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What's up everyone looking for some further knowledge on my car. I bought it like this it has a 306 comp cam bored .30 over whole engine rebuilt K&N intake long tube headers. Just recently I seen my AEM air fuel ratio gauge at idle go as high as 25.2 and when I'm driving it's now around 15 to 19 depending on how much throttle I got on it and the week before it was idleing at 19-20. Car does have a tune on it. I personally have not done anything to the engine so I'm looking for someone with some insight from a similar situation. Car still runs fine just smells kinda rich. Car is a 95 z28
parts list from previous owner
Where is the wide band sensor located- bank 1, bank 2, in Y-pipe, or one in each bank? Is it before or after the catalytic converter (if there is one)?
Generally, closed loop the PCM's target A/F ratio is 14.7:1, for both idle and partial throttle. The PCM rapidly toggles the A/F ratio back and forth between slightly rich and slightly lean, to make the cat work. Each bank of the engine is controlled independently.
When decelerating, the PCM usually cuts fuel off until the engine drops below (roughly) 1,300 RPM, so the exhaust goes very lean.
In power enrichment mode (roughly WOT) the stock programming target A/F ratio is typically an overly rich 11.7:1. For a normally aspirated engine, for better power/torque, it isn’t unusual to lean this out in the tune to the range of 12.8:1 to 13.2:1.
Cold start/open loop, the A/F ratio is significantly richened, depending on coolant temperature. In extreme cold can drop to 2:1 for starting. Gradually leans out to 14.7:1 as the engine warms up, and the PCM enters closed loop.
The wideband is plugged into the Y pipe no Cats. I was told car has an aggressive tune(not much knowledge on tunes)91 only. The picnic attached with this response is me going around 75mph with a quarter throttle. Thanks for your help BTW.
Can you scan the car? Ensure the Factory O2s are showing same type of readings?
Issue with either the factory or wideband O2s themselves throwing off the EMC or wideband readings/values?
Has the car been sitting? I have the LM2 wideband system and occasionally when the car sits for a few months, the readings go nuts. If I do the re-calibration process they reading go back to normal. When I see odd things this is the first thing I do to validate the ECM against the LM2.
At 75 MPH what was the RPM? The lower the RPM, the more important valve overlap becomes. At low RPM some of the incoming air/fuel mixture can go out the exhaust valve. The O2 sensor “sees” the air, but it can’t see fuel, so it will read leaner than the actual incoming mixture would be. No sure that applies to the CC306 with its 112° LSA. I suspect at idle RPM it is a factor that has to be taken into account in the tune, Just a thought, may not be a very good one. I’m NOT a tuner.
Have you checked the spark plugs for a lean condition? Any evidence of knock retard? What kind of A/F ratios are you seeing on cold start? Any chance there is something other load on the wire from the wide band controller to the gauge? Or is the AEM controller integral with the gauge? Any chance of a leak in the headers before the wide band sensor? The AEM instructions mention a screw that has 5 positions that select the sensor calibration, but that is unclear, as to whether it only controls the output signal to a secondary gauge.
Can you scan the car? Ensure the factory o2s are showing same type of readings?
Issue with either the factory or wideband o2s themselves throwing off the emc or wideband readings/values?
Has the car been sitting? I have the lm2 wideband system and occasionally when the car sits for a few months, the readings go nuts. If i do the re-calibration process they reading go back to normal. When i see odd things this is the first thing i do to validate the ecm against the lm2.
the car did sit for about 2 months transmission went out. I will take it some were and have it scanned ...how do you do the recalibration process?
At 75 MPH what was the RPM? The lower the RPM, the more important valve overlap becomes. At low RPM some of the incoming air/fuel mixture can go out the exhaust valve. The O2 sensor “sees” the air, but it can’t see fuel, so it will read leaner than the actual incoming mixture would be. No sure that applies to the CC306 with its 112° LSA. I suspect at idle RPM it is a factor that has to be taken into account in the tune, Just a thought, may not be a very good one. I’m NOT a tuner.
Have you checked the spark plugs for a lean condition? Any evidence of knock retard? What kind of A/F ratios are you seeing on cold start? Any chance there is something other load on the wire from the wide band controller to the gauge? Or is the AEM controller integral with the gauge? Any chance of a leak in the headers before the wide band sensor? The AEM instructions mention a screw that has 5 positions that select the sensor calibration, but that is unclear, as to whether it only controls the output signal to a secondary gauge.
I believe the rpm at 75 mph was at like 2200 and at cold start it reads nothing just three flat red bars. I have not checked the plugs they are fairly new but I was gonna see what would be the best kind to get for my ride cause I wanted to change them out anyway
the car did sit for about 2 months transmission went out. I will take it some were and have it scanned ...how do you do the recalibration process?
Not sure about your system? mine your pull the O2s out so they are in fresh air. Turn the ign to on ( not starting the car ) so the O2s come up to temp, then there is a calibration button you depress. Let the O2s cool down and reinstall.
