1976 Corvette sputtering, dying randomly
Thread Starter
Cruising
Joined: Jan 2017
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1976 Corvette sputtering, dying randomly
My 1976 Corvette L48 is having an odd issue. It drives fine when cold, but it seems that after its warm it will randomly start sputtering, almost as if its not getting enough fuel. It comes and goes randomly, but seems to get worse under harder acceleration. After it starts sputtering, it becomes extremely sluggish, if you give it gas, it will die.
I have a clear fuel filter right before the carb and it is staying full. It has a new electric fuel pump (I converted it), took the sock out of the fuel tank, all new lines. The car also has a new thermostat, coil pack, plugs, and wires. I tested spark while its sputtering and it is good.
I feel like I've replaced every part possible. Any ideas? My buddy seems to think its an electrical part overheating, because when its sputtering, if you open the hood and let the heat out, it will return to running normal. I'm not sure about this though.
Thanks for your help!
I have a clear fuel filter right before the carb and it is staying full. It has a new electric fuel pump (I converted it), took the sock out of the fuel tank, all new lines. The car also has a new thermostat, coil pack, plugs, and wires. I tested spark while its sputtering and it is good.
I feel like I've replaced every part possible. Any ideas? My buddy seems to think its an electrical part overheating, because when its sputtering, if you open the hood and let the heat out, it will return to running normal. I'm not sure about this though.
Thanks for your help!
Race Director
Joined: May 2006
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which carburetor are you using and which electric fuel pump?
what intake manifold are you using?
did the car have a fuel return line and are you still using it?
is there any kind of insulator between the carburetor and the intake manifold?
what intake manifold are you using?
did the car have a fuel return line and are you still using it?
is there any kind of insulator between the carburetor and the intake manifold?
Thread Starter
Cruising
Joined: Jan 2017
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Not sure on carb but I believe it is the stock one (Ill check when i get home). 5-9 psi inline fuel pump, stock intake, I am not using the fuel return line but it did have one, and there is still what looks like the factory spacer between the carb and intake.
What is the HEI module? I replaced the ignition coil with an Accel performance one... don't know if that matters or not.
What is the HEI module? I replaced the ignition coil with an Accel performance one... don't know if that matters or not.
Le Mans Master
Joined: Dec 2006
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http://www.speedwaymotors.com/Accel-...Fd64wAod2mkKuw
Accel ain't my thing, but GM still makes them, as do DUI.
Le Mans Master
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From: Hermosa
These guys already hit on two items I would check, module and spacer to prevent fuel boiling.
One other item is the fuel pressure. the Q-jet does not like too much pressure. 3-5 psi is about the max. 5-9 psi might be forcing the float needle off the seat and flooding the engine. Fine when it's cold as it needs more fuel to run then, once warmed up though it would flood the engine.
Look for fuel around the air horn or fuel getting forced into the primary venturies after it dies.
One other item is the fuel pressure. the Q-jet does not like too much pressure. 3-5 psi is about the max. 5-9 psi might be forcing the float needle off the seat and flooding the engine. Fine when it's cold as it needs more fuel to run then, once warmed up though it would flood the engine.
Look for fuel around the air horn or fuel getting forced into the primary venturies after it dies.
Race Director
Joined: May 2006
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your modifications are somewhat self defeating. The return line is there to prevent fuel peculation and as stated if you are running as much as 9 PSI on a Quadrajet you have too much pressure.
you replaced the ignition coil in the HEI distributor cap?
the module is inside the HEI distributor and can fail when hot.
you replaced the ignition coil in the HEI distributor cap?
the module is inside the HEI distributor and can fail when hot.
Thread Starter
Cruising
Joined: Jan 2017
Posts: 11
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Thank you all for your help. It is the Quadrajet carb still on there. Today I replaced the HEI module inside the distributor. Still no relief from this issue.
The more I mess with it the more it seems like a fuel issue. The way it sputters and tries to grab and dies, seems like either too much or not enough. Now, the fuel filter only stays about 1/3 full at all times.
The reason I converted to electric was the mechanical one stopped working. Replaced it with an oem pump but no luck. I tested the pumps by hand and they were indeed working. Something internally must be wrong. So I bolted a block off plate there and added the electric one. Tomorrow I'll try slightly pinching the line with a clamp to decrease pressure and see if it helps. I'll also check for unburned fuel after it dies.
The more I mess with it the more it seems like a fuel issue. The way it sputters and tries to grab and dies, seems like either too much or not enough. Now, the fuel filter only stays about 1/3 full at all times.
The reason I converted to electric was the mechanical one stopped working. Replaced it with an oem pump but no luck. I tested the pumps by hand and they were indeed working. Something internally must be wrong. So I bolted a block off plate there and added the electric one. Tomorrow I'll try slightly pinching the line with a clamp to decrease pressure and see if it helps. I'll also check for unburned fuel after it dies.
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Le Mans Master
Joined: Dec 2006
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Thank you all for your help. It is the Quadrajet carb still on there. Today I replaced the HEI module inside the distributor. Still no relief from this issue.
The more I mess with it the more it seems like a fuel issue. The way it sputters and tries to grab and dies, seems like either too much or not enough. Now, the fuel filter only stays about 1/3 full at all times.
The reason I converted to electric was the mechanical one stopped working. Replaced it with an oem pump but no luck. I tested the pumps by hand and they were indeed working. Something internally must be wrong. So I bolted a block off plate there and added the electric one. Tomorrow I'll try slightly pinching the line with a clamp to decrease pressure and see if it helps. I'll also check for unburned fuel after it dies.
The more I mess with it the more it seems like a fuel issue. The way it sputters and tries to grab and dies, seems like either too much or not enough. Now, the fuel filter only stays about 1/3 full at all times.
The reason I converted to electric was the mechanical one stopped working. Replaced it with an oem pump but no luck. I tested the pumps by hand and they were indeed working. Something internally must be wrong. So I bolted a block off plate there and added the electric one. Tomorrow I'll try slightly pinching the line with a clamp to decrease pressure and see if it helps. I'll also check for unburned fuel after it dies.
Install a regulator, preferably with a return line. Try leaving the gas cap off in case its not vented.
Do you have a heat shield under the carb? Are the lines routed close to heat? This 10% alcohol **** boils easily.
Thread Starter
Cruising
Joined: Jan 2017
Posts: 11
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Crimping the line will decrease flow, not pressure. 5lbs is plenty.
Install a regulator, preferably with a return line. Try leaving the gas cap off in case its not vented.
Do you have a heat shield under the carb? Are the lines routed close to heat? This 10% alcohol **** boils easily.
Install a regulator, preferably with a return line. Try leaving the gas cap off in case its not vented.
Do you have a heat shield under the carb? Are the lines routed close to heat? This 10% alcohol **** boils easily.
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
Under the carb looks to be the factory heat shield. I rerouted the lines using rubber line from the auto parts store, and it is not up against any hot parts like manifold, engine block, etc. I'm going to find an inline fuel pressure regulator with a return and see if that does the trick. Should I look for one that regulates at 5 psi?