Engine running ruff after setting 78 L82
Thread Starter
Burning Brakes
Joined: Jul 2017
Posts: 1,114
Likes: 149
From: Frisco TX
Engine running ruff after setting 78 L82
My engine started running rough today. I think it has been several weeks since I drove it. I does have a full tank of gas.
I pulled on of the spark plugs and it look great.
I never have had a gass problem before if this s what it is.
Any thoughts or suggestions?
Thanks in advance for your help.
I pulled on of the spark plugs and it look great.
I never have had a gass problem before if this s what it is.
Any thoughts or suggestions?
Thanks in advance for your help.
Thread Starter
Burning Brakes
Joined: Jul 2017
Posts: 1,114
Likes: 149
From: Frisco TX
Race Director
Joined: Mar 2017
Posts: 11,923
Likes: 4,495
From: Virginia
The last time my engine ran rough, the vac advance was plugged into ported vacuum, and it could barely idle at all. Oops, that was my fault. Easy fix! Only at idle, though.
If your distributor hold down is loose, you can lose timing, and that will affect you at all RPMs.
While you're in there with your timing light, you may find something obvious. Please post some photos! You'd be surprised what the Forum can notice.
Drifting
Joined: Jul 1999
Posts: 1,542
Likes: 43
From: Plano TX
Had that happen to a couple of vehicles with HEI. Would start fine then begin to run rough after the engine warmed. Found it to be a typical HEI module failure mode.
Of course there can be other causes but the module can suddenly fail into a running rough condition. With cap moved out of the way remove the rotor to see if rust like particles are on bottom of rotor and advance weights. If so sparks can leak through rotor to the module over time.
Key to this is it runs OK until warm.
Of course there can be other causes but the module can suddenly fail into a running rough condition. With cap moved out of the way remove the rotor to see if rust like particles are on bottom of rotor and advance weights. If so sparks can leak through rotor to the module over time.
Key to this is it runs OK until warm.
Race Director
Joined: Nov 2006
Posts: 13,177
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From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
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Cruise-In VIII Veteran
Well, you looked at one spark plug and you say.it looks fine. What about the other 7?
Ran fine, then you let it sit for several weeks. most likely a fuel issue. But that's certainly not carved in stone.
3 things make your engine run. Compression, spark, and fuel. Not really likely your Compression would suffer in just a few weeks. A year or so, very much so.
So, just a few weeks, rule that out.
Fuel can and does go stale, creating varnish and gum in the fuel system. Low hanging fruit, remove and properly clean the carburetor and check all it circuits and operation.
Another low hanging fruit kinda thing, remove the distributor cap and look inside. Moisture inside cap?
Ran fine, then you let it sit for several weeks. most likely a fuel issue. But that's certainly not carved in stone.
3 things make your engine run. Compression, spark, and fuel. Not really likely your Compression would suffer in just a few weeks. A year or so, very much so.
So, just a few weeks, rule that out.
Fuel can and does go stale, creating varnish and gum in the fuel system. Low hanging fruit, remove and properly clean the carburetor and check all it circuits and operation.
Another low hanging fruit kinda thing, remove the distributor cap and look inside. Moisture inside cap?
Thread Starter
Burning Brakes
Joined: Jul 2017
Posts: 1,114
Likes: 149
From: Frisco TX
Had that happen to a couple of vehicles with HEI. Would start fine then begin to run rough after the engine warmed. Found it to be a typical HEI module failure mode.
Of course there can be other causes but the module can suddenly fail into a running rough condition. With cap moved out of the way remove the rotor to see if rust like particles are on bottom of rotor and advance weights. If so sparks can leak through rotor to the module over time.
Key to this is it runs OK until warm.
Of course there can be other causes but the module can suddenly fail into a running rough condition. With cap moved out of the way remove the rotor to see if rust like particles are on bottom of rotor and advance weights. If so sparks can leak through rotor to the module over time.
Key to this is it runs OK until warm.
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Thread Starter
Burning Brakes
Joined: Jul 2017
Posts: 1,114
Likes: 149
From: Frisco TX
Well, you looked at one spark plug and you say.it looks fine. What about the other 7?
Ran fine, then you let it sit for several weeks. most likely a fuel issue. But that's certainly not carved in stone.
3 things make your engine run. Compression, spark, and fuel. Not really likely your Compression would suffer in just a few weeks. A year or so, very much so.
So, just a few weeks, rule that out.
Fuel can and does go stale, creating varnish and gum in the fuel system. Low hanging fruit, remove and properly clean the carburetor and check all it circuits and operation.
Another low hanging fruit kinda thing, remove the distributor cap and look inside. Moisture inside cap?
Ran fine, then you let it sit for several weeks. most likely a fuel issue. But that's certainly not carved in stone.
3 things make your engine run. Compression, spark, and fuel. Not really likely your Compression would suffer in just a few weeks. A year or so, very much so.
So, just a few weeks, rule that out.
Fuel can and does go stale, creating varnish and gum in the fuel system. Low hanging fruit, remove and properly clean the carburetor and check all it circuits and operation.
Another low hanging fruit kinda thing, remove the distributor cap and look inside. Moisture inside cap?
Le Mans Master
Joined: Jun 2019
Posts: 7,649
Likes: 2,466
From: Indiana
i don't think 2 weeks will have gas turn but maybe..
sitting and moisture / drying may expose some weakness.. spark plug wires, cap , module, etc..
Maybe more detail on how running rough? idle, driving, hot cold etc..
sitting and moisture / drying may expose some weakness.. spark plug wires, cap , module, etc..
Maybe more detail on how running rough? idle, driving, hot cold etc..
Burning Brakes
Joined: Dec 2017
Posts: 1,043
Likes: 414
2023 C3 of the Year Finalist - Modified
Thread Starter
Burning Brakes
Joined: Jul 2017
Posts: 1,114
Likes: 149
From: Frisco TX
It starts ok but runs rough especially at low speeds. It possible it cold be any of the items you listed. But it's kept in my grarageand we have pretty low humidity here in north Texas.
Racer
Joined: Dec 2022
Posts: 299
Likes: 87
Probably more like 3-4 weeks since I drove it. The last time I drove it I filled it with gas from the same station I always use.
It starts ok but runs rough especially at low speeds. It possible it cold be any of the items you listed. But it's kept in my grarageand we have pretty low humidity here in north Texas.
It starts ok but runs rough especially at low speeds. It possible it cold be any of the items you listed. But it's kept in my grarageand we have pretty low humidity here in north Texas.
Thread Starter
Burning Brakes
Joined: Jul 2017
Posts: 1,114
Likes: 149
From: Frisco TX
The module would still work but cause a rough engine? Is there anyway to test the module to see if that could be the issue?
Drifting
Joined: Jul 1999
Posts: 1,542
Likes: 43
From: Plano TX
No easy way to test the module. I used to keep a spare for a quick swap test. Other components in the distributor like the main coil and pickup coil can be checked with an ohm meter. I used to carry a spare distributor in some of my vehicles when on long trips.
When you first start the car does it run normal at idle? If you drive it right away does it seem OK but then get worse as the engine warms up?
When you first start the car does it run normal at idle? If you drive it right away does it seem OK but then get worse as the engine warms up?
Thread Starter
Burning Brakes
Joined: Jul 2017
Posts: 1,114
Likes: 149
From: Frisco TX
No easy way to test the module. I used to keep a spare for a quick swap test. Other components in the distributor like the main coil and pickup coil can be checked with an ohm meter. I used to carry a spare distributor in some of my vehicles when on long trips.
When you first start the car does it run normal at idle? If you drive it right away does it seem OK but then get worse as the engine warms up?
When you first start the car does it run normal at idle? If you drive it right away does it seem OK but then get worse as the engine warms up?
Safety Car
Joined: May 2001
Posts: 4,747
Likes: 1,642
From: Fairfax Virginia
That sure sounds like a HEI Ignition Controller or the Ignition Coil itself. Have you run the engine in the dark and had the hood open? That shows the "voltage leaks" from the spark plug wires. It is a simple test and very helpful just to be sure. The last time I did that I had leaks all over the place.
I have a 1988 Corvette that has an HEI ignition and therefore I keep older ignition modules as well. I am using parts from D.U.I. like their ignition coil, distributor cap with a stock Module. I keep a spare Ignition coil, Distributor Cap and Ignition Module in my garage as I am not that impressed with the longevity of the components.
I have a 1988 Corvette that has an HEI ignition and therefore I keep older ignition modules as well. I am using parts from D.U.I. like their ignition coil, distributor cap with a stock Module. I keep a spare Ignition coil, Distributor Cap and Ignition Module in my garage as I am not that impressed with the longevity of the components.
Thread Starter
Burning Brakes
Joined: Jul 2017
Posts: 1,114
Likes: 149
From: Frisco TX
That sure sounds like a HEI Ignition Controller or the Ignition Coil itself. Have you run the engine in the dark and had the hood open? That shows the "voltage leaks" from the spark plug wires. It is a simple test and very helpful just to be sure. The last time I did that I had leaks all over the place.
I have a 1988 Corvette that has an HEI ignition and therefore I keep older ignition modules as well. I am using parts from D.U.I. like their ignition coil, distributor cap with a stock Module. I keep a spare Ignition coil, Distributor Cap and Ignition Module in my garage as I am not that impressed with the longevity of the components.
I have a 1988 Corvette that has an HEI ignition and therefore I keep older ignition modules as well. I am using parts from D.U.I. like their ignition coil, distributor cap with a stock Module. I keep a spare Ignition coil, Distributor Cap and Ignition Module in my garage as I am not that impressed with the longevity of the components.