fuel pressure question
07-05-06, 04:31 PM
#1
Senior Member
Thread Starter
Join Date: Dec 2001
Location: WEST
Posts: 354
Likes: 0
Received 0 Likes
on
0 Posts
fuel pressure question
What would cause a pressure gauge to bounce (a little) at idle and cruise?
I seem to be having a hesitation problem and I got it traced to that I think.
At decel, the gauge is solid but when I get on the gas even slightly, the needle bounces. Not a whole lot but enough to notice. The regulator is an HKS and there's no leak in any connections. Te other night I noticed the gauge read 2.0 bar which seemed low at cruise and idle. I tried to raise the pressure but it's almost at it's max setting. The gause reads fine on boost and rises to proper pressure and stays solid. What would cause this? The gauge is a Greddy electric unit. Thanks for any help.
I seem to be having a hesitation problem and I got it traced to that I think.
At decel, the gauge is solid but when I get on the gas even slightly, the needle bounces. Not a whole lot but enough to notice. The regulator is an HKS and there's no leak in any connections. Te other night I noticed the gauge read 2.0 bar which seemed low at cruise and idle. I tried to raise the pressure but it's almost at it's max setting. The gause reads fine on boost and rises to proper pressure and stays solid. What would cause this? The gauge is a Greddy electric unit. Thanks for any help.
07-06-06, 05:46 PM
#3
Ideas:
- fuel pressure pulses from injectors firing, might need to change settings in electronic fuel pressure gauge to increase the number of samples averaged for displayed reading (this seems likely, since it doesn't bounce on decel, which is a time when the injectors are not firing)
- do you have a pulsation damper (FPD)? if not, that might be why your fuel pressure bounces so much
- manifold pressure pulses, might need restrictor in air line to FPR to smooth out fuel pressure
You should be aware that changing your fuel pressure will change your mixture, which requires new fuel maps (if your map was "right" before). If you increase the base pressure, you will run richer than you did before the fuel pressure adjustment, all the time. Conversely, if you reduce the base pressure, you will run leaner under all conditions.
2.0 bar = 29 psi or so. Stock base pressure is ~38 psi and it drops lower when you subtract your manifold vacuum at idle/cruise. Dropping 9 psi is a fairly large drop, but if you have a lot of idle vacuum or pull a bunch of vacuum when you let off the gas, 29 psi doesn't seem all that unreasonable.
You can easily blow your engine by leaning out your car with a fuel pressure adjustment. Be careful. I recommend developing a solid understanding of what your fuel pressure should be under various conditions (and why), and how your fuel pressure interacts with your fuel maps, before making adjustments.
-Max
- fuel pressure pulses from injectors firing, might need to change settings in electronic fuel pressure gauge to increase the number of samples averaged for displayed reading (this seems likely, since it doesn't bounce on decel, which is a time when the injectors are not firing)
- do you have a pulsation damper (FPD)? if not, that might be why your fuel pressure bounces so much
- manifold pressure pulses, might need restrictor in air line to FPR to smooth out fuel pressure
You should be aware that changing your fuel pressure will change your mixture, which requires new fuel maps (if your map was "right" before). If you increase the base pressure, you will run richer than you did before the fuel pressure adjustment, all the time. Conversely, if you reduce the base pressure, you will run leaner under all conditions.
2.0 bar = 29 psi or so. Stock base pressure is ~38 psi and it drops lower when you subtract your manifold vacuum at idle/cruise. Dropping 9 psi is a fairly large drop, but if you have a lot of idle vacuum or pull a bunch of vacuum when you let off the gas, 29 psi doesn't seem all that unreasonable.
You can easily blow your engine by leaning out your car with a fuel pressure adjustment. Be careful. I recommend developing a solid understanding of what your fuel pressure should be under various conditions (and why), and how your fuel pressure interacts with your fuel maps, before making adjustments.
-Max
07-07-06, 02:04 AM
#4
Rotary Enthusiast
iTrader: (9)
Join Date: Jun 2003
Location: west
Posts: 1,191
Likes: 0
Received 0 Likes
on
0 Posts
Understood. Thanks Max.
I don't mess around with fuel pressure and I'm always glancing at the gauges to see everything is good. The pressure is set at base stock pressure.
Shouldn't the pressure increase when the vacuum line is disconnected? It doesn't.
I don't mess around with fuel pressure and I'm always glancing at the gauges to see everything is good. The pressure is set at base stock pressure.
Shouldn't the pressure increase when the vacuum line is disconnected? It doesn't.
Originally Posted by maxcooper
Ideas:
- fuel pressure pulses from injectors firing, might need to change settings in electronic fuel pressure gauge to increase the number of samples averaged for displayed reading (this seems likely, since it doesn't bounce on decel, which is a time when the injectors are not firing)
- do you have a pulsation damper (FPD)? if not, that might be why your fuel pressure bounces so much
- manifold pressure pulses, might need restrictor in air line to FPR to smooth out fuel pressure
You should be aware that changing your fuel pressure will change your mixture, which requires new fuel maps (if your map was "right" before). If you increase the base pressure, you will run richer than you did before the fuel pressure adjustment, all the time. Conversely, if you reduce the base pressure, you will run leaner under all conditions.
2.0 bar = 29 psi or so. Stock base pressure is ~38 psi and it drops lower when you subtract your manifold vacuum at idle/cruise. Dropping 9 psi is a fairly large drop, but if you have a lot of idle vacuum or pull a bunch of vacuum when you let off the gas, 29 psi doesn't seem all that unreasonable.
You can easily blow your engine by leaning out your car with a fuel pressure adjustment. Be careful. I recommend developing a solid understanding of what your fuel pressure should be under various conditions (and why), and how your fuel pressure interacts with your fuel maps, before making adjustments.
-Max
- fuel pressure pulses from injectors firing, might need to change settings in electronic fuel pressure gauge to increase the number of samples averaged for displayed reading (this seems likely, since it doesn't bounce on decel, which is a time when the injectors are not firing)
- do you have a pulsation damper (FPD)? if not, that might be why your fuel pressure bounces so much
- manifold pressure pulses, might need restrictor in air line to FPR to smooth out fuel pressure
You should be aware that changing your fuel pressure will change your mixture, which requires new fuel maps (if your map was "right" before). If you increase the base pressure, you will run richer than you did before the fuel pressure adjustment, all the time. Conversely, if you reduce the base pressure, you will run leaner under all conditions.
2.0 bar = 29 psi or so. Stock base pressure is ~38 psi and it drops lower when you subtract your manifold vacuum at idle/cruise. Dropping 9 psi is a fairly large drop, but if you have a lot of idle vacuum or pull a bunch of vacuum when you let off the gas, 29 psi doesn't seem all that unreasonable.
You can easily blow your engine by leaning out your car with a fuel pressure adjustment. Be careful. I recommend developing a solid understanding of what your fuel pressure should be under various conditions (and why), and how your fuel pressure interacts with your fuel maps, before making adjustments.
-Max
Thread
Thread Starter
Forum
Replies
Last Post
trickster
2nd Generation Specific (1986-1992)
25
07-01-23 04:40 PM
