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Old 12-30-2008, 06:16 PM
runn141's Avatar
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electric fuel pump?

i have an 89 chevy full size truck with a 350 tbi. i had just put another motor in using all the same throttle body and everything else that wired up. now, the fuel pump doesn't work and i install a new one it doesn't work either. so i check the fuel pump fuse, its not blown. i change the relays no different. with a test light, with float assembly and pump and all out of the tank, i have two hot wires going to the fuel gauge sender and two dead the pump. so i then swap one hot wire from the sender to the + on thy fuel pump and it starts and runs. but now, when i turn the ign. off the pump continues to run until i unplug the harness to it? then i talk to another mechanic, and he said the wires were the correct way before i swapped them and i should put them back because the problem was somewhere else. but he couldn't figure out why it still ran. so i did, using another harness from another float assembly. and now, i have no juice getting thru the harness that plugs in to the tank.

i can also take the fuel pump fuse out, and and neither side in the plug is hot. so i thought i woul bypass it, i can take a wire directly from the battery and stick it to one side and the pump will run. but using a 12 volt ign. source and it wont, and i used 4 different ones?

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Old 12-30-2008, 06:49 PM
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2 things on a fuel injection vehicle

crash switch/inertia switch
fuel pump relay.

There is a crash switch in that truck somewhere---I do not know where.
it may have come unplugged or jostled enought to 'cut off'.

Also--fuel pump relay----again no idea where----this is wired to your ignition and the ECM. Should pump for a moment then cut off when you turn the key to "ON" but do not start.

It is designed to do this so it will cut fuel when the 'puter senses that there is no spark happening.

Both of these can be triggered by an impact somwhere.

Better get a diagram or manual to find out where these are.
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Old 01-01-2009, 03:53 PM
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i found out that this truck has no crash switch/inertia switch. but i finally got juice thru to the pump fuse and now have power to pump. i turn the key on and i hear it run but it wont pump any fuel. could it be that the ign. source is too weak? because directly from the battery, it will pump.
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Old 01-02-2009, 10:31 PM
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Maybe an oil pressure switch?

On some (maybe all) GM's with EFI, the fuel pump relay grounds through through an oil pressure switch on the engine. The ECM grounds the relay before and during startup, after that the relay grounds through the pressure switch. That way if the engine quits or runs out of oil the fuel pump will shut off. Also if the vehicle is in a wreck and a fuel line is ruptured, the fuel pump will shut off and reduce the risk of a fire.

Just a thought.
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Old 01-03-2009, 04:19 PM
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im going to check all ground wires next, and hope for the best.
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