I was having an upper RPM miss under load in all gears so I changed the coil, coil wire, fuel filter, and readjusted all the rocker arms.

I just took the car out for a drive and it still misses in 3rd and 4th but not as bad as it did before. Otherwise it runs like a raped ape and feels like it has a ton more power than it did before.

Anyone have any idea??

 

I think you're on the right track with the ignition system. Plug gap can affect your high RPMs under load with a miss. Throw on some new plugs (and put dielectric grease on the plug threads and boots - inside).

Also, find a dark place at night with no street lights (under a tree). Start your car and open the hood. Look around the engine for a few minutes and let your eyes adjust. Look for any sparks that may be jumping from your plug wires... they may be difficult to see under your exhaust system... but keep searching. Let us know if you see sparks... if so, change the wires.

Good luck

PS - you may want to keep a swear jar handy.

 

The plugs are brand new(less than 150 miles) although I think they maybe gapped a little too much. I have them at .050, should I try .040 or lower with the increased power and 11.1 compression?

Ill check the wires tonight....and post back..

 

can you make it miss by brake torqueing?

it could end up being a lean miss, possible injector or o2 sensor

 

I never tried that, it shouldnt be running too lean it was dynotuned, and a bad O2 shouldnt be effecting WOT.

 

I bet you have a bad plug wire.

 

Ill check for arcing again tonight.

I just took the car for a ride and it will fight through the miss and rev more, just not as good. Also it doesnt happen at part throttle, only WOT. I took the car up through the gears part throttle with no problem...


Lets hope its just a wire.

 

i was having the same problem as your describing...mine turned out to be a small rubber elbow, that connects to the intake. look on the passenger side just above the exhaust manifold there is a small black box, with two plastic lines, and a connector of some sort on it...then the lines to the throttle body and there should be a small rubber elbow that connect the plastic line to the throttle body...mine was all cracked and dry rotted...i changed it and mine runs like a raped ape!!!

more or less check for vacuum leaks around the throttle body!

hope this helps!
steve

 

You know what I know exactly what your talking about my rubber boot is doing the same EXACT thing. Its been like that for quite a while now and I never thought it would cause all that much trouble. Ill change it out tommorow and post back. Hopefully its just this!!

Could anyone possibly explain why this little vacuume leak could cause so much problem? could it be letting in unmetered air?

 

Yep, the leak is letting unmetered air slip into the system. You can test that by spraying WD-40 carefully and listening for the RPMs to rise.

The plug gap is my first guess with 11:1 compression ratio. Second is the wires. The leak would be very noticeable at idle but less so at WOT, however it is a possibility.

 

Which plug gap would you reccomend than?

 

.040 should work much better. Guys with blowers and N2O gap and .030 - .035 depending on application.

 

Thats what I was thinking too, Ill see if that helps any....

 

Let us know what happens... we like happy endings

 

My intake elbow did the same thing