1992 Corvette loses fuel pressure
Team Owner
Joined: Jul 2004
Posts: 28,495
Likes: 3,298
From: Hartford WI
I doubt this is a fuel pressure problem, more then likely you have a modified engine and you need a tune that will add more cranking fuel, and open loop fuel. If the pressure hits 40 with the key on and then slowly drops it will be fine when you are cranking because the fuel pump is on when you are cranking.
FYI, the fuel pressure drop get blamed for all kinds of issues when it is usually not the main starting or running problem. If the fuel pressure rail pressure stays in the 30's and 40's when the car is running the problem is located somewhere else.
My car does not have a starting problem and my fuel pressure will drop to zero in 10 seconds. There is no starting problem because as soon as I hit the key and start cranking the pressure jumps up to 40 PSI and the car immediately starts. Fuel is non compressable and even a very slow leak back to the tank will cause the fuel pressure to drop to zero very quickly.
FYI, the fuel pressure drop get blamed for all kinds of issues when it is usually not the main starting or running problem. If the fuel pressure rail pressure stays in the 30's and 40's when the car is running the problem is located somewhere else.
My car does not have a starting problem and my fuel pressure will drop to zero in 10 seconds. There is no starting problem because as soon as I hit the key and start cranking the pressure jumps up to 40 PSI and the car immediately starts. Fuel is non compressable and even a very slow leak back to the tank will cause the fuel pressure to drop to zero very quickly.
Team Owner
Joined: Jul 2004
Posts: 28,495
Likes: 3,298
From: Hartford WI
That was my confusion too. That it takes a while to DE-pressurize makes me think it is a pump issue. Either current or the pump itself. We might know more if he comes back with a test result.
Thread Starter
Heel & Toe
Joined: Dec 2016
Posts: 22
Likes: 0
I doubt this is a fuel pressure problem, more then likely you have a modified engine and you need a tune that will add more cranking fuel, and open loop fuel. If the pressure hits 40 with the key on and then slowly drops it will be fine when you are cranking because the fuel pump is on when you are cranking.
FYI, the fuel pressure drop get blamed for all kinds of issues when it is usually not the main starting or running problem. If the fuel pressure rail pressure stays in the 30's and 40's when the car is running the problem is located somewhere else.
My car does not have a starting problem and my fuel pressure will drop to zero in 10 seconds. There is no starting problem because as soon as I hit the key and start cranking the pressure jumps up to 40 PSI and the car immediately starts. Fuel is non compressable and even a very slow leak back to the tank will cause the fuel pressure to drop to zero very quickly.
FYI, the fuel pressure drop get blamed for all kinds of issues when it is usually not the main starting or running problem. If the fuel pressure rail pressure stays in the 30's and 40's when the car is running the problem is located somewhere else.
My car does not have a starting problem and my fuel pressure will drop to zero in 10 seconds. There is no starting problem because as soon as I hit the key and start cranking the pressure jumps up to 40 PSI and the car immediately starts. Fuel is non compressable and even a very slow leak back to the tank will cause the fuel pressure to drop to zero very quickly.
Safety Car
Joined: Sep 2001
Posts: 4,160
Likes: 554
From: Glenbeulah Wi
How did you obtain the reading you listed for fuel pressure if you are buying a gauge tomorrow?
Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
The psi comes up to appx 40 psi, and it appears it is a "slow leak" the longer it sits the more it leaks down. If the vehicle sits for say 12 hrs or so it takes a good 5 min or so to pump the fuel back up to the injectors. The motor is still an lt1, to compound the issue once it does finally start the motors revs between 1-2 thousand rpm's. It takes about 20-25 minutes before the motor starts running properly (even after warming up for about 10 min prior to driving). Is there any chance the initial rough idling is related to the leak down issue? Thanks for all your help, I have been restoring this car for about 2 years now, its been to multiple shops and to this point no luck in figuring out the leakdown problem.
Pressurization should be pretty much instant. When you turn the key to the "on" position, you should hear a buzzing noise from the back, that's your fuel pump. Pressure should be between 41 and 35 psi. When turned off, it should take about 30 min to fully depressurize.
I suspect one of two things, assuming of course that the regulator is good, and installation was correct. Either you don't have enough fuel pump for a 383, or the open loop tune is off. Or both.
Thread Starter
Heel & Toe
Joined: Dec 2016
Posts: 22
Likes: 0
Put a fuel pressure gauge on the rail and crank the car, does the fuel pressure rise up to around 40 PSI quickly and stay there as long as you are cranking the car? If it does it maybe a chip issue, if the pressure stays low until the car finally starts the issue will be fuel pressure related.
How did you obtain the reading you listed for fuel pressure if you are buying a gauge tomorrow?
How did you obtain the reading you listed for fuel pressure if you are buying a gauge tomorrow?
Thread Starter
Heel & Toe
Joined: Dec 2016
Posts: 22
Likes: 0
What happens to fuel pressure when you rev it?
Pressurization should be pretty much instant. When you turn the key to the "on" position, you should hear a buzzing noise from the back, that's your fuel pump. Pressure should be between 41 and 35 psi. When turned off, it should take about 30 min to fully depressurize.
I suspect one of two things, assuming of course that the regulator is good, and installation was correct. Either you don't have enough fuel pump for a 383, or the open loop tune is off. Or both.
Pressurization should be pretty much instant. When you turn the key to the "on" position, you should hear a buzzing noise from the back, that's your fuel pump. Pressure should be between 41 and 35 psi. When turned off, it should take about 30 min to fully depressurize.
I suspect one of two things, assuming of course that the regulator is good, and installation was correct. Either you don't have enough fuel pump for a 383, or the open loop tune is off. Or both.
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Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
. After the motor gets completely warmed up it revs fine however with that being said if I am running say 65 or 70 in 5th gear and I step on it, the motor stumbles. As long as the acceleration is slow and smooth at the top end it's fine but if you step on it hard it stumbles.
What size injectors are you running? From everything that I've heard and read, most people going 383 also upgrade the fuel pump as well.
Last edited by lt4obsesses; Dec 22, 2016 at 07:53 PM.
Thread Starter
Heel & Toe
Joined: Dec 2016
Posts: 22
Likes: 0
5th gear is an overdrive gear, so stepping on it, while it shouldn't be a huge chore for the engine, isn't ideal. However, stumbling on acceleration is typically a fuel delivery issue. Kind of why I asked about the fuel pressure when revving. It may rev okay without a load on it, but the pressure gauge may show a larger than normal drop in pressure. Supply needs to match demand.
What size injectors are you running? From everything that I've heard and read, most people going 383 also upgrade the fuel pump as well.
What size injectors are you running? From everything that I've heard and read, most people going 383 also upgrade the fuel pump as well.
Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
Thread Starter
Heel & Toe
Joined: Dec 2016
Posts: 22
Likes: 0
Team Owner
Joined: Jul 2004
Posts: 28,495
Likes: 3,298
From: Hartford WI
Getting it from Walbro is $121 and it doesn't have the gasket or the bolts to replace the old ones. Why not get it all for $90
Team Owner
Joined: Jul 2004
Posts: 28,495
Likes: 3,298
From: Hartford WI
Thread Starter
Heel & Toe
Joined: Dec 2016
Posts: 22
Likes: 0
Thank you for your help, I did give all the specs when the chip was ordered, I have had a ton of problems getting the motor to run consistently. The performance or lack thereof changes almost every time I drive the car. Its very frustrating.
Team Owner
Joined: Jul 2004
Posts: 28,495
Likes: 3,298
From: Hartford WI
That said, let's look at the fuel pressure to rule it out. Check compression just to make sure
Thread Starter
Heel & Toe
Joined: Dec 2016
Posts: 22
Likes: 0
Hate to say that but an off shelf or mail order tune has never left me satisfied. I usually get it done at the facility so they can fine tune it instead of guessing what you have and write the program conservatively. Also in introduces another variable.
That said, let's look at the fuel pressure to rule it out. Check compression just to make sure
That said, let's look at the fuel pressure to rule it out. Check compression just to make sure