booming resonance 1000-1500rpm

[citroennut]

hi all,
car has started a booming resonance at between 1000 and 1500 rpm. associated with this is a marked reduction in fuel economy - evidenced by the mpg on the dash. it is also impossible for the car to keep steady revs between this range whilst idling, lumpy at 900rpm, goes to 1100rpm and then climbs quickly to 1700rpm will not stay between these. the problem is it is not all the time but an intermittant fault and clears if switched off - typical
btw it's a w203 54plate 220d
cheers
simon

 

[Jim Lambert]

If it`s intermittent it`s electrical! Check all connections to sensors and injectors. Make sure that cables are not kinked, stretched or cooked, multiplugs are locked and any cable ties are not cutting into harness. If the car has been in a accident, be very thorough about checking damage to the harness where the repairers have been. Plugging into a diagnostic unit will show non transient type faults and memory corruption, which can occur when unusual electrical events happen eg application of arc welder....Back in the bad old days, I would have checked the governor of a mechanical pump, or even the propshaft for failure of the universal joints - you have to feel that resonance to believe it.

 

[jberks]

I agree it's electrical but doubt there will be anything to see. I'd suspect a dodgy sensor as the car transtions from idle running.
It sounds like overfuelling at this point and so whilst the symptoms are unusual I'd be suspecting our old friend the MAF.
I take it there is no warning light coming on when this happens? Not that this proves much.
It's going to be hard to prove when its intermittent but one of the things Id try next time it happens is disconencting the MAF and seeing if that affects it.
Aside from that, I'd check to see whether there are any fault codes recorded.

 

[citroennut]

hi guys,
overfuelling does sound like an option, as when running for a while it sounds as though it is tappity at idle, though a deeper sound than a tappit and quite loud, i know it's difficult being a diesel. there are no fault codes logged and of course doesn't do it when at the garage. it happens possibly twice a week at most, when hot or from immediate start in the morning.
simon

 

[slr-executive]

I have a smiliar problem with an E220 auto although it happens between 1500 and 2000rpm. Only happens when hot. Cold running the car is great. If I get anywhere I will let you know.

 

[citroennut]

update to previous post, -
started booming on way home and fuel consumption dropped to about 25mpg through town, this from a previous ave. of 40 on clear run through town. took straight round to mercedes without switching off, technician test drove - agreed diesel knock and booming. car was plugged into diagnostic and air mass at 458 - normal, injectors at .3 - normal, no fault codes, no software updates, burned off particulate 163km ago, everything normal car switched off and restarted, back to normal and fuel consumption up to 45mpg around town which is better than normal. technician confused and now emailing mercedes in germany who will undoubtfully ask for a fault code
simon

 

[television]

Sorry to see that you have this rotten fault. I do hope that an answer comes along

 

[Glenn Smith]

Do you have EGR, with a particulate filter i guess you have, it could be a fault with this or the throttle valve.

 

[citroennut]

problems fixed -- finally

hi guys,

after more than a year of hassle with this car, mecedes have finally managed to find out the cause and fix it. i inc a link to another post which gives an idea of some of the other symptoms - sorry i cannot find/remember how to shorten it [URL="http://forums.mercedesclub.org.uk/showthread.php?t=33760[/URL]

i have decided to replace the car due to the problems, but as said it is now fixed and will come with a years mb warranty as way of recompense for the grief caused to me. i have left out the fix to see if any of you can figure out what was replaced to fix it.

simon

 

[djcheung]

Hi Simon,

I am having the same problem.
I did get MB to change the DPF under warranty but still not getting anymore that 200 miles between filter regenerations.

So, was the new ecu fixed the problem or the motor oil?

I am very interested in finding out.

Please reveal the answer.

Thank you.

 

[citroennut]

hi guys,
in the end the dpf was changed as it was clogged with ash, mercedes took the car to milton keynes and a technician from germany came to look at it. he put water through the exhaust and found the back box was blocked as well. this has been replaced and the car is running beautifully. it was driven back to ensure it was running well and over 380 miles averaged 43.2mpg at an average speed of 60mph. so after a new ecu, maf, dpf, dpf sensors and all the time involved, a new dpf and back box was all that was required. at least i ended up with a years warranty for my trouble. it's now for sale as the shine has gone from ownership.

simon

 

[djcheung]

Hi Simon,

Thanks very much for the info.
I have the new dpf fitted a few weeks ago.
The first burn off was just under 300 miles
The second burn off was just under 190 miles
The latest was just under 130 miles

Each time the regeneration took very 20 minutes.

When the car was serviced last October, it had Castrol GTX motor oil instead of Low Ash oil.
Would it that make a difference ?

 

[ernieh]

Loe Ash Oil

Hi DJcheung,
Somebody will correct me if I'm wrong, but I think you will find that cars fitted with DPFs need low ash oil as the ash formed when the other stuff burns blocks the DPF. A MB Dealer or Authorised Repairer should know what to use, though.

Regards,


Ernie

 

[djcheung]

Hi Ernie,

I know. The dealer should know what to use.
It was a MB dealer who put the Castrol GTX in Last October.
I am checking with the dealer I bought the car from last November (different dealer) to see what they can do about it. If the oil does burn off and clog the dpf, then they will have to change it again under warranty.

Regards,

David.