ongoing fuel pump issue ... i now know what the problem is

[chatham]

i have been able to pin down that the problem is the fuel pump relay is only sending 7 volts out to the pump. what i need help with is where/why is the relay only getting/sending 7 volts? is this an ECM problem? something else?

 

[chatham]

i started this thread because i was testing the wrong relay at the beginning. that is why some of the info i was getting didnt make any sense to me. here is what i know at this point.

the ECC realy is working

fuel pump relay
the blk/y wire has 12v constant.
the red wire has 12v with ing on.
the red? wire at the pump gets 12v with ing on but then immediately drops to 7v.
the red? wire at the pump gets 12v constant with ing at start.
the pk/blk wire at the intertia switch gets 12v with ing on but then immediately drops to 7 v.
if i jumper the fuel pump with a hot 12v lead from the battery to the pk/blk wire at inertia switch the pump will run and i can start the vehicle.

for some reason the fuel pump relay starts to put out 12v but then drops to 7v. this happens with the old relay and a brand new one.

so what i dont know is why this is happening. it appears that the relay is closing but then opens up again. i assume that the 7v is probably just ghost v. so why isnt the relay staying closed? is this a PCM issue? it makes no sense to me.

 

[adsm08]

Throw a jumper across the relay terminals and test it again. If it works, you have a control issue. If it still happens you have a resistance issue.

 

[chatham]

i ground the test plug with ing on and the pump runs. so i have a control issue. my question then is, is it necessary to replace the PCM or can i just ground the fuel pump before the inertia switch? is there some other function in the PCM that just grounding the fuel pump directly would create a conflict? seems simple enough just to ground the pump.

 

[nosrac04]

i have the same problem and cant seem to pinpoint the issue. I have been driving around with the test plug hooked to the negative side of the battery. If you get this figured out, could you send a message to me. The master tech at our shop is not able to figure it out and is about ready to retire because of it. Thank you for your time.

 

[Earl43P]

That 7v is a ghost (not real).

The 12v is only there for 2 seconds (as designed) to prime the fuel system before cranking the starter (normal condition).

Once you crank it over, the PCM sees that the engine is rotating and provides a ground for the fuel pump relay. Your problem MAY BE that the PCM isn't seeing a good enough rotation signal from, in your case, the distributor (PIP).

First though, I'd clean all the grounds in the engine bay (fenders and core support) and verify that all the wiring to the core support grounds is good.

Here's a good diagram: http://www.therangerstation.com/tec...les/Diagram_ElectronicEngControls2_3_1of3.JPG

http://www.therangerstation.com/tech_library/EDiagrams/files/Diagrams_StartIgnition83to88_2_3.JPG

 

[nosrac04]

You know, does the TFI module have anything to do with this mess. You know, that thing stuck on the side of the distributor. Does that have anything to do with fuel?