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Background Info:
- 1997 Porsche 911 993 with a 3.6 L engine with a resonance intake manifold set up (i.e. change the length of the intake runners based upon load and rpm range)
- no codes (not sure if customer got "clear happy" with his little scan tool - said he didn't clear codes
- emission monitors not ready
- vehicle will not pass smog
- replaced left and right rear / downstream O2 sensors as they were giving crappy signals
- after replacing left rear and right rear O2 sensors engine now has a misfire at idle (not sure this is related to replacement of the rear O2s)
- fuel trims at idle: Left bank 1 - STFT: -0.8% LTFT: 1.6% Right Bank 2 - STFT: 3.1% LTFT: 2.3%
Some observations:
- Left bank 1 fuel trims look okay
- Right bank 2 fuel trims don't look good when comparing that to Bank 1 fuel trims
- Right bank 2 has a slightly lean condition (i.e. more air then fuel) and thus the ECU is adding fuel
What I don't understand:
- could the lean condition be caused by an inefficient burn in one of the cylinders of Bank 2 (i.e. cylinder 4, 5, or 6)? But wouldn't an inefficient burn / ignition misfire cause the air/fuel ratio leaving the cylinder to be rich and if so the fuel trims for Bank 2 should go negative for such a case (i.e. ignition misfire) - no????
Confused - please help.
As always - thanks in advance.
Last edit: 3 years 9 months ago by Smeter12. Reason: wanted to make subject title easier to understand the post
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