ml270 cdi Loss of Power

tony jr

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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?

Any advice would be very much-appreciated

Thanks
 

Cole@MBS

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Could be anything from airmass sensor to blocked Cat to a inlet port shut off motor!!

needs a short test really!!
 
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tony jr

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If the CAT was blocked would you not expect power loss all the time and not intermittent
 

johnyb

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I was experiencing the exact same problems with my ML270. After getting hooked up to the Star Diog and Mercedes it came up with a fault in the Inlet Port Shut Off. What I have found so far is that the rod connecting the Servo Motor and long shaft that the flaps attach to wich make them open and close was missing and must have broken off.

Does anyone know if I should be able to move that long rod wich is attached to the inlet port flaps? I figured I should be able to open and close them by moving with my hand back and forward. If it does not move does that mean one or more could be jamed?

Cheers,
 

kebo57

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I was experiencing the exact same problems with my ML270. After getting hooked up to the Star Diog and Mercedes it came up with a fault in the Inlet Port Shut Off. What I have found so far is that the rod connecting the Servo Motor and long shaft that the flaps attach to wich make them open and close was missing and must have broken off.

Does anyone know if I should be able to move that long rod wich is attached to the inlet port flaps? I figured I should be able to open and close them by moving with my hand back and forward. If it does not move does that mean one or more could be jamed?

Cheers,
Hi yes you are correct, that link could still be there but only connected at one end & rotated round in line with the long rail so might look like its is missing

Kevin
 

ruane

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My 270cdi had a problem with very similar symptoms. Started off fine, then after a few miles it seemed like the turbo stopped working. Boot to the floor, but no signifigant response, very very slugish to accelerate of climb, and topped out around 75mph. Stopping the car, turning off, and restarting it would temporarily clear the prob, only for it toi reoccur after 10 or 15 mins. Few days later a hissing noise developed, and was related to acceleration, and turbo pressure. Assumed I'd blown a pipe off - no big deal like.

Brought it to a local indie, who diagnosed it as a blocked cat. Repaired that day and 5000miles later haven't had a problem.
 
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tony jr

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blocked cat sounds expensive - any idea of cost?
 
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tony jr

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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
 

television

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You could unplug the MAF and try the car,,they seldom clean up, and on a diesel the air flow is much greater than on a petrol.

I would say that a replacement will fix it. JiB on the forum sells then at around £60
 
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tony jr

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You could unplug the MAF and try the car,,they seldom clean up, and on a diesel the air flow is much greater than on a petrol.

I would say that a replacement will fix it. JiB on the forum sells then at around £60

Hi

When I unplugged the MAF it did not appear to make any difference at all - still limited revs. Would you have expected this to have solved the problem or does the ml "fail safe" and go into limp mode when the sensor fails or you unplug it? Does this affect your recomendation to replace the MAF?
 

television

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The unplugging does not always work, it would be cheaper to replace the MAF than to have the car checked on STAR,,,

I cannot just tell someone to go and buy some thing, its a hard call
 
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tony jr

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update

Just picked up a new MAF sensor from my local MB dealer (£51 + VAT - good price). Will fit tonight and let you know how I get on. I will also change the fuel filter just in case. Does anyone know if the ml has a pre-filter or just the main filter (with a built in prefilter).

thanks
 

Alex Crow

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it`s just the main filter. also check you air filter. other likely causes are sticking egr valve, shot/sticking manifold flaps, blocked cat/s, split intercooler or hose or wastegate vacuum modulator.
 
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tony jr

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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!

A very big thanks to everyone who offered useful advise.
 

Rourkester

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I have the same model (ML270cdi) and have had the same problem. I changed the MAF sensor which seemed to cure the problem but it has now reoccured after 2 weeks. I had a lot of exhaust gasses from the back box so assumed the cat was ok but now can not get it to rev past 3000. I am suspecting a blocked cat.
 

norraban

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Hi,
Am experiencing the same intermittent loss of power with my ML270 CDI as "Tony jr" as it becomes dangerous to drive on the highway especially where a hill is concerned or when overtaking. The car will not exceed 40kph on some hills. Switching off and restarting temporarily fixes the problem. MAF sensor has been replaced, but did not fix problem. According to my mechanic, the problem is caused by a lack of boost pressure, but the cause of this could be a variety of things including a faulty or blocked Cat converter.
It is not a requirement of Australian design rules to retain the Cat converter, so will the car run properly without the Cat converter in place. ie replace the Cat converter with a matching piece of exhaust tubing ??
Norraban
 

oigle

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Hi,
Am experiencing the same intermittent loss of power with my ML270 CDI as "Tony jr" as it becomes dangerous to drive on the highway especially where a hill is concerned or when overtaking. The car will not exceed 40kph on some hills. Switching off and restarting temporarily fixes the problem. MAF sensor has been replaced, but did not fix problem. According to my mechanic, the problem is caused by a lack of boost pressure, but the cause of this could be a variety of things including a faulty or blocked Cat converter.
It is not a requirement of Australian design rules to retain the Cat converter, so will the car run properly without the Cat converter in place. ie replace the Cat converter with a matching piece of exhaust tubing ??
Norraban

Even though it isn't mandatory for diesels to have a cat here, if the vehicle is fitted with one, it must be retained.
Of course, this is just the law. Sugest that you remove the guts of the cat but leave the original "box" there for visual recognition.
The car will run quite perfectly without a cat. Little bit noisier.
Sounds like you should get the motor on star for a diagnosis before spending any more money. You could be getting a problem with your egr valve sticking - this causes limp mode. There are a couple of big threads on the egr problems and a way of taking them out of the system. Worth a read.
 

norraban

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Thanks Oigle,
Will suggest this to the service agent before they remove the Cat.
 

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