fuel PSI

[directinjktn1stgen]

wondering whats good fuel psi on a slightly modded inter cooled engine ? I have M3 fuel pin and 1/8 bump timing and constantly adjusting everything and cannot seem to get past 15psi of boost! Hooked a fuel pressure gauge up to it with factory timing and it pulls down to 2psi fuel pressure i haven't adv. timing since then to see what i get but I'm sure it'll be lower.

[AHineman]

10-15 psi would be cool. (with a better than factory lift pump setup)


Have you ran the fuel screw in and done a gov. spring yet? That would really wake the old girl up if you haven't.

[directinjktn1stgen]

oh yeah 3200 spring and fuel screw is maxed out egts dont rise above 1000, i was thinking lift pump would help but i was told even 1psi was plenty for our injection pump. So thats what ill being getting next!

[AHineman]

I see you have a cam and that will lower boost...


but, at one time I had this setup with my '93: fuel screw in to almost run away, deny t fuel pin, 3200 spring, to the head timing, 4" exhaust and cut air box with a k&n filter (I know, but it came with the truck). Low pressure piston lift pump. Stock everything else and I could hit 32 or 33 psi of boost. That was with a lot of timing for stock intercooled injectors.


Throw a better lift pump and bigger supply lines at it and I think it will help. Bump the timing back up some and make sure you have no boost leaks and I think you will have a really good runner for what you've done to it.


Also I didn't see if you had an auto or a standard. If you have a stock auto, you may not be loading up the engine very much. It may be blowing throw the trans.

[directinjktn1stgen]

its an auto, if wondered for months if that was my problem and asked a diesel power, who rebuilds these pumps they said 1psi was plenty. Which i didnt think was so just from all the vehicles i have worked on required more and if was shy ran just as mine does. thanks for the input!

[AHineman]

Other things like not getting full throttle travel, or having a boost leak in the line to your AFC could be your problem....


But I could tell a difference when I replaced my stock lift pump with a low pressure piston lift pump with a setup similar to yours (minus the fancy cam).

[directinjktn1stgen]

I replaced my line going to AFC with DOT line and all brass fittings. I have my boost gauge plumbed to the intake horn. Im going to tinker on it some today and see if everything is right and adv timing to see what my fuel PSI goes too.

[RCCUMMINS89]

Fuel pressure requirements depend solely on the injectors and the overall amount of fuel that one is running.

If you are holding psi with the factory diaphragm pump...... then there will be minimal gain with an aftermarket lift pump.

What you will notice is throttle response, but for wot or dyno performance..... it won't make much of a difference.


Now once you are pulling it down to 0 with the factory lift pump, then you'll need a lift pump.

Once you go into very large injectors (case psi dropping big) and 15 psi will out perform 10 psi and so forth.

[BC847]

Jeffry, when are you gonna bring that thing by the house for some wrench-time?

[AHineman]

I wouldn't call 1psi of fuel pressure keeping up, but that's just me.

[ellis93]

I wouldn't call 1psi of fuel pressure keeping up, but that's just me.

Nope,me neither

[RCCUMMINS89]

It's not keeping up. But if one is only drawing a stock wee little bitty lift pump only down to 1 psi, the internal injection pump's vane pump is still moving more than enough fuel of what's actually going out of the injection pump.

[directinjktn1stgen]

bc847 whenever im available every weekend! Also i need to get that turbo from you if its still available! Thanks for the input everybody ill see what i can do to pull it to nothing