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I AM WORKING ON A 1997 C-230. I HAVE A TROUBLE CODE OF 0170, FUEL TRIM OUT OF LIMITS. I HAVE CHANGED THE SPARK PLUGS, FLUSHED THE INJECTORS, REPLACED THE PRIMARY OXYGEN SENSOR AND THE CODE RECURS AFTER 10 TO 15 MILES OF DRIVING. ANY IDEA OR SUGGESTIONS ON WHAT TO TRY NEXT? APPRECIATE ANY HELP ANY OF YOU CAN GIVE ME. THANKS

sounds like you have a bad air mass meter. To verify it you would have to ck actual vaues with a scaner. Also ck for no vacum leaks.

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I AGREE CHECK THE AIR MASS METER VOLTAGE WITH ENGINE OFF IGN ON .
POSS THAT THE AIR FILTER HAS NOT BEEN REPLACED IN A WHILE & DIRT HAS AFFECTED THE READINGS...

Other than replacing the AMM which is usually the problem, a real answer based on diagnosis needs to know which fuel adaptation is over limit and whether it is over limit rich or lean. The values are expressed in the actual values on the scanner. The two types are part load (multiplicative) and CTP (closed throttle position - which is additive).

The limits of part load are 32%. This means that the original fuel calculation is changed in all mapped ares by multiplying by + or - 32% or expressed as seen on the scanner up to 1.32 or down to .68 with the original calculation equal to 1.00. Once aquired this calculation is applied to all conditions including such non controllable states as cold running and sudden acceleration (not controllable because in the first case the O2 sensor isn't working and in the second case the O2 sensor can't react fast enough to help).

The multiplicative adaptation also applies to idle and as such is then recorrected by the CTP adaptation which is a straight additive change of plus or minus 1ms from the injector pulse width occuring due to the original calcualtion and now corrected by the multiplicative correction.

If the adaptation that is out of range is a CTP with a plus correction with a multiplicative correction that is normal one would look for airleaks. If CTP was hitting the negative bounds but not effecting multiplicative then one might look for a leaking fuel pressure regulator or possibly even a leaking injector. A uniform correction (one that is out of range multiplicative but has no CTP correction) usually is a AMM or other signal input uniformly skewed such as fuel pressure that is too high or low.

AMMs (air mass meters) do have the unique ability to be non linearly skewed. Such a condition has them wrong at load but right at idle (or close). In such conditions the part load value might be 1.2, well within the multiplicative correction range. But because the unit is correct at idle the idle is now 20% too rich (due to the multiplicative correction) which then gives a CTP adaptation number of -1.00ms the end of range for CTP correction trying to correct.

Lots of info in those numbers especially on the 6 and 8 cylinders which have two numbers for each type of adaptation (left and right on "V" motors and front versus rear on inline ones).

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

What voltage specs does one look for with the engine not running?

Could you please turn your caps off? Read Steve's response, it outline precisely how to diagnose the problem. I take it you're a tech. Did you charge the customer for all the stuff you've already replaced without solving the problem?

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John Shellenberg
1998 C230 "Black Betty" 240K

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