chasing a miss
 

I've been chasing a high speed/load miss in my starboard motor all summer. So far I have changed everything in the ignition including cap, rotor,pick up sensor,wires and plugs. I have new fuel filters and checked the screens at the carb. I was told that a fuel pump going bad could cause this so tonight I changed the fuel pump. While picking up tools I found a piece of carbon like material under the alternator...now I've never had a alternator apart but I have taken electric motors apart and I'm thinking this might be a brush or something, could my alternator be causing my miss??? my motors are stock 330/454's

If the alternator is charging well, my guess would be no. I would first swap coils side to side, and if that doesn't work, swap distributors. but only one thing at a time. BTW Ya might want to take a real close look at the carb. Two years ago I was chasing a miss on my ski boat. And sure enough, one tiny air passage on the Holley carb was plugged. A little high pressure air and all has been well. It took a number of trips out to pin point it.



Darrell.

Do a leak down test.

Just for grins disconnect the tach. I had one that gave me all sorts of grief but only fro 3200 to 3900 rpm or so.

Fixx
 

Had a friend that had a miss at idle and the alternator puked so when he replaced it the miss went away..Check your valve springs also,i have seen them brake and still close the valve at idle but when you put a load on the engine it wouldn't keep the valve closed enough and blew the compression out the exhaust early and caused a miss..

I second the leak down test. I would also pull the valve covers and check for a broken spring. It happened to me several years ago, and would only miss at near full throttle.

I have had the gear at the end of the distributor wear-down to the point of no return.... also, had the iginition box go out on one of my engines, it would not advance the timing as you went to get on plane. ( making the engine sputter and choke ) my personal experiences, good luck with your search.

Upon further investigation the carbon like material was nothing. Checked the alternator and it was putting out 13.8 volts and I have new battery's. The frustrating part is it's not a consistent miss, sometimes it won't miss at all then sometimes only at high RPM than sometimes it miss at 2800-3200. I did disconnect the tach this weekend and run it a couple of times up and down the river and it didn't miss at all, I'll run it longer this week and see what happens.

I had a high rpm misfire on a supercharged street car. Same as you I changed most everything. It turned out to be the alternator. My guess is a diode was bad and the dc power was not clean enough and wacking out the electronics in the ignition. If you have a good battery try disconnecting the alternator and try it.

Found It!!!! I knew it would be a simple, stupid thing. :lolhit: It ended up being a loose plastic connector at the ICM. I wedged a piece of plastic on the side of it and ran good the rest of the day, now it won't drive me crazy all winter long and I can come up with a permanent fix