Ok... last week my fuel pump decided not to spin up for me... see this post...

Fuel Diagnosis Thread


Well yesterday me and a buddy of mine decided to try and troubleshoot the problem... we had the car running and everything was fine...I shut the car off after about 20 minutes of running and when I go to restart the car same thing happens...no spin up...

So we tried jumping the two large wires in the fuel pump relay connector (orange and the brown/white) and all I could hear was the pump "tapping", tap tap tap.... normally if you jump these two wires the fuel pump will spin up regardless (not adviseable to keep them jumped as you could burn out a fuse, but a good quick test to see if the pump is getting power). After about 30 minutes the pump decides to spin again... the cycle seams to be...

- Fuel pump is in use for 20 or 30 minutes

- Shut down the car... wait a second

- Try and fire her up and nothing...

- Wait approximately 30 minutes, fuel pump spins again.

One thing that did have us scratching our heads was that when the fuel pump was working we could pull the fuel pump relay connector off, turn the key and the fuel pump would spin up, the fuel pump would even stay running and the car would start and idle no problems... Is this normal???

 

ttt

 

The fuel pump power relay has a redundant path through the auxilliary oil pressure switch:

 

Thanks for the diagram Vader!! That is just what I am looking for...

So I am assuming that if the fuel pump has a redundant path other than the fuel pump relay then it is normal that when the fuel pump relay is disconnected the fuel pump will still spin up (if the pump is working). At least that is what I am thinking?? Yes??

So my diagnosis of a faulty, intermittantly working fuel pump is probably correct...

By applying power to the fuel pump directly by jumping the Orange (12v) and the Tan/white (to the pump) and all I hear is the pump "tapping" it seems to me that the motor in the pump gets "stuck" or "hot" after continuous use and when the power is cut it sticks until it cools down and "unsticks"

A reasonable assumption yes?

 

Sounds good to me (or, bad to me, because you have to change the pump). Assuming a running engine and a good fuel pump relay, you could either unplug the relay and the pump would keep going, or unplug the oil pressure switch and the pump would keep going.

Plus, since you're not moving the car, it doesn't seem likely that there's a wiring short. You could aways disconnect the pump at the body connector in the back of the car, and give it 12 volts to "eliminate" any problems in the wiring between the front of the car and the back of the car.

One tip for the pump: The pulsator!! It's between the pump outlet and the fuel inlet... a little square sucker. Two options: Replace with new, or eliminate it. Don't re-use the old one!! It's only sealed with o-rings... which can, over time, dry up, crack, and leak.

The first time I changed my pump (same wiring/setup as you v8 guys), I re-used my pulsator- I didn't know any better. Second time I used the short piece of high-pressure fuel hose that came with the pump. I bought "Fuel injection clamps"- basically a worm drive clamp that provides a 360 degree seal, instead of like a radiator clamp that doesn't quite crimp the hose all the way. They have 'em at Pep Boys next to the normal clamps for $1 or $2 more.

Also, replace all the vent hoses in the back. You can use normal fuel line for those three (instead of fuel injection hose) if you want, they're not under pressure. There's one hose for the tank vent, one for the return line, and one for the charcoal canister. The high pressure feed line is usually a special-order part from the dealer; see if you can get one.

Final tip: The tank seems to go back in easiest if you put the "forward-facing" end into the car first, and then push the "rearward facing" end up.

Good luck... the job's 90% pain-in-the-butt work and 10% technical work. Ignoring any setup time and rusted bolts/nuts, it should only take a few hours.