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  #1  
Old 01-07-2001, 12:51 PM
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Location: Indpls.,IN. USA
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Working in an Independent shop leaves something to be desired when it comes to fault code diagnosis. I have been working on a 1997 E320 with 88K miles on it. Twice about three weeks apart, it has set a code in the engine management system . The code is P0170 which is a fuel trim fault. The basic descriptions for failures don't seem to apply. Those are fuel pressure, vacuum leak, worn engine, etc. Has anyone out there ventured into this part of the OBD II world? Your thoughts would be much appreciated.
Thanks for yuor help.
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  #2  
Old 01-07-2001, 01:20 PM
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Very tough situation. Do you have access to a scanner with actual data? If so you will want to see freeze frame data and see O2 sensor reaction times. The long term fuel trim should be evaluated to see if the problem is intermittant or always borderline. In other words if the car runs at high fuel trim the this is an area to pursue. If it looks low during evaluation then an intermittant can be the problem.

Common failures are the airflow meter, oxygen sensors, and possibly fuel supply issues (filter, pressure regulator, plugged injectors).

One interesting thing I have found is that the scanners that pattern the factory scanner leave out many of the OBDII protocols. I have pulled pending codes off OBDII cars with my MasterTech scanner in Generic OBDII that weren't apparent with the AST retreiver or CS2000. The MasterTech or EASE PC program will calculate O2 sensor reaction times also.
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  #3  
Old 01-07-2001, 07:09 PM
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The 1997 E320 is a ME fuel system & the air flow sensor will cause this code 99/100 times. About the only other factor is fuel pressure!! If you can read live data I'm sure you will find the lower partial adaptation level at 1.25-1.3 which is at the MAX lean level! Part number is 000-094-10-48 & has list of $490. Bet we installed 50-60 last year & it fits only 1997 M104s.
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  #4  
Old 01-07-2001, 07:59 PM
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diagnostic tool question

Could i use the generic OBDII feature on my snapon scanner to retrieve the codes out of OBDII equiped benz's. These cars do not come into my shop so often as much as i try to cannot justify the 1300$ europeon software for this machine.As i pay for every tool in my box this very expensive for such limited use

thankyou
James
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  #5  
Old 01-07-2001, 08:17 PM
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Yes, the generic OBDII module in a Snap-On scanner will do some good on the OBDII models. When the first C cars started coming in our Snap-on Scanner was the only one that would clear the diagnostic module.

The Snap-On scanner is a real pain though as you have to figure out which key to install in their connector. The MasterTech inquires on all data lines and talks to whichever one responds.

Live data is very limited with the generic scanners even though they do offer some features under OBDII that factory clones don't offer.
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  #6  
Old 01-07-2001, 11:14 PM
ARJAY
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I replaced a leaking fuel pressure regulator on my '95 C280 and within 30 minutes the "Check Engine" lamp came on. When I returned home, I connected my generic OBD11 scanner and retrieved the same code. I cleared the code and it hasn't returned in 6 months. I assume that the change in fuel pressure behavior, due to the replacement regulator, may have triggered an event. Just my two cents.
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  #7  
Old 02-04-2001, 02:23 PM
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Thanks to all of you that took time to reply to my information request. I'm sorry it took me so long to reply.
As it turned out the car in question did have a bad airflow meter. Our Baum DataScan does not have a snapshot function but does access live data. Interestingly I had faxed the Bosch Tech Line and mentioned the adaptation value and wondered about the airflow meter. They could only suggest that I compare my values with that of a similar car. This is easier said than done in our shop. As one of you guessed, the adaptation was at 1.31. The voltage signal at idle was only 0.02 volts which seemed very low. However the new unit had the same value at idle, but as I drove the car the adaptation values dropped slowly and I'm guessing approached 1.00? The earlier LH airflow meters have a signal of something in the range of 1.5 volts at idle and its my thought that the later technology uses the lower power consumption to increase durability.
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