[Antharro]

Hi forum!

I have a 93 GTO auto, completely stock. Rebuilt transmission less than 500 miles ago. ECUs rebuilt a couple of years ago.

A week or so ago, I went to drive it. Started fine, made it about quarter of a mile, then it lost all power. Coasted into a lay-by. Wouldn't rev, died when I tried. Started it again, popped, spluttered, died. Over the next ten minutes it went though all sorts of problems - backfiring (repeatedly), running on maybe 2 or 3 cylinders, repeatedly dying, not revving. Eventually, out of nowhere, it cleared up and ran absolutely perfect for the rest of the day. It had been raining hard so figured something electronic had become a bit too damp.

Today, went to drive it. Reversed it out of its parking spot, manoeuvred it around my yard... and it died. Cranked just fine but wouldn't start. I was in a rush so left it there. Came back about an hour later. It started absolutely fine but died after about ten seconds of running. Started it again, ran for a second, died. Wouldn't start again. Pulled off the air intake and sprayed in some starter spray - nothing. Pulled one of the front three plugs to check for spark - none. Also couldn't smell fuel from the cranking. Left it a few minutes, tried again. Spark, and could smell fuel, and it fired up. Shut it off, put everything back together, wouldn't start. Tried disconnected the MAF tho I wouldn't expect it to make much difference, and it didn't.

Spent about an hour trying to figure out how it sometimes has spark and doesn't. Tried different leads (at least on the front three), checked all obvious wiring, reset the alarm/immobiliser, let the fuel pump cycle a few times to build up pressure (couldn't hear it but assume it was working). Eventually gave up. Put it back together and was about to push it off the side of my yard when I decided to try it once more just in case... and it fired up, stayed running and ran perfect. Except for an odd noise I hadn't noticed before.

Sounds like it's coming from the area where the gearbox meets the engine. I don't recall hearing it before and it's somewhat concerning.

I've read up on testing the crankshaft sensor and checking gearbox ground/earth, but I'm not sure if I'm looking in the right area.

Your help is appreciated - thanks!

 

[white93gt]

Sounds like maybe failing capacitors in ECU, common especially in 1gen cars. Below link explains what/where to look for problems, but they can be a problem with no visual evidence.

Stealth 316 - ECM Removal

 

[Antharro]

Damnit, I should have mentioned. I've already had both main and gearbox ECUs overhauled. First job when I got the car. I'll update the original post.

 

[Paul H.]

Sounds move like the MAF to me. When cold it doesnt monitor the air the same but once it warms up a little the maf kicks in and if its bad wont run right. Try just unplugging the MAF and see how it runs. Sometimes that works a while.

 

[box]

Check for engine fault codes, might shed some light on the situation.

You say alarm/immobiliser. Is this a factory fitted alarm or is it aftermarket? If it's aftermarket, check the immobiliser circuits are working correctly, if they're tapped into an EFI related circuit, bypass it temporarily.

No spark or fuel makes me think you've got a cam/crank sensor issue, this should give you a fault code.

When it cranks but doesn't start, make sure the check engine light is on.

 

[Antharro]

I don't know why I didn't think to pull codes. Should have done that as the first thing. Ok, so I did it and have many codes:

12 - Air flow sensor
13 - Intake air temperature sensor
22 - Crank angle sensor
23 - Top dead center sensor

The first two are likely from me messing with the air intake system when troubleshooting so I'm not too worried. The latter two though, oof.

 

[box]

Engine: Troubleshoot Camshaft and Crankshaft Position Sensors - 3000GT/Stealth Wiki

www.3swiki.org

 

[Antharro]

Wiring loom checks out fine. I don't have a scope so I can't check the sensors. Car is due for a timing belt and a service anyway so I may have to get it trailered to my mechanic.

 

[box]

You can check the sensors with a digital multimeter, wind the engine by hand slowly and watch the 5v, which will pull down to ground and go back to 5v as the vanes on the timing wheel pass through the sensor.

 

[wc711]

Hi forum!

I have a 93 GTO auto, completely stock. Rebuilt transmission less than 500 miles ago. ECUs rebuilt a couple of years ago.

A week or so ago, I went to drive it. Started fine, made it about quarter of a mile, then it lost all power. Coasted into a lay-by. Wouldn't rev, died when I tried. Started it again, popped, spluttered, died. Over the next ten minutes it went though all sorts of problems - backfiring (repeatedly), running on maybe 2 or 3 cylinders, repeatedly dying, not revving. Eventually, out of nowhere, it cleared up and ran absolutely perfect for the rest of the day. It had been raining hard so figured something electronic had become a bit too damp.

Today, went to drive it. Reversed it out of its parking spot, manoeuvred it around my yard... and it died. Cranked just fine but wouldn't start. I was in a rush so left it there. Came back about an hour later. It started absolutely fine but died after about ten seconds of running. Started it again, ran for a second, died. Wouldn't start again. Pulled off the air intake and sprayed in some starter spray - nothing. Pulled one of the front three plugs to check for spark - none. Also couldn't smell fuel from the cranking. Left it a few minutes, tried again. Spark, and could smell fuel, and it fired up. Shut it off, put everything back together, wouldn't start. Tried disconnected the MAF tho I wouldn't expect it to make much difference, and it didn't.

Spent about an hour trying to figure out how it sometimes has spark and doesn't. Tried different leads (at least on the front three), checked all obvious wiring, reset the alarm/immobiliser, let the fuel pump cycle a few times to build up pressure (couldn't hear it but assume it was working). Eventually gave up. Put it back together and was about to push it off the side of my yard when I decided to try it once more just in case... and it fired up, stayed running and ran perfect. Except for an odd noise I hadn't noticed before.

Sounds like it's coming from the area where the gearbox meets the engine. I don't recall hearing it before and it's somewhat concerning.

I've read up on testing the crankshaft sensor and checking gearbox ground/earth, but I'm not sure if I'm looking in the right area.

Your help is appreciated - thanks!

92 3000gt sl I had similar problems. My scanner (the same one shown on 3sx.org products) actually works! It turned out the problem was the Engine Coolant Temperature Control sensor. I ignored it because I thought it must be for the thermostat or something, but that sensor does a few other things as well. It monitors the Air/fuel mixture too. If it's not working you will have intermittent starting problems and a rough-running engine. All of this is intermittent. I got the sensor from Pit Stop Auto in Mansfield, TX. They have replacement parts that are built using OEM specs. The sensor cost me $29.00. www.pitstopauto.com.