C280 ck eng lgt P0170 and P0173
 

Help!!! 1999 C280 with 36K miles ck eng lgt on ..displays codes P0170 and P0173.."lean fuel trim"....replaced gas filter and replaced both O2 sensors...still same problem...replaced gas cap...still same problem..replaced air filter..same problem...cleaned MAF sensor...still same problem....ck lgt was turned off with ob11 after each attempt to resolve problem but ck lgt returns!...funny thing is the engine does not exhibit any run problems and runs great.....help!!

Does it run smoothly and eagerly up to redline in the lower gears.. or is performance flat, with an occasional stumble, above 4K RPM?

I have not noticed any driveability problems from start to cruise...have not tested up to redline in the lower gears....this engine has been well taken care of...its clean and never a problem...louietwo

Well try it, as those codes usually go with a bad air mass meter. With proper tooling one would look at the adaptation values, reset them to base and see how it ran with no adaptation. A new unit then viewed in comparison proves the case.

sorry..i'm just an old back yard sunday mechanic and dont have the proper 'tooling'..i have a basic obdII for reading codes and resetting the ck eng lgt and I try to follow basic troubleshooting test and problems but I dont know how to reset this to base and test against a new one..I'm trying to look at known problems and fixes from you guys before I throw another $258 bucks into this for a MAS that nobody seems to know how to test...wish i had my 60 chev back!!!

Yea, a current debate is centered around legislation that many believe is designed to dumb down the level of technology so that technicians can keep up.

Sorry to say they will really have to dumb them down to keep them servicable with with home shop testing capabilities.

The problem with your basic question is that there really isn't any way to pin the common AMM problems except by monitoring adaptation numbers and comparing known good devices. The amount the device is failing is too small to be determined through absolute testing in a dynamic framework.

i really appreciation and thank you for the help...and understand the problems associated with new technology...I did go back and road test the car in the lower gears with high rpm...above 4000 and close to redline....all worked fine..no misses or stumbles....all power and good surge....crazy--no noticable problems .. but a check engine light that codes P0170 and P0173...

If you are having no performance problems I would suspect that you are blowing the additive adaptative CTP (closed throttle position). if you were to view adaptation numbers you would probably see that the multiplicative adaptation - part load - will be between 1.15 and 1.25. The limit here is 1.32.

What happens at say 1.25 is that through the multiplicative process the original fuel calculation is multiplied by the adaptation number 1.25 giving a 25% larger amount of fuel everywhere.

In AMMs with this kind of problem the sensors capabilities are reduced at higher air flow non linearly. This means that where they were 25% off at load they are not so far off at low flow. So at idle (CTP) the mixture is too rich so the second form of adaptation (additive CTP) takes over and reduces the injection time with an additive or subtractive time value up to 1 millisecond. The actual injectoion open time is usually around 4ms so 1ms is very significant.

I presume that you are bumping against the idle additive correction limit at -1ms. In such cases there will be little performance defect. The fact that adaptation has reached the limit does not mean the system isn't in control. What has happened is that the center of range no longer can be moved and mixture correction can then be bottomed out. This last part needs a whole other thread, actually.

I see what you're saying...guess I go for the amm and see if that solves the problem...I'll let you know...thanks again

4/12/04 replaced amm....what do you know ..ck light problem is fixed....(as a side note....I found the AMM on EBAY for $145 plus shipping $5....half price from anything I could find, also I found it interesting to see some of the AMM sellers stating that "changing the air filter on MBZ's will cause a failure of the AMM!!!!).......I would like to thank those of you.... stevebfl and jgl1 who took the time to try and help me with this "Fuel Trim" problem...you were right...