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Old 10-08-2021, 10:30 AM   #1
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Default Fuel pump goes on then off sometimes

Hey everyone, i have a 1991 hardbody ka24e. My problem with the truck is that sometimes the fuel pump goes on then off for about 1 or 2 seconds with the first turn of the key and then the next turn of the key the fuel pump turns on normal. It stays on for about 5 seconds.

The only part i have changed is the fuel pump. I've been checking the wiring but im not to sure if this is a wiring issue or a mechanical issue.

Thanks everyone for the help👍
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Old 10-08-2021, 01:20 PM   #2
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Does the engine start and run properly?
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Old 10-08-2021, 03:12 PM   #3
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Quote:
Originally Posted by Nismo91 View Post
My problem with the truck is that sometimes the fuel pump goes on then off for about 1 or 2 seconds with the first turn of the key



I've been checking the wiring but im not to sure if this is a wiring issue or a mechanical issue.

If my truck, when it won't start the fuel pump, THAT'S when I'd test the electrical part of the ignition switch.


Do the dash warning lights light up or not during that situation?
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Old 10-08-2021, 09:03 PM   #4
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Get yourself a can of contact cleaner and hit all the connections you broke and reconnected. Break them again, spray... if needed, an old toothbrush is handy to have around... reconnect. Oxidised contacts can play hell in diag...


OH, I've (many times) seen bad parts come in, NEW! QC is not what it used to be... sad to say!

You could still have a bad pump.


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Old 10-08-2021, 11:02 PM   #5
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Originally Posted by alabama_lowlife View Post
Does the engine start and run properly?
Yes it runs fine when the fuel pump primes for a good 5 seconds but when it does the on and off thing it bogs out or dies out
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Old 10-08-2021, 11:04 PM   #6
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Quote:
Originally Posted by Cusser View Post
If my truck, when it won't start the fuel pump, THAT'S when I'd test the electrical part of the ignition switch.


Do the dash warning lights light up or not during that situation?
Dash lights light up yes. I'm thinking to replace the ignition it still has the original one on it and the key is hard to turn sometimes.
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Old 10-08-2021, 11:06 PM   #7
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Quote:
Originally Posted by 89'HBV6 View Post
Get yourself a can of contact cleaner and hit all the connections you broke and reconnected. Break them again, spray... if needed, an old toothbrush is handy to have around... reconnect. Oxidised contacts can play hell in diag...


OH, I've (many times) seen bad parts come in, NEW! QC is not what it used to be... sad to say!

You could still have a bad pump.

Ok thanks will try this out. Hopefully it solves the problem
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Old 10-09-2021, 03:30 AM   #8
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Also it only happens in the morning. Then after that it runs fine. Hut when does the on and off thing the truck bogs out
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Old 10-10-2021, 03:34 AM   #9
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What have you done under the hood lately?

Does your PU have a relay that switches the pump on and off based on oil pressure?
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Old 10-10-2021, 12:15 PM   #10
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The relay for the pump is under the hood in the passenger side. It has two black/white wires that get switched 12vdc from the fuse box. The white/blue wire is the 12vdc output to the pump. The white/red wire is the ground that is provided by the ECU to turn the pump on. If you can get it to fail again you may be able to test the wire for power or ground as appropriate to narrow down which wire is causing the trouble. Otherwise, cleaning all the contacts and replacing the relay and even the fuse may cure the issue.

If the problem persists the ecu could be bad. When you replaced the pump did you replace the entire assembly or just the pump itself? The wiring was flaky in the assembly on my son’s truck so I had to replace the entire assembly.
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