High RPM miss

kenewagner

Registered User
When I last raced the car at Earlville it had a bad missfiring at around 4000 RPM. I had thought it was a fouled plug. Along with a ton of other things to do to get the car back running I decided to change the plugs. I dont see anything that looks fouled on the plugs I pulled. Any thoughts as to why the car would have a bad miss. Even just before I pulled the old blower off I got on it and it was cutting out. Any imput is appriciated

Ken
 
Ken,
Plugs go bad without looking bad and when they are stressed --as in a high compression engine or a boosted one they can look perfectly normal and still misfire under heavy load or high rpm---only way to know for sure is change them and see if it gets better---if it does that was the problem and if it doesn't then you have some known good ones---the only way to actually tell from looking at the plugs is to do it at the track or on a dyno under a failing condition---if you drive them home and they do alright at cruising speeds they will cleanup before you get there and appear normal................Dan
 
Ken,
Plugs go bad without looking bad and when they are stressed --as in a high compression engine or a boosted one they can look perfectly normal and still misfire under heavy load or high rpm---only way to know for sure is change them and see if it gets better---if it does that was the problem and if it doesn't then you have some known good ones---the only way to actually tell from looking at the plugs is to do it at the track or on a dyno under a failing condition---if you drive them home and they do alright at cruising speeds they will cleanup before you get there and appear normal................Dan

New one are in so I will see when I get the car fired up if there is a miss when I put my foot into it:D

Ken
 
Ken,

A bad or loose fitting plug wire could also cause the same symptoms. Are you using that electrical grease stuff on the plug and coil pack connections ?

David
 
When I last raced the car at Earlville it had a bad missfiring at around 4000 RPM. I had thought it was a fouled plug. Along with a ton of other things to do to get the car back running I decided to change the plugs. I dont see anything that looks fouled on the plugs I pulled. Any thoughts as to why the car would have a bad miss. Even just before I pulled the old blower off I got on it and it was cutting out. Any input is appreciated

Ken

Couldn't you attribute all of your problems at Earlville to the supercharger? It could have easily been starting to bind on the first pass and finally seized on your last pass.
 
Spark blow out can be caused by alot of boost. So make sure you are not gapping them to stock specs. The gap should be smaller if you are running high boost.
 
Ken,

A bad or loose fitting plug wire could also cause the same symptoms. Are you using that electrical grease stuff on the plug and coil pack connections ?

David


No grease on the coil pack or plugs. Only have the dielectric grease under the DIS. I know that is an ongoing debate.

I freed up the blower and reconditioned it and still I had the miss so I dont think it was the problem. Just seems to cut out at WOT so I can only hope new plugs solve the problem. Plugs are gapped at 35 thousands

Keen
 
I had a similar issue in the spring at earlville. I swapped the plugs later in the summer. No more problem, and no obvious issues with the plugs. I believe I had flooded once after forgetting to connect the coil pack, and while it didn't seem to be a problem at first it apparently had caused a problem with at least one spark plug. I run standard copper plugs, so I expect them to be a bit more sensitive to fuel fouling.
 
When I was running high boost I had that issue. Denso iridiums at factory gap cleared it up for me. That was with a restrictive(exhaust , cam, heads) 21 psi. Seemed to work better then the autolite platinums I had
 
Pressure test

Ken,
At work we have a machine for testing aircraft plugs, you can bring yours by if you want. Not sure what the machine is called exactally (I'm more familiar with turbines), but I do know that it produces a spark while pressurizing the hot side of the plug. Basically it simulates how the plug will react at a given brake mean effictive pressure. Our engines are also force inducted, but are never operated above ambient pressure (normal procedures). I would think this machine will work, as long as the plug fits the hole. Let me know, and good luck
JJ
402-350-8866.
 
How old is your coil? I had a similar problem about a year ago, and it was a weak coil. It was the original one with 170,000 miles. Could potentially be any part of the ignition system.

How's the fuel pressure?
 
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