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Old 07-11-2018, 06:18 PM   #1
randywa
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Question fuel pump quits on hot days

I may be overlooking something simple and obvious. The fuel pump on my 93 5.7 with auto has been quitting me, but only when on and off throttle a lot (hills and curves), the air temp is above 90, and running the a/c. It doesn't surge, stumble, or give any warning. It apparently doesn't even care how deep the ditch is or if the road has a shoulder to park on. It will always start after 30 minutes or so. Sometimes I can switch out the relay and it starts right away, but not always. Today I noticed it threw a blink code 15 - Engine coolant temp sensor error (low temp indicated). The code went away as soon as the motor started back up. I've pulled the bed and repaired the frame ground at the pump and cleaned all the grounds I can find. While the bed was off I fought thru a very fast idle problem, replace the knock sensor, tps, and coolant sensor. I've also chased more wire than a truck should have, just looking for bad spots. I've read all the threads I could find about fuel pumps and can't seem to figure it out. The people with the big butterfly nets are going to come take me away soon if this keeps up. Any and all help is greatly appreciated.
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Old 07-11-2018, 09:26 PM   #2
ChevyTech
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Re: fuel pump quits on hot days

Look at all the grounds at the front of the intake manifold.

The 1993 schematic shows the ground for the fuel pump terminates at the front of the intake manifold on G108 & G109.

The computer & sensor grounds share the same grounds on G108 & G109. One ground is by the thermostat and the other under an intake bolt / stud on the drivers side front of the intake.

If the coolant sensor loses its ground it will set a code 15, which will case the computer to command a faster idle speed.
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Old 07-11-2018, 09:54 PM   #3
randywa
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Re: fuel pump quits on hot days

I just looked at mine again. Instead of being split up all 4 wires are all on the stud by the sensor. Should I split them up or does it matter as long as they're clean and tight?
And come to think of it, when I was have idle problems, the TPS was showing short to ground so I changed it out. I'm beginning to think I better run the wiring harness again. Maybe a rub in there I missed before. Thanks for the reply.
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Old 07-11-2018, 10:31 PM   #4
ChevyTech
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Re: fuel pump quits on hot days

The grounds should be split up.

I do not like having any of the grounds connected at the thermostat housing. I have seen to many that have lost their connection to ground when at the thermostat. I always move them to a intake stud.
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Did you give the model, year, engine, fuel system type, and transmission information?
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Old Yesterday, 07:57 PM   #5
Tom
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Re: fuel pump quits on hot days

Whats the fuel pressure when its running correctly?
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