misfire under load; thoughts?
 

New motor. Dynotuned by genius Miata Wizards . Road tested on a recent BMW track day. It ran strong;a minimal hot start issue. Ready to race, or so I thought...

A double race weekend, so no test/practice sessions; just (1) qualify and (1) race. Car is rich on start-up and fouls the plugs. Replace with one heat range hotter (NKG 7-->6). Still issues. I just figure that I'd get the car running well in advance of the race and then roll into grid at the 1 min mark (after the "racers start your engine" thing)... no worries. I'd have to start last, but that gives me more slow cars to pass. Fun right?

I get out to qualify and then problem #2 crops up. The car misfires (pop,pop,pop)... like a rev limiter consistently at 6200rpm. I did 2 laps and then came in to change out the plugs/wires... (the local auto store didn't stock coilpacks). As it turned out, this played right into my plan... you see, since I did in fact qualify last place, I didn't have to loose any positions on the grid when I rolled in late!

The first 5-6 laps it was like the Megasquirt rev limiter had been re-set. 6200 rpms at every shift.. pop,pop,pop. I could still pass and work thru traffic but it left me dead slow in the straights. Lap 7 and 8 gave me 6500 rpm. Then, viola! 7400 rpm!! I just had a great time... those back markers never even saw me coming. While I still had an occasional misfire, it was random.

This leaves me a bit reluctant to enter the next race. I just hate showing up unprepared/unreliable; 'hate getting pushed or towed. What are your thoughts? Coilpacks going south? Can a Megasquirt do this? (2004 msm, ms3, moderate boost levels, oem coilpacks (60k miles).New wires, NKG 7,6 plugs tried, oem crank sensor looks to have a .060-.090" gap by eyeball method, lightweight alt and lithium battery recently removed and replaced with oem 80amp charging system and a new oem style lead battery.)

My build notes say that the first set gapped to .038". Second set was replaced trackside and were installed as they came out of the box ... likely .040".?

BTW, do you know that a set of oem coilpacks cost less than $ 40.00? Why didn't I have an extra set for spares??

Crikey. IIRC stock NKG's are around 0.045". Try 0.025" and report back, that will probably fix your issue.

Gap down the plugs, man! And eventually buy better coils.

Will do. I've got a test/tune tomorrow and I'll re-gap and give it a try. Hopefully, my new coil packs arrive today. That way I've got my bases covered if it's also a coil problem.

My guess is, your coils are fine. You should return those ones and buy some LS coils and a bracket (do a search).

I was running lower boost (12-13lbs) with my prior configuration. It ran great for 8+ years. This time I am running 16lbs. I guess a few lbs makes a lot of difference.

Also,' is the LS coil pack the most reliable option? I remember having a LS coilpack failure back in 2001 when I raced a T1 corvette.

At stock gap, I started having spark blowout at 12psi. I'm still running stock coils, but many of the guys here have moved to the DB585 coils and report good results.