chief455

iTrader: (21)

my set up is in another thread asking LT1 boost questions.
Procharger, no FMU.

Here I want to understand what should occur looking at my fuel pressure gauge as I drive.

Areomotive boost reference rail mount regulator, 60lb injectors.

What does the ' 1:1' ratio boost reference mean?

Say it reads 40psi at idle and cruise - but under boost - should fuel pressure rise?
1 psi fuel pressure for every 1 lb of boost?

or does the regulator keep pressure the same based on the boost?

please explain how to set the regulator and what it should read as boost increases

thank you.

98Camarod

iTrader: (43)

You have a vacuum line hooked up to the regulator. That line will see the boost and raise the fuel pressure in a 1:1 ratio. So like you said, for every one pound of boost that's created, it will raise fuel pressure 1 pound as well.

Having a boost referenced regulator will also affect your tune, so don't forget about that.

chief455

iTrader: (21)

ok, so if I see my boost gauge jump from idle to 10lb during WOT,
the fuel psi should jump from idle 40psi to 50psi - correct?

affect the tune in what way?

KILLER-LS1

iTrader: (18)

yes, think of it this way... lets say youre seeing 10psi of boost in the intake manifold. when those injectors open, there is 10 PSI pushing AGAINST the fuel. So you want to increase the fuel pressure 1:1 (1 psi of fuel : 1 psi intake pressure). that way you injectors dont have to fight as much anginst the pressure holding the fuel back.

chief455

iTrader: (21)

Ahhh - explained so I can easily understand!
Thank you

ChevyChad

iTrader: (50)

As said above, it raises pressure in the fuel rails to compensate for pressure in the manifold to keep a constant difference in pressure. But, unless you have a check valve in the line, it will also decrease pressure with vacuum. So at idle, you may be seeing 20inHg of vacuum. This is equivalent to about 9.8psi of vacuum. This will lower your fuel pressure by 9.8psi. So, say your base pressure is 50psi at 0vac/boost. At idle, you could see as low as 40psi of fuel pressure, and then at WOT with 10psi of boost, you will see 60psi fuel pressure.

chief455

iTrader: (21)

ChevyChad

interesting that vacuum reference will pull fuel pressure down.
I must have a check valve because while the car was running - i have tons of vacuum pull at idle, deceleration etc and fuel pressure stayed at 40psi

What was not happening is as I went into boost, the fuel pressure not going up 1:1.

it just went up a bit - maybe 42psi more like a voltage increase from the one wire alternator set up it has.

I'm guessing from this, and the fact I then lost all fuel presure during a test drive and the car died, my fuel pump was failing to pump over ~40 psi at all.

ChevyChad

iTrader: (50)

Dumb question, but do you have a vacuum line hooked up to your regulator? If not, there is no way it will know when to add (or pull) pressure..

chief455

iTrader: (21)

yes, aeromotive regulaor, racetronix single pump, hot wire kit in car when I got it.
seems to have just been killing the fuel pump. I didn't know for sure if my fuel psi should have stayed steady or went up with boost.
when psi dropped to 20psi, then died, then restarted after sitting an hour with 40psi, now i'm pretty sure the pump is not right.

ChevyChad

iTrader: (50)

Yea, sounds like a bad pump. Exactly what my first pump (alleged walbro- think i got a knock off) did when it went bad.

chief455

iTrader: (21)

Chad

I was debating stepping up to twin walbros and adding another racetronix wire, but cash and labor time is tight
I have ~ 10lb boost at max based on my pullies, 60lb injectors, made 550rwhp when 1st built/tuned with new fuel pump in 2005 and 2000 miles ago.
sat for a year at a time in Nevada then sat all winter here in freezing Ct. - maybe low fuel level at times too.

think those conditions helped kill the pump prematurely?

you think I'll be safe enough just replacing my single walbro for right now?

what should I set my regulator at with vacuum line off/capped?

maybe this winter I'll add the 2nd walbro and wire kit.

seem reasonable to you?

robbyredneck

iTrader: (1)

remember that your base pressure is referenced around neither boost or vac. i set mine using the hpt scanner to run the pump and then i set my pressure.engine off. i had an issue like yours and it turned out to be my relay. your tune and setup will dictate your pressure.

FastKat

iTrader: (10)

A check valve is a one-way valve, right? If your vacuum line pressure took the fuel regulator up to 10psi, wouldn't a check valve make it stay at +10psi, even after your manifold boost went back to vacuum? In other words, I think a check valve would keep the regulator boosted at 10psi even after the pull was over?

ChevyChad

iTrader: (50)

Thats a good point. I never thought of that, but you would be absolutely correct.

pwrtrip75

iTrader: (8)

Hook the vacuum line up to the charge pipe/before the throttle body. This way it only sees boost otherwise remains at atmosphere. I had mine ran to the intake and it wasnt consistant the pressure always fluctuated, I switched it to the charge pipe and now the pressure stays even. I was having a lot of surging problems (other things) but then as it surged the vacuum would go up and down and cause the fuel pressure to go up and down and spiraled into a pain in the ***...lol.

Boosted One

iTrader: (6)

This is how I do it. I want it to see boost only. Makes tuning the cruise area of the ve table much easier.

dschmittie1

iTrader: (64)

Looks like I might be moving mine.

FastKat

iTrader: (10)

Ahh that makes much more sense. I guess the throttle body blade is what actually creates the restriction in the intake manifold. If you put the fuel regulator reference in the charge pipe, you would only be exposing it to the restrictions of the air filter, compressor, and intercooler, which is probably minimal compared to the restriction that the throttle body blade creates.

I've never setup a vacuum referenced fuel pressure regulator before. Do you set the pressure with the engine off or the engine idling??

LS1RedZ

iTrader: (19)

I was having problems with mine dumping fuel at idle and the a/f was all jacked up at idle. So I should run the line to the charge pipe somewhere?

chief455

iTrader: (21)

Will the feed from this area of boost to the reference port on the regulator still perform a 1:1 fuel pressure gain ?

As opposed to a manifold vacuum port they suggest sourcing the regulator from?

In other words - under WOT - is '1lb' of boost before the throttle body - the same as '1lb' measured at a manifold port?

I guess trying a boost gauge at both areas would tell something..might have to try that.