320 V6 engine...down on 2 cylinders

[Vlad]

Here's an odd one for you.

Friend of mine has a ML320 with the V6 engine and its down on two cylinders...codes say faulty coil packs. His local Bosch garage have replaced the offending coil packs and have replaced all 12 spark plugs, cleared the codes and the car fires up and all seems well, until it resorts to running on 4 cylinders...both rear cylinders not firing...codes say failed coil packs again.....coil packs have then been moved around and the same sequence starts all over again, ie runs fine, then resorts to running misfiring on the rear cylinders.

Any clues to whats going on???

 

[jaymanek]

bad/dodgy wiring loom?

 

[Dieselman]

Agreed. Sounds like the feed or return from both rear coils is defective.
does the code specifically say faulty coils or just cylinder misfire. if misfire check the injectors and rail for contamination or airlocks.

 

[kenshaaka]

Faulty wiring or Faulty ECU (Just pray its not the ECU)

 

[Vlad]

Update: turns out it was blocked CATS...what was happening was as follows:

Back two cylinders failed....diagnosed as coil packs...these were changed and then the car was run back up and after a short period the car started to misfire.....then turned out to be the middle two cylinders.

Basically the back pressure from the blocked CATS was causing stress on the engine management system and this was finding its way out through the coil packs....basically the older coil packs couldn't cope and failed whereas the replaced coil packs just passed the problem onto the next coil pack.....if this makes sense.

Anyway problem solved.