1G 1990 GSX not starting, got it narrowed down to engine not getting fuel

[Co-Bolt]

So I drove my gsx up to the auto store to top off the oil, drove there with no problems at all. Then after I add the new oil and get back in, it would crank but wouldn't start. My friend towed my car to his place where we did some troubleshooting.

We made sure there was spark while cranking; that was good.

We removed the fuel return line to see if there was fuel flow while I cranked it; no fuel came out of the line.

We manually touched the positive battery terminal to the fuel pump test wire, and fuel started pumping out of the line just fine, we even plugged in a pressure gauge and we have proper fuel pressure as well.

We put the fuel line back on and kept the positive on the fuel pump test wire as I cranked it, no start even though there is fuel flowing manually.

We took the positive off the test line and sprayed WD-40 into the air intake as I cranked it; it starts momentarily then shuts off. So it looks like something is keeping the injectors from spraying fuel into the cylinders. I've tried adjusting the cas and still no luck.

I figure this is an ECU or sensor problem, but I do not know exactly. Any ideas on what it could be?

 

[edculley57]

Sounds like either a bad relay or cas. Your fuel pump gets its signal from the cas.

 

[Co-Bolt]

Sounds like either a bad relay or cas. Your fuel pump gets its signal from the cas.

We tested the fuel pump relay and it works properly, it might be the CAS then. Are they known to fail instantly without any signs beforehand?

 

[pauleyman]

Do you still get the ecu cel test at key on? Has to be something sensor, wire or ecu related. at least try wiggling connectors one by one.id start with cas and coolant.

 

[rangerguy]

Id suggest trying another CAS. As others have mentioned, if the car doesn't know its cranking it wont supply fuel. So sure the pump will work, but the injectors wont fire.

CAS. Let us know!

 

[Co-Bolt]

Do you still get the ecu cel test at key on? Has to be something sensor, wire or ecu related. at least try wiggling connectors one by one.id start with cas and coolant.

Yes the CEL comes on when I crank it, but the CEL always stays on anyway because of some mods the previous owner did (like the vacuum hose deletion kit.) I'll start with cas when I can.

 

[Co-Bolt]

Id suggest trying another CAS. As others have mentioned, if the car doesn't know its cranking it wont supply fuel. So sure the pump will work, but the injectors wont fire.

CAS. Let us know!

Definitely, I already have a spare working cas in my old eclipse, but it's locked up and I can't get to it until after the holidays.

 

[Co-Bolt]

Okay so I replaced the CAS with a new one, and it's still not starting. This has to be some computer/electrical issue.

 

[DSM1G90]

Bet the ECU took a dump.

Mine did and my vehicle experienced the similar problems...and it died in the middle of town at a stop light where I had to call up my daughter to tow me back home.

Did the same checks as you did - fuel, ignition and similar tests were fine.

Replaced the ECU and was back on the road in a heartbeat.

 

[Seamus]

I had a 90 ecu go bad with no physical problems on the board when u opened it. It did the dame thing only it wad intermittent.

 

[Co-Bolt]

Bet the ECU took a dump.

Mine did and my vehicle experienced the similar problems...and it died in the middle of town at a stop light where I had to call up my daughter to tow me back home.

Did the same checks as you did - fuel, ignition and similar tests were fine.

Replaced the ECU and was back on the road in a heartbeat.

Ouch, I'll look into that. Is there a way to test the ecu first? I don't want to buy one just to find out that wasn't the problem.

 

[hotrodssnova]

If the cel is on, you need to pull the codes.

 

[Mischif]

Did you check and test the mpi fuse? How about the injector resistor? Have you tested the injector harness to make sure they are putting out power?

 

[DSM1G90]

One thing I did forget that can also cause this issue is the temp sensor.

This unit plays havoc with the ECU when they begin to get flaky or go bad.

I fought the same issue until I pulled the 21 code to point to a bad sensor.

Replaced it and all is good.

 

[Co-Bolt]

If the cel is on, you need to pull the codes.

Okay everyone, pulled the error code by putting an led to pins 1 and 12 on the mpi terminal. It gave a constant glow, so apparently the ECU needs replaced.

 

[hotrodssnova]

Sounds like it. On a code free ecu, it would give a heart beat like code.on, off, on, off steady. Good job!

Edit:
that is pin 1 and 12 on the DIAGNOSTIC port under the dash.

 

[Co-Bolt]

Sounds like it. On a code free ecu, it would give a heart beat like code.on, off, on, off steady. Good job!

Edit:
that is pin 1 and 12 on the DIAGNOSTIC port under the dash.

Woo! I'll put an ECU from my old GST into it tomorrow.

And yep, this connector:

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[hotrodssnova]

If your car is a 1990, you will need a 1990 ecu. Those were the odd year for ecus. You can switch some pins out and run a 91-94 ecu.

 

[Co-Bolt]

If your car is a 1990, you will need a 1990 ecu. Those were the odd year for ecus. You can switch some pins out and run a 91-94 ecu.

Thanks for the heads up. Luckily my old gst is a 1990 as well. I just hope there aren't any other issues other than the ecu.

 

[hotrodssnova]

Good deal. Open your ecu and look for any leaking from capacitors, or burnt traces on the board.
One more thing, when was your car made? Month of 1990?

 

[Co-Bolt]

Good deal. Open your ecu and look for any leaking from capacitors, or burnt traces on the board.
One more thing, when was your car made? Month of 1990?

Not sure which month. I put the other ECU in and it started right up. Only thing is that it makes odd sounds at idle and while driving; it feels and sounds completely different. Might be the fact that it's 20 degrees out, or maybe the old ecu was tuned and this one isn't. I'll crack open the broken ecu as soon as my fingers thaw.

 

[hotrodssnova]

Glad to hear. Did you let the car idle and reach operating temperature? The new ecu takes a few minutes to learn the new fuel trims.
Does the car have any mods? What kind of sounds?

 

[Co-Bolt]

Glad to hear. Did you let the car idle and reach operating temperature? The new ecu takes a few minutes to learn the new fuel trims.
Does the car have any mods? What kind of sounds?

Yeah I let it idle a good 20 minutes, still very shaky while driving and it's not putting out much power at all. Feels like it's struggling, to the point where I can't drive it around like this. As for mods: it had vacuum hose deletion, a 14b turbo, and an open vented blow off valve. (I haven't modded it any myself)

Here are a couple videos I took of it:

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[jimsgsx]

Have you replaced your fuel filter.

 

[Co-Bolt]

Have you replaced your fuel filter.

I have not replaced this yet. I can do that soon. Would that be part of the issues?