Randomly dies

Chuck

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#16
Another version of "jumper diagnostics" would be to run jumper directly from battery to fuel pump relay pump feed pin.
1. Walk to the back of the truck. Can you hear the fuel pump running? Yes?
2. Start the engine. Wait until it quits. Quit? Don't shut off the key, don't slam the door, walk to the back of the truck. Is the pump still running?
I will definitely be trying that today.
 

Chuck

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#17
Another version of "jumper diagnostics" would be to run jumper directly from battery to fuel pump relay pump feed pin.
1. Walk to the back of the truck. Can you hear the fuel pump running? Yes?
2. Start the engine. Wait until it quits. Quit? Don't shut off the key, don't slam the door, walk to the back of the truck. Is the pump still running?
Well I tried the jump test you recommended and when it died the pump was still running.
 

billr

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#18
When the pump was "still running", did you check to see if the FP was still OK? That's why you need to attach a gauge and leave it there for a while.
 
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#19
Another low-tech test, if you haven't done it...after starting, you release key and ignition switch springs back to "On". With engine running, rotate key a scoch towards off and a scoch towards crank. Gently, slowly. Engine keep running?
 
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#20
Another test would be to rig starter to crank engine without disturbing a suspect ignition switch. Connect a jumper to starter solenoid or maybe starter relay. A "pre-test" would be to turn key to ON and then crank engine with your jumper. Cranks but won't run? Well, I guess this test won't work. Cranks and runs? Great...now shut down, restart with key, let it run till it quits. Quit? Don't touch the key, don't slam the door, and the hood is already up, I hope. Now crank with your jumper. Cranks but won't run? Suspect ignition switch or associated connections. Cranks and runs? Suspect computers ability to operate coil or injectors.
 

Chuck

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#21
Another low-tech test, if you haven't done it...after starting, you release key and ignition switch springs back to "On". With engine running, rotate key a scoch towards off and a scoch towards crank. Gently, slowly. Engine keep running?
Tried this test just now. No premature dieing.
 

Chuck

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#22
When the pump was "still running", did you check to see if the FP was still OK? That's why you need to attach a gauge and leave it there for a while.
Unfortunately the guy that tested it for me the other day has called in both yesterday and today and the only reason I haven't done a FP test at home is that I don't have the gauge for it and buying or even renting one at this time is not financially doable.
 

Chuck

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#23
I have been able to remove the Ignition control module, ignition coil, ignition switch, fuel pump, and fuel filter as possible culprits.
 
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#24
Is your fuel system TBI, MPI, or CFI? (two injectors, eight injectors, or the "spider injection" inside the intake manifold) Is your distributor cap the small one or the fat HEI? I'm having trouble finding info on your old truck. Have you done a (gentle) wiggle test to ECU connectors and a ECU "tap test"?

:edit: Looking back at previous posts, looks like you have the TBI system.
 
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Chuck

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#27
Is your fuel system TBI, MPI, or CFI? (two injectors, eight injectors, or the "spider injection" inside the intake manifold) Is your distributor cap the small one or the fat HEI? I'm having trouble finding info on your old truck. Have you done a (gentle) wiggle test to ECU connectors and a ECU "tap test"?

:edit: Looking back at previous posts, looks like you have the TBI system.
Yes, it's the TBI system. I will check the ECU as soon as I can today. It is the newer style HEI were the coil is mounted separately from tthe distributor
 

Chuck

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#28
Is your fuel system TBI, MPI, or CFI? (two injectors, eight injectors, or the "spider injection" inside the intake manifold) Is your distributor cap the small one or the fat HEI? I'm having trouble finding info on your old truck. Have you done a (gentle) wiggle test to ECU connectors and a ECU "tap test"?

:edit: Looking back at previous posts, looks like you have the TBI system.
does it mean anything when I disconnect the oil pressure switch, run a jumper wire across, start the car, disconnect the jumper wire and the car continues to run?
 

nickb2

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#29
In principle, logic tells me that the ECM should shut down fuel pump after two seconds if the ecm does not receive reference from the crank sensor. The oil pressure sensor is a back up source of power should the fuel pump relay circuit fail. This is a safety feature which I think GM did away with altogether. It would be normal for the engine to continue running if oil pressure sensor is unplugged if the fuel pump relay is still on.

Looking at my post in # 13 of this thread, I was wrong to write that. The oil pressure sensor is not a fuel pump cut off switch. It is merely a back up system, once the oil pressure has gotten up to about 4psi, it is now a second source of power to FP.

Many apologies for that error of mine.
 

Chuck

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#30
In principle, logic tells me that the ECM should shut down fuel pump after two seconds if the ecm does not receive reference from the crank sensor. The oil pressure sensor is a back up source of power should the fuel pump relay circuit fail. This is a safety feature which I think GM did away with altogether. It would be normal for the engine to continue running if oil pressure sensor is unplugged if the fuel pump relay is still on.

Looking at my post in # 13 of this thread, I was wrong to write that. The oil pressure sensor is not a fuel pump cut off switch. It is merely a back up system, once the oil pressure has gotten up to about 4psi, it is now a second source of power to FP.

Many apologies for that error of mine.
No, worries. But the only issue with current logic is that I believe this truck was built before crank sensors were used in anything bigger than an S10. I could be wrong though.