Weird fuel delivery problem, need help!!
Thread Starter
Instructor
Joined: Sep 2007
Posts: 129
Likes: 0
From: Ewa Beach Hawaii
Weird fuel delivery problem, need help!!
Did a search, didn't really find anything.
--- Turn on key, fuel pump runs normal 2 seconds, no fuel pressure
--- Start car (takes about 5 seconds) car runs great, 42 PSI fuel pressure
--- Shut car off, fuel pressure immediatly goes to zero
I changed out 2 fuel pump relays I had, but car did same thing. No noticeable gas or smell from fuel pressure regulator vent line.
Could I still have a bad regulator?
1987 Coupe L98
Thanks guys.
--- Turn on key, fuel pump runs normal 2 seconds, no fuel pressure
--- Start car (takes about 5 seconds) car runs great, 42 PSI fuel pressure
--- Shut car off, fuel pressure immediatly goes to zero
I changed out 2 fuel pump relays I had, but car did same thing. No noticeable gas or smell from fuel pressure regulator vent line.
Could I still have a bad regulator?
1987 Coupe L98
Thanks guys.
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
Not a relay problem. Best bet is the check valve in the fuel pump. With the pressure dropping sooooo fast it can't be injectors. If it was the pressure regulator, it would more than likely be the diaphram and you would have fuel in the small line attached to the regulator.
Le Mans Master
Joined: Feb 1999
Posts: 9,922
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
If it is holding pressure while running your regulator is good. The fuel filter goes one way, and I have changed them out to have my fuel pressure drop off after the engine was shut off. The most important part you need to check is fuel pressure while under load, and to verify it is going up as you give it more throttle, telling you the pump is working and the regulator is being pulled by the vacuum, therefore increasing fuel pressure.
When I had an L98, I had 133300 miles and never had a regulator go out, even with my LT1 I havent replaced it since 97 as I went to an adjustable. Waste of money, as you should tune to your pressure anyways.
I think there is a check valve in your system for fuel return. Not sure. But regardless I wouldnt sweat it unless your injectors are leaking. Unfortunately you need to pull them to do that, the rail that is with injectors and connectors on it, then turn the ignition to on, and see if they leak.
When I had an L98, I had 133300 miles and never had a regulator go out, even with my LT1 I havent replaced it since 97 as I went to an adjustable. Waste of money, as you should tune to your pressure anyways.
I think there is a check valve in your system for fuel return. Not sure. But regardless I wouldnt sweat it unless your injectors are leaking. Unfortunately you need to pull them to do that, the rail that is with injectors and connectors on it, then turn the ignition to on, and see if they leak.
Last edited by steve40th; Feb 27, 2008 at 11:51 PM.
Thread Starter
Instructor
Joined: Sep 2007
Posts: 129
Likes: 0
From: Ewa Beach Hawaii
Once started, the car runs great. Lately it takes cranking it two to three times in the morning to start. I just changed the fuel injectors last month and they are good.
I just went out and tried it again after letting it sit about 3 hours.
--- turn key, fuel pressure to 42 PSI for one second, and then immediatly zero
--- Start car, runs fine, fuel pressure holds at 42 PSI
--- shut down car, fuel pressure to zero.
I just went out and tried it again after letting it sit about 3 hours.
--- turn key, fuel pressure to 42 PSI for one second, and then immediatly zero
--- Start car, runs fine, fuel pressure holds at 42 PSI
--- shut down car, fuel pressure to zero.
Safety Car
Joined: Apr 2004
Posts: 4,532
Likes: 7
From: Lahaina Hi
I would lay my money on the pulsator in the tank, inline with the fuel pump,it keeps the fuel from draining back into the pump and losing presure in the line.You could have a bad fuel pump but not likely.
Thread Starter
Instructor
Joined: Sep 2007
Posts: 129
Likes: 0
From: Ewa Beach Hawaii
Can I buy just a pulsator? or does it come with the fuel pump?
Team Owner
Joined: Jan 2003
Posts: 20,306
Likes: 242
From: Summerland B.C. Canada
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
If the fuel pump runs for 2 seconds, then the electrical part is fine. The loss of fuel pressure so quickly could point you to a few different places. I would pull the fuel pump assembly and do as AGENT 86 suggested and replace the pulsator with a short hose and clamps. The pulsator is the master cylinder looking object the top fuel pump nipple fits into. If that doesn't solve the problem, then the check valve is the next place. You have to replace the fuel pump to replace the check vavle. While the fuel pump assembly is out of the tank, look at the sock and strainer on the fuel pump. The strainer should be debris free.
Thread Starter
Instructor
Joined: Sep 2007
Posts: 129
Likes: 0
From: Ewa Beach Hawaii
If the fuel pump runs for 2 seconds, then the electrical part is fine. The loss of fuel pressure so quickly could point you to a few different places. I would pull the fuel pump assembly and do as AGENT 86 suggested and replace the pulsator with a short hose and clamps. The pulsator is the master cylinder looking object the top fuel pump nipple fits into. If that doesn't solve the problem, then the check valve is the next place. You have to replace the fuel pump to replace the check vavle. While the fuel pump assembly is out of the tank, look at the sock and strainer on the fuel pump. The strainer should be debris free.
--- no fuel pressure when I turn on key, pump seems to be working though (2 second cycle)
--- Car takes at least 3 crank cycles to start
--- once started, the car runs fine, 42 PSI fuel pressure
--- shut off car and fuel pressure drops quickly (1-3 seconds)
The strainer looked good. Is the check valve built into the fuel pump? Thanks.
Safety Car
Joined: Apr 2004
Posts: 4,532
Likes: 7
From: Lahaina Hi
If you have an after market fuel pump it usually will not hold presure when shut down,atleast not for very long.The by pass in the fuel pump has a spring but that can only be replaced with a new pump.
How old is the fuel filter ,you might have gotten some crap passed the filter and it is lodged in the by pass in the pump.
How old is the fuel filter ,you might have gotten some crap passed the filter and it is lodged in the by pass in the pump.
Thread Starter
Instructor
Joined: Sep 2007
Posts: 129
Likes: 0
From: Ewa Beach Hawaii
If you have an after market fuel pump it usually will not hold presure when shut down,atleast not for very long.The by pass in the fuel pump has a spring but that can only be replaced with a new pump.
How old is the fuel filter ,you might have gotten some crap passed the filter and it is lodged in the by pass in the pump.
How old is the fuel filter ,you might have gotten some crap passed the filter and it is lodged in the by pass in the pump.
Team Owner
Joined: Jan 2003
Posts: 20,306
Likes: 242
From: Summerland B.C. Canada
I tested my check valve by removing the supply line from pump and sticking on a piece of hose. If you can blow through the hose, your check valve is not working.
