Bad HEI Ignition Module or Coil?
Thread Starter
Instructor
Joined: Jan 2017
Posts: 175
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Bad HEI Ignition Module or Coil?
My 1974 corvette just started running rough yesterday when I went to drive it. It started fine, but it would not idle correctly, the rpms would not drop, and the car was very hesitant when I pressed the accelerator. So I bought a new rotor, cap, coil and module. From what I've read, if the car starts with no problems, and then idles and accelerates roughly then it is a control module.
Is it safe to assume that I only need to replace the rotor, cap and ignition module? or should I replace the coil as well? Also, could I still use my OLD HEI coil? it is only like a year old and hasn't been used much.
Is it safe to assume that I only need to replace the rotor, cap and ignition module? or should I replace the coil as well? Also, could I still use my OLD HEI coil? it is only like a year old and hasn't been used much.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
OP when you say "would not idle correctly" And "rpm would not drop" ...
Most will idle high at first until choke pulls off ... do you mean yours idles high but does Not drop as expected ?
Most will idle high at first until choke pulls off ... do you mean yours idles high but does Not drop as expected ?
Race Director
Joined: Mar 2017
Posts: 11,944
Likes: 4,506
From: Virginia
Before throwing too many more parts at it, have you checked the timing, and the ignition wire routing? This could be a carb issue, too, especially if your choke never opens fully and you never drops off of the high-idle cam.
Email @lars for his timing papers (there are dozens of example threads on this Forum), and use a digital timing light to check that you are set up correctly (this will not be exactly the way it came from the factory, it will be much better).
Email @lars for his timing papers (there are dozens of example threads on this Forum), and use a digital timing light to check that you are set up correctly (this will not be exactly the way it came from the factory, it will be much better).
Thread Starter
Instructor
Joined: Jan 2017
Posts: 175
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This problem suddenly happened to me. I drive it usually twice a week and I just went out there yesterday and fired it up it it started giving me trouble. That is what makes think it is the module and/or the coil. I feel like if the carb was bad the idling and driving problems would have been gradually noticed.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Carb issues are really IGN gremlins.
False ignition issues, are usually fuel related.
Modules usually fail like an ON / OFF switch and are usually heat related. Such as a fully warmed up car that is trying to restart. The electrical contacts inside the "Modge" will expand and loose conductivity. Once cooled off, contact is restored.
Your coil is likely fine at only a yr old. The modge can be tested at your favorite car parts box store.
But just for piece of mind: Remove four plugwires off one side of the distributor cap. Unlock cap and lay it on its side. Take a dry paper towel and wipe the entire inside of it and the tip of the rotor, plus the center of the rotor. This will remove any moisture and carbon tracking.
False ignition issues, are usually fuel related.
Modules usually fail like an ON / OFF switch and are usually heat related. Such as a fully warmed up car that is trying to restart. The electrical contacts inside the "Modge" will expand and loose conductivity. Once cooled off, contact is restored.
Your coil is likely fine at only a yr old. The modge can be tested at your favorite car parts box store.
But just for piece of mind: Remove four plugwires off one side of the distributor cap. Unlock cap and lay it on its side. Take a dry paper towel and wipe the entire inside of it and the tip of the rotor, plus the center of the rotor. This will remove any moisture and carbon tracking.
Last edited by HeadsU.P.; Dec 23, 2019 at 12:38 PM.
Thread Starter
Instructor
Joined: Jan 2017
Posts: 175
Likes: 14
Ok j just drove my car and it does feel better with a new coil and module, BUT i did adjust the carb and it did improve the quality of driving but not by much. So I think it may a fuel issue.
my problem is that I do not have tools to drain all the fuel, I only have half a tank so I will drive it until it’s almost empty and then just fill up and then go from there.
I opened the tank and the fuel smelled bad, plus I’ve had that fuel in there for about 2 months now.
Thanks for the help!
my problem is that I do not have tools to drain all the fuel, I only have half a tank so I will drive it until it’s almost empty and then just fill up and then go from there.
I opened the tank and the fuel smelled bad, plus I’ve had that fuel in there for about 2 months now.
Thanks for the help!
Carb issues are really IGN gremlins.
False ignition issues, are usually fuel related.
Modules usually fail like an ON / OFF switch and are usually heat related. Such as a fully warmed up car that is trying to restart. The electrical contacts inside the "Modge" will expand and loose conductivity. Once cooled off, contact is restored.
Your coil is likely fine at only a yr old. The modge can be tested at your favorite car parts box store.
But just for piece of mind: Remove four plugwires off one side of the distributor cap. Unlock cap and lay it on its side. Take a dry paper towel and wipe the entire inside of it and the tip of the rotor, plus the center of the rotor. This will remove any moisture and carbon tracking.
False ignition issues, are usually fuel related.
Modules usually fail like an ON / OFF switch and are usually heat related. Such as a fully warmed up car that is trying to restart. The electrical contacts inside the "Modge" will expand and loose conductivity. Once cooled off, contact is restored.
Your coil is likely fine at only a yr old. The modge can be tested at your favorite car parts box store.
But just for piece of mind: Remove four plugwires off one side of the distributor cap. Unlock cap and lay it on its side. Take a dry paper towel and wipe the entire inside of it and the tip of the rotor, plus the center of the rotor. This will remove any moisture and carbon tracking.
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Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Two month old gas is nothing. Cars sit all winter, 6-8 months with same gas. However, you can bet that moisture is in the tank and fuel lines, fuel filter, etc. It goes with the territory with Ethanol.
Put a couple of ounces of Lucas Safe Guard anti-Ethanol treatment in the tank. (Walmart, green plastic bottle)
And Lucas,
Still waiting on my Christmas bonus - endorsement check.
Put a couple of ounces of Lucas Safe Guard anti-Ethanol treatment in the tank. (Walmart, green plastic bottle)
And Lucas,
Still waiting on my Christmas bonus - endorsement check.
Last edited by HeadsU.P.; Dec 23, 2019 at 06:46 PM.
Thread Starter
Instructor
Joined: Jan 2017
Posts: 175
Likes: 14
Two month old gas is nothing. Cars sit all winter, 6-8 months with same gas. However, you can bet that moisture is in the tank and fuel lines, fuel filter, etc. It goes with the territory with Ethanol.
Put a couple of ounces of Lucas Safe Guard anti-Ethanol treatment in the tank. (Walmart, green plastic bottle)
And Lucas,
Still waiting on my Christmas bonus - endorsement check.
Put a couple of ounces of Lucas Safe Guard anti-Ethanol treatment in the tank. (Walmart, green plastic bottle)
And Lucas,
Still waiting on my Christmas bonus - endorsement check.
Safety Car
Joined: Jan 2004
Posts: 4,549
Likes: 343
From: Glastonbury CT
Just drain the tank with a cheap Harbor Freight punp into a container and ask your local gas station if he will dispose of it. Another item in your fuel tank on the float there is an item called the sock. If you add lucas or stal bil it will act as a jell and clog your fuel delivery.even more. So pump it out because the ethanol today will gum up every rubber or vitrol fitting in your tank and carburetor. A lot of people do not read the gas station pump labels as far as ethanol content. Some as low as 5% and as high as 20%. That 93 High Test gas does have better additives in it then some of the generic gas stations
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
I have never had any issues with Lucas Safe Guard and my gas tank sits for 8 months. But with any additive in the gas tank, you can't just pour it in and expect it to mix well. You need to swish things around, mix thoroughly.
Last edited by HeadsU.P.; Dec 23, 2019 at 09:59 PM.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Seafoam is a great product, but I use it in the summer as a fuel system cleaner. Half a bottle down the carb of running engine, half bottle in the tank. But you can do what you want.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Drain or run it near-empty ... then visit a local Small airport which primarily caters to General Aviation (private pilots) ... fill with $ Aviation Gasoline.
AV gas contains relatively high levels of solvents such as toluene/benzene; AV gas is very effective for dissolving gum-varnish; keep it off your paint.
You'll notice how AV gas smells different from pump gas and how a little on your hands evaporates quickly & temporarily leaves them rather "dry."
Merry Christmas
AV gas contains relatively high levels of solvents such as toluene/benzene; AV gas is very effective for dissolving gum-varnish; keep it off your paint.
You'll notice how AV gas smells different from pump gas and how a little on your hands evaporates quickly & temporarily leaves them rather "dry."
Merry Christmas
Thread Starter
Instructor
Joined: Jan 2017
Posts: 175
Likes: 14
After reading all the comments and all I think it is either a carb issue or a an issue with ignition timing possibly.
For a carb that is bad, is it possible for it to work fine one day and the next day act all screwy and stuff? I’ve never had a carb do that before and like mentioned above I don’t want to throw extra unnecessary parts in.
Safety Car
Joined: Oct 2004
Posts: 3,926
Likes: 739
From: Youngstown Ohio
....Yes. I've had gremlins screw up my floats overnight for no apparent reason. As for the module, when I had one go bad, the car would not start at all.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
sometimes the "no apparent reason" is simply a bit of crap/crud/schmutz/sh7t partially or fully plugging an orifice or slot. Clean it out.
some times brass floats' seams fail or crack... leaking gas into them and sink; causing flooding.
some times polymer floats begin soaking up gas (gas-logged) then sinking; causing flooding.
some times brass floats' seams fail or crack... leaking gas into them and sink; causing flooding.
some times polymer floats begin soaking up gas (gas-logged) then sinking; causing flooding.