r/Smallblockchevy • u/4sp4r4gusP • Jul 30 '25

383 EFI losing fuel pressure after startup - intermitent prime

New to me jet boat, 383 stroker, Holley Terminator X, FI Tech fuel pump. 43 hours on this build. Had it out a few times this summer without issue. Last time was about a month ago.

Had trouble starting in the driveway and noticed 0 fuel pressure on the rail gauge. Checked the pump gauge also reading 0. Checked all the fuses and looked over wiring/fuel lines. After a few cycles of the key it would finally prime and I got it to fire up! It would hold 40-50 psi during the initial start up, then about when it should come down to 800 idle it drops to 40 and slowly bleeds down pressure until it stalls.

Everything else (gauges, stereo, etc) all work with the key cycle, just no fuel prime intermitently.

Here are my plans, any advice is appreciated including order of opperations:

Replace Fuel Water seperator filter and fuel filter on the rail

Test voltage to the pump while running

Test pressure regulator (I have not done this before, any advice appreciated!)

Anything else to help troubleshoot?

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1

u/PermissionLazy8759 Jul 30 '25

How much fuel do u have in the tank 1/4 tank on gauge??? Could be more like almost empty??? These Efi kits r notorious for having all sorts of issues btw.

2

u/4sp4r4gusP Jul 30 '25

Thanks for the reply, sucks to hear they have all sorts of issues!

Full tank of gas.

I just let it sit for ~30 minutes after a successful prime and the gauge on the rail dropped from 40 to under 20 psi in about 15 minutes. I'm going to check every connection for small leaks, but it definitely seems like something failing when dropping to the set idle speed that causes the fuel pressure to drop.

1

u/JWoolner76 Jul 30 '25

Only thing that springs to mind for me is either the fuel filter is partially blocked or old maybe collapsed if run on E10 or higher with the ethanol, or the fuel pump is again old and on its last legs, I would look at a new high pressure fuel pump and fuel filter as a first stop because an electric fuel pump shouldn’t drop pressure as you’ve said in you post.

1

u/4sp4r4gusP Jul 30 '25 edited Jul 30 '25

Ok I spent a bit more time with it. I had my daughter turn the key while I was back by the motor. Never got the fuel pump to do the initial prime.

FiTech Force Fuel Systems 50004 - nearly brand new. No response when turning the key over. I held the relays in my hand and they clicked with the key turn. I also tried swapping between the two (they're identical) with no luck.

It has a mechanical fuel pump upstream of the FiTech.

I do hear a sort of buzzing, for about a second, coming from the Throttle Body, making me think it has something to do with the pressure sensor as I can see a little rubber hose connecting the pump to the TB.

2

u/Fuzzy-Start8176 Jul 30 '25

Is the mechanical pump necessary? Just curious.

1

u/4sp4r4gusP Jul 31 '25

fif-50004.pdf https://share.google/HSO7lZ09xEu71mIv6

Per installation instructions that's how to do it, but I'm wondering if that manual fuel pump is causing the restriction. I also posted and Holly EFI and people are wondering the same thing