C4 fuel quesions
Thread Starter
Navigator
Joined: Oct 2021
Posts: 9
Likes: 0
From: Blythe, CA
C4 fuel quesions
So i have a 94 c4 lt1 i had an issue with my fuel pump fixed it drove the car to cali no problem. Sometimes it just dies on me. Thought it was fuel related. Just recently changed fuel filter and another brand new fuel pump, car started fine but then died. Checked rhe pressure and it barely dribblea out. How do i fix the pressure issue and why won't the car start fully now or stay running ? Anyone know anything similar or how yo fix it. I have a videl of pervious fuel pump nose that i recently fixed are now just running into the problem of not starting or stay running
Le Mans Master
Joined: Oct 2004
Posts: 6,314
Likes: 508
From: South-central Missouri
So i have a 94 c4 lt1 i had an issue with my fuel pump fixed it drove the car to cali no problem. Sometimes it just dies on me. Thought it was fuel related. Just recently changed fuel filter and another brand new fuel pump, car started fine but then died. Checked rhe pressure and it barely dribblea out. How do i fix the pressure issue and why won't the car start fully now or stay running ? Anyone know anything similar or how yo fix it. I have a videl of pervious fuel pump nose that i recently fixed are now just running into the problem of not starting or stay running
And, a (OBD-I) scanner would be an excellent tool to have with these cars. Excellent tool!
Thread Starter
Navigator
Joined: Oct 2021
Posts: 9
Likes: 0
From: Blythe, CA
It sounds like a fuel pressure issue. The pressure for the LT1 (according to my "Corvette Fuel Injection" by Probst) is steady 41# across the RPM range. And, for what it is worth, I have experienced a bad out-of-the-box fuel pump on my ZR-1; put the shine on the statistics axiom: "Infant Mortality" is the #1 failure mode for any new component first put into service."
And, a (OBD-I) scanner would be an excellent tool to have with these cars. Excellent tool!
And, a (OBD-I) scanner would be an excellent tool to have with these cars. Excellent tool!
I dont know how to adjust the pressure. It is supposed to be 40psi but unsure what randomly caused the pressure to drop and how i go about fixing that
Le Mans Master
Joined: Aug 2015
Posts: 6,119
Likes: 1,996
From: St. Charles MO
Cassie, Paul is basically telling you your brand new fuel may have been bad right out of the box. And he's right - it may be. You need to do at least two things: get a fuel pressure gauge and find out what the pressure really is on your fuel rail, and listen to make sure the pump is even running at all when you first turn the key to "run" (before you crank the starter). You don't adjust fuel pressure on these cars: they have a pressure regulator that maintains the proper pressure...or at least it's supposed to. I don't know if they have failure mode that causes loss of nearly all fuel pressure, but maybe they do. If your pump is working and your regulator is good, there's not much else that could cause low pressure.
Thread Starter
Navigator
Joined: Oct 2021
Posts: 9
Likes: 0
From: Blythe, CA
Cassie, Paul is basically telling you your brand new fuel may have been bad right out of the box. And he's right - it may be. You need to do at least two things: get a fuel pressure gauge and find out what the pressure really is on your fuel rail, and listen to make sure the pump is even running at all when you first turn the key to "run" (before you crank the starter). You don't adjust fuel pressure on these cars: they have a pressure regulator that maintains the proper pressure...or at least it's supposed to. I don't know if they have failure mode that causes loss of nearly all fuel pressure, but maybe they do. If your pump is working and your regulator is good, there's not much else that could cause low pressure.
Thread Starter
Navigator
Joined: Oct 2021
Posts: 9
Likes: 0
From: Blythe, CA
now what?
okay so i replaced now the fuel pump and filter, pressure is good at 40 psi, and cleaned my ICM yesterday which helped so today I replaced it and no nothing. still will not stay running, when it dies the battery light comes on and it dies gently(if thats a thing), starts back up right after and my alternator is good so now im out of ideas on what could be wrong. HELP
Team Owner
Joined: Sep 2001
Posts: 62,160
Likes: 1,733
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
What did you do with the ICM?
FP with key to On position stays at 40-45psi, you turn it over, and does that hold level or not?
FP with key to On position stays at 40-45psi, you turn it over, and does that hold level or not?
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
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
Melting Slicks
Joined: Jul 2005
Posts: 2,649
Likes: 863
You might want to check the wiring to the Fuel Pump.
The newest C4 is now 25 years old - wiring can be an issue on any car - but it gets more likely as the car gets older. You need to know what the fuel pressure is as the car "dies" - that'll help you diagnose what the next steps are.
The newest C4 is now 25 years old - wiring can be an issue on any car - but it gets more likely as the car gets older. You need to know what the fuel pressure is as the car "dies" - that'll help you diagnose what the next steps are.
Thread Starter
Navigator
Joined: Oct 2021
Posts: 9
Likes: 0
From: Blythe, CA
Team Owner
Joined: Sep 2001
Posts: 62,160
Likes: 1,733
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
If the engine does not catch and start, you do not have spark and fuel. You are losing one or the other.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Not if it's not starting.
Are you telling us that you checked for spark, while the symptom was occurring...and you had spark at that point?
And you have checked for fuel pressure, while the symptom was occurring, and you had fuel pressure at that point?
Are you telling us that you checked for spark, while the symptom was occurring...and you had spark at that point?
And you have checked for fuel pressure, while the symptom was occurring, and you had fuel pressure at that point?
Thread Starter
Navigator
Joined: Oct 2021
Posts: 9
Likes: 0
From: Blythe, CA
yes i got spark when cranking and checked pressure and it was fine as well. Before changing the icm it would die and it started fine with the new then died and now wont start at all or if it does it takes forever and will eventually die again and thats when its sitting
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Well...that's not too clear. You checked pressure while it also would not start?
If you changed the ICM and now it won't start, I think that is a pretty good clue that you should change the ICM back. Put the old one back in. It's also a clue that it's not starting, b/c of lack of....spark, likely.
When it won't start, will it start on ether?
If you changed the ICM and now it won't start, I think that is a pretty good clue that you should change the ICM back. Put the old one back in. It's also a clue that it's not starting, b/c of lack of....spark, likely.
When it won't start, will it start on ether?
Thread Starter
Navigator
Joined: Oct 2021
Posts: 9
Likes: 0
From: Blythe, CA
Well...that's not too clear. You checked pressure while it also would not start?
If you changed the ICM and now it won't start, I think that is a pretty good clue that you should change the ICM back. Put the old one back in. It's also a clue that it's not starting, b/c of lack of....spark, likely.
When it won't start, will it start on ether?
If you changed the ICM and now it won't start, I think that is a pretty good clue that you should change the ICM back. Put the old one back in. It's also a clue that it's not starting, b/c of lack of....spark, likely.
When it won't start, will it start on ether?