Fuel Pump Question
Thread Starter
Instructor
Joined: Aug 2007
Posts: 151
Likes: 0
From: Mesquite Tx
Fuel Pump Question
1996 Collector Edition
Started to take 5-7 times to crank over and start the last 3 months. Now, "IF" it starts it will only run for about 3 minutes and then die. It seems that if I let it sit for about an hour it will start and die again. Replaced fuel filter with no luck. I put a fuel pressure gauge on it and it reads 38 PSI. As I watch it idle it will drop to 15 PSI in a couple of minutes and then die. Then there is no fuel pressure when I try to crank it again. I am hearing some humming when I turn the key but that seems to be coming from the left front part of the engine bay. Am on the right track to replace the fuel pump and strainer? Also should I replace the sending unit with the pump as long as I'm in there?
Thanks Eveyone. I appreciate your advise.
Started to take 5-7 times to crank over and start the last 3 months. Now, "IF" it starts it will only run for about 3 minutes and then die. It seems that if I let it sit for about an hour it will start and die again. Replaced fuel filter with no luck. I put a fuel pressure gauge on it and it reads 38 PSI. As I watch it idle it will drop to 15 PSI in a couple of minutes and then die. Then there is no fuel pressure when I try to crank it again. I am hearing some humming when I turn the key but that seems to be coming from the left front part of the engine bay. Am on the right track to replace the fuel pump and strainer? Also should I replace the sending unit with the pump as long as I'm in there?
Thanks Eveyone. I appreciate your advise.
Advanced
Joined: Jun 2013
Posts: 81
Likes: 0
From: Junction City Oregon
I have a 90 vert and replaced the fuel pump and strainer recently. Replacing the fuel pump is easy on a C4, only takes 30 minutes or so. Replacing the sending unit is costly, so I wouldn't if it is working properly. How long does the pressure hold when you turn the key on but not start the engine?
Thread Starter
Instructor
Joined: Aug 2007
Posts: 151
Likes: 0
From: Mesquite Tx
I have a 90 vert and replaced the fuel pump and strainer recently. Replacing the fuel pump is easy on a C4, only takes 30 minutes or so. Replacing the sending unit is costly, so I wouldn't if it is working properly. How long does the pressure hold when you turn the key on but not start the engine?
Sometimes I don't get any pressure when 1st turning the key. If I do get pressure I have always started it then. If I shut the car off while it's running the pressure will hold for about 30 minutes but gradually goes to 0 PSI
Advanced
Joined: Jun 2013
Posts: 81
Likes: 0
From: Junction City Oregon
Well, it is not terribly expensive to replace the fuel pump and it is very easy to do. I think mine was around 90 bucks. It sounds like yours is intermittent when you first turn the key to on, which means it could be a bad connection. If it were me, I would replace the fuel pump. Others may say do a little more diagnostic work to prevent spending money on something that doesn't fix the problem. Let us know how it comes out.
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
Your pressure should build when you turn the key to the on position and hold strong for a good 30 minutes and then belled down to nothing over a 7-8 hour period. I would have to say that it is your pump.
••••• TESTING FOR LOSS OF FUEL PRESSURE
... Here are the sure fail tests for the fuel system to save you time and money.. Take a fuel pressure gauge attach it to the Schrader valve.. Turn the key on and off a few times to build up the pressure in the system... If you are having starting trouble the pressure will probably drop as soon as it hits 38 or 40 and the pump turns off it will probably leak back to zero within a few minutes. Ok now right after you prime the system pinch off the return line near the tank if the pressure drop stops it is a bad fuel pressure regulator.... Next pinch off the feed line if the pressure holds then the leak is before the point where you pinched the line IE fuel pump check valve..hole in the metal line on the sending unit caused by it rubbing on the inside of the tank you should visibly be able to see this if you pull the pump and the sending unit...(this was my problem) or the pulse dampener which is the piece between the pump and metal line on the sending unit.. the diaphragm tears.. and last if you pinch both the feed and return line near the tank and the leak down of the pressure continues then a fuel injector is your problem.. This is the GM test.. saves time and money..
•• disconnect the vacuum line from fuel pressure regulator
••••• TESTING FOR LOSS OF FUEL PRESSURE
... Here are the sure fail tests for the fuel system to save you time and money.. Take a fuel pressure gauge attach it to the Schrader valve.. Turn the key on and off a few times to build up the pressure in the system... If you are having starting trouble the pressure will probably drop as soon as it hits 38 or 40 and the pump turns off it will probably leak back to zero within a few minutes. Ok now right after you prime the system pinch off the return line near the tank if the pressure drop stops it is a bad fuel pressure regulator.... Next pinch off the feed line if the pressure holds then the leak is before the point where you pinched the line IE fuel pump check valve..hole in the metal line on the sending unit caused by it rubbing on the inside of the tank you should visibly be able to see this if you pull the pump and the sending unit...(this was my problem) or the pulse dampener which is the piece between the pump and metal line on the sending unit.. the diaphragm tears.. and last if you pinch both the feed and return line near the tank and the leak down of the pressure continues then a fuel injector is your problem.. This is the GM test.. saves time and money..
•• disconnect the vacuum line from fuel pressure regulator
Thread Starter
Instructor
Joined: Aug 2007
Posts: 151
Likes: 0
From: Mesquite Tx
Your pressure should build when you turn the key to the on position and hold strong for a good 30 minutes and then belled down to nothing over a 7-8 hour period. I would have to say that it is your pump.
••••• TESTING FOR LOSS OF FUEL PRESSURE
... Here are the sure fail tests for the fuel system to save you time and money.. Take a fuel pressure gauge attach it to the Schrader valve.. Turn the key on and off a few times to build up the pressure in the system... If you are having starting trouble the pressure will probably drop as soon as it hits 38 or 40 and the pump turns off it will probably leak back to zero within a few minutes. Ok now right after you prime the system pinch off the return line near the tank if the pressure drop stops it is a bad fuel pressure regulator.... Next pinch off the feed line if the pressure holds then the leak is before the point where you pinched the line IE fuel pump check valve..hole in the metal line on the sending unit caused by it rubbing on the inside of the tank you should visibly be able to see this if you pull the pump and the sending unit...(this was my problem) or the pulse dampener which is the piece between the pump and metal line on the sending unit.. the diaphragm tears.. and last if you pinch both the feed and return line near the tank and the leak down of the pressure continues then a fuel injector is your problem.. This is the GM test.. saves time and money..
•• disconnect the vacuum line from fuel pressure regulator
••••• TESTING FOR LOSS OF FUEL PRESSURE
... Here are the sure fail tests for the fuel system to save you time and money.. Take a fuel pressure gauge attach it to the Schrader valve.. Turn the key on and off a few times to build up the pressure in the system... If you are having starting trouble the pressure will probably drop as soon as it hits 38 or 40 and the pump turns off it will probably leak back to zero within a few minutes. Ok now right after you prime the system pinch off the return line near the tank if the pressure drop stops it is a bad fuel pressure regulator.... Next pinch off the feed line if the pressure holds then the leak is before the point where you pinched the line IE fuel pump check valve..hole in the metal line on the sending unit caused by it rubbing on the inside of the tank you should visibly be able to see this if you pull the pump and the sending unit...(this was my problem) or the pulse dampener which is the piece between the pump and metal line on the sending unit.. the diaphragm tears.. and last if you pinch both the feed and return line near the tank and the leak down of the pressure continues then a fuel injector is your problem.. This is the GM test.. saves time and money..
•• disconnect the vacuum line from fuel pressure regulator
Now it may be a few weeks before I can look at it. I will keep ya'll posted. Thanks for everything.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
I would look at the vacuum line to the fuel pressure regulator before replacing anything. It sort of sounds like the diaphragm is ruptured.
Remove the vacuum line and turn on the key (don't start the engine). Check the FPR to see if any fuel came out. Simple and quick and might save you some time and money.
Remove the vacuum line and turn on the key (don't start the engine). Check the FPR to see if any fuel came out. Simple and quick and might save you some time and money.
Race Director
Joined: Dec 2000
Posts: 17,551
Likes: 26
From: El Paso Texas
Your pressure should build when you turn the key to the on position and hold strong for a good 30 minutes and then belled down to nothing over a 7-8 hour period. I would have to say that it is your pump.
••••• TESTING FOR LOSS OF FUEL PRESSURE
... Here are the sure fail tests for the fuel system to save you time and money.. Take a fuel pressure gauge attach it to the Schrader valve.. Turn the key on and off a few times to build up the pressure in the system... If you are having starting trouble the pressure will probably drop as soon as it hits 38 or 40 and the pump turns off it will probably leak back to zero within a few minutes. Ok now right after you prime the system pinch off the return line near the tank if the pressure drop stops it is a bad fuel pressure regulator.... Next pinch off the feed line if the pressure holds then the leak is before the point where you pinched the line IE fuel pump check valve..hole in the metal line on the sending unit caused by it rubbing on the inside of the tank you should visibly be able to see this if you pull the pump and the sending unit...(this was my problem) or the pulse dampener which is the piece between the pump and metal line on the sending unit.. the diaphragm tears.. and last if you pinch both the feed and return line near the tank and the leak down of the pressure continues then a fuel injector is your problem.. This is the GM test.. saves time and money..
•• disconnect the vacuum line from fuel pressure regulator
••••• TESTING FOR LOSS OF FUEL PRESSURE
... Here are the sure fail tests for the fuel system to save you time and money.. Take a fuel pressure gauge attach it to the Schrader valve.. Turn the key on and off a few times to build up the pressure in the system... If you are having starting trouble the pressure will probably drop as soon as it hits 38 or 40 and the pump turns off it will probably leak back to zero within a few minutes. Ok now right after you prime the system pinch off the return line near the tank if the pressure drop stops it is a bad fuel pressure regulator.... Next pinch off the feed line if the pressure holds then the leak is before the point where you pinched the line IE fuel pump check valve..hole in the metal line on the sending unit caused by it rubbing on the inside of the tank you should visibly be able to see this if you pull the pump and the sending unit...(this was my problem) or the pulse dampener which is the piece between the pump and metal line on the sending unit.. the diaphragm tears.. and last if you pinch both the feed and return line near the tank and the leak down of the pressure continues then a fuel injector is your problem.. This is the GM test.. saves time and money..
•• disconnect the vacuum line from fuel pressure regulator
Saved me the trouble of typing it. 
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Thread Starter
Instructor
Joined: Aug 2007
Posts: 151
Likes: 0
From: Mesquite Tx
Update on the fuel pressure. I hope nobody gets mad at me but time is more valuable to me than money. LOL. I ordered a complete pump and sending unit from Corvette Central. Problem Fixed. 
I did order the 9 new replacement bolts to be safe. Good thing. The O-Rings on the bolts were shot. I know, I know, I could have just replaced the O-Rings. The bolts were only $4.95.
I must say though. This was one of the easiest things to replace EVER on the Corvette. THANKS for Everyones help. I really appreciate it.
I did order the 9 new replacement bolts to be safe. Good thing. The O-Rings on the bolts were shot. I know, I know, I could have just replaced the O-Rings. The bolts were only $4.95.
I must say though. This was one of the easiest things to replace EVER on the Corvette. THANKS for Everyones help. I really appreciate it.