Random misfire during start sometimes

[alrodri8]

Ok guys, I figure someone on here might off suggestions. So I installed the Whipple 2.9 Stage 2 kit this weekend and have also data-logged WOT pulls with my NGauge and all looks good. I also performed my crank relearn while the car was at operating temperature. It ran a few 6.9s in the 8th mile at the track last night where I did my logging. The issue I'm having is, shortly after turning my car off, then turn the car one a few minutes afterwards, I get a random misfire code on cylinder 8 in the first 1000 revolutions(checking codes with my NGauge). It did not happen this morning when my car was started when completely cold and seems to happen randomly when starting the car. I have been clearing the code and seeing if it happens again after the first 1000 revolutions and it does not happen. Also this morning when I started it, it also seemed to have trouble finding steady idle for about 2-3 seconds, that was from a complete cold start but it did not misfire that time. I performed a crank relearn again this morning, went to pump fuel at Shells with 93 octane. Started the car pulled forward about 5 or so seconds after startup and got the random misfire on cylinder 8 code again. Cleared it and it did not happen on the drive home. I also seem to get a secondary O2 sensors rich code when it happens SOMETIMES and SOMETIMES at the same time as the random misfire in first 1000 revs code. I usually clear the secondary O2 rich code because I have vibrant defoulers, although that code happens more randomly. My question is, what could be causing that cylinder 8 misfire(also sometimes says cyl 6 along with cyl 8 sometimes) during first 100 revs code?

Thanks in advance, I tried to be as descriptive as possible.

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[Jeff_oddo]

Check plugs...

 

[alrodri8]

Did that, I moved Coil pack and plug from cylinder 8 to Cylinder 2 and Vice Versa. Thing is, I don't hear a misfire and the car does not get the code after its cleared. Still the same thing, I'm leaning towards a crankshaft position sensor.

These are the codes word for word, again only sometimes and near startup.

P0316(Confirmed) - Misfire Detected on Startup (First 1000 Revolutions)
P0308(Pending) - Cylinder 8 Misfire Detected

 

[Csb1992]

interesting gonna tune into this

 

[kcc0521]

Did u resolve this

 

[Tornado]

I had something similar in my f-series truck. Cleaning the MAF sensor resolved it for me. Good luck

 

[Tommy V]

Did that, I moved Coil pack and plug from cylinder 8 to Cylinder 2 and Vice Versa. Thing is, I don't hear a misfire and the car does not get the code after its cleared. Still the same thing, I'm leaning towards a crankshaft position sensor.

These are the codes word for word, again only sometimes and near startup.

P0316(Confirmed) - Misfire Detected on Startup (First 1000 Revolutions)
P0308(Pending) - Cylinder 8 Misfire Detected

Im going through exact thing,excat,but u have whipple,on mine i think i might havd broke my imrc when doing clutch.I know u dont have them now with whipple but i will let u know what ifind out.

 

[alrodri8]

Did u resolve this

I did resolve the issue. The codes were not confirmed misfires but were pending misfires. What I did was run a KOER test and it gave me a code that says the post catalytic O2s were not functioning properly or were switched. I basically had the secondary O2s slip flopped. Once switching them back to their appropriate connector I stopped receiving the misfire pending codes. :headbonk:

 

[sigintel]

Thats an excellent find! Good job!

 

[Tommy V]

I thought the upstream and downstream 02's had different connectors,i could be wrong though.

 

[kcc0521]

I think he means he has right sensor connected to left bank

 

[alrodri8]

I think he means he has right sensor connected to left bank

Exactly what I meant

 

[Nerass]

dumb question.. is it easy to swap the left and right side unintentionally? maybe this may be my issue lol

 

[alrodri8]

​

dumb question.. is it easy to swap the left and right side unintentionally? maybe this may be my issue lol

It was real easy for me lol. I actually did this several times :doh:

 

[Nerass]

cool im gonna check that out

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