Random misfire/ lean

[TungstenGT]

So i went and did a little data logging on my car to get ready for a tnt next weekend, and on the way home the car randomly started missing/ running rough
wideband shot up to about 16.xx and as soon as i could get out of traffic, it started running just fine, wideband went back to normal (low 14.s under part throttle) and it ran just fine. No CEL but it did have a code for a coil primary circuit, however all the coils were plugged in tight. And even if it was a coil, why would it go lean?

Mods are as followed
K&n intake
Msd coils
autolite ht0 gapped at .032
o/r exhaust
sct with bama tune
100 shot of nitrous (nos single nozzle)

 

[RLF9409]

What is the most recent mod? Sounds like an air leak to me.

 

[TOWGUNNER]

^^^ what he said air leak.

 

[Alfiedagr8]

Missfire can cause the wideband to read lean. What are your fuel trims both long and short ?


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[nawagner]

I had a similar situation once that ended up being a bad plug. Had misfire cyl# error, exchanged two of the COPS and the error stayed on the original cylinder, so knew it was the plug.

 

[TungstenGT]

Im thinking its a plug being i just gapped them, ordered 8 new ones.
however it hasnt had a hiccup since this happened.

Under WOT af reads 11.8 on nitrous, n/a reads 12.2 (same tune)
however according to the short fuel trims its commanding a a/f of 11.2
So why would it be off like that?

 

[BruceH]

Im thinking its a plug being i just gapped them, ordered 8 new ones.
however it hasnt had a hiccup since this happened.

Under WOT af reads 11.8 on nitrous, n/a reads 12.2 (same tune)
however according to the short fuel trims its commanding a a/f of 11.2
So why would it be off like that?

Can you explain this a little more? What are the stft and ltft?

 

[TungstenGT]

Stft under wot is .77 (both)
And ltft is 1.0 -1.01 under wot

 

[BruceH]

Stft under wot is .77 (both)
And ltft is 1.0 -1.01 under wot

FYI fuel trims aren't used under wot on 10 and earlier Mustangs. They use a prediction based on the maf transfer function during open loop.