blkchevyz

ok i've been fighting this ever since i installed my ported heads and 306 cam about 3 years ago

my car will miss between 5800-6500
it really only does it under a higher load, like in 3rd or 4th gear.
i know its not the rev limiter.

i've changed the following parts

3 different optis
who knows how many sets of plugs and wires
2 different coils and ignition moduals.
2 sets of vavle springs
new fuel pump
many fuel filters
ran without accell box
ran with steve's accell box
put a new ground on the motor
re adjust rocker arms
02 sensors
i know their something i've missed.

http://home.earthlink.net/~blkchevyz/dynosmall.jpg

"White Knight"

Do you have an LT4 knock module? if not get one!........ made my high miss disapear

My Red 93Z-28

do you have good enough valve springs?
Could it be valve float?

DonHood

I'm in the exact same boat as you, except I'm pretty close to stock. My miss doesn't come around till about the top of 3rd gear, but only if I start in 1st gear. If I start out in 3rd, I can take it all the way to redline, no problem. I've watched my Scanmaster as this happens, and my O2 millivolts start at around 920 where they're supposed to, then drop like a rock around 3k rpm. By redline they're around 400 or so, and that's when you notice it most.

I thought maybe my fuel pump was failing, but I ruled that out with a pressure gauge today. Now I'm stumped.

Zepp

I would check the Fuel Injectors next.

MJ_Z28

have you changed the coil pack as part of your numerous plugs/wire changes? I had the same problem and the new coil/coil wire did the trick. Every once in a while, I have to pop the coil wire off, clean up the white powered residue from the dielectric grease and apply a new coat. Apparently, the dry residue acts as an electrical inhibitor and not enough spark goes through at high RPM...

EDIT: sorry just re-read your post...bummer, thought I had an easy fix for you

--mj

blkchevyz

yeah i have the lt4 knock module.

and the valve spring should be good. i had k motion spring when i first got the heads, last year i put on some comp cam 987 springs hoping to fix this problem.


DonHood
your problem has to be either be a fuel issue or bad o2 sensors.
whats your injector pulse width?

blkchevyz

here's a datamaster file of my above dyno run

http://home.earthlink.net/~blkchevyz/chris1.uni

DonHood

My injector pulsewidth never gets above the 9.4 or so on either side, even at WOT. Is that low? I've heard you should see pw's of up to 15 at full throttle.