E320 Check Engine Light (a bit long!)

[Graham]

Decided to start a new thread because I have new symptoms that I just don't understand. I need professional help (in more than one way )

I had posted previously about my partial success in cleaning my Mass Air Sensor. Now, not so sure that it is the cleaning that "cured" the problem.

On one day, I reset the CE light and drove the car about 50km - by that time all monitors on my OBD II reader had gone solid indicating that all diagnostics had been completed - no pending DTC,s after a dozen or so short trips.

Next day, I attach the Code Reader before setting out and immediately I get a CE light! No pending codes before hand - just the DTC,s (P0170 and P0173). Thought it just may be a glitch of the meter, so reset and went for drive - in very short distance ( 3 km) CE ligbt comes back on. Next time, I repeat the process, make several short stop start trips (~10 km) and NO CE light. Next time, CE light is back on.... and so on.

Other Background:
- I have checked vacuum and it is steady at 20" HG - no apparent leaks.
- OBD meter says that O2 sensor checks have completed, presumably with no problem.
- Same for other monitors (other than Misfire, Fuel system and CC which run continuously)
- New spark plugs installed
- New air filter installed
- Previously when I had this problem, I cleaned MAS and problem disappeared for about 3 months.
- Voltage to MAS is 5.02v and resistance of MAS at 8 deg C is 4060 ohms.
- the engine runs well with no hesitation or misfire.

Given this background, is there something other than the MAS that could be causing this inconsistent behaviour? Perhaps an over rich mixture at start-up that does not happen every time?

I do plan to buy a new MAS but am not convinced that it wil solve problem

Sorry for long post and repeating infpo posted in other thread.

[Graham]

Looking on-line for MAS. I find that websites list two different Bosch part numbers for '98 E320.

Some say B3130-98064

others say B3130-98298

Autohauzaz have a different number - probably their own

Any idea which is correct?

[CLK320MIA]

Originally Posted by Graham

Looking on-line for MAS. I find that websites list two different Bosch part numbers for '98 E320.

Some say B3130-98064

others say B3130-98298

Autohauzaz have a different number - probably their own

Any idea which is correct?

All v6 112 engines use the same MAF. Your best bet is to get one off of ebay. I got 2 new ones for 100 bucks each and they were perfect.

[fredfisher]

I have a 98 C230 and stood on my head trying to clear a P0170. Cleaning the AMM just prolonged the time it would take for the CEL to come on. I too, changed everthing, sprayed everything, and finally bought the damn thing. Best $300 I ever spent. More power, better gas mileage, smoother trans shifting, yes the AMM affects the transmission too. Buy it, you probably won't regret it.

[stevebfl]

The reason the light was off the first time for an extended period was that you reset the adaptation values. It takes time for the reservoir of adaptation potential to be used up. By just clearing the codes the other times you left the adaptation numbers at their limits and the light comes back quickly.

Like I said in the cleaning post you have not show any accomplishment without being able to see the adaptation numbers.

The proper number for the AMM is 112 094 00 48 MB or 0 280 217 515 Bosch. Any other number is BS.

[Graham]

The proper number for the AMM is 112 094 00 48 MB or 0 280 217 515 Bosch. Any other number is BS.

Thanks Steve!

I will order a new unit, but will also experiment with old one and cleaning methods as a learning experience and so as to have a spare for next time this happens.

[Graham]

Another question!

There are 5 pins on sensor. 1,2,3,4,5

Pin 5 seems to be 12v positive
Pin 3 seems to be 12v negative (ground?)
Pin 1 may be sensor ouput, but not sure?

Anyone know what the full pinout is?

I want to set up a test so I need to power the unit and measure output.

[Arthur Dalton]

Is #1 yl/wt ??

If so , that may be sig.

Just back probe with DMM and blow air in the MAF...correct sig wire/pin# volts should rise.

[Graham]

I was about to order a new Mass Air Flowmeter from an on-line source. Best price I found in USA was $289.00. However, to ship to Canada, there was an extra 10.95 paperwork charge plus the cost of shipping (Free in USA). Then we would have customs clearance when it enters Canada - With the current exchange rate, this worked out to over C$400.

I decide to check MB Canada price and it was C$380. They used to cost a lot more than that!

I have it in hand, but have also ordered Digimoto OBD II software and interface - I want to check air flows and other readings before I take out the old unit and then repeat with the new unit. If this is not the cure, the differences in readings may tell me something.

If this IS the cure, I will try and "really" clean the old unit (ultrasonically or??) and see if it makes a difference - It would be nice to have a spare and would be something others may find useful.

BTW, I looked on eBay, but they want US$299 for new units - Not prepared to buy a used unit. One seller says he has re-conditioned units - reconditioned by a certified MB technician!! Wonder how they did that?

[stevebfl]

If you wish a comparable airflow reading do it with the key on and engine off. That is the only comparable situation. When running the difference between a good AMM and a bad one in a dynamic situation will be hard to identify.

The real test is the adaptation readings. I'm not sure how good an OBDII scanner will be at adaptation numbers as OBDII gives long and short term but MB has three. The important numbers are not what OBDII calls short term, they are CTP (closed throttle position - idle) and part load. Both of these would be long term fuel trim by OBDII standards. I'm not sure what they look like when combined. Long term fuel trim would be the best of the OBDII numbers I would say.

[Graham]

OK - Thanks Steve - Have to wait until stuff arrives - probably a week or so.