Intermittent Misfiring with Wideband reading Lean.

[ryan97cobra]

After getting everything up to date, and replacing a leaky pinion seal a new gremlin has appeared. So far this issue has only happened twice, and both times it only lasted about 1-2 minutes then the truck was running as smooth as could be. The first instance was after i filled up and started it up to leave, and it was misfiring and the my Wideband that i installed was reading 16.5-17.5 at idle. As soon as i pulled out of the station, and started accelerating (very very light throttle) it stopped and the wideband moved back to where it normally is 14.7 - 15.3 at idle and light throttle. The truck ran great the rest of the way home.

Today leaving work, i was stopped at a light and the truck started missing again and the wideband moved to the same place 16.5-17.5 at idle and then continued for about 1/2 mile under the very light throttle. As i started from the next light it went away just like before and ran perfect the rest of the way home.

So the truck runs great most of the time. I put the diablosport 91 octane pulley tune on the truck in between those two instances, and I will say it made a nice difference in throttle response and my a/f at WOT has been in the 10.9-11.3 range the few times ive been there. Now that this issue has appeared twice I am going to keep my foot out of it until i can find out what is causing this issue.

So my question is what could cause the truck to misfire intermittently like this, and also cause my wideband to read so lean during the misfire?
I went with the Innovate wideband, mounted on the drivers side just after the header flange.


Performance Mods are:
4lb lower
Cold air
Longtubes/catback

 

[ryan97cobra]

I replaced the plugs(Motorcraft 12FM1's which are 2 steps colder than stock were in it), and the number 8 plug was loose with evidence of blow by on the plug and COP. I had listened under the hood and while driving, and was didn't hear any "tick" type sounds that would have indicated this was the happening. I put NGK tr6ix's gapped at .35, and the number 8 plug went in normally and i was able to torque it down to spec without issue.

I didn't observe any other issues with vacuum lines, and i also checked the fuel pressure which was normal.

I have been driving the truck the past 3 days on the new plugs, and the throttle response and overall running of the truck is much better. I have not had any issues since i replaced the plugs with either the intermittent missing issue or the hot hard starting issue.

 

[Bootbox]

Thanks for coming back and posting an update, glad it's running better. I'm having similar issues, going to do all the plugs this weekend and measure the coils with my multimeter.