I´m getting to know my new scan tool and logged some info about the short and long term fuel trim to see if everything is ok with the engine.

From what I´ve read the long term fuel trim shows how much (permanent) fuel correction has to be done to bring a lean/rich condition to an optimal condition. Then a value of 128 (or 0%) would indicate that no fuel has to be added or subtracted, right?

Here is some data from a run today:

IDLE:
Short term Bank 1 & Bank 2 around 0%
Long term B1 = 6.2% (positive value), B2 = 11.7%

CRUISE:
Short term B1 & B2 fluctuating between -5% and 5%
Long term B1 = 12.5%, B2 = 14.1%

WOT: (only got Long term data on this one)
Long term B1 = 11.7%, B2 = 12.5%

What can be said about these values? Is the computer compensating too much???

Thanks
/Stefan


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1996 Black WS6 M6
TB Bypass, LT4KM, !MAF Screen, Hooker Catback (love the sound)

 

It means that if the PCM uses its "standard" fuel calculation equation, based on the airflow reported by the MAF, the resulting A/F mixture appears to the O2 sensors to be leaner than 14.7:1. As a result, the PCM is having to add a significant percentage of extra fuel to the amount it would normally calculate, in order to achieve the stoichiometric A/F ratio of 14.7:1.

Something in the equation is messed up. The MAF might not be calibrated correctly. The measure of engine load (MAP) may not be accurate. The fuel pressure may not be adequate causing the injectors to flow less fuel than the PCM program was told they can flow. There may be a source of air flow into the engine other than through the MAF. The O2 sensors could be mislead by exhaust system leaks or by excessive misfires.

You need to look at the complete data log to see how each of these items is varying as the engine operates across a wide range of conditions.

Have you read this:

http://members.aol.com/InjuneerZZ/ScanMast.htm


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Fred
94 Formula A3+1: 381/TH400+OD/N2O

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11.513@115.59 on motor; 11.162@127.67, 1.643 60' on a 125-shot. Going with a 275-shot this year

 

Well my MAF is homeported, I will swap the MAF ends for stock ones and see if I notice any changes... Could a MAF problem explain why the two banks differ by a factor of 2, seems like maybe something else is spooky. I have no idea how to get info about the knock data from the scanner so I don´t know if I have any knocks or misfires.

Thanks for your help Injuneer

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1996 Black WS6 M6
TB Bypass, LT4KM, !MAF Screen, Hooker Catback (love the sound)