I have a 1998 Mercedes E320 that generates P0170 and P0173 codes about every third driving cycle. I suspect the air mass meter, but would like to be certain before shelling out almost $300.
Is this air mass meter a whetstone bridge as in other air mass meters where the element exposed to the air is a resistor? Does anyone have a schematic diagram of this part?
Thanks.
Dan
"Dan Dubosky" wrote in news:Y7MEb.1643$ snipped-for-privacy@newsread3.news.atl.earthlink.net:
Before buying that mass airflow meter.....
P0170 Fuel trim malfunction. Self adpatation of fuel mixture "partial load", right cylinder bank, at limit from engine control module (N3/10).
possible causes *intake air leak*, injectors, fuel pressure regulator diaphragm, engine wear.
P0173 Fuel trim malfunction. Self adpatation of fuel mixture "partial load", right cylinder bank, at limit from engine control module (N3/10).
possible causes *intake air leak*, injectors, fuel pressure regulator diaphragm, engine wear.
Thanks for the response.
Since I posted the original message, I have obtained the hardware and software necessary to attach my laptop to the OBD II port.
The output of the MAF sensor is a maximum of 10.6 lbs/cubic foot at 4675 RPM (engine almost at maximum load). This translates to about 141 cubic feet/ min. for air at the temperature at the input. Since an average for airflow versus HP is 1.5 to 1.6 cubic feet/min. for each HP developed, this in turn translates to a maximum of about 94HP. The car is operating beautifully with no evidence of any problem other than the check engine light, and the engine is stated to produce 221 HP at 5500 RMP.
Yes, I could have a leak after the MAF sensor but it would have to be large enough to supply an additional 141 cubic feet/min. of air. Not likely.
Based on this analysis, I have already ordered a new Air Mass Meter. I'll let you know if that solves the problem.
If there is a hole in my analysis, please let me know.
Thanks again.
Dan
My 1998 CLK320 looks like it needs a new one of these as well, but I'll thankfully have the cost covered by my extended warranty -- I heard a quote of $700 for it, but perhaps that's retail. Similarly, the engine seems to be operating fine despite the codes. I don't know precisely what codes it's throwing though since that info wasn't shared. So how is it then that a device whose input is supposed to affect timing and fuel mixture doesn't appear to affect engine operation when it starts having trouble?
I've also found it interesting that I've been assured that operating the engine with this type of failure won't cause it any harm? Any comments or suggestions?
My 1998 CLK320 looks like it needs a new one of these as well, but I'll thankfully have the cost covered by my extended warranty -- I heard a quote of $700 for it, but perhaps that's retail. Similarly, the engine seems to be operating fine despite the codes. I don't know precisely what codes it's throwing though since that info wasn't shared. So how is it then that a device whose input is supposed to affect timing and fuel mixture doesn't appear to affect engine operation when it starts having trouble?
I've also found it interesting that I've been assured that operating the engine with this type of failure won't cause it any harm? Any comments or suggestions?
As I understand it from my research, the amount of fuel added by the fuel injectors is dictated primarily by the Oxygen sensors. The electronic control unit (ECU) causes the fuel mix at the catalytic converters to cycle from slightly too rich, to slightly too lean, to slightly too rich etc., in order to achieve maximum efficiency from the catalytic converter. Periodically, the ECU does a check to determine if the amount of fuel being used is correct in accordance with the amount of air coming into the engine which in turn is indicated by the air mass meter. If the air mass meter is defective and puts out a figure which is too low, the ECU will believe that there is much too much fuel being used for the amount of air that is coming into the engine. Accordingly, the long term fuel trim will rise (in my case it got up to 34.4%) indicating that there is much more fuel being used than should be required by the amount of air coming into the engine. Result is a check engine light.
If the air mass meter is not defective and still indicates too little air for the amount of fuel being used, there could be a leak between the air mass meter and the engine in which case the same trouble codes would be triggered.
Dan
thankfully have the cost covered by my extended warranty -- I heard a quote of $700 for it, but perhaps that's retail. Similarly, the engine seems to be operating fine despite the codes. I don't know precisely what codes it's throwing though since that info wasn't shared. So how is it then that a device whose input is supposed to affect timing and fuel mixture doesn't appear to affect engine operation when it starts having trouble?
engine with this type of failure won't cause it any harm? Any comments or suggestions?
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