- City
- Biloxi
- State
- MS
My tan Scrambler has been running great since I got it running a few years ago. Its been to Michigan several times, South Dakota and back, all over around home, generally runs fine, except for the hot fuel issues.
Anyway, this past Saturday it was running fine, and it just shut down, almost like the key turned off. Will not restart.
No fuel at the throttle body, I did not diagnose the problem, just swapped fuel pumps. Still no fuel, can hear pump running, so started diagnosing.
I would get an injector pulse sometimes, but not all the time. Then, with key ON, throttle at idle position, the injectors would spray like the throttle was at wide open. In a few seconds, the injectors would fill the throttle body!!
Besides the either "Wide open throttle" or zero injector pulse, I also have no spark at coil, so no spark to distributor or plugs.
What I have done:
Verified voltage at coil and ICM at distributor, key ON and START, voltage good.
Checked pick up coil resistance, checked out fine.
All fuses fine, Jeep Chassis and TBI harness fuses/Relays.
Fuel pump operates fine, pressure fine.
Engine at TDC on damper, rotor at #1 inside cap, distributor does spin with engine correctly.
I had swapped some parts out when I was broke down in the woods, fuel pump, coil and ICM, no change. Even though the pick up coil inside the distributor checked out, I swapped distributors yesterday, no change.
I have a 91 GM Factory Service Manual, went through the diagnostic charts, everything checks out. The only thing I have not checked, that the FSM talks about, is some "Tack Signal Wire" that is taped up inside a factory GM harness. Not sure if my aftermarket harness has this or not, will have to look and see.
I see no external evidence of a wire harness damage, but my next step is to inspect the entire TBI/Jeep underhood harness looking for shorts/damage.
Scan tool found one problem, bad MAP sensor, pretty sure this issue would not cause all these problems, but swapped in a new one, no change.
Scan tool verified TPS voltage fine at idle position, coolant temp sensor showing outside temp of 73 degrees, other sensors showed correct voltage with key ON/ throttle at idle position.
One thing I did notice with the Scan tool - I put it on operating data while cranking, RPM's show zero while cranking 99% of the time, but every once in awhile the RPM on the Scan tool would spike to 5200 RPM while cranking?? Now, I have never paid attention to RPM on the scan tool while cranking when everything workes, maybe this is normal, not sure??
So, I am "assuming" for some reason either:
1) the computer is not receiving a signal it needs to supply spark and injector pulse at "Start" and "Run"
2) or the computer is not sending out the signal to the injectors and coil
I have a spare computer, condition unknown, plugged it in, no change.
My TBI system is typical GM TBI, except for the coil. I use a "small cap HEI" distributor with external coil, which I think is common on the GM TBI factory set ups. My harness was wired up to use a "can" style coil, so I use that instead of the more modern style coils. My fuel pump is wired through the oil pressure switch, like a stock GM. Fuel pump does work for three seconds when key turned ON, and pump runs while Cranking, too.
Ideas, comments, suggestions
I thought about pushing it down the hill in the back yard into the river, but that would probably not be too constructive
Anyway, this past Saturday it was running fine, and it just shut down, almost like the key turned off. Will not restart.
No fuel at the throttle body, I did not diagnose the problem, just swapped fuel pumps. Still no fuel, can hear pump running, so started diagnosing.
I would get an injector pulse sometimes, but not all the time. Then, with key ON, throttle at idle position, the injectors would spray like the throttle was at wide open. In a few seconds, the injectors would fill the throttle body!!
Besides the either "Wide open throttle" or zero injector pulse, I also have no spark at coil, so no spark to distributor or plugs.
What I have done:
Verified voltage at coil and ICM at distributor, key ON and START, voltage good.
Checked pick up coil resistance, checked out fine.
All fuses fine, Jeep Chassis and TBI harness fuses/Relays.
Fuel pump operates fine, pressure fine.
Engine at TDC on damper, rotor at #1 inside cap, distributor does spin with engine correctly.
I had swapped some parts out when I was broke down in the woods, fuel pump, coil and ICM, no change. Even though the pick up coil inside the distributor checked out, I swapped distributors yesterday, no change.
I have a 91 GM Factory Service Manual, went through the diagnostic charts, everything checks out. The only thing I have not checked, that the FSM talks about, is some "Tack Signal Wire" that is taped up inside a factory GM harness. Not sure if my aftermarket harness has this or not, will have to look and see.
I see no external evidence of a wire harness damage, but my next step is to inspect the entire TBI/Jeep underhood harness looking for shorts/damage.
Scan tool found one problem, bad MAP sensor, pretty sure this issue would not cause all these problems, but swapped in a new one, no change.
Scan tool verified TPS voltage fine at idle position, coolant temp sensor showing outside temp of 73 degrees, other sensors showed correct voltage with key ON/ throttle at idle position.
One thing I did notice with the Scan tool - I put it on operating data while cranking, RPM's show zero while cranking 99% of the time, but every once in awhile the RPM on the Scan tool would spike to 5200 RPM while cranking?? Now, I have never paid attention to RPM on the scan tool while cranking when everything workes, maybe this is normal, not sure??
So, I am "assuming" for some reason either:
1) the computer is not receiving a signal it needs to supply spark and injector pulse at "Start" and "Run"
2) or the computer is not sending out the signal to the injectors and coil
I have a spare computer, condition unknown, plugged it in, no change.
My TBI system is typical GM TBI, except for the coil. I use a "small cap HEI" distributor with external coil, which I think is common on the GM TBI factory set ups. My harness was wired up to use a "can" style coil, so I use that instead of the more modern style coils. My fuel pump is wired through the oil pressure switch, like a stock GM. Fuel pump does work for three seconds when key turned ON, and pump runs while Cranking, too.
Ideas, comments, suggestions
I thought about pushing it down the hill in the back yard into the river, but that would probably not be too constructive
