Lean fuel mixture warning
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Lean fuel mixture warning
Though related to the removing of air boxes I thought I'd start a new thread. I've now gotten my second warning light telling me I'm running lean. This time it was just while cruising down the freeway at about 70mph. Once again I've cleared it and it has yet to return.
So should I be worried? I've gotten two over about 400 miles. I'm wondering if I'm running just on the borderline of the lean warning all the time or if a sudden gust of wind or such triggers it?
So should I be worried? I've gotten two over about 400 miles. I'm wondering if I'm running just on the borderline of the lean warning all the time or if a sudden gust of wind or such triggers it?
If you have removed the air boxes you have effectively changed the MAF transfer functions. These tell the PCM how much airflow is passing through the MAF tubes based on the MAF voltage. Assuming no other problems(vacuum leak etc), then it appears the reduced airflow restriction is making your MAFs read low(real airflow is now greater than the measured values). This is compensated for by fuel trims up to a certain percent, after that you get a lean bank error because the car can't maintain a lambda of one in closed loop.
If fuel pressure, O2 sensors, injectors OK, MAF sensors not oil fouled and no intake/exhaust leaks, then you need to recalibrate your MAF transfer function. I would consider a lean bank warning as true and potentially serious ... this car runs in open loop at high loads(no closed loop feedback protection) where lean conditions could hurt the motor. If you are running an aftermarket tune this is especially risky as the A/F has already been leaned out at high loads to maximize horsepower.
If fuel pressure, O2 sensors, injectors OK, MAF sensors not oil fouled and no intake/exhaust leaks, then you need to recalibrate your MAF transfer function. I would consider a lean bank warning as true and potentially serious ... this car runs in open loop at high loads(no closed loop feedback protection) where lean conditions could hurt the motor. If you are running an aftermarket tune this is especially risky as the A/F has already been leaned out at high loads to maximize horsepower.
Last edited by rmrmd1956; Dec 30, 2016 at 06:19 PM. Reason: Added info
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It would be my guess that the number would be around 1.05, meaning it is taking around 5% fuel out to maintain lambda 1 in closed-loop conditions. But, when the fuelling goes open loop (for maximum performance when you open the throttle fully), the adaptions are not always carried across with reliability from closed to open-loop conditions.
So in this scenario, the reason the system might take 5% out, means it is now over fuelling by ~5%.
The reason in most cases is the MAF meters themselves being out of tolerance (meaning they return a value which is either higher or lower than the actual airflow).
This is not a problem, this is something expected from manufacturing.
However, if the MAF meters measure higher airflow than is actually being consumed by the engine, open loop, when fuelling corrections are not reliably carried across, a higher than needed amount of fuel will be delivered than is actually needed-but this is normal and expected in these conditions.
If there was a blockage or dirt in the system, it would be pre MAF meters, meaning this would cause a measured, lower, airflow and the correct lower amount of fuel would be delivered.
In most cases, lean running is due to an air leak (post MAF meters), as un-metered air is additionally introduced to the fuel diluting the mixture. Whereas rich running is more to do with a higher than actual measurement of air, although injector leakage could also be the cause, amongst a few other quirky conditions.
Under no circumstances blow the MAF meters out with compressed air to clean them, they are very sensitive components.
MBR
http://www.pistonheads.com/gassing/t...&t=978848&i=60
So in this scenario, the reason the system might take 5% out, means it is now over fuelling by ~5%.
The reason in most cases is the MAF meters themselves being out of tolerance (meaning they return a value which is either higher or lower than the actual airflow).
This is not a problem, this is something expected from manufacturing.
However, if the MAF meters measure higher airflow than is actually being consumed by the engine, open loop, when fuelling corrections are not reliably carried across, a higher than needed amount of fuel will be delivered than is actually needed-but this is normal and expected in these conditions.
If there was a blockage or dirt in the system, it would be pre MAF meters, meaning this would cause a measured, lower, airflow and the correct lower amount of fuel would be delivered.
In most cases, lean running is due to an air leak (post MAF meters), as un-metered air is additionally introduced to the fuel diluting the mixture. Whereas rich running is more to do with a higher than actual measurement of air, although injector leakage could also be the cause, amongst a few other quirky conditions.
Under no circumstances blow the MAF meters out with compressed air to clean them, they are very sensitive components.
MBR
http://www.pistonheads.com/gassing/t...&t=978848&i=60
chr