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I've been getting some strange misfiring at seemingly exclusively high RPMs. There is a rapid burst of bassy pulses coming out the exhaust at 6500 rpm. It also seemed to be just in first gear tonight, but has happened in second on occasion. My AFRs seem to be fair enough, sitting at 10:1 when flooring it into high rpms.

I recently changed:
-Iridium plugs
-Distributor cap
-Distributor rotor
-Added bottle of injector cleaner

I'm not 100% if any of those changes are related, but surely they should all be for the better! Timing was of course done after putting the dizzy back in. The car is pulling well other than this misfire.

This is on the KLZE car whose mods are in my signature should that help. Still running stock ignition.

Suspects on my mind are:
New plugs
HT Leads
Timing belt tensioner
Probinator chipped ECU
Injectors

I have uploaded a video with sound in slow motion, please check it out. This is so frustrating!
http://uk.youtube.com/watch?v=Lg3lGucnEFM

that happend to me and i changed the plugs i put ngk and the wires and also z-max injector cleaner and it was still miss firing so i changed the o2 sensor and 2 more sensors where the radiator cap is on the left side n front of the passanger side like next to the housing of the cap the 2 sensors sre hard to c but its 2 nuts stickng out and its that right there so just look carefully cuz its right there man sorry i tryed my best to explain.

mazda915 wrote:2 more sensors where the radiator cap

Hmm I guess that could be an issue, with the engine coolant temps being part of the fuel loop. My codes I think are neglegable: EGR (as it's gone) and 69-coolant fan switch (because I have 2 sensor wiring harness, so the third is unconnected). Fan still works normally though.

I'm getting AFRs of 10 when I'm at WOT. Surely that's too rich?

It's exclusively missing in first gear at 6.5k+. I guess first gear is the fastest gear to get through the revs, so perhaps spark can't keep up? Or is excessive fuel deteriorating combustion? Both are possible. I've an FPR on the way, maybe that will clear it up

Just because your plugs are new dosen't mean one isn't bad. I changed my plugs and right off the bat my #3 was misfiring (said so on my LapTop). Installed a old plug and it was fine.

Daninski wrote:Just because your plugs are new dosen't mean one isn't bad.

Thanks but I just tested with my old set, same deal Think I shall do the HEI/external coil mod soon, something I've been meaning to do regardless of whether it will fix it or not.

Additionally, I crept up to 7500rpm (about 1/3 throttle) and it was totally fine. So it really must be something to do with load. AFRs where 14 or so doing that. I was going to go drag racing this weekend too

Hopefully, the ext. coil will fix it. I had a disty go out that way; missing at higher RPMs, and the problem slowly crept to the lower RPMs. I checked everything else because I thought that when they went out, it was all or nothing.
You can have the MegaSquirt control the spark, instead of the HEI module, right? Save $25.

Your words give me hope I'll get onto ordering the necessary soon.

But argh... mr megasquirt is another nightmare altogether! I think I'll rock the HEI/coil mod first, to ensure I have a solid engine running before getting the MSnS involved.