99 ml 320 runs rough please help
 

I currently have a customers ml 320 in my shop with 50k on it that cancels out # 2 injector after running for 30 seconds. I did the following things fuel pressure test , compression test , ignition system test ,replaced # 2 injector. It had pulse when i checked it. Little did i know that pulse whent away after 30 seconds. I called mercedes and talked to one of the guys in the shop and we went through everything he sugested that i put a air flow sensor on it so i did it didnt help. They actually told me if that dosent solve my problem they will take it back i was supprised to hear that. In any case does anyone have any sugestions? By the way the system i use is alldata and the only thing i found is that it is possible for the computer to cancle individual injectors if it detects a problem. Thanks for any help. If you can suggest a tech line i dont mind paying i just need to fix this thing. :o

Well I don't have an answer but I don't see anyone else saying anything so I will ask a question: What in the world would cause the computer to decide to shut down ONLY ONE injector? Is there ever a reason for this to happen? What the he** does an air flow sensor have to do with it? Are you sure it is just #2 shutting off and all others are fine? Is it always the same 30 seconds until shutting off?

Mike

First thing I would suggest, is to swap number 2 coil with number 3 or 1, and then see if fault/bad cylinder still occurs on number 2.
Do this and post back result. :)

I think you are on to something Ozzy!

What would be the connection between a bad coil and the injector being turned off by the computer? If it detects a bad coil it turns off the injector? Then wouldn't that affect 2 injectors? And wouldn't it store a code?

MP

mpolli,
If an engine miss is detected, i.e.; bad coil, failed plug lead or dead spark plug, the engine control unit will shut injector off for that cylinder, this prevents unburnt fuel entering the cat.
No, only shuts down bad cylinder, so if the coil was suspect, swapping with another cylinder will confirm so, as this would cause injector cut on that cylinder.
As far as faults codes, yes it would definitely have fault codes stored.

OK. Makes sense, but I thought that each coil drives 2 spark plugs like on my car. So a bad coil would cause 2 cylinders to fail.

MP

Yes each coil drives two spark plugs, two spark plugs per cylinder.
There are six coils (one per cylinder) and twelve spark plugs (two per cylinder).