SOLVED - 1990 Suburban L05 - Crank, no start. Bad ECM?

[dixiebandit69]

My 1990 Suburban has been running great for years, and Sunday afternoon refused to start.
It has spark, it has fuel pressure (12+ psi), and it has injector pulse.

However, the SES light will not come on with the key; if the key is left on, the light will randomly come on for a few seconds, then go out again for awhile (30+ seconds or more). There does not seem to be any discernible pattern/ regularity for the light coming on.

I cannot get code 12 to come on when jumping the A and B terminals on the ALDL connector.
I verified that the ECM has B+ voltage (12+ volts), Key-on power, and good ground (less than 3 ohms). ALDL has good ground as well.

According to the GM service procedure for that situation, it looks like I have a bad ECM, but I don't want to replace it unless I'm positive.
The engine will start for a second or so with a small shot of starting fluid, so you can take that as you may.

Just for transparency's sake, here are some of the other tests I've done:

- Verified that the distributor is in-time with cylinder 1
- Tried a know-good ICM
- Tried a known-good distributor cap and rotor
- Known-good Ignition coil
- Pulled a couple of plugs from each side of the engine - not fouled
- Compression tested a couple of cylinders (150+ psi)
- ALL fuses are good, and have power when appropriate

Thank you, gentlemen, and let me know if there is anything else I should test.

EDIT: The ECM number is 7747, if that makes any difference.

 

[Schurkey]

If you have fuel pressure, and the injectors "pulse", do you not have fuel spray? I don't know why it would run briefly only with starting fluid if the thing is spraying gasoline.

The Check Engine light does signify either wire harness problems, intermittent connection between the bulb and instrument cluster, or between the cluster and the connections that power it...or a faulty ECM.

 

[evilunclegrimace]

Find a scan tool and see if it will communicate with the ECM.

 

[dixiebandit69]

If you have fuel pressure, and the injectors "pulse", do you not have fuel spray?

Yes, when I said "injector pulse," I meant that fuel is spraying out of the injectors in a pulsating manner.

I do not have access to an OBD1 scanner at this time.

 

[Schurkey]

I do not have access to an OBD1 scanner at this time.

That'll have to change.

 

[dixiebandit69]

UPDATE: I found out why the bulb would only turn on intermittently: The mounting-hole inside the instrument cluster had a crack, so it wasn't making good contact.

You must be registered for see images attach

I bent the terminals out on the bulb, now I can get code 12... And only code 12.

Still won't start.

Since last time, I have tried a known good distributor, and checked the fuel filter (not clogged).

At this point, the only other thing I could think of would be bad gas, but it was running around just fine the days prior.

 

[Schurkey]

UPDATE: I found out why the bulb would only turn on intermittently: The mounting-hole inside the instrument cluster had a crack, so it wasn't making good contact.

Excellent diagnosis...

I bent the terminals out on the bulb, now I can get code 12... And only code 12.

...Sketchy repair. May work long-term, but I don't have confidence.

Still won't start.

Since last time, I have tried a known good distributor

Do you have spark at the spark-plug end of each of the plug wires? If not, do you have spark at the distributor end of the coil wire?

Are the spark plugs fouled?

and checked the fuel filter (not clogged).

Does fuel spray from the injectors?

At this point, the only other thing I could think of would be bad gas, but it was running around just fine the days prior.

Sample some fuel being sprayed out of the injectors. Put a match to it. Does it burn?

 

[dixiebandit69]

...Sketchy repair. May work long-term, but I don't have confidence.

How would you recommend repairing this, then?

Yes, getting spark at the end of the wire, tested with HEI spark tester.
The plugs I checked were NOT fouled.

I did test the volatility of the fuel - stuck a piece of fiberglass cloth under an injector, and the fuel did burn.

 

[Schurkey]

How would you recommend repairing this, then?

Perhaps replace entire cluster.

Maybe epoxy the socket so it's not the wires on the bulb holding it in place.

Yes, getting spark at the end of the wire, tested with HEI spark tester.

WHICH wire?

The plugs I checked were NOT fouled.

How many plugs did you check? Before or after the most recent cranking?

I did test the volatility of the fuel - stuck a piece of fiberglass cloth under an injector, and the fuel did burn.

OK, good.

 

[dixiebandit69]

How many plugs did you check? Before or after the most recent cranking?

This is what they look like right now:

You must be registered for see images attach

I checked spark at a few different cylinders. I'm getting spark everywhere I check.