If the FP is set at 50psi using the FPR with 650cc injectors, should it always hold 50 psi, whether at idle or normal driving, or under boost?

 

I have mine set at 52psi. If my car doesn't sell on ebay in the next 2 days, i was thinking of getting an FP gauge that i could actualy see. I'm guessing it moves a little bit, but i don't know since i can't see it.

 

FP should raise w/ boost.

 

+1

I thought I read at one time that for every pound of boost, the fuel pressure rises one psi. Maybe someone can tell me if this is true or not?

 

set your static pressure with the vacuum line unhooked and plugged when using an aftermarket fpr return system. 50psi is a normal setting. it will raise and lower then once you plug the vacuum line back in depending on boost or vacuum conditions.

 

hmmm so if it goes from 40 psi to 35 psi when free reving (in neutral) to around 5k rpm and holding the rpm there it would seem that 'normally' a FPR should not operate like that correct? Normally the idle fuel pressure seems to be around 50psi. But after a long cruise I've seen the FPR register 30psi at idle, and I just noticed it dip today with a buddy watching the guage as I free revved the motor to 5k rpms and held it there. It was ideing at 40psi and went down to 35psi during the rpm's being held a 5k rpm. So I'm trying to see if there may be a fuel pressure issue.

 

+100 the general rule, thats what Air to Fuel is all about.

 

fuel pressure should be a direct product of manifold pressure with about a 1:1 ratio. Its not so much precisely what the ratio is that is important, but that it is consistent so your tune stays good.

If your base is 50psi, at idle I would expect around 41-44psi, depending on your manifold vacuum. At about 5psi of boost, it should be about 55psi.

When revving your engine and holding an RPM, you can generate plenty of vacuum to get your fuel pressure pretty low... but the only way to check the ratio is to moniter your engine vacuum at the same time.

Based on what your saying, it sounds like your fuel pressure is acting pretty normal.