wierd bizzarre occasional misfire

In reply to 16vCorey:

yes even tried a completly diff set of injectors. one from ford racing and one set of oem injectors.

There were similar issues caused by a sticky EGR valve on some Proteges I know. cant hurt to clean it out and check before more drastic measures.

KATYB wrote: the pids are showing a miss on cyl 1. picked up by the knock. nothing shows up ignitition or fuel wise.

I'm a little baffled by that statement. I've yet to meet a knock sensor that would detect an engine miss. They detect knock, but not a miss. How are you getting a miss signal through a knock sensor?

So are you and the cars computer seeing false knock signals from the knock sensor? If the computer is seeing this, it would be reacting by retarding the ignition timing. Those retardations can feel like a stumble.

Food for thought, sometimes the knock sensor is listened to only at certain rpm ranges. Usually low. It may be taken off the map at higher rpms.

Is the knock sensor in the correct location? Is the knock sensor "hearing" the aftermarket headers? Is one of the headers close to the sensor? What oil is being run? 0w30? 5w30? Try a 10w40. When the mods were done were bearings replaced? Pistons? Rings? Complete gasket kit? OEM gaskets? Is one of the gaskets strangling an oil feed or return hole? Is the fuel map able to cover for the modifications? is it leaning out when this happens? Is there an adjustable fuel pressure regulator? Where is your base pressure? What about 3K RPM loaded? What about 4.5K RPM loaded? What fuel pump is in the tank? OE? Consider a Walbro 110LPH in the OE hangar with a high flow Mustang sock.

Oh and put some Autolite Dual Platinum / Platinum Pro plugs in it, I have had issues with NGKs Iridium IX plug on Nissans, switched to the Dangerzone/Retarded auto parts specials and cleaned house.

john i decided to try your idea of the headers being the cause so i wrapped the headers and it has seemed to work nothing at all showing up now. but to answer your question. i run 10/30 schaefers have since she had 25k on her. no lower end work still have the fragile stock duratex bearings (eventually one will go(but then its an excuse to offset grind a crank 30 and overbore 20 and put in some 11.5 pistons. yes i run a maf custimizer that is mapped to rpm and throttle points. af never goes leaner than 12.2 at wot. cruise it sits right at 14.7. no fuel pressure regulator... all controlled by the pump in the tank. i did suspect the pulse dampner but no. she is back to herself. and no no no on the autolites.... they do not get along with my coils in the least. same with motorcrafts. the iridium ix and laser iridium are all i will use. car is over all fairly lightly modded. just p&p heads/lil hardwelds and a lil change to the grind on the cams/ported intake manifold upper and lower/ bored throttle body/cai/headers and exhaust for engine mods.

In reply to foxtrapper: i was saying the miss was showing up at time of ignition for cyl 1. however nothing on the occiloscope for the coil or injector. thus only way it was picked up was by the knock sensor.