check the shrader valve first and then the FPR. for the injectors if it is bleeding off real fast after the key is off you can pull the plugs to see which are wet.
Low Fuel Pressure
Thread Starter
Racer
Joined: Sep 2005
Posts: 304
Likes: 1
From: Carson City Nevada
Low Fuel Pressure
Hi all, just checked the fuel pressure on my a7 and it is at 12psi with the 2 second key on and 15 while running(if you can call it that). Any thoughts on what could cause this? Do these fuel pumps die like this? I can hear it running and it sounds ok. Can the regulator cause this? Relay?
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
I believe the pump is a constant volume unit and the regulator simply allows excessive flow to return to the tank. In which case a defective regulator could cause low pressure.
BTW, are you sure you have the gauge installed properly on the Schraeder valve? Try removing the valve core and taking a reading.
BTW, are you sure you have the gauge installed properly on the Schraeder valve? Try removing the valve core and taking a reading.
Team Owner
Joined: Feb 2006
Posts: 24,460
Likes: 7
From: sw Ohio
Yes low pressure can be a sign of a bad fuel pump. An old weak diaphragm can cause low pressure as well. Can you smell fuel in the vacuum line coming out of the regulator? That means its going bad. Leaking injectors can cause low pressure too.
Thread Starter
Racer
Joined: Sep 2005
Posts: 304
Likes: 1
From: Carson City Nevada
No, no fuel in the vacume line.
Thread Starter
Racer
Joined: Sep 2005
Posts: 304
Likes: 1
From: Carson City Nevada
Race Director
Joined: Aug 2000
Posts: 14,130
Likes: 7
Cruise-In II Veteran
I have the same exact problem right now in a GM van right now.It does the exact same thing..it still runs but has very low pressure.It misses once in a while because of it.Can still drive it but lacks in power.
I changed the filter to see if any improvement and none.When I did that,I checked the FP right after installing the new filter.
It took a while for the gauge to even move a few points back to 15 psi and the system was completely depressurized during the test.A new pump should push alot of gas into the rail within seconds.The car would not start for a while...I knew there wasnt enough gas getting into the rail.Regulator has no gas smell,nor leaks and no obvious signs of trouble.
I had this happen on another GM car I had few years ago.Pressure was stuck around 25 psi.Did same thing,new pump fixed it.
I changed the filter to see if any improvement and none.When I did that,I checked the FP right after installing the new filter.
It took a while for the gauge to even move a few points back to 15 psi and the system was completely depressurized during the test.A new pump should push alot of gas into the rail within seconds.The car would not start for a while...I knew there wasnt enough gas getting into the rail.Regulator has no gas smell,nor leaks and no obvious signs of trouble.
I had this happen on another GM car I had few years ago.Pressure was stuck around 25 psi.Did same thing,new pump fixed it.
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If you can stand behind the car with the engine idling and hear the fuel pump running....replace the pump.
Pro
Joined: Oct 2005
Posts: 721
Likes: 1
From: Charlotte NC, behind someone going 10 under the speed limit
Stay away from NAPA pumps. I just got done replacing a 3 yr old one with 10,000 miles. Fuel pressure started to tank after key is shut off. Put a new one in (unfortunately another NAPA since this is my ride home from work) and its ok now, BUT FOR HOW LONG?????
Team Owner
Joined: Oct 2006
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St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16-'17
NCM Member '09
A trick for testing whether you FPR diapragm has burst or ripped is to roll up a square of toilet paper, and
stick it in teh vacuum line hole....if it's a torn diapragm, it will be wet.
stick it in teh vacuum line hole....if it's a torn diapragm, it will be wet.
Thread Starter
Racer
Joined: Sep 2005
Posts: 304
Likes: 1
From: Carson City Nevada
Just changed the filter about 5 months ago. Pulled the Shrader valve and no change, just sits at about 15psi running. I looked at the instructions for pulling the fuel pump and it looks like a pain. Just filled the gas tank too....Here we go....
Last edited by 87FIREREDRAGTOP; Jun 17, 2008 at 11:51 PM.
Race Director
Joined: Aug 2000
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Cruise-In II Veteran
Beats dropping a gas tank down under the car,while on your back!
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
pump
you don't have to drop the tank, or even drain it.
You take off the door, remove the boot, unbolt the fuel quantity transmitter, remove the ground wire, unplug the connector, remove the hoses, brush away any dirt from around the opening and VOILA! the pump is in your hand. pull up and then at an angle.
If it takes you half an hour, your goofing off.
Be sure you have a replacement pump, and stop by Chevrolet to obtain a new gasket prior to starting the pump removal.
Use duct tape, or 2 inch wide masking tape to tape the opening, then use a small wire brush to clean the gasket area after you scrape the gasket from the sender and the tank. tape the tape from underneath, and use a string or wire to tie to the tape incase the fuel vapors or fuel eat the glue off the tape, so it won't fall into the tank and be unobtainable.
You take off the door, remove the boot, unbolt the fuel quantity transmitter, remove the ground wire, unplug the connector, remove the hoses, brush away any dirt from around the opening and VOILA! the pump is in your hand. pull up and then at an angle.
If it takes you half an hour, your goofing off.
Be sure you have a replacement pump, and stop by Chevrolet to obtain a new gasket prior to starting the pump removal.
Use duct tape, or 2 inch wide masking tape to tape the opening, then use a small wire brush to clean the gasket area after you scrape the gasket from the sender and the tank. tape the tape from underneath, and use a string or wire to tie to the tape incase the fuel vapors or fuel eat the glue off the tape, so it won't fall into the tank and be unobtainable.
Racer
Joined: May 2006
Posts: 426
Likes: 16
From: Concord CA
Might not be related, but I thought I tell the story.
I had a problem where the Regulator was causing the pressure to return to the tank.. ( i most likely have leaky injectors too, but that is another story). My pressure would drop to zero right away when the key was turned off.. Measured the pressure and it was right on with both vacuum and without.. but it keep dropping to zero right way.. I took the vacuum and pop it off and on a few times quickly and after that.. I didn't lose pressure when shutting down (at lease not for a period of expected time). I guess I had a sticking regulator or diapragm and popping it off and on must have unstuck it.
I had a problem where the Regulator was causing the pressure to return to the tank.. ( i most likely have leaky injectors too, but that is another story). My pressure would drop to zero right away when the key was turned off.. Measured the pressure and it was right on with both vacuum and without.. but it keep dropping to zero right way.. I took the vacuum and pop it off and on a few times quickly and after that.. I didn't lose pressure when shutting down (at lease not for a period of expected time). I guess I had a sticking regulator or diapragm and popping it off and on must have unstuck it.