89 K5 Fuel pump relay control voltage low (6 volts)

[mentholi]

Hello everyone!

I have been reading this forum for I while and found loads of great info but now I'm stuck and needed to do my first post!

So my problem is that my 89 K5 gets only 6 volts to fuel pump relays control side. This then is not enough power to activate the relay and my fuel pump does not get any power. Fuel pump runs fine if I use jumper wire to bypass the relay. The always hot 12v side of the relay harness is fine and is getting voltage there. Also ground seems to be fine on the relay.

Relays also works, I have tested that with multimeter and 9v battery. I hear it click and also don't have resistance when open so it is working.

So my question is what could be the cause to low voltage on fuel pump relay control side? I think the wire should go directly to ECM? One thing that I also noticed was that when I turn the key to on position (not cranking) the control wire has 5-6 volts all the time.. Not for two seconds that it should have for fuel pump priming. Could that 6 volts come from oil pressure switch which should be in same wire I think?

Thank you already for any advice on this!

 

[dyeager535]

Hello everyone!

I have been reading this forum for I while and found loads of great info but now I'm stuck and needed to do my first post!

So my problem is that my 89 K5 gets only 6 volts to fuel pump relays control side. This then is not enough power to activate the relay and my fuel pump does not get any power. Fuel pump runs fine if I use jumper wire to bypass the relay. The always hot 12v side of the relay harness is fine and is getting voltage there. Also ground seems to be fine on the relay.

Get the wiring manual off of here: http://67-72chevytrucks.com/vboard/showpost.php?p=5621043&postcount=1

Should be pretty simple to figure out looking at the diagram, I just can't remember how the relay is controlled. You are correct that the ECM controls that portion of pump operation. Would be an unusual ECM problem to allow some voltage, but not all.

The oil pump pressure switch is just an open/closed deal. If the relay supply side has 12V, so will the oil pressure switch, unless the wiring is cut.