high LTFT misfire on cyl 3 and lean at WOT

Matt Dickey

Matt Dickey

Greenie N00B Member
Greenie Member
Okay so im dealing with a slightly lean condition and a cylinder 3 misfire right now. Ive ruled out it being the new turbo i installed because i flagged the misfire the day before the install i have checked every air orifice before the turbo and after the TB and i took them off and reinstalled them and nothing changed. not worse or better. hpfp numbers look good and ITFP numbers look good. at idle it is popping and spitting black soot from the exhaust pipe. im lost. please help

LOGS 5&6 MAF cal
logs 7&8 WOT
log 9 idle
 

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Do a compression test and a cylinder leak down test. Report back with numbers
 
compression test was 175 150 165 170

i just realized while i was tuning this last time my occ line to the intake manifold was kinked and not allowing the manifold to draw air from it. and just before this all started i un-kinked it. then today i deleted the occ completely to eliminate any possibility that it was causing this issue, do you think this extra air that is present now but was not present during the tuning process could possibly be at fault?
 
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Matt Dickey said:
compression test was 175 150 165 170
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What order are those numbers in? Did 3 have the lowest compression? A 15-20 psi difference from the lowest to highest COULD indicate an issue. I would retest that cylinder and if low add a little bit of oil into the cylinder then check it again. If compression raises it would indicate worn rings.

Matt Dickey said:
i just realized while i was tuning this last time my occ line to the intake manifold was kinked and not allowing the manifold to draw air from it. and just before this all started i un-kinked it. then today i deleted the occ completely to eliminate any possibility that it was causing this issue, do you think this extra air that is present now but was not present during the tuning process could possibly be at fault?
Click to expand...

The purpose of the PCV system is to relieve crankcase pressure so you don't blow your seals out and to help the rings seal. They use the vacuum of the intake manifold to do it. A kink would cause the rings to improperly seal and allow oil to bypass the rings since the kink was the line at the intake manifold it would've been as you didn't have a pcv valve at all.

Your fuel trims are based off two things. The air coming in read by the MAF sensor and the output from the oxygen sensor. Your computer see's X from the MAF and Y from the O2, has a set range where they should be related together. Anything out of that range and it says it's either rich or lean. If it sees the airflow is one value but there is a vacuum leak or air leak after the MAF sensor it is taking in extra air and the O2
 
They were in that order. #2 was the lowest cylinder. I just plugged the intake manifold hole and let the pcv vent to atmosphere and the fuel trims immediately started changing. Now im back to where i was before all this with the ltft at +10 because my MAF was dirty during the tune and i added a bigger air filter after the tune was done so i suspect this is from the maf registering more air flow. But its dead on where it was before the misfire and high trims. And i just did 2 WOT pulls and it didnt flag a misfire and afrs are back to normal.
 
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