Hawaiian C4

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.

John A. Marker

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.

steve40th

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.

Hawaiian C4

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.

aminnich

Pull the vac line off the FPR and check for gas smell. If it smells then replace the FPR.

REDC4CORVETTE

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.

Hawaiian C4

Can I buy just a pulsator? or does it come with the fuel pump?

AGENT 86

Toss the pulsator and replace with a piece of fuel injection hose and 2 clamps.
That was my pressure loss area, all good now.
It is right above the fuel pump.

ScaryFast

Do you have an aftermarket adjustable FP regulator? They don't hold pressure.

REDC4CORVETTE

I did what Agent 86 said, when I installed the adjustable regulator.Yes you can buy the Pulsator by itself.

RRT vette

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.

Hawaiian C4

I removed the pulsator and replaced with hose, I still have the same problem:

--- 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.

REDC4CORVETTE

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.

Hawaiian C4

The fuel pump and filter are about 4 months old. I bought the pump at Checkers, so it is probably crap. Brand name was Carter. Everything was good until about 2 weeks ago.

AGENT 86

Diagnose where the pressure loss area is http://members.shaw.ca/corvette86/Fu...mDiagnosis.pdf
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.