ml270 cdi Loss of Power - Mercedes-Benz Forum
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#1 (permalink) Old 07-06-2009, 09:44 AM
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Question ml270 cdi Loss of Power

Hi

Can someone please help me ? My ml 270 cdi 2003 has just started to loose power (sound familiar!) – but not all of the time. When you drive off in the morning the car works fine if you put your foot down you can feel the car accelerate and hear the turbo kick in with the engine revving past 4000 rpm. However, after about 20 min when the car has warmed up it suddenly looses power feeling very sluggish not revving beyond 2500 rpm even with your foot to the floor (almost like limp home mode but without any warning light). This makes it slow to go uphill or overtaking when you need the power.

I have been looking at similar problems that people have reported and come to the conclusion that it might be a faulty MAF sensor or possibly the fuel filter. I have tried unplugging the MAF sensor but this does not appear to make any difference.

Can someone please advise if I’m on the right track and should I try cleaning the MAF sensor with isopropanol or just replace it? If this fails what should I do next? inlet port valve/motors? cat?

Any advice would be very much-appreciated

Thanks
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#2 (permalink) Old 07-06-2009, 10:11 AM
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Since the diesel models were never released in the USA the following is just generic diesel advice.

90% of the time it is a fuel flow problem. The other 10% is the turbo not providing pressure. Electronics issues tend to be rare.

Check your filters first. Then check your tank vent. After that you may need to get your injectors tested.
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#3 (permalink) Old 07-07-2009, 03:39 AM
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Unhappy update

Update:

After crawling home last night I decided to try cleaning the MAF sensor. I removed the MAF sensor (Pierburg A6110940048) from it’s housing and soaked the end of it in isopropyl alcohol for a few minutes (this released some dirty oily grime from the sensor) then sprayed the sensor with electrical contract cleaner, before replacing back in the car. I then took the car for a quick test drive around the block. The result was amazing the car felt like new the acceleration was much better than I can remember.

This morning I took the car on a 30 mile trip the power, acceleration, turbo performance was great to start with then after about 25 miles the power dropped off feeling sluggish not revving beyond 2500 rpm again.

Any ideas what to try next? Do you think the MAF is faulty and needs a more thorough clean or replacing? Or do you think that the MAF is nothing to do with the problem? Could it be the CAT? How would I tell? Could anyone explain to me if it is the cat why the problem is not there all of the time and why it does not effect the tick over (when the cat blocked on my E-class the engine would stall at tick over)? Someone suggested changing the fuel filter and or fuel pre-filters – where are the pre-filters?

Thanks for all your help so far
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#4 (permalink) Old 07-07-2009, 06:45 AM
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Could be a number of things. This matrix may assist as a start:

More at TurboByGarrett.com - Tech Center

Last edited by mohawk; 07-07-2009 at 06:47 AM.
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#5 (permalink) Old 07-09-2009, 02:44 PM
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Smile Problem Solved

I have just replaced the mass air flow sensor then taken the car on a 6 mile test drive. What a difference the new sensor made - never had so much power! Who would have thought a small sensor would make such a difference!
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#6 (permalink) Old 07-09-2009, 04:38 PM
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The MAF sensor gives the computer info about air mass, so it can adjust fuel ratio.
Without it the computer went into emergency mode -basically working blind.
That said on my gasser sedan the MAF went bad 20,000 miles into my ownership.
New MAF gave me almost 15% fuel savings.
I wish I got new MAF sooner.
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#7 (permalink) Old 06-17-2013, 06:36 AM
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Smile paul ml270

For any others with similar problems with ML270, the MAF could be the issue!!! My problem was a bit confusing..... car would drive perfectly for for hours but as soon as car was stopped and then restarted there was suddenly no power. Car would drive but would not rev above 2300rpm! Very sluggish. Next day all was good with full power again until car was stopped. Then same problem... I did a simple check... in the morning when all was good I disconnected electrical connection to the MAF (with the engine running) and then found again no power!!!! Reconnected and instantly off again with full turbo boost. (After stopping engine and restarting again no power!!!!!)
Thought that a new MAF (after market?) might be an option. I'm in Australia so a quick search found several sites in Europe that offered very reasonable prices compared to what is available in OZ. (au$30 vs au$180+!)
Made purchase and waited for arrival with some trepidation.
It came...I installed it and the car went like a rocket!!!!!!
All I can say is that interpreting the posts made by others on the forum has saved me hundreds of dollars in service costs. Thanks.
SarsfieldML270 likes this.

Last edited by paul ml270; 06-18-2013 at 08:45 PM.
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#8 (permalink) Old 06-18-2013, 05:14 PM
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MAF SEnsor

Hi, I had the same problem and replacing the MAF sensor was the answer and yes what a difference. One other tip I read was that if its the MAF sensor then when it struggles release the accelerator re-accelerate and if it performs better then its most likely the MAF sensor. Cleaning made no difference to my ML and I found that MBenz were cheaper than EBay for a new one!!!
Happy Motoring
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#9 (permalink) Old 03-04-2014, 03:15 PM
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Quote:
Originally Posted by paul ml270 View Post
For any others with similar problems with ML270, the MAF could be the issue!!! My problem was a bit confusing..... car would drive perfectly for for hours but as soon as car was stopped and then restarted there was suddenly no power. Car would drive but would not rev above 2300rpm! Very sluggish. Next day all was good with full power again until car was stopped. Then same problem... I did a simple check... in the morning when all was good I disconnected electrical connection to the MAF (with the engine running) and then found again no power!!!! Reconnected and instantly off again with full turbo boost. (After stopping engine and restarting again no power!!!!!)
Thought that a new MAF (after market?) might be an option. I'm in Australia so a quick search found several sites in Europe that offered very reasonable prices compared to what is available in OZ. (au$30 vs au$180+!)
Made purchase and waited for arrival with some trepidation.
It came...I installed it and the car went like a rocket!!!!!!
All I can say is that interpreting the posts made by others on the forum has saved me hundreds of dollars in service costs. Thanks.
Hi Paul,
seems (hopefully) I am in the same boat with my wife's 2004 ML270 CDI. We are also in Australia (Sarsfield, Vic) and have lost faith in "professional" mechanics so I have started (last 18 months+) maintaining the vehicle myself. Do you recall which brand of MAF you purchased and whether it was the complete MAF or just the insert? Cheers, Paul
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#10 (permalink) Old 03-04-2014, 10:41 PM
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Bosch only sells the MAF Sensor with the housing. Any other is rebuilt or a knock-off.
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