Can anyone help. The fuel pressure drops after 10-15mins of driving from 41psi to 18psi. Got battery voltage at pump. I've fitted another Bosch 023 pump. Fitted new fuel filter

 

You dont say what car, but sounds like the regulator is fecked

 

It's an escort cosworth with RS500 inlet and regulator

 

So presumably the car also stops after this happens ?

Because if it really is happening, it would be driving like fuck all.

 

Unable to accelerate. Only way to drive is to just rest foot on accelerator. If you lift off fuel pressure increase but as soon as put foot on peddle pressure drops.

 

Could be the fuel filler cap failing to vent the fuel tank - could try loosening and re-trying.

When filling with fuel do you get a large "Whoosh" noise?

 

Tank vent/breathing is very possible. As above try leaving the cap loose and driving for a bit.

It sounds unlikely to be a regulator from the description.

 

A mate had this on a Sierra, it was something bloking inside fuelline from tank

 

Is the car used regularly ?

 

Sounds like a dodgy gauge to me otherwise it would not drive well as you have said.

 

He replied, it doesnt drive right

 

Bloody phones.....

 

I've undone the fuel filler cap when it's happening and it's not a breather problem.
It's a track day car with fuel lines inside. I've put a fuel pressure gauge in the feed pipe at the fuel rail and it's not a blockage in the feed pipe. It's happening when you put your foot on the accelerator and you get that anitial vacuum in the inlet

 

Initially you said this problem happened after 10-15 mins of driving.

Now you're saying it happens only when you put your foot on the accelerator ? So is it a momentary loss of pressure or a constant loss of pressure ?

Details seem to be misleading.

 

It's constant. Same fault if light throttle or heavy throttle.

 

Fuel pressure should track manifold pressure. Are you saying this never happens ?

If you test the reg and apply pressure, does fuel pressure do what it's supposed to do ?

ie fairly closely 1:1 track manifold pressure

 

I've got a vacuum/pressure tester at work. I'll try it tonight.

 

So I pulled a vacuum on the fuel pressure regulator and the fuel pressure dropped to 41 psi, and then put a pressure of 14psi and the fuel pressure went up to 61psi

 

Regulator has some ability to work fine then

blockage in the fuel tank does sound reasonable.

 

I've had the pump out of tant several times and all looks clean and nothing blocking bottom of pump.

 

Did you try it with the filler cap loose ?

 

Yes tried it with cap off.

 

You're going to need to do some proper testing.

Monitor both pump voltage and current draw, as close to the pump as possible. This will at least give some clues as to how hard the pump is working and whether the power supply is holding up during this problem.

And also while monitoring pressure as close to the reg as possible

or you could just change the reg...as it seems about the only major item you have not changed ?

Has the problem just happened suddenly, or what ?

 

Ok I'll check those. It's only just started.