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  #1  
Old 09-29-2008, 06:22 PM
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722.6 Issues

I have read all of the 722.6 threads, and I'm quite sure my issue is different.

I bought this car (99 C230 K) 2 weeks ago, I did not notice any problems at the time.

The main issue is intermittent, seems to happen both when warm or cold, but I think its more common when the tranny is cold. I cant confirm this, since its only been a couple of days.

Regular driving, with slow acceleration is 100% normal. As soon as I try to accelerate quickly, like when merging, or just quick accelerating from the stoplight, strange things begin to happen. The car will hold gears (I think its usually third) and instead of shifting into 4th will sort of bounce back at around 4k RPM, as if it was hitting a rev limiter. Then it may start dropping RPMS, or just jerk back and forth until I back off on the throttle. Quite dangerous during merging.

Then other times, after restarting the car, it will just behave normally and accelerate through the gears flawlessly.

Other symptoms include holding gears for far too long when cold, and the odd time, the engine will race while the car barely accelerates.

It almost feels like the ASR is kicking in, but the ASR light is not coming on, also I believe the ASR operates after the transmission and thus would not affect my revs?

I just bought this car, and am definately not in the mood for a tranny replacement. Will take to dealer in a few days for diagnostics.

Any help would be appreciated.

Thanks,

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  #2  
Old 09-29-2008, 10:13 PM
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Always start with a check of the fluid level. You need to be able to check fluid temp, and there is the special tool dipstick I'm sure you have read about.
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  #3  
Old 09-29-2008, 11:10 PM
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Originally Posted by Gilly View Post
Always start with a check of the fluid level. You need to be able to check fluid temp, and there is the special tool dipstick I'm sure you have read about.
Gilly
So far without the thermometer my experience has worked out filling it midway between the 2 marks in the 25 range when cold. Then make sure it gets into but never exceeds the upper line in the 80 range.
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  #4  
Old 09-30-2008, 12:31 AM
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Although opposed by some members, I would start with an oil and filter change. The dealer here not recommends, but imposes an oil change on 722.6s every 30,000 miles. They have seen more than a handful of failed 722.6s with less than 50,000 miles on them.

After that, if the problem persists, have the transmission electronics checked (it is usually one of the first and few things to give problems on 722.6s). Besides that, the transmission is very reliable.
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  #5  
Old 09-30-2008, 11:21 AM
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Originally Posted by Trelinski View Post
Regular driving, with slow acceleration is 100% normal. As soon as I try to accelerate quickly, like when merging, or just quick accelerating from the stoplight, strange things begin to happen. The car will hold gears (I think its usually third) and instead of shifting into 4th will sort of bounce back at around 4k RPM, as if it was hitting a rev limiter. Then it may start dropping RPMS, or just jerk back and forth until I back off on the throttle. Quite dangerous during merging.

Then other times, after restarting the car, it will just behave normally and accelerate through the gears flawlessly.....Any help would be appreciated.

Thanks,
About two weeks after I purchased my 00 230K my car exhibited exactly the same behaviour, it turned out to be a faulty air mass sensor.

I'd have the dealer check the fuel mixture adaptation values, If they are above 1.20 there is a pretty good chance you need a new air-mass sensor.

It was amazing to me how much the new air-mass sensor changed the behavior of the 722.6 transmission in my car - when the bad AMM was in place the shifts were sometimes harsh and the car seemed to make odd decisions about when to upshift and downshift. After the new AMM the transmission behaves (at least to me) perfectly.
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  #6  
Old 09-30-2008, 11:36 AM
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Originally Posted by Trelinski View Post
I believe the ASR operates after the transmission and thus would not affect my revs? Thanks,
When activated the ASR system can certainly reduce throttle inputs to stop wheelspin, I don't think it should ever increase throttle inputs beyond what the driver is asking for with the accelerator pedal.
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  #7  
Old 09-30-2008, 03:48 PM
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Thanks for the responses.

Today it got a lot worse, and I had to actually abort a merging attempt, as I could not get up to speed. I pulled over onto the shoulder.

Tim, I was thinking today as I was nursing it home, that this really doesnt feel like a transmission problem. It does seem to have the characteristics of a sensor or computer.

I dont have the time or location right now to do any work myself, so I will go in to the dealer and have them check the fluid level, possibly change it, as well as the air mass sensor. I will post my results here.

Thanks again.
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  #8  
Old 09-30-2008, 04:57 PM
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If you must drive your car, you're stuck with the dealer. If it is the MAF and you can wait, you can save alot of money by just buying the insert and installing yourself. I just did this and paid $147 for the insert. I've seen them on ebay for around $100. I also bought some security torx bits but I don't recall if I actually needed them.

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  #9  
Old 09-30-2008, 05:06 PM
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The MAF sounds right with the lack of power; doesnt sound right for over-reving.

It ought to set a CEL.
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  #10  
Old 09-30-2008, 09:20 PM
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Originally Posted by TMAllison View Post
The MAF sounds right with the lack of power; doesnt sound right for over-reving.

It ought to set a CEL.
My car didn't set a check engine light when I had my problems - my adaptation value was 1.29 and I've heard the CE light won't come on until it reaches 1.32. IIRC there was a pending P0170 but no CE light.

I agree about the over-reving issue, my car never exhibited that behaviour.
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  #11  
Old 09-30-2008, 10:38 PM
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Ditto for my 722.6 - the erratic behavior was caused by a bad AMM (or MAF). And there was no CEL and no codes either. Whatever you do, DO NOT BUY THE EBAY ONE!!! I went through 3 of those within 3 months; fortunately the vendor was reasonable and replaced at no charge, but by the time I needed the 4th one I knew I would be pushing my chances with him. I got one from Phil - I think it was $200 or $250, but it has been a year and many thousands of miles and no problem. I now keep the 3 EBAY ones as spares in the trunk. They work OK, it's just that they have a "flat" spot in the power curve so acceleration isn't as smooth. But in the case of a total AMM failure, where the car won't run, these spares will be just fine.
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  #12  
Old 09-30-2008, 11:56 PM
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OP might try cleaning his with CRC MAF spray cleaner first.

Cheap enough its worth a try.

Tim - I've also read there is a threshold that must be passed to set the CEL. Mine did set codes when it went bad; codes, no turbo, and it falling flat on it face between 3-4K made it easy to figure out.
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  #13  
Old 10-01-2008, 11:16 AM
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Quote:
About two weeks after I purchased my 00 230K my car exhibited exactly the same behaviour, it turned out to be a faulty air mass sensor.
I agree that it is almost certainly the MAF. It takes 10 minutes to change and you only need a screwdriver to loosen a hose clamp and retighten.

Make sure that you only buy the Bosch brand MAF:

http://www.***************/search/product.aspx?sid=jw52q2nbux2s0tvwq024kd55&makeid=800016@Mercedes&modelid=1356285@C230%20KOMPRESSOR&year=1999&cid=22@Fuel%20%26%20Air%20System&gid=5068@Air%20Mass%20Sensor
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  #14  
Old 10-01-2008, 02:30 PM
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Oh yeah, cleaning my MAF helped for about a day and then the problem returned. Was a waste of time for me. The hot film type are, after all, extremely difficult to clean when compared to hot wire.
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  #15  
Old 10-01-2008, 09:13 PM
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Thanks guys. Local dealer wants $460 for the MAF, but I think I can get a used one for cheap, at least for diagnostic purposes.

If it doesn't work out, I do have another car, so I'll probably just order online and wait.

I took the morning off tomorrow, so first thing I will do is try cleaning it and see what happens.

I think the over-revving may have been a misunderstanding. The engine never revs past what I input through the gas pedal.

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