Whats base fuel pressure?

[79turbostang]

I do believe i have a fuel pressure problem, I have a 87 thunderbird 2.3t swapped into my 79 mustang and for some reason it still feels like it has no power after about 3800rpms. The only mods i have are front mount inter cooler BOV and about 15lbs of boost. I have brand new motorcraft plugs gaped to .32 new wires timing is set perfect and have not jumped timing belt. Now at idle with the vacuum line no disconnected the fuel pressure is 28lbs and at full boost it only get to about 48lbs does this sound about right, and also i have brown top injectors.

[svslow]

With no vacuum source it should be around 39-40 psi.

[khantyranitar]

Sounds to me like your regulator is holding the pressure too low. Might have a bad diaphragm.

Your pressure at idle should be between 38 - 42 lbs or so. With full boost with an IHI, if you assume 18 psi boost the fuel pressure should be between 56 - 60 psi.

I would double check to make sure you got an accurate reading, but to me it sounds like the pressure is just too low.

[79turbostang]

I just had a second at work to unplug the vacuum line and recheck with the line unpluged it sits around 40psi at idle. And no I got a turbo off a svo and full boost pull at 15psi with line pluged in its at about 48psi.

[Stinger]

Fuel pressure should rise 1:1 with boost. This means if you have 40psi at idle with the vac line removed, you should have 55psi fuel pressure (40+15) with 15psi boost.

I'd first try replacing the inline fuel filter because it's dirt cheap. If it's the stock pump though, I'd suspect it's probably failing.

[oneowner88lx]

We went with a Kirban adjustable fuel pressure regulator and a 255 lph pump. We replaced the pump first and our car still had pressure problems under boost. Then we replaced the regulator and the problem was solved. The pick up screen in the tank might be clogged too. I would do what Stinger says first and replace fuel filter since that is cheap and easy. With the low pressure you have I would stop boosting it until you get that fixed. Otherwise you might hurt the engine.

[79turbostang]

Ok well let me ask one more question what should the pressure be at idle with the vaccum line pluged in?

[Stinger]

It varies with how much vacuum you have at idle. It's typically in the low 30's though.

[79turbostang]

I vacuum right at about 21psi.. So I guess all disconnect the fuel pressure regulator and see what the psi goes to.

[Stinger]

How many inches of vacuum ultimately doesn't matter for this case because testing with the vacuum connected is not a proper way to check the base fuel pressure (which is why there is no pressure spec given for that process). The only proper way is with the vac line to the regulator unplugged from the regulator and plugged so it doesn't create a vacuum leak.

[jeremyt]

So the best way to set your pressure regulator is with line discounted and have the line from the regulator plugged and have it set in the low 30s ? Or what should it be set at idle ..the truck has walbro 255 fuel pump and Russel racing inline filter full braided lines high pressure an return with brown top injectors I only have the hx35 set at 8lbs just for now until I get it tuned better.. with the line plugged in I'm sitting at around 32psi

[Stinger]

With vac line removed from the regulator, you set it to 39psi with a stock ECU or stock injectors, or 43.5 psi if you've got aftermarket injectors as that's the pressure they are rated at.

[jeremyt]

The ecu is your pimpx so do I still set it to stock rating ?

[Stinger]

Stock injectors with the stock flow rate (35 lb/hr) entered in Tunerstudio = stock Ford pressure of 39psi.

Non-stock injectors = 43.5psi.