No fuel pressure key-on-engine-off

[maillemaker]

1995 GT

When the engine is cold, if I go to key-on-engine-off, I hear the fuel pump come on for prime. But I am only getting 0-2 PSI on my fuel pressure gauge. When I go to start, it takes about 2 seconds of cranking and then it fires up. Pressure goes straight to ~34 PSI at idle. If I remove vacuum line from fuel pressure regulator, goes to ~40 PSI at idle.

If I shut off and then go to key-on-engine-off again, it will spike to about 20 PSI, and then bleed down within a minute to 7-8 PSI.

I've heard suggestions about some kind of check valve on the fuel pump going bad. I'm just surprised it runs fine and pressure is fine once the engine is running.

Ideas?

 

[lwarrior1016]

Sounds like your pump is getting weak, or the filter is clogged. The prime for the pump (key on, engine off) is only a couple seconds. Then when you crank the pump comes on, so it makes sense that pressure is ok after it finally starts, because voltage is going to the pump.

I would try a fuel filter, if that doesn’t fix it then you need a pump.

Try cycling the key off and on 2-3 times before starting and see if it starts faster.

 

[maillemaker]

Thanks, I was going to try fuel filter first as an easy fix. At 30 years it probably needs one anyway.

If I cycle the key multiple times you get ~20 PSI each time, which bleeds down to around 8 PSI in about a minute.

 

[Musturd]

you’re on the right track . Start with the filter it’s easiest and cheapest to swap .

 

[maillemaker]

Well, I've ordered the filter. Motorcraft. Will be ready for pickup this afternoon. Watched some YouTube vidoes - doesn't look too hard to do. I'll update when job is finished.

 

[Terrorist 5.0]

Well, I've ordered the filter. Motorcraft. Will be ready for pickup this afternoon. Watched some YouTube vidoes - doesn't look too hard to do. I'll update when job is finished.

Be careful with the clips though, I actually bought two fuel filters when I did mine because if you don’t fit the clips in right they can break. It’s cheap insurance.

 

[maillemaker]

Yes, I broke clips doing my 1990 E350 van RV. Fortunately, they sell a multi-pack replacement at the auto parts store. Hopefully I will be careful with them and they will survive!

 

[ttocs]

gotta love those little white clips. ya just know they designed them to break.....

 

[maillemaker]

The more I think on this the more I'm pretty sure it must be the fuel pump.

As someone lwarrior said above, what seems to be happening is that when you prime, the pump comes on for a couple of seconds, and then it should hold that pressure so that the car starts quickly. Clearly it is not holding pressure, so it's either bleeding through the FPR or back through the fuel pump check valve. I'm betting on the latter. If the FPR was bad I'd expect low pressure all the time.

The fact that the pressure stays correct while the engine (and thus pump) is running points the finger back at the pump, I would think.