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454 TBI fuel pressure?

fortcollinsram

fortcollinsram

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I recently installed a new fuel pump in my 87 k5 with a swapped in 454 TBI thinking it would hepl with my fuel pressure leak down. After the vehicle is shut off is the pressure suppose to hold steady at the rated pressure? when i turn the truck off the pressure drops rapidly to 3 psi after stalling around 6psi. i have been trying to solve a mid-high end sag issue at WOT



Thanks for the help
 
First off is the engine a swapped in 454 or just the TBI from a 454 on the 350?

After re-reading your post again i'm thinking you installed a 454 TBI unit onto your 350 engine. Did you also have a new chip burned? If not that is your problem. The 454 injectors are a bunch bigger than the 350 injectors and the dwell time for the 350 injectors is too much for the 454 injectors.

Now to answer your question, it is normal for the fuel pressure to drop back to little or nothing once the engine is turned off. Mine drops back to zero once it's turned off and i have no issues at all with my rig.
 
4X4HIGH said:
First off is the engine a swapped in 454 or just the TBI from a 454 on the 350?

After re-reading your post again i'm thinking you installed a 454 TBI unit onto your 350 engine. Did you also have a new chip burned? If not that is your problem. The 454 injectors are a bunch bigger than the 350 injectors and the dwell time for the 350 injectors is too much for the 454 injectors.

Now to answer your question, it is normal for the fuel pressure to drop back to little or nothing once the engine is turned off. Mine drops back to zero once it's turned off and i have no issues at all with my rig.
Click to expand...


I should have clarified a bit more...My I swapped in a complete 454 out of a 1993 K3500 into my 87 K5... I am running the 454's ECM and it is pretty much stock except for higher compression (~9:1) and a GMPP truck Torque cam (still very lower on the duration side of the fence).

Do you think the marginal increase in overall compression and the small increase in duration warrant burning a chip?
 
Any change you make warrants a chip burn to optimize the potential of the engine. Have you checked your fuel pressure while the engine is running? You are looking for 9-13psi with 12-13 optimal.
 
4X4HIGH said:
Any change you make warrants a chip burn to optimize the potential of the engine. Have you checked your fuel pressure while the engine is running? You are looking for 9-13psi with 12-13 optimal.
Click to expand...
Yes, which leads me to my next question...

I have the Vacuum Referenced FPR on it and it and a permanently mounted gauge. It sits about 12.5psi at idle but jumps up pretty high (beyond the limits of the 15psi gauge)


How much fuel pressure is TOO much on this TBI's? I was talking to a GM tech the other day and he said anything over about 14psi will actually cause a lean condition b/c the high Fuel pressure will actually hold the pintle closed for longer b/c the injector doesn't have the strength to open it up as quickly with the higher fuel pressure....Is this true?

Should i get rid of the VRFPR and just put a standard adjustable on is and set it and forget it?
 
I don't know much about the VRFPR other than they increase fuel pressure at WOT. Not sure what fuel pressure is too much as there are many variables that will affect that answer. Is the fuel pump you installed a high pressure pump? If not and it's just a stock replacement pump they will only achieve about 15-16psi and nothing more. I have a high pressure fuel pump in my rig and i run 18psi through my 454 TBI on my 350 but i also have a custom chip from Brian.

I also think that if your fuel pressure is too high it could hold an injector open not the other way around.
 
4X4HIGH said:
I don't know much about the VRFPR other than they increase fuel pressure at WOT. Not sure what fuel pressure is too much as there are many variables that will affect that answer. Is the fuel pump you installed a high pressure pump? If not and it's just a stock replacement pump they will only achieve about 15-16psi and nothing more. I have a high pressure fuel pump in my rig and i run 18psi through my 454 TBI on my 350 but i also have a custom chip from Brian.

I also think that if your fuel pressure is too high it could hold an injector open not the other way around.
Click to expand...

Who is Brian, how do I find him and what info does he need to burn a chip??
 
Before you do anything you need to get that pressure regulator issue taken care of!!

Try unhooking and plugging the vacuum line then setting the fuel pressure to a constant 13 psi. LEAVE THE VACUUM LINE OFF!! TBI systems are designed to have a constant 12-13 PSI. Variable fuel pressures require a chip, it's a lot of work with little gain.

I'll bet the high fuel pressure was causing a rich situation and consequently your sag/power loss at WOT.

I agree with Scott get a chip burned for it, but you need to get all your other issues taken care of first.
 
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