Fpr Vsv

[lagged]

heres a tech question for you guys;

the vsv for the fpr cuts off the vacuum (or diverts it to ATM...) when the motor is hot in order to bump up the fuel pressure to help combat vapor lock in the fuel rail, correct?

ok, so lets say you start up your car and arent having any hot start problems, car is already warmed up, oil pressure has risen and you go boosting. if the VSV is keeping vacuum/boost from the FPR will the fuel pressure rise with the manifold pressure?

can the VSV fail closed? or diverted? so the FPR dosnt get a vacuum/boost source in order to control fuel pressure?

 

[Jr24dawg]

Wow, that's a good question.

I have been told by a number of people that it doesn't matter if you remove it, so I'm just getting rid of it to clean stuff up, good question none-the-less.


Justin posting as Jr24Dawg cuz I'm too lazy to log him out and me in.

 

[shaeff]

not sure there, lagged. that's a damn good question. i completely bypassed mine while troubleshooting my car...

-shaeff

 

[Slow Poopra 7MGTE]

i hope so, i tossed all the vsv stuff...

 

[lagged]

theres no problem running without it, just might have hot start problems, especially on hot days.

id like to keep my fpr vsv, ill have to take it off and test it out to see if its good.

so does anyone know? i suppose i could figure it out my self when i test the thing later this week. if i do before anyone posts back ill post my results.

 

[Shawndude]

ok, so lets say you start up your car and arent having any hot start problems, car is already warmed up, oil pressure has risen and you go boosting. if the VSV is keeping vacuum/boost from the FPR will the fuel pressure rise with the manifold pressure?

No, it will just stay open to the atmosphere in that scenario, as you already figured out. However I would think the ECU is smart enough to turn it off (for manifold feed) once you aren't idling (AFM flow and/or IDL switch sensor). I guess easy enough to check, but a rather boring experiment.

 

[steve_mk3]

I thought the FPR needed to have a vacuum/boost referance. That referance was controled by the VSV. So that the FPR knows when there is boost and can raise the fuel pressure and you wont run lean. or is that just for an aftermarket AFPR ?

 

[lagged]

I thought the FPR needed to have a vacuum/boost referance. That referance was controled by the VSV. So that the FPR knows when there is boost and can raise the fuel pressure and you wont run lean. or is that just for an aftermarket AFPR ?

no the stock fpr is the same way. the VSV is there to bump up the fuel pressure in hot starting situations to combat vapor lock as i stated earlier.

at idle, the motor pulls ~21ingh of vacuum, this affects the fuel pressure by lowering from your base setting (~7psi) so, if your base pressure is 40psi at idle you will see it drop to around 33psi (numbers are guesses as i am not sure exactly how much it lowers the FP from base.....)

when the VSV opens the FPR now has no vacuum pulling it so your FP will rise to whatever the base setting is at.

 

[lagged]

No, it will just stay open to the atmosphere in that scenario, as you already figured out. However I would think the ECU is smart enough to turn it off (for manifold feed) once you aren't idling (AFM flow and/or IDL switch sensor). I guess easy enough to check, but a rather boring experiment.

welp, heres the reason why i asked this question. being the nervous person that i am i tend to check things here and there whenever i start up the car. i check the oil, coolant level blah blah blah. i also have a FP gauge hooked up to my aeromotive FPR so i check the initial fuel pressure as well.

the other day i happend to start the car, and, being brainless half the time as well i forgot about the vsv for the fpr and saw that the fuel pressure was at my base setting. i pulled the vacuum line off and said to my self, "self, this vacuum line must be clogged"

anyway, i bypassed it and remembered later that the computer tells the vsv to do this for a reason........

heres why i ask this question, the vsv seemed to be diverting vacuum for a long time, and not having a fuel pressure gauge in the car it made me nervous to think that i wouldnt be getting a fuel pressure rise based on boost.

im gonna leave it bypassed for now, until i have a chance to test the vsv to make sure it is working.

thanks for your response shawndude!

i have another question, how does the computer determine to turn off the vsv? no matter what, revving the engine, holding the RPMs above idle, the VSV continued to vent.

so either mines broken or....

 

[Justin]

at the risk of going slightly to the left of the intended topic....

What is vapor lock? Is that a bad thing? I'm not planning on putting the VSV back in when I drop my engine back in. I don't mind a few more cranks to turn the engine on. Hell, I don't even crank it, my alarm does it for me but this vapor lock thing sounds bad.

 

[lagged]

when this happens, the motor will usually start right up, (may take an extra crank) but will stumble around for a while. youll have to give it some gas until it evens out.

 

[Shawndude]

...What is vapor lock? Is that a bad thing?....

There is fuel sitting in the rail and injectors when you shut off your engine. That fuel will heat up and start boiling from the heat of the sitting engine. The fuel will turn from a liquid into a a vapor, and when you go start the engine, instead of spraying fuel, the injectors are spraying a mix of liquid, vapor, and nothing, at random. The car will run like crap, until new cool fuel reaches the injectors.

It's not really harmful to the engine, just annoying to the driver. All you have to do is keep the revs up for a few seconds, so the new fuel from the gas tank can make its way to the fuel rail, and all will be good again.