Hi all,

I was hoping someone could point me in the right direction on this issue.

I've got an 89 F150 XL Lariat.
There seems to be a wiring issue with the fuel pump wiring circuit.

Running direct power(bridging the relay to the fuel pump output-yellow to brown) works fine and the truck will run.
The relay has been replaced.

Constant power on the yellow wire to the relay is good as indicated above.

12V from the EEC relay on the red wire is good when key forward.

12V Output to the brown wire(fuel pump) is good when nothing is connected to it, and key forward. When I connect the fuel pump, that voltage drops out.

The inertia switch is being bypassed.

When I test the ground(tan/lt grn) wire with the key off, it is fully grounded. When the key is turned forward, it drops to around 6V.

Is this indicative of an issue with the PCM? And if so, is it ok to use a normal switching relay instead of the fuel pump relay to just supply power to the fuel pump at key on, and make sure I don't let the key sit forward without cranking? Or will that configuration cause other problems?

Any insight

 

First: replace the relays as described in this caption & the NEXT few.



Second: look inside the EEC.

 

Thanks for the reply. Ok, so the relay has been replaced. I'll pull out the EEC next, check it out and post the results.

 

Yeah, it looks like there is some burning on it. I suppose it needs to be replaced, since I'm not sure what other issues it may be causing. With the fuel pump being powered through an independent relay, the truck is running. Like I said, I'm just not sure if more damage will be caused with this configuration.

 

You replaced the relay socket as well when you changed the relay?

Adrianspeeder

 

The green socket/harness 'pigtail' as they called it - yes. Clipped the wires and crimped them back to the main wire harness.

 

The discoloration on the PC board is just electrolyte leaking out of the capacitors - it's not "burning". I've heard that alcohol will remove it, but it's just on top of the potting compound - it's not hurting anything. Many people replace the capacitors themselves; others pay ~$100 for a reman EEC with a warranty (which is an old EEC that a pro replaced the caps in).

 

Oh I see, yeah just on top. Ok, so you're saying that cap went bad and can just be replaced, and not the whole EEC? If so, that should be easy enough for me to do.