stock fuel pressure?

[BlackVert]

i'm going to measure my fuel pressure during lunchtime today.

i am going to read it at idle with the vaccuum tube off and also with the tube on. should i also read it at higher rpms?

what should it read if everything is OK?

 

[mackey]

It will be the same all the time or should be with the vacuum line off. Stock FP is around 39psi. With a 255 walboro and 24lb injects and stock Fpr my psi is 43 though...

 

[Killercanary]

39 is the stock reading. FPR's work this way... the more vacuum there is (like at idle) the less the FP is, the less the vacuum is (like under WOT) the MORE FP you will have. Checking it at idle with the vac. line on and off should show this.

 

[BlackVert]

line on: 33
line off: 42
part throttle: 34 or so

what's it mean ... bad fpr?

or could it be that since the ported heads and trick flow intake flow better, the engine creates more vaccuum, which is brings the fuel pressure down?

i'm gonna take the line off, plug it with a pencil, and drive it around. maybe it won't stumble anymore. i'll post the results after ...

how bad would it be to leave it disconnected and tune for it with my tweecer?

 

[95Vert]

I'm also interested in the outcome!!

 

[BlackVert]

there wasn't really a difference; it still "stumbles".

does 33 with the line on and 42 with it off indicate that my fpr may be bad?

it still is weird to me that it only happens when the engine is warm. it runs great fine when cold.

now i'm thinking the injectors may be clogged or something. (grasping at straws)

 

[MysteryMachine]

so if you get a adj. FPR whats the highest you can set it at with the stock 19's

 

[final5-0]

line on: 33
line off: 42
part throttle: 34 or so

what's it mean ... bad fpr?

or could it be that since the ported heads and trick flow intake flow better, the engine creates more vaccuum, which is brings the fuel pressure down?

i'm gonna take the line off, plug it with a pencil, and drive it around. maybe it won't stumble anymore. i'll post the results after ...

how bad would it be to leave it disconnected and tune for it with my tweecer?

I don't know about all of that afpr stuff as I've never had one but I do know that the pcm makes it's calculations based on the stock fuel pressure which I have been told is 39 psi.

Since you have the Tweecer I think you should find a way to return to stock pressure and make sure it does not change or fuel adjustments made by you later on will be skewed by the fuel pressure change.

Later
Grady

 

[HISSIN50]

that spread sounds a bit far off. FWIW, foxes are 39 vac line off, 32-34 with it on (stock cam and vac).

remember the puter will adjust the pulsewidth of the injectors to accomodate FP changes. i dont know snot about TwEECers, etc, so i dont know if that changes stuff.

did you plug the vac line when you set the pressure? theoretically it makes a small difference (vac leak= higher idle, etc).
how much vac do you pull at idle?

done rambling. good luck.

 

[mo_dingo]

that spread sounds a bit far off. FWIW, foxes are 39 vac line off, 32-34 with it on (stock cam and vac).

remember the puter will adjust the pulsewidth of the injectors to accomodate FP changes. i dont know snot about TwEECers, etc, so i dont know if that changes stuff.

did you plug the vac line when you set the pressure? theoretically it makes a small difference (vac leak= higher idle, etc).
how much vac do you pull at idle?

done rambling. good luck.

Good points. Check your vacuum. This will make your car run rich at idle (as far as the FPR is concerned)and part throttle.

The computer does compensate for extra fuel when the car is warm & at part throttle (closed loop = O2 sensors). That all changes when you go to open loop (WOT = MAF/ECT/IAT).

Get your car warm, and put the pedal to the floor. What happens? This will test the MAF/ECT/IAT.

When the car is warm, accelerate at part throttle. What happens? This will test the O2 sensors.

Your fuel pressure sounds close enough to stock. It's not going to cause any serious problems like you are experiencing.

At idle, the throttle blade is closed. This creates a vacuum, which literally sucks the fuel out of the injectors. That is why the FPR needs a vacuum line to run. When the engine is under vacuum, the FPR lowers the pressure to compensate for the suction.

Scott

 

[BlackVert]

Good points. Check your vacuum. This will make your car run rich at idle (as far as the FPR is concerned) and part throttle.

i think i can get a gauge at sears. i'll look tomorrow.

The computer does compensate for extra fuel when the car is warm & at part throttle (closed loop = O2 sensors). That all changes when you go to open loop (WOT = MAF/ECT/IAT).

the O2 sensors were new 6 months ago when the heads and intake were installed. this behavior seems to coincide with the installation of the fpr. seems wierd that installing the fpr would make the O2s go bad ...

Get your car warm, and put the pedal to the floor. What happens? This will test the MAF/ECT/IAT.

i don't know, i'll try it tomorrow on the way to work in 3rd and 4th gears. i can say that it runs great when cold and i put the pedal to the floor.

When the car is warm, accelerate at part throttle. What happens? This will test the O2 sensors.

it stumbes like crazy from about 1800 to about 3000 and feels like it is about to run out of gas. the warmer it is, the worse the stumbling. sounds like the O2s went bad somehow when i installed the stock fpr? fwiw, my TwEECer does show them switching and the check engine light has not come on. can the O2 sensors be cleaned?

Your fuel pressure sounds close enough to stock. It's not going to cause any serious problems like you are experiencing.

that sounds like a good thing to me. i didn't want to have to replace the fuel pump.

At idle, the throttle blade is closed. This creates a vacuum, which literally sucks the fuel out of the injectors. That is why the FPR needs a vacuum line to run. When the engine is under vacuum, the FPR lowers the pressure to compensate for the suction.
Scott

thanks for the explanation. i think i understand it a little better.

 

[BlackVert]

did you plug the vac line when you set the pressure?

i can't set the pressure. it is a stock fpr. i figured i was close enough to stock that i didn't need an adjustable one. maybe i was wrong ...

how much vac do you pull at idle?

i dunno, i'll price them tomorrow. if they aren't too much, i'll buy one and check the vacuum.

 

[BlackVert]

It will be the same all the time or should be with the vacuum line off. Stock FP is around 39psi. With a 255 walboro and 24lb injects and stock Fpr my psi is 43 though...

mine is 42 (line off). i wonder if that means i have an aftermarket pump ...