Tysgre

I just 5.3 swapped my 2001 mustang and have been having problems with the fuel pressure. I have a 300lph fuel pump, 42lb holley injectors, and summit racing FPR. There's no leaks from what I can tell. The fuel pressure shoots up to around 50 on first prime then starts falling off fast then slows around 40 and overnight drops to 0. If I start the car while it's at 50 psi the fuel pressure drops to 0 once running. Im just at a loss for what could be causing this

LS_caddy

Maybe your not depressing the schrader valve all the way. While running vibrations might have it not depressed at all. Mine would barely idle with 10psi

Tysgre

I have a fuel pressure sensor right after the rail and there's a dialog gauge on my fpr and they're both reading the same thing

strutaeng

Is this a return style fuel system? Can you temporarily cap the return line or pinch with with those special pliers?

Once you do that prime the pump and it should produce maximum fuel line pressure and it should hold. If the pressure drops you have have an injector stuck open?

Does the engine run okay?

Codys89RS

I had the same issue with mine and it was low on fuel.

Car ran fine but once I threw 5 gallons of e in it fuel pressure bounced right back up.

This of course was after I pulled my injectors, fuel filter, and regulator apart.... lol

Tysgre

​​​​​ Plugging the return line with pliers didn't change anything. Pressure still slowly drops after sitting and drops to 0 immediately when started
The engine bounces between 10 to 30 afr and does not rev

Tysgre

I thought this too and added fuel up to half a tank and it didn't change

LSswap

Maybe a problem with hose on in-tank pump setup? Maybe loose hose clamp or cracked in-tank fuel line. Also could be empty tank.

Also can you hear the pump running for sure once you start the engine?

Old Buzzard

How is the system plumbed?

Tysgre

I blocked off the fuel lines right before the rail and after the fpr and the pressure still stopped after sitting. I made sure there were no leaks within this area and couldn't find any. This would mean my injectors are leaking but I've ran two sets of injectors with the same problem so could it be the computer? I'm running a terminator x system. Also I found out my map was set up wrong I now have it running on the internal sensor with a vacuum line to the computer and it won't idle now. But if I unplug it and cap it it'll run. Kpa readings are fine with key on engine off but goes to 30 ish kpa when running is that right?
I'm leaning towards I just need to take it to a tuner?

LSswap

I don't think pressure dropping after it's been sitting off is your issue. I don't think a tuner will solve your problem unless your fuel pump is turning off after it starts. If you're sure your fuel pump is staying on and the pressure drops to zero, then look at my previous post.

Old Buzzard

Start with answering the ? in post # 9.
And post the tune file. The 20 questions game is going nowhere.

Tysgre

Dropped the tank and there's no leaks on the hoses attached to the fuel pump. Plenty of fuel in the tank. And my multimeter is showing my pump getting 14 volts while running, the engine is too loud to tell by ear if the pump is running or not

Tysgre

Fuel pump/ filter/ inline check valve/ fuel rail/ fps/ fpr/ and return back to tank