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Discussion Starter · #1 ·
Just like the title says, the ECU will not trigger the fuel pump relay to prime the injectors. When the truck is cold it fires and runs great. Once the truck reaches operating temperature, it wont start unless i pour fuel down the throttle body to start it. Once the truck has started the ecu signals the fuel pump to run as it should. I have tested voltages to the relay, and it is doing its job when the truck is running. If I use a wire to trigger the relay manually, the fuel pump runs and the truck starts right up. What circumstances/sensor would cause the ECU not to trigger the relay when the vehicle is hot?
 

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Year?
Does the truck die?
Or is this a hot soak only condition?
 

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When you pour fuel down the TBI it starts, but does it continue to run uninhibited?
 

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I have a 93 sonoma w/ the 2.8 that sounds like it was doing the same thing as yours. Would start fine when it was cold but when it was warmed up it wouldn't start unless I put starting fluid into the carb. My issue turned out to be the ICM (ignition control module) which is under the distributor cap. They can be tested, I brought mine into Oreillys and they put it on the tester and it was bad. Put the new one in and starts cold and warm now.

On a side note, I had an oil leak on the back side of my engine and I took the distibutor out to change the ICM and realized there was no seal on it. Put a new seal on and the oil drips on the driveway have stopped for now. :)
 

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Discussion Starter · #5 ·
JTCFANOF3:

1: Yes, It will continue to run uninhibited
2: 1987 S10 2.8L Auto
3: Yes, It idles

Side note: Fuel pump and fuel pump relay function they way they should, this problem is somewhere before that in the system.

BRYAN723: Thank you for your sugguestion, I will check that out. :)
I am in a smaller city in Canada so we dont have AutoZone or Oriellys, ect. We have a few local shops, a Napa, and Lordco. Does Napa test parts?
 

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I don't know if they would be able to test them or not. Would just have to bring it in with you and see. At least its not all that expensive of a part if they are not able to test it. Think mine was in the $30 range and don't think yours would be all that different then what mine is.
 

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I was staying away from the ICM, mainly because it will start hot if you pour fuel in the intake, nine times out of ten it will not with a bad ICM. But have it tested or replaced if its cheap enough of a part for you to throw it at the problem.
The fuel pump is turned on by the ECM, but the injector circuit is pulsed via the ECM via the ICM(cam sensor in a sense). Have you tested or swapped the fuel pump relay? But even if the fuel pump relay fails, the oil pressure sending unit will close the fuel pump circuit in place of the relay. Unless your oil sender is not closing the circuit in the case of an overheated fuel pump relay.

Does the relay click and you verified voltage to or not to the pump during a hot soak KOEO?
 

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I am interested in this also. I have the same problems except that on a cold start, i have to turn it over 3 to 4 times before I hear the pump turn on / pressureize and if I drive it for more than 10-15 minutes and turn it off, it is at least an hour before I can start it without the help of starting fluid.

jtcfanof3: where is the realy for the fuel pump? I have an '86 2.8l. I thought it was on the left firewall where there are 3 relays. However, I pulled all 3 of them and the fuel pump still came on. So I am assuming it is in a different place.

Thanks in advance for any help.
 

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The fuel pump will still come on because the oil pressure sender is the back up to the relay, so if the relay fails the oil pressure will turn the pump on.
 

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I made an account just to state not to over look this ^-^-^-^ THE FUEL PUMP WILL STILL RUN WITH BAD RELAY, BUT WILL NOT PRIME. Wish I would have found this piece of information days ago. thanks you vary much jctfanof3 hope you see this one day.
 

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I made an account just to state not to over look this ^-^-^-^ THE FUEL PUMP WILL STILL RUN WITH BAD RELAY, BUT WILL NOT PRIME. Wish I would have found this piece of information days ago. thanks you vary much jctfanof3 hope you see this one day.
10 years later...nope.
 
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