Engine missing
Thread Starter
Instructor
Joined: Oct 2013
Posts: 144
Likes: 24
From: New Jersey
Engine missing
My 80 L48 has developed a missing issue especially at
high speed under load. Tach needle starts bouncing around and engine misses and hesitates. it also then starts doing the same thing at lower speeds. It seems ok after startup until i put it under high load and then performance turns to crap. I recently replaced the coil as preventive maint and a bad control module. Any ideas? Is this fuel issue or ignition issue? Engine is stock all emissions are intact.
high speed under load. Tach needle starts bouncing around and engine misses and hesitates. it also then starts doing the same thing at lower speeds. It seems ok after startup until i put it under high load and then performance turns to crap. I recently replaced the coil as preventive maint and a bad control module. Any ideas? Is this fuel issue or ignition issue? Engine is stock all emissions are intact.
Team Owner
Joined: Jan 2007
Posts: 53,648
Likes: 878
From: Southern Cal Ca
St. Jude Donor '22
My 80 L48 has developed a missing issue especially at
high speed under load. Tach needle starts bouncing around and engine misses and hesitates. it also then starts doing the same thing at lower speeds. It seems ok after startup until i put it under high load and then performance turns to crap. I recently replaced the coil as preventive maint and a bad control module. Any ideas? Is this fuel issue or ignition issue? Engine is stock all emissions are intact.
high speed under load. Tach needle starts bouncing around and engine misses and hesitates. it also then starts doing the same thing at lower speeds. It seems ok after startup until i put it under high load and then performance turns to crap. I recently replaced the coil as preventive maint and a bad control module. Any ideas? Is this fuel issue or ignition issue? Engine is stock all emissions are intact.
How are the wires?
Under load misfire can signify plugs can't fire.
A saying is, 99 percent of carb problems are ignition.
The only thing left is the pickup coil in the dist.
Check for a weak spark.
good luck
Team Owner
Joined: Jan 2007
Posts: 53,648
Likes: 878
From: Southern Cal Ca
St. Jude Donor '22
You could have the wrong/bad coil. Or something isn't connected properly.
Last edited by calwldlife; Oct 9, 2021 at 09:31 PM.
Le Mans Master
Joined: Jan 2001
Posts: 6,742
Likes: 1,384
Yeah. Put the old coil back. I suggest next time you post a concern you start with information about what you changed last. When putting the old coil back ensure that all the connections are in good shape. More than likely it's the coil but it could also have been something you disturbed so just look over the leads that you disturbed.
...and I suggest that you don't change anything else so we can isolate the problem.
You could have also gotten a faulty module but that will be addressed after you return the old coil to service.
...and I suggest that you don't change anything else so we can isolate the problem.
You could have also gotten a faulty module but that will be addressed after you return the old coil to service.
Last edited by carriljc; Oct 10, 2021 at 02:30 AM.
Thread Starter
Instructor
Joined: Oct 2013
Posts: 144
Likes: 24
From: New Jersey
Ok thanks, I should have mentioned I changed the dist cap and rotor at the same time the coil was done. Its something i have done before and never had a problem. Anything I should double check concerning cap and rotor installation?
Le Mans Master
Joined: Aug 2017
Posts: 8,336
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From: Cool Northern Michigan
Most new coils have a coating on them to prevent rust. Which it does. But also may prevent a good connection.
On one corner of the coil, a black GRD wire attaches under the mounting bolt. Remove that and file off the paint until you see bare metal. Reattach.
It is imperative that the coil receives an excellent GRD.
I would also suspect improper reattachment of the four wire pigtail at the HEI distributor cap. Sometimes all those terminals don't line-up correctly for the harness.
The two wires in the front are Tach & 12V. But behind that is the larger four pin. Have the coil dust cover off and watch as the connectors are snapped in place.
And as Derek mentioned, the brass spring button under the coil may be wonky. Should have a rubber washer there also.
On one corner of the coil, a black GRD wire attaches under the mounting bolt. Remove that and file off the paint until you see bare metal. Reattach.
It is imperative that the coil receives an excellent GRD.
I would also suspect improper reattachment of the four wire pigtail at the HEI distributor cap. Sometimes all those terminals don't line-up correctly for the harness.
The two wires in the front are Tach & 12V. But behind that is the larger four pin. Have the coil dust cover off and watch as the connectors are snapped in place.
And as Derek mentioned, the brass spring button under the coil may be wonky. Should have a rubber washer there also.
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Safety Car
Joined: May 2001
Posts: 4,759
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From: Fairfax Virginia
I would focus some of your energy on the spark plug wires to be sure they are working properly. I have for decades used MSD Super Conductor 8mm wires but recently I had a set that was shorting to ground before the spark ever got to the spark plug. They are less than 6 months old and are shot. I am not impressed as that is the second set in two years that I have had issues with. MSD quality is not there anymore it seems when dealing with their spark plug wires.
They make a tool that has a adjustable gap for testing coils and sparks. It allows you to open the gap to see just how far it will reach and you can see the spark to tell if it is Yellow or Blue (provided you are not Color Blind like me)!
Like suggested above I would go back to the old coil and find the problem before fixing anything else. Coils are something that I have been replacing every few years as they (The Canister style) can fail just from the vibration it is exposed to.
DeOxIt will clean those connections down to the base metal under the corrosion!
They make a tool that has a adjustable gap for testing coils and sparks. It allows you to open the gap to see just how far it will reach and you can see the spark to tell if it is Yellow or Blue (provided you are not Color Blind like me)!
Like suggested above I would go back to the old coil and find the problem before fixing anything else. Coils are something that I have been replacing every few years as they (The Canister style) can fail just from the vibration it is exposed to.
DeOxIt will clean those connections down to the base metal under the corrosion!
Last edited by ctmccloskey; Oct 10, 2021 at 09:30 AM.
Thread Starter
Instructor
Joined: Oct 2013
Posts: 144
Likes: 24
From: New Jersey
Update: The "new" coil was bad. Replaced it with the 42 year old one and it runs fine.
I just noticed the made in Mexico "new" coil has a date of 1995 on the box and looks like its been sitting on shelf for 26 years.
I just noticed the made in Mexico "new" coil has a date of 1995 on the box and looks like its been sitting on shelf for 26 years.
Le Mans Master
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From: Indiana