Need HELP - Running lean after H/C swap C5
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Joined: Nov 2007
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From: San Juan Puerto Rico
Need HELP - Running lean after H/C swap C5
Recently I installed LS6 heads, LS6 intake, 232/234 Comp cam,918 springs, 850-16 lifters, 7638-16 Magnum Pushrods, LS2 timing chain, Melling oil pump, ATI Super Damper, LS1 to LS6 PCV and coolant crossover pipe conversion, Custom fuel rail kit with AN fittings, ceramic coated long tube headers, LS6 titanium cat-back system, cold air intake and Spec light weight flywheel. The car is a 6 Speed.
When I took my Vette to the tuner he found it hard to find a sweet spot in which the car would run smoothly while idling. When he tried to make runs for higher RPM adjustments he found that after 4k RPM the fuel mixture was getting lean fast. Since I installed an aftermarket fuel rail with a pressure gauge he asked me to let him know if the needle was dropping. Right after the engine hit about 4k RPM the needle started dropping fast, going below 30 at the moment the car was stopped.
He told me to get a Racetronix gas pump harness, which I did, but didn't work. The tuner says that it must be the gas pump, but I'm not sure about that. Please let me know your thoughts...
When I took my Vette to the tuner he found it hard to find a sweet spot in which the car would run smoothly while idling. When he tried to make runs for higher RPM adjustments he found that after 4k RPM the fuel mixture was getting lean fast. Since I installed an aftermarket fuel rail with a pressure gauge he asked me to let him know if the needle was dropping. Right after the engine hit about 4k RPM the needle started dropping fast, going below 30 at the moment the car was stopped.
He told me to get a Racetronix gas pump harness, which I did, but didn't work. The tuner says that it must be the gas pump, but I'm not sure about that. Please let me know your thoughts...
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Joined: Nov 2007
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From: San Juan Puerto Rico
I have done a lot of work on my Vette, including a gas pump swap. I never did find the gas filter on it. It's a 98, do you know where I can find it?
Team Owner
Joined: May 2003
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From: East Meadow NY
St. Jude Donor '12
EDIT: You have a '98 so it is an easy one. The later years have the fuel filter in the tank. Check it to make sure you don't have a leak or to see if its clogged.
Last edited by chaase; Mar 10, 2014 at 03:47 PM.
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From: San Juan Puerto Rico
Chaase, I appreciate your recommendation and I will do a gas filter swap.
In case there are other reasons for running lean, I request that anyone that has another possibility to please post it.
This is an early LS1, which has been upgraded over time and is using the original equipment, software and hardware. It seems to me that, if an engine is running perfectly well below 4k RPM and just after those RPMs are increased, the gas supply is decreased, there is some component that isn't receiving the signal that the gas input must be maintained or even increased. The higher input hardware that has been installed in this Vette is demanding more than what the original LS1 had to offer.
I will change the gas filter, but there could be something else that can be the culprit. Please advise...
In case there are other reasons for running lean, I request that anyone that has another possibility to please post it.
This is an early LS1, which has been upgraded over time and is using the original equipment, software and hardware. It seems to me that, if an engine is running perfectly well below 4k RPM and just after those RPMs are increased, the gas supply is decreased, there is some component that isn't receiving the signal that the gas input must be maintained or even increased. The higher input hardware that has been installed in this Vette is demanding more than what the original LS1 had to offer.
I will change the gas filter, but there could be something else that can be the culprit. Please advise...
Team Owner
Joined: Sep 2001
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From: Lake Elsinore, CA
Did you upgrade injectors? I went to 30 lb. SVT's (36 lb. on our fuel pressure) when I did a comparable upgrade to my engine a few years back due to hitting 100% duty cycle on the stock injectors.
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Team Owner
Joined: May 2003
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From: East Meadow NY
St. Jude Donor '12
I have a question for those saying he needs injectors. How would the injectors being too small cause a fuel pressure issue? He may still need them for his build but I am just confused on how that would cause a big drop in fuel pressure after 4k RPM. I can understand the going lean part but not sure I get how the pressure would get really low is all.
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From: San Juan Puerto Rico
I'm not trying to say that the injectors aren't the problem, I just would like to know what else could turn off the fuel supply. Maybe something electronic?
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
You may have an electrical issue with your fuel pump circuit. The circuit may not be providing enough current to run the pump properly umder a full load.
Use a meter and see if the voltage on the fuel pump fuses reads full battery voltage at all times. Then measure the voltage directly on the terminals on the tank to chassis ground.
If you have good voltages, do a fuel flow test on the pump. See if it flows the proper volume as observed from the shrader valbe on the end of the fuel rail.
NOTE! The fuel pump is powered by the IGNITION SWITCH Feed. Our C5 Ignition switches are FAMOUS for failing and not properly powering circuits. CHECK THAT VOLTAGE on the fuse and pump.
2002 fuel pump circuit. Thats all I have acccess to at work:::
Use a meter and see if the voltage on the fuel pump fuses reads full battery voltage at all times. Then measure the voltage directly on the terminals on the tank to chassis ground.
If you have good voltages, do a fuel flow test on the pump. See if it flows the proper volume as observed from the shrader valbe on the end of the fuel rail.
NOTE! The fuel pump is powered by the IGNITION SWITCH Feed. Our C5 Ignition switches are FAMOUS for failing and not properly powering circuits. CHECK THAT VOLTAGE on the fuse and pump.
2002 fuel pump circuit. Thats all I have acccess to at work:::
Burning Brakes
Joined: Jul 2006
Posts: 968
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From: Regina Sask
Your stock injectors are more than adequate for your car. As mentioned, replace the fuel filter. And as Bill pointed out, check for at least 12V at the fuel pump with the engine idling.
My 418 stroker still has the stock fuel pump & maintains 56 psi at WOT @7000 rpm. And I have 36 lb/hr Bosch injectors.
This is a 1998 C5 fuel pump schematic.
Russ Kemp
My 418 stroker still has the stock fuel pump & maintains 56 psi at WOT @7000 rpm. And I have 36 lb/hr Bosch injectors.
This is a 1998 C5 fuel pump schematic.
Russ Kemp
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From: San Juan Puerto Rico
My son has a 99 Camaro with exactly the same early LS1 engine as mine, which went though almost the exact level of upgrading as mine did and he didn't change anything on it. He kept the same fuel pump and injectors. His car was tuned and is working nicely. We have a race in store so I need to get my C5 ready soon...
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Joined: Nov 2007
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From: San Juan Puerto Rico
Your stock injectors are more than adequate for your car. As mentioned, replace the fuel filter. And as Bill pointed out, check for at least 12V at the fuel pump with the engine idling.
My 418 stroker still has the stock fuel pump & maintains 56 psi at WOT @7000 rpm. And I have 36 lb/hr Bosch injectors.
This is a 1998 C5 fuel pump schematic.
Russ Kemp
My 418 stroker still has the stock fuel pump & maintains 56 psi at WOT @7000 rpm. And I have 36 lb/hr Bosch injectors.
This is a 1998 C5 fuel pump schematic.
Russ Kemp
I appreciate greatly your input. The checking of the circuit is a little above my tech skills but I have a good friend that can help me there. I'll get right on it this week end.
I did do the Racetronix fuel pump harness install and it's running directly from the alternator. As I read about it, by being connected directly to the alternator it is supposed to get more than 12 volts, closer to 12.5 to 13.
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Joined: Nov 2007
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From: San Juan Puerto Rico
Burning Brakes
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From: Regina Sask