fuel pressure questions
05-12-2010, 08:14 PM
#1
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fuel pressure questions i have been batteling some fuel pressure problems, and i have a new racetronix pump in the car with a new filter. but the fuel pressure is not consistant and can be anywhere from 20psi to 46 psi. the car always starts and runs. could this be the relay or is ith the regulator? is it posible to have the fuel lines backwards? i think the fuel rail is off of a 94, is it different than the 97?
05-12-2010, 09:52 PM
#3
It won't be the relay. If it was bad you'd have no pressure and the pump would either run or not.
You could have a leaky injector or the FPR could be bad. Pull the vacuum line off the regulator and look for fuel out the back with the system primed and/or running. A leaky injector is also easy to diagnose - pull up the fuel rails with the injectors still attached and prime the fuel system. Any leaky injectors will drip fuel.
You could have a leaky injector or the FPR could be bad. Pull the vacuum line off the regulator and look for fuel out the back with the system primed and/or running. A leaky injector is also easy to diagnose - pull up the fuel rails with the injectors still attached and prime the fuel system. Any leaky injectors will drip fuel.
05-12-2010, 10:54 PM
#4
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ok thanks for the replies, it is the stock type regulator. i changed it once and thought it fixed my problem but the fuel pressure is down again. would a leaky injector really make the fuel pressure that low? it runs around 13.2 to 1 afr at idle
05-13-2010, 10:39 AM
#7
I would suspect the FPR, but you have already replaced it. So I would ask if you are having voltage issues. If the power to your fuel pump is not constant, that could cause fluctuations. How's your alternator? Sometimes when an alternator is going out the system voltage flutters. Also check fuel pump wiring. Make sure it's not loose or rubbing, etc.
I also second the motion that you check for a leaky injector (s) as yet another possible problem source.
I also second the motion that you check for a leaky injector (s) as yet another possible problem source.
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05-13-2010, 12:59 PM
#9
Well You have to look at the engine enviorment factors like is it cold start, is it hot start, or warm start that it wil do that. The best way to tell is to look at the O2 readings. If one is stuck open you should have some kind of miss fire history and when the O2 starts being used once the engine and o2 are up to temp you should see a rich condition on one bank with the PCM cuting back on fuel trim and timing being adjusted. The other bank should look just fine. I say scan it and see if there are signs of an injector stuck open. A data log with a trained eye will be able to tell you if it is an injector stuck open or not.
Another way to check for a leaky injector is pull the fuel rail with injectors still atached out of the intake and presureize the system with all of the injecotrs still in the rail. If you have one stuck open it will spray.
What kind of FP regulator did you replace your stock one with? Did you pull the vac line to make sure it holds at 43 to 46psi? I would run the car with the fuel pressure gage hooked up and cap the vac line that runs to the regulator and see if it holds good pressure.
Check your voltage at the pump wire harness to make sure you keep good voltage there while the pump runs. Another is to make sure you got the feed line from the pump hooked up right inside the tank.
Another way to check for a leaky injector is pull the fuel rail with injectors still atached out of the intake and presureize the system with all of the injecotrs still in the rail. If you have one stuck open it will spray.
What kind of FP regulator did you replace your stock one with? Did you pull the vac line to make sure it holds at 43 to 46psi? I would run the car with the fuel pressure gage hooked up and cap the vac line that runs to the regulator and see if it holds good pressure.
Check your voltage at the pump wire harness to make sure you keep good voltage there while the pump runs. Another is to make sure you got the feed line from the pump hooked up right inside the tank.
05-13-2010, 01:07 PM
#10
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Well You have to look at the engine enviorment factors like is it cold start, is it hot start, or warm start that it wil do that. The best way to tell is to look at the O2 readings. If one is stuck open you should have some kind of miss fire history and when the O2 starts being used once the engine and o2 are up to temp you should see a rich condition on one bank with the PCM cuting back on fuel trim and timing being adjusted. The other bank should look just fine. I say scan it and see if there are signs of an injector stuck open. A data log with a trained eye will be able to tell you if it is an injector stuck open or not.
Another way to check for a leaky injector is pull the fuel rail with injectors still atached out of the intake and presureize the system with all of the injecotrs still in the rail. If you have one stuck open it will spray.
What kind of FP regulator did you replace your stock one with? Did you pull the vac line to make sure it holds at 43 to 46psi? I would run the car with the fuel pressure gage hooked up and cap the vac line that runs to the regulator and see if it holds good pressure.
Check your voltage at the pump wire harness to make sure you keep good voltage there while the pump runs. Another is to make sure you got the feed line from the pump hooked up right inside the tank.
Another way to check for a leaky injector is pull the fuel rail with injectors still atached out of the intake and presureize the system with all of the injecotrs still in the rail. If you have one stuck open it will spray.
What kind of FP regulator did you replace your stock one with? Did you pull the vac line to make sure it holds at 43 to 46psi? I would run the car with the fuel pressure gage hooked up and cap the vac line that runs to the regulator and see if it holds good pressure.
Check your voltage at the pump wire harness to make sure you keep good voltage there while the pump runs. Another is to make sure you got the feed line from the pump hooked up right inside the tank.
well i dont have access to a scanner right now, but i have a guage that is hooked up all the time and it just fluctuates pressure all the time. i just ordered new injectors so hopefully that is the problem. but i just replaced the regulator with another stock regulator that i had laying around the shop so it is possible that it was bad too. would there be a benifit to upgrad to an adjustable regulator even if i just keep stock pressure?
05-13-2010, 03:13 PM
#13
You do realize that the pressure varies with engine vacuum right? Take the vacuum line off and the pressure will be stable. What the fuel pressure regulator does is keep the pressure RELATIVE to the engine vacuum so the differential pressure is always the same.
If the regulator is set at 40psi static (no vaccuum line connected) and you have 20 psi vacuum (line connected) you will only see 20 on your gage which is exactly what it is supposed to be.
If the regulator is set at 40psi static (no vaccuum line connected) and you have 20 psi vacuum (line connected) you will only see 20 on your gage which is exactly what it is supposed to be.
05-13-2010, 03:30 PM
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You do realize that the pressure varies with engine vacuum right? Take the vacuum line off and the pressure will be stable. What the fuel pressure regulator does is keep the pressure RELATIVE to the engine vacuum so the differential pressure is always the same.
If the regulator is set at 40psi static (no vaccuum line connected) and you have 20 psi vacuum (line connected) you will only see 20 on your gage which is exactly what it is supposed to be.
If the regulator is set at 40psi static (no vaccuum line connected) and you have 20 psi vacuum (line connected) you will only see 20 on your gage which is exactly what it is supposed to be.
05-13-2010, 04:01 PM
#15
You do realize that the pressure varies with engine vacuum right? Take the vacuum line off and the pressure will be stable. What the fuel pressure regulator does is keep the pressure RELATIVE to the engine vacuum so the differential pressure is always the same.
If the regulator is set at 40psi static (no vaccuum line connected) and you have 20 psi vacuum (line connected) you will only see 20 on your gage which is exactly what it is supposed to be.
If the regulator is set at 40psi static (no vaccuum line connected) and you have 20 psi vacuum (line connected) you will only see 20 on your gage which is exactly what it is supposed to be.
With the vacuum compensation line disconnected, with 41-47psi at idle is an acceptable range with 43.5psi being spot-on (what the injectors are rated at). Reattach the vacuum line, and the pressure will drop proportional to intake manifold vacuum. A 3-10psi drop below the "no vacuum" pressure is normal for a stock cam.
At no point should the fuel pressure drop below ~32psi.
05-14-2010, 07:38 AM
#18
Did you test the injectors? why would you go out and spend that kind of money if you don't know if it's the problem? Like ram air was saying and I have said but you still have not said weather you did it or not is to pull the vac line on the FPR. If your checking it with the thing hooked up then you are going to see a flux as engine vacume changes. If it is jumping around that much you should also check the vac line it's self to make sure it is good. It gets really expensive when you start throwing **** against the wall waiting for something to stick. I would take the time and spend a little now to find the problem.
05-14-2010, 02:44 PM
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Did you test the injectors? why would you go out and spend that kind of money if you don't know if it's the problem? Like ram air was saying and I have said but you still have not said weather you did it or not is to pull the vac line on the FPR. If your checking it with the thing hooked up then you are going to see a flux as engine vacume changes. If it is jumping around that much you should also check the vac line it's self to make sure it is good. It gets really expensive when you start throwing **** against the wall waiting for something to stick. I would take the time and spend a little now to find the problem.