I have a late 2003 ML270 CDI. The car drives fine and accelerates strongly from standing.
I have noticed however that at 70 mph cruising on the motorway if I accelerate gently I get a pulsing or surging acceleration. The rev counter echoes this pulsing by moving up and down.
This is not a violent pulse and up to that speed the car drives perfectly. I have changed the air filter thinking that may be causing it, and although extremely dirty the problem has not been fixed.
I have a late 2003 ML270 CDI. The car drives fine and accelerates strongly from standing.
I have noticed however that at 70 mph cruising on the motorway if I accelerate gently I get a pulsing or surging acceleration. The rev counter echoes this pulsing by moving up and down.
This is not a violent pulse and up to that speed the car drives perfectly. I have changed the air filter thinking that may be causing it, and although extremely dirty the problem has not been fixed.
All thought appreciated.
I rarely work on diesels but since you said that your air filter was very dirty, I would remove the Mass Air Flow insert and spray clean it with CRC Mass Air Flow Cleaner. Not knowing where you are from, I do not know its' availability, but try and get this product, it works very well. If not use an electronics spray cleaner.
Also, try hooking up a scanner to the truck and see if there are any codes stored.
Many thanks for your reply. I invested in the spray cleaner mentioned this morning. I cleaned the socket and removed the air box cover and MAF and cleaned both of those thoroughly. There was quite a bot of crud on the wire mesh before the sensor. Letting everything dry I put it all back together and took it out for a drive.
Initially the problem seemed to have all but gone, but as the car got warmer the surging came back and now occurs with light acceleration through 60 - 75 mph.
I hooked the car up to a fault code box and it returned no codes, so the car thinks its ok.
My next step is to replace the fuel filter and flush through with injector cleaner.
Were you able to spray the very thin wire on the insert? That is the important one. Remove the two screws (see phot #7) pull out the insert and spray the wire clean. If after doing this the truck runs remarkably different (worse) then you need a new MAF.
Note: The screws holding the insert need a #25 Torx Plus w/security socket, but don't waste your time finding one. Either use a vise grip or cut a groove in each screw so you can use a flat screwdriver.
I did manage to clean the thin wire in the MAF, but dont think it is a MAF problem.
Speaking to several people it is suggested I try the gearbox oil level. Apparently if this is low, or if the gearbox oil cooler has split and the oil is contamiated a misfire type symptom may occur.
I found this out after I changed the fuel filter. Doh
Now to work out how to check the oil lecel withougt going to a Main Dealer.
Just had the gearbox oil and filters changed by Merc. While the problem is 99% gone there was still a very very slight pulsing felt at around 70 mph. To be honest I think I only felt it because I was looking for it.
The oil that came out of the box was described as black so this needed doing anyway.
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