I have a walbro 450 pump, adjustable fuel pressure regulator set at 40 psi static. Everything is new including my fuel filter, fuel rails, injectors, etc... I took it for its first drive today and it seemed like it was hitting fuel cut as soon as I pulled out of my driveway. I pulled it back up to the garage and if I hit the throttle it will rev to 8k then start dropping fuel pressure to about 5psi. At that point it will sit and act like it’s hitting a rev limiter and stay around 3500 rpm. I pulled my fuel pump to make sure something wasn’t plugged up and everything seems to be fine. It will rev at about half throttle all the way to 8k. But once I hit the pedal past half then my fuel pressure drops and it falls on its face. I then turned my fuel pressure up to see if it made a difference and it didn’t much. Any ideas?

 

Um... forgive me if I'm dumb, but why are you running a static pressure instead of rising rate?

Additionally, what ecu are you running? Has your car been tuned? (It appears not) Have you made other changes?

Based on what you've said it sounds like you just threw parts at the car and expected it to figure itself out...

 

Also... please DON'T free rev up to 8k, that **** is horrible for any vehicle!!

 

Ehh. It's ok to rev. No less harm on the motor than when it's loaded.

By static pressure he might have meant static without boost at 40, it could still be boost referenced and increasing when boost increases.

Although, if it's 40psi at all times, that could be part of the issue. Seems like there is something bigger going on though if it happens when leaving the driveway.

 

you would get closer to the solution if you would provide more info. when you changed your fuel system did you change injector size? what ECU? has it been previously tuned and did you make any changes to the tune if you changed injector sizing? what does your AFR read when it stumbles, assume lean but it is possible to be otherwise.

since you were able to change fuel pressure i assume you have a boost referenced FPR. check the reference hose to the UIM.

you have a fuel flow problem and i would be looking very carefully at the FPR.

more info please. don't know if you have a digital fuel pressure sensor but a simple log of the event would be of great help.

 

Pressure is set at 40psi with the vacuum source unhooked and then it is at around 35 with the vacuum source hooked to the fpr when at idle. As soon as I hit the gas to try and rev it the fuel pressure jumps to 40 psi then immediately drops to about 5 or 10 psi and stays there until I let off the throttle. I unhooked my intercooler pipe and revel it so there was nothing coming to the motor from the turbo and when I rev it that way it’ll drop to 15 psi and hold there till I let off. I assumed it was a fuel delivery issue between the tank and pump so I checked my voltage to my pump today and it’s good so at this point I kind of thing maybe my walbro pump is bad already.

 

And to the response of “I threw parts at a car expecting to figure it out” this is all new parts. Also static fuel pressure is the pressure of your fuel system when vacuum and boost are not affecting your pressure which is also referred to as base fuel pressure. The single turbo set up and everything on the car is fresh. It has never been driven with this set up and I’m trying to get it to run correctly so I can tune it. Asking for help is not asking for criticism. Maybe ask questions and give help instead of immediately jumping to the conclusion you did. I bought he car from a buddy who was going through a nasty divorce. He started the build years ago and ran out of money and never finished it. I’m simply putting it together and finishing it the way he was and then selling it back to him once he gets back on his feet. The car is running a single 70mm turbo now, 50mm external wastegate, walbro 450 pump, 850 primaries, 1650 secondaries, greedy front mount, greedy intake pipe, racing beat exhaust, full 3” exhaust, under drive pulleys, air pump delete, Pettit racing AST, Apexi power fc, fluidyne radiator, new water pump, new thermostat, stainless single turbo header, new cooling hoses, all emissions are deleted, and air pump bypass pulley. I’m just trying to get the car to run and rev clean and everything to work together at this point so I know everything is “correct”. From that point I’m pulling the motor and having it ported and doing a full rebuild on the motor.

 

What brand FPR did you put on the motor??? How are you running the fuel lines, and what size are they???

IMO, It sounds to me like your FPR isn't working right as the walbro 450 should be more than enough pump for what you have even at high loads and high boost.

 

Clogged fuel filter, crushed/kinked line, debris in line, vac line to reg is contaminated/blocking or pump suction problem assuming the reg itself is ok.

 

Running the walbro through the stock bulkhead connector? That's caused more than a few problems locally!

If your FPR has an inbuilt gauge - and that's where you're getting the pressure info - I'm not sure I'd be relying on that too much either, notoriously inaccurate. I'd be surprised 5psi would let the car run to 8k, playing with fire with an untuned motor, even if the pressure was good.

 

I would make sure you don't have any kinked lines. Also shouldn't you be setting the FPR with the vac line connected at idle??

 

No, you shouldn't.

 

First, Fuel pressure doesn't drop with "fuel cut".

If your fuel pressure drops that low free revving, it has nothing to do with injector size or ECU settings, unless maybe you have some set-up that controls duty cycle to the fuel pump.

First thing I would do is check the voltage to the fuel pump including while you rev it up.

If that's ok, check the plumbing. Make sure it's set up correctly, fuel pressure regulator isn't backwards, etc

There's probably something basic wrong.

With diagnostics,,,,,ALWAYS START WITH THE BASICS!

 

I would most likely change the fuel filter or consider looking at the hose connections inside the tank. I've heard that sometimes even with double clamps, the fuel hanger is notorious for leaking fuel back in to the tank before even leaving it. It sounds like it's simply running out of fuel in the lines.

 

Yea I guess you can always make a line that goes into a gas jug and jump the F/P relay in the diagnostics box and see if the actual flow of gas changes. It should be obvious going from 40Psi to 5...

you could also make sure the pump is getting a constant voltage at the same time.

my vote might be something like a split feed line in the tank, or it makes a partial connection.

 

1. Connect an air pressure regulator to the FPR input, initial set to 0 psi.
2. Pull out the fuel pump speed relay. Put a jumper across the two rear post of the fuel pump relay.
This will short across the low pressure speed resistor giving full electrical voltage to the fuel pump.
The ecu normally does this when the engine is under load.
3. Start the engine, let it idle.
4. As you increase the pressure to the FPR using the air pressure regulator, the fuel pressure gauge reading should increase with it.
5. If you apply 10 psi to the FPR, your gauge should read 50 psi.
6. If not you have problems some where.
7. If you pull out the fuel speed relay jumper while doing this test, the fuel pressure should drop 1 to 2 psi.
This is how I adjust base fuel pressure with my system.

 

No response tells the truth of the matter.