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What should my fuel pressure be?
04-16-2009, 07:00 PM
#1
Thread Starter
Join Date: Jan 2008
Location: MA
Posts: 35
What should my fuel pressure be?
Hello all...
Sorry if this is a dumb question and yes I did try the search function...
ok with that out of the way here's my question:
What should my fuel pressure be in a stock 01' GT?
I recently got my Dynotune gauges hooked up and I'll admit I thought I would see a constant pressure.
Right now it is at about 30psi at idle and when not under load... it goes up to 41 - 43 under WOT but even that drops as the load drops...
Does this sound right?
Thank you in advance!
Mike
Sorry if this is a dumb question and yes I did try the search function...
ok with that out of the way here's my question:
What should my fuel pressure be in a stock 01' GT?
I recently got my Dynotune gauges hooked up and I'll admit I thought I would see a constant pressure.
Right now it is at about 30psi at idle and when not under load... it goes up to 41 - 43 under WOT but even that drops as the load drops...
Does this sound right?
Thank you in advance!
Mike
04-16-2009, 08:45 PM
#4
Join Date: Mar 2008
Location: Georgia
Posts: 19
I am not an expert on this by any means, so I decided to look at an old data log I recorded about 3 weeks ago for you. I have an 02 GT with a completely stock fuel system, and it held pretty consistantly between 38-39 psi at idle and stayed pretty steady even at WOT, it spiked to 42 psi during acceleration but came back down. Once I let off the throttle, it would start to fluctuate between 35 and 43 psi, but after the car had a second to kind of settle out, it was right back in that range. Mine never dropped that low, and I tore it down a little bit on that log.
Does it idle rough? or is there a reason why you are worried about it? factory regulators aren't THAT great, but if its not broke, dont fix it haha, you know what I mean?
John
Does it idle rough? or is there a reason why you are worried about it? factory regulators aren't THAT great, but if its not broke, dont fix it haha, you know what I mean?
John
04-17-2009, 06:26 AM
#7
Thread Starter
Join Date: Jan 2008
Location: MA
Posts: 35
John: No it doesn't idle rough and it runs great... I'm in the middle of a Nitrous install so I want to make sure my FP is right. I did buy the SVT Focus pump and will be installing it however I assume the regulator is not part of that pump.
Mustangman: That's exactly what my car is reading, 30 at idle, 43 at WOT which settles in around 40 until I let off... So I guess I'm all set! Thank you!
Mike
Mustangman: That's exactly what my car is reading, 30 at idle, 43 at WOT which settles in around 40 until I let off... So I guess I'm all set! Thank you!
Mike
04-17-2009, 08:32 AM
#8
4th Gear Member
Join Date: Aug 2007
Location: Shelbyville, Indiana
Posts: 1,088
Our cars have a returnless variable fuel pressure system. What you are seeing on your aftermarket gage is perfectly normal.
There is a difference between the fuel pressure that the aftermarket gage reads and adjusted fuel pressure that the car's computer records. I spent a couple of hundred dollars having my fuel system checked before I learned the difference. The computer keeps the adjusted fuel pressure near 40 psi. If you want to see the adjusted fuel pressure on your aftermarket gage turn on the key but don't start the motor. At zero vacuum and zero boost the after market gage will read the same as the computer.
Our motors need less "real" fuel pressure when they have vacuum and more when they are under boost. To calculate the non-adjusted fuel pressure numbers subtract vacuum (in inches) divided by two from 40 or add boost (in psi) to 40. At idle our cars have about 18 inches of vacuum so we would see approximately 31 psi on an aftermarket gage (40-18/2). Mine reads 30. At wide open throttle vacuum drops to near zero so you would see the aftermarket gage swing up to approximately 40 psi. With 8 lbs of boost you would see the after market gage swing up to around 48 psi (40+8). The entire time that your after market gage is swinging up and down the computer is recording a near constant 40 psi.
Engine air inlet tempature also affects the readings on your aftermarket fuel pressure gage. The computer uses air inlet tempature to estimate fuel tempature. On very hot days the computer will increase the fuel pressure to prevent a vapor lock in the fuel rails. Superchargers heat the inlet air and aggrevate this situation. On hot days in congested traffic my aftermarket fuel pressure gage read 53-55 psi at idle. That is why I had the system checked. The mechanic's datalog at the time showed a fairly constant 43 psi.
There is nothing wrong with your gage. It just measures fuel pressure differently than the computer.
There is a difference between the fuel pressure that the aftermarket gage reads and adjusted fuel pressure that the car's computer records. I spent a couple of hundred dollars having my fuel system checked before I learned the difference. The computer keeps the adjusted fuel pressure near 40 psi. If you want to see the adjusted fuel pressure on your aftermarket gage turn on the key but don't start the motor. At zero vacuum and zero boost the after market gage will read the same as the computer.
Our motors need less "real" fuel pressure when they have vacuum and more when they are under boost. To calculate the non-adjusted fuel pressure numbers subtract vacuum (in inches) divided by two from 40 or add boost (in psi) to 40. At idle our cars have about 18 inches of vacuum so we would see approximately 31 psi on an aftermarket gage (40-18/2). Mine reads 30. At wide open throttle vacuum drops to near zero so you would see the aftermarket gage swing up to approximately 40 psi. With 8 lbs of boost you would see the after market gage swing up to around 48 psi (40+8). The entire time that your after market gage is swinging up and down the computer is recording a near constant 40 psi.
Engine air inlet tempature also affects the readings on your aftermarket fuel pressure gage. The computer uses air inlet tempature to estimate fuel tempature. On very hot days the computer will increase the fuel pressure to prevent a vapor lock in the fuel rails. Superchargers heat the inlet air and aggrevate this situation. On hot days in congested traffic my aftermarket fuel pressure gage read 53-55 psi at idle. That is why I had the system checked. The mechanic's datalog at the time showed a fairly constant 43 psi.
There is nothing wrong with your gage. It just measures fuel pressure differently than the computer.
04-17-2009, 10:31 AM
#9
Thread Starter
Join Date: Jan 2008
Location: MA
Posts: 35
Our cars have a returnless variable fuel pressure system. What you are seeing on your aftermarket gage is perfectly normal.
There is a difference between the fuel pressure that the aftermarket gage reads and adjusted fuel pressure that the car's computer records. I spent a couple of hundred dollars having my fuel system checked before I learned the difference. The computer keeps the adjusted fuel pressure near 40 psi. If you want to see the adjusted fuel pressure on your aftermarket gage turn on the key but don't start the motor. At zero vacuum and zero boost the after market gage will read the same as the computer.
Our motors need less "real" fuel pressure when they have vacuum and more when they are under boost. To calculate the non-adjusted fuel pressure numbers subtract vacuum (in inches) divided by two from 40 or add boost (in psi) to 40. At idle our cars have about 18 inches of vacuum so we would see approximately 31 psi on an aftermarket gage (40-18/2). Mine reads 30. At wide open throttle vacuum drops to near zero so you would see the aftermarket gage swing up to approximately 40 psi. With 8 lbs of boost you would see the after market gage swing up to around 48 psi (40+8). The entire time that your after market gage is swinging up and down the computer is recording a near constant 40 psi.
Engine air inlet tempature also affects the readings on your aftermarket fuel pressure gage. The computer uses air inlet tempature to estimate fuel tempature. On very hot days the computer will increase the fuel pressure to prevent a vapor lock in the fuel rails. Superchargers heat the inlet air and aggrevate this situation. On hot days in congested traffic my aftermarket fuel pressure gage read 53-55 psi at idle. That is why I had the system checked. The mechanic's datalog at the time showed a fairly constant 43 psi.
There is nothing wrong with your gage. It just measures fuel pressure differently than the computer.
There is a difference between the fuel pressure that the aftermarket gage reads and adjusted fuel pressure that the car's computer records. I spent a couple of hundred dollars having my fuel system checked before I learned the difference. The computer keeps the adjusted fuel pressure near 40 psi. If you want to see the adjusted fuel pressure on your aftermarket gage turn on the key but don't start the motor. At zero vacuum and zero boost the after market gage will read the same as the computer.
Our motors need less "real" fuel pressure when they have vacuum and more when they are under boost. To calculate the non-adjusted fuel pressure numbers subtract vacuum (in inches) divided by two from 40 or add boost (in psi) to 40. At idle our cars have about 18 inches of vacuum so we would see approximately 31 psi on an aftermarket gage (40-18/2). Mine reads 30. At wide open throttle vacuum drops to near zero so you would see the aftermarket gage swing up to approximately 40 psi. With 8 lbs of boost you would see the after market gage swing up to around 48 psi (40+8). The entire time that your after market gage is swinging up and down the computer is recording a near constant 40 psi.
Engine air inlet tempature also affects the readings on your aftermarket fuel pressure gage. The computer uses air inlet tempature to estimate fuel tempature. On very hot days the computer will increase the fuel pressure to prevent a vapor lock in the fuel rails. Superchargers heat the inlet air and aggrevate this situation. On hot days in congested traffic my aftermarket fuel pressure gage read 53-55 psi at idle. That is why I had the system checked. The mechanic's datalog at the time showed a fairly constant 43 psi.
There is nothing wrong with your gage. It just measures fuel pressure differently than the computer.
04-17-2009, 03:18 PM
#10
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
Our cars have a returnless variable fuel pressure system. What you are seeing on your aftermarket gage is perfectly normal.
There is a difference between the fuel pressure that the aftermarket gage reads and adjusted fuel pressure that the car's computer records. I spent a couple of hundred dollars having my fuel system checked before I learned the difference. The computer keeps the adjusted fuel pressure near 40 psi. If you want to see the adjusted fuel pressure on your aftermarket gage turn on the key but don't start the motor. At zero vacuum and zero boost the after market gage will read the same as the computer.
Our motors need less "real" fuel pressure when they have vacuum and more when they are under boost. To calculate the non-adjusted fuel pressure numbers subtract vacuum (in inches) divided by two from 40 or add boost (in psi) to 40. At idle our cars have about 18 inches of vacuum so we would see approximately 31 psi on an aftermarket gage (40-18/2). Mine reads 30. At wide open throttle vacuum drops to near zero so you would see the aftermarket gage swing up to approximately 40 psi. With 8 lbs of boost you would see the after market gage swing up to around 48 psi (40+8). The entire time that your after market gage is swinging up and down the computer is recording a near constant 40 psi.
Engine air inlet tempature also affects the readings on your aftermarket fuel pressure gage. The computer uses air inlet tempature to estimate fuel tempature. On very hot days the computer will increase the fuel pressure to prevent a vapor lock in the fuel rails. Superchargers heat the inlet air and aggrevate this situation. On hot days in congested traffic my aftermarket fuel pressure gage read 53-55 psi at idle. That is why I had the system checked. The mechanic's datalog at the time showed a fairly constant 43 psi.
There is nothing wrong with your gage. It just measures fuel pressure differently than the computer.
There is a difference between the fuel pressure that the aftermarket gage reads and adjusted fuel pressure that the car's computer records. I spent a couple of hundred dollars having my fuel system checked before I learned the difference. The computer keeps the adjusted fuel pressure near 40 psi. If you want to see the adjusted fuel pressure on your aftermarket gage turn on the key but don't start the motor. At zero vacuum and zero boost the after market gage will read the same as the computer.
Our motors need less "real" fuel pressure when they have vacuum and more when they are under boost. To calculate the non-adjusted fuel pressure numbers subtract vacuum (in inches) divided by two from 40 or add boost (in psi) to 40. At idle our cars have about 18 inches of vacuum so we would see approximately 31 psi on an aftermarket gage (40-18/2). Mine reads 30. At wide open throttle vacuum drops to near zero so you would see the aftermarket gage swing up to approximately 40 psi. With 8 lbs of boost you would see the after market gage swing up to around 48 psi (40+8). The entire time that your after market gage is swinging up and down the computer is recording a near constant 40 psi.
Engine air inlet tempature also affects the readings on your aftermarket fuel pressure gage. The computer uses air inlet tempature to estimate fuel tempature. On very hot days the computer will increase the fuel pressure to prevent a vapor lock in the fuel rails. Superchargers heat the inlet air and aggrevate this situation. On hot days in congested traffic my aftermarket fuel pressure gage read 53-55 psi at idle. That is why I had the system checked. The mechanic's datalog at the time showed a fairly constant 43 psi.
There is nothing wrong with your gage. It just measures fuel pressure differently than the computer.