AMM Replacement Intervals
 

Seems like the AMM is a regular maintenance item, but one that causes people a lot of puzzling sometimes before they finally just change it out. So I am wondering if people could respond with how long their AMM lasted before it died, in miles and years. I am also curious if the life span is more closely related to years or miles. Here is the data I have so far:

1998 C230 101,000 miles, 6 years
1998 C230 61,000 miles, 3 years
1997 C230 83,000 miles, 5 years

What is AMM?

Sorry, Air Mass Meter, the thing in between the air filter and the throttle.

Mike

I replaced my AMM on my 1998 C230 (bought new) at six years and sixty-three thousand miles.

replaced mass air meter
 

2000 W210 M112 replaced mass air meter at four years and about 40,000 miles. Tried to clean it, no success with that. CEL went out on it's own.

I hope we can collect some more data, but so far the mileage is ranging from 40,000 to 101,000 miles and the age is ranging from 3 to 6 years (and my car is the one at 3 years and I am not too confident of the dealers diagnosis since they also replaced the AMM a week after they changed it the first time, along with some other parts. I had to scratch my head on that.

So far the life span seems slightly more aligned with age than miles. The real test would be if it could be measured against engine run cycles (trips).

Mike

The AMM can be ruined by contaminants finding their way into the unit. This means changing your engine air filter probably has an effect on AMM life. Many people have found that switching to a "high flow" K&N or other filter assembly means constanct AMM failures. The theory is that more air flow also means more gunk and more gunk means short AMM life.

Not many people I know with a 98 model still had their original AMM. My indie was quite surprised when he found out I was on my original unit until a few weeks ago. I change my engine air filter every 15K-km's (about 9-10K-miles) without fail. Why? Originally, not to extend AMM life, but engine life. I have "nursed" many engines past 250K-miles by changing the air filter and oil/filter frequently. Keep the crankcase clean and keep the intake air clean.

I would think that an old air filter would have poor air flow but not necessarily let dirt through.

I disagree. Once the carrying capacity of the filter is reached, I believe particles will be allowed through. I saw a car with a black OE filter, and there was tons of grit in the post-filter intake runner.

OK. I will be changing that air filter then. Thanks for that info. (Still looking to hear others experience with AMM lifespans though)

Mike

1998 C230- 175,000 miles. I had to replace AMM last week to cure P0170 code with CEL on. It was time to get smogged here in California to renew registration. CEL on in CA means no pass and no renewal.

First one lasted about four years/65,000 miles. Time/mileage wise, I'm coming up on number two. I'm hoping, though, that my air filter diligence will pay off.

What John said! Before poping in a new filter, vacuum out every spec of dust from the housing.

Can someone help explain what an AMM does and how it works? My understanding is it's a film sensor that measures in near real time the air/fuel mixture in order to provide data (so that it may make any necessary adjustments) to the engine's computer.

Is this even close?

To fredfisher, I think you are the new record holder for miles on a 1998 C230. You can get your 250,000Km badge (20,000 miles ago).

To Michael,

Here is what I think I know: It has a thin platinum wire that has some electrical current running through it to heat it up. As air flows through it it is cooled. The resistance of platinum changes (slightly) with temperature. There is a control circuit that always tries to keep the resistance the same by putting more current through the wire to keep it heated up. In this way the computer can tell the exact mass of the air passing by by how much current is flowing into the wire. I believe that there is a seperate ambient temp sensor so it can correct for that. This system is improved over the old "spring loaded door" sensor that measured air flow but did not compensate for differences in air density. Anyway, for it to work it has to be kept clean, and I am told it does this by heating up red hot at every turn off, like a self cleaning oven sort of. I imagine that over time it erodes a bit and would lose accuracy as its surface area changes. Also some gunk could possibly build up. And they can even just break altogether. The engine uses the air measurement to decide how much fuel to add (by controlling the injector on time) and the O2 sensor(s) measure the results to fine tune the whole thing. Much better than a caburetor!!

Mike

What Mike said!

The density is the key for the ME fuel injection computer to determine the amount of fuel is required to optimize the ratio. That is why your car can run like crap when the AMM is going south, as the fuel mixture may be incorrect.

Measuring air density that quickly and accurately has been a challenge for most makes, and the AMM is not an uncommon failure on many OBD-II compliant cars.

Talking to a tech, he figured the cycling of the AMM was responsible for less wear than the damage to the "strand" caused by the abuse of teeny particles slamming into it. He explained that it gets "pitted" and the increase in surface air erodes it's accuracy. Larger particles can wreck it altogether. Now, I don't know the validity of this, but he has lots of happy customers that get very high mileages out of their AMMs by changing engine air filters frequently and only using OE filters in OE housings. He had a new customer come in with an ML that had an old air filter and the AMM housing was filled with gunk and so was the downstream intake plumbing. The AMM was shot.

Now, I didn't start out seven years ago on the C230 changing my air filter often to save the AMM. Heck, I had no idea of what one WAS! But, after years of changing the filters often (along with frequent oil/filter changes) and my engines still in top form at 400,000km's or more, I figured I must be doing something right. It works. Our 190E 2.6 is just about to roll over 400K (250K-miles) and the head has never been off, the tranny is original (serviced often) and the car runs like a top.

As to the fellow with the C230 with 175K-miles, perhaps he could take the time (appreciated by the many C230 owners around) to give us some insights into his C230. Tranny problems? Any mileage related difficulties? I know a fellow with a 96 C220 with about 410,000kms and he's had some AC problems (replaced a couple condensors) and a few small complaints, but otherwise he's had over 250K-miles of trouble free motoring.

Swapped mine on the W163 @ 60K...