High rpm miss
 

Got a question about a friend's boat.........
'96 454 mag
Engine starts to miss at high rpms after running for awhile ( heating up). Eventually gets to where will only idle...... Not a fuel problem. After it sets for awhile, runs ok for awhile. Defininately sounds like some kind of ignition miss.

Have changed dist. cap, rotor, plugs, wires, coil.....no help.
Ignition module? , bad tach?
Any ideas appreciated.

Thanx, George

George sounds like the box is bad !

Since all the basics have been replaced, I would guess that the ignition module is getting hot and going bad. Probably not advancing the timing like it should.

Also check the ground connections on the module.

Could be the coil too. They get hot when run for long periods, especially if they are going bad. Will cause a miss.

I relocated my ignition module to the transom, just be sure to run a ground to it. Less heat buildup. Mounted to a hot exhaust manifold seems like a bad place for an electronic component.

The module is the next thing he's gonna swap. I have a spare T-IV , but his was different. It actually has 2 "boxes" bolted next to the distributor that have plugs. One was a GM part, the other was a Nippon!.........T-V?
I tried advancing the timing while running when it started missing, only helped a little. Figured if the "box"was going bad, it was interupting the signal to the dist....??
My thoughts anyway:confused:
Thanx for the input

George

I would have hollered "coil" immediately if I hadn't read that you already had replaced it...

I know this might sound stupid, but do you find any moisture in the distributor, is it a marine distributor? I had some problems similiar to mine and it was somehow getting moisture inside and causing it to miss at high rpms. I replaced the distributor with a Billet MSD and no more problems.

I looked at the dist. right after we shut it down........it was dry. Also checked the "pickup" inside the dist. for cracks, corrosion, etc. .......everything looked new.

Appreciate all the ideas / input.
Gonna try a new module later this week if weather holds, will let ya know what we find.

Thanx, George.