounding out.
Also, if the engine was run for years that rich, the cat may be plugged with carbon. It may have to be replaced if you can't get it to burn itself clean.

Ward

iTrader: (1)

I think I've solved the problem, finally. The SES light wasn't blinking a trouble code, but was flickering randomly, almost like a bad connection. After some searching on here and a couple other boards, that appears to be a common issue if the PROM isnt plugged in good, the PROM connections are dirty, or the ECM pins are dirty. I cleaned the PROM ECM pins with a toothbrush, and the SES light is working as it should. I also picked up a spare ECM at the junkyard, just in case. It looks like it was just an odd combination of problems: burned out SES light, no ECM power, and dirty ECM connections.

I also found where the fuel pump was hot wired. Someone ran a new wire from the fuel pump, and it was just stuck in the back of the fuse panel. to the ECM ignition fuse. I pulled the wire out, and the fuel pump primes and works as it should.

The only other thing I noticed is that the clutch safety switch has been bypassed, allowing the car to start without pressing the clutch in. Once I fix that, hopefully that will take care of all of the car's electrical gremlins.

kabal

sorry to jump in what would casue my engine light not to come on when you turn the key , other then the bulb i check that already how do i get the seat belt light to go off it is on all the time , until i turn the car off need help thanks