Can a coil go kinda bad?

[y5mgisi]

Trying to figure out why my gmc just started running bad. Without going into crazy detail, can a coil go kinds bad? It's a 78 with hei. Can it go bad to where it sparks poorly at idle but works pretty much ok other wise? And can it go back and forth between working fine and working bad without failing all together?

 

[lectric80]

I would be looking for a bad connection at this point. At idle most of our vehicles run a bit rougher than they do when we are driving, and that may be causing an intermittent break in one of the connections. Check all the wires going into the distributor to see if one of them has been loosened up, or if one is under high tension somewhere.

From there check the coil itself, and clean up the contacts to help.

Coils are pretty solid, and I don't believe they can go kinda bad, it is more an all or nothing type of deal.

Of course now someone will post up that they had the same thing happen and it was the coil.

 

[y5mgisi]

Well I just don't understand cause I did a tune up(cap rotor plugs and wires) and it ran amazing. Ultra smooth. Then all the sudden it runs bad. And if that weren't enough, on the way home from work tonight it ran perfect again!

 

[lectric80]

That would make me look very closely for a bad connection. The cap you put on would have required you to use the coil from the old cap, right? If so it may be a bad connection where the coil hooks to the cap, or one of the wires might just be a bit loose connecting to the distributor.

 

[Jason4x4]

did u put the little nub that connects the cap to the coil in correctly?

 

[jsasada81]

Maybe your EGR valve is dirty causing it to not open and close properly. THat may explain the running rough one minue and running smooth the next the next... Although usually, when the EGR is bad it will not idle at all.

 

[abig85]

yeah ive had it happen. pretty much what you discribed. the truck ran like, crap at idle. but ok when driving. i swapped it out and kept it in the truck as a spare. actually needed it a few years later and it got me home running like crap the whole way.

also had a cracked one in a s10, truck would die on me when it was humid out alot

 

[Hubnut]

Yes my coil was bad and doing something similar to yours. Ran okay at idle, but at speed it was sputtering. Like it wasn't getting fuel. Pulled the coil and it had separated--inner piece was sliding inside causing poor current sometimes. It was an intermittent problem for me. Changed it out and ran great since. It's a cheap and easy fix too. Change it.

 

[jonathon]

Yep they can.... usually it's due to corrosion causing the spark to find other paths to ground. My stock one was shorting on the intake, causing some odd shifting patterns in my 4L80E and it just didn't run quite right because of that.

Put in a new MSD Coil and all was good I'd highly recommend it.. only $20 or so more than the parts store cheapy, but very good quality.

 

[LOGANSTANFORTH]

my coil is messing up and it breaks up bad when i get it hot......i know the feeling.....