Engine cutting out when hot
Thread Starter
2nd Gear
Joined: Apr 2014
Posts: 2
Likes: 0
Engine cutting out when hot
Hi All........has anyone encountered the frustrating issue of their engine cutting off when the engine is hot, especially on a hot day? We brought a 1979 C3 to Australia from California, so she is used to pretty extreme heat. We have installed a new HEI distributor and new fuel filter thinking that would solve the problem but it hasn't. If the engine is allowed to cool, maybe 15 mins or so, she starts back up just fine and runs beautifully. Thanks in advance 
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Most likely candidates are 1) failing ignition module in the HEI distributor; 2) failing coil in the distributor cap; 3) electrical connections in the distributor cap losing good contact when heated.
Advice: Don't buy low-dollar ignition parts from the 'basic' auto parts stores (or GM parts...which are ALL foreign made, now). Get "best" quality stuff at NAPA or a reputable local parts outlet.
Advice: Don't buy low-dollar ignition parts from the 'basic' auto parts stores (or GM parts...which are ALL foreign made, now). Get "best" quality stuff at NAPA or a reputable local parts outlet.
Melting Slicks
Joined: Feb 2006
Posts: 3,105
Likes: 96
From: Sunrise FL
If you installed a complete HEI AFTER the problem started, that shows its not in the coil/module.
When it cuts out, use a test light and probe the power feed to the HEI.
I would make sure its not a fuel issue too.
When it cuts out, use a test light and probe the power feed to the HEI.
I would make sure its not a fuel issue too.
Race Director
Joined: Mar 2016
Posts: 14,406
Likes: 8,212
From: Napa Valley California
Could be the fuel tank is not venting properly and it's starving for fuel. Try removing the fuel cap when it's warmed up and running rough. If you hear air sucking into the tank when you remove the cap, start checking there. If it is carbureted, check to be sure the choke is functioning correctly. Good Luck
Last edited by OldCarBum; Dec 12, 2016 at 01:12 PM.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
You could also have some problem with fuel percolating. Ethanol has a lower boiling point and can cause problems when the fuel gets too warm. Several items can be addresssed to help cool the carb and/or fuel:
1) Make sure the heat riser valve (exhaust manifold outlet) is opening when the engine is warm (or is blocked permanently open). That will minimize heat in the intake manifold crossover channel (under the carb). It is also possible to install an insulator plate between carb and manifold to limit carb heating.
2) Insulate the metal line running from fuel pump to carb. A foam tube used to insulate home air conditioner refrigerant lines would work; or a wrap of some open-cell foam with metal foil tape to retain it could do that job.
1) Make sure the heat riser valve (exhaust manifold outlet) is opening when the engine is warm (or is blocked permanently open). That will minimize heat in the intake manifold crossover channel (under the carb). It is also possible to install an insulator plate between carb and manifold to limit carb heating.
2) Insulate the metal line running from fuel pump to carb. A foam tube used to insulate home air conditioner refrigerant lines would work; or a wrap of some open-cell foam with metal foil tape to retain it could do that job.
Race Director
Joined: Mar 2016
Posts: 14,406
Likes: 8,212
From: Napa Valley California
This was a problem in many '70's vehicles where I grew up in the California desert. General Motors installed metal heat shields between the intake manifold and carburetor. some people took them off, only to reinstall them when the summer heat returned.
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Thread Starter
2nd Gear
Joined: Apr 2014
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Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
I would pull off the air cleaner, look down the carb and see if gas squirts in when you depress the gas pedal, if not then it's a fuel issue, could be vapor lock, plugged fuel filter or filter sock in the tank.
If there are 2 streams of gas going in when you depress the pedal, then look for an ignition problem, loss of spark.
If there are 2 streams of gas going in when you depress the pedal, then look for an ignition problem, loss of spark.
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
I would pull off the air cleaner, look down the carb and see if gas squirts in when you depress the gas pedal, if not then it's a fuel issue, could be vapor lock, plugged fuel filter or filter sock in the tank.
If there are 2 streams of gas going in when you depress the pedal, then look for an ignition problem, loss of spark.
If there are 2 streams of gas going in when you depress the pedal, then look for an ignition problem, loss of spark.
Shipping may have finished off the filter sock. Or the pump is sucking air. Check hoses out of tank and at the fuel pump.Sounds like fuel to me. Perhaps float level, float is stuck. A few things to check.
Melting Slicks
Joined: Jun 2016
Posts: 2,979
Likes: 332
From: Woodinville WA
There are a few old really long threads on here with people troubleshooting these issues on this era C3s.
In my recollection vapor lock and dying starters from being over heated were the 2 most common causes.
My C3 has the same problem but the starter doesn't turn over like yours (mine issue is the starter). I want to use a lightweight starter but I know there's fitment issues with some stepped starters and my Steeroid rack and pinion and I haven't figured out what starters will work.
Try the heat riser fixes and insulating spacer that 7T1Vette mentioned.
In my recollection vapor lock and dying starters from being over heated were the 2 most common causes.
My C3 has the same problem but the starter doesn't turn over like yours (mine issue is the starter). I want to use a lightweight starter but I know there's fitment issues with some stepped starters and my Steeroid rack and pinion and I haven't figured out what starters will work.
Try the heat riser fixes and insulating spacer that 7T1Vette mentioned.
Last edited by NewbVetteGuy; Dec 12, 2016 at 06:48 PM.
Melting Slicks
Joined: May 2011
Posts: 2,753
Likes: 119
From: Springfield Missouri
check the fuel pump "S" hose, that someone did not replace the fuel line with a straight piece of line. This needs to be the molded hose(anyway on my 76 it does) or else when it gets warm under the hood the hose will kink(ask me how I know).
Drifting
Joined: Aug 2009
Posts: 1,346
Likes: 160
From: new iberia la
You could also have some problem with fuel percolating. Ethanol has a lower boiling point and can cause problems when the fuel gets too warm. Several items can be addresssed to help cool the carb and/or fuel:
1) Make sure the heat riser valve (exhaust manifold outlet) is opening when the engine is warm (or is blocked permanently open). That will minimize heat in the intake manifold crossover channel (under the carb). It is also possible to install an insulator plate between carb and manifold to limit carb heating.
2) Insulate the metal line running from fuel pump to carb. A foam tube used to insulate home air conditioner refrigerant lines would work; or a wrap of some open-cell foam with metal foil tape to retain it could do that job.
1) Make sure the heat riser valve (exhaust manifold outlet) is opening when the engine is warm (or is blocked permanently open). That will minimize heat in the intake manifold crossover channel (under the carb). It is also possible to install an insulator plate between carb and manifold to limit carb heating.
2) Insulate the metal line running from fuel pump to carb. A foam tube used to insulate home air conditioner refrigerant lines would work; or a wrap of some open-cell foam with metal foil tape to retain it could do that job.
percolation is a real problem here too.. very very hot summers will literally boil the fuel in the carb and the line.. vaporized fuel won t do
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,754
From: Charlotte NC
I would pull off the air cleaner, look down the carb and see if gas squirts in when you depress the gas pedal, if not then it's a fuel issue, could be vapor lock, plugged fuel filter or filter sock in the tank.
If there are 2 streams of gas going in when you depress the pedal, then look for an ignition problem, loss of spark.
If there are 2 streams of gas going in when you depress the pedal, then look for an ignition problem, loss of spark.
and waiting on a reply.Also posting a good photo of your carb so we can see if you have the thick base gasket installed with it on the intake would be great also so we can see what you have going on.
I assume you can drive your Corvette with NO problems until the fuel runs out? And then the only time you are having a problem is when you go to restart it????
FOR WHAT IT IS WORTH:
This is a for real. I had customer who could drive his Corvette with a full tank of gas and drive it until it went dry. Thus letting me know FUEL was not an issue....or at least that is what I thought.
Anytime he drove it and it got hot and shut it off...he had to let it sit and cool down and it would finally restart and he could drive it for how long he wanted. But restarting it after it was hot and shut off...it just wouldn't do it.
After much investigation....I FINALLY FOUND that the fuel pump push rod was worn...and looking up in the engine I could see the cam lobe on the cam was worn badly....and thus...is was not getting the fuel needed when it was HOT...but it was odd that he could drive it even if it was hot and he could drive it. I still have the cam and push rod to show people.
DUB