ludelvr

Okay, I've done a search and can't find much on this topic. First of all, what is the purpose of this and how exactly does it work? Secondly, I'll be running a pretty big inline pump and an 8:1 FMU on about 6-7 psi of boost. Will my idle fuel pressure be high and if so, what will it be? I'm sitting at around 35 in NA form. Also, how exactly does an FMU raise idle fuel pressure if there is no boost? Thanks guys!

B20LS-T

Well Im not sure about your other questions, becuase i am not boosted yet, but as far as drilling the FPR try this site, he gives detailed instructions: http://www.theoldone.com

schwett

read the TOO article. you will get high idle pressures if you have certain high flow pumps. the gss-342, for one, will definitely give you a 50+psi idle.

the fmu "raises" pressure because the return orifice is only designed to return a certain amount of fuel, and when you are pumping so much more, it can't return enough to keep the pressure at 35psi.... so it goes up.

ludelvr

O I C!! Couple more questions. How safe is drilling that relief pressure hole in the stock fpr? As well, can it be done even if I don't have an after market adjustable regulator like the B and M? Thanks again guys! That's a pretty good link! Some nice articles too! Oh yah, where's the best place for the inline pump I have?

b16ahybrid

I would recomend getting a b&m fpr so you can fine tune the fuel pressure after you drill it.If not you will end up playing a guessing game and having to go with whatever fuel pressure the stock one gives you,and if you go to big then your screwed because you have no way to raise the fuel pressure back up.
Drilling the fpr works but i don't recomend it for a perm.fix but just a temp fix.Reason being is after you shut the car off (after driving) and let it sit for about 1/2 hour all the fuel will drain out of the fuel rail,so when you go to start the car (every time) you will have to prime it to get the fuel pressure up otherwise you will just be cranking the engine with no fuel pressure for a few seconds.
Pain in the ***...Plus i don't think it's to good for your fuel pump.
Thats why i went with an aem fpr.

Sonny

My AEM FPR would drop the fuel pressure almost immediately after the pump was primed. I had the TOO mod and it was equally effective as the AEM FPR for dropping idle pressure with a big pump (Walbro GSS317/342). The trick was to start the car while the pump was being primed. Typically, when you turn the key, the ECU will prime the pump for about 3 seconds. I'd start the car after about 2 seconds.

The B&M chop-top style uses the bottom half of the OEM fpr (where the diaphram) is at, so it will not alleviate the high pressure at idle problem caused by a large pump unless you drill it. I had to use a .060" bit to get my idle pressure down to 38 psi on stock injectors.

Sonny