I have a got e250 coupe on 2012 plate. been having problem with slight misfire / engine hunting with car shaking for past 2 years. main dealer and independent have looked at the car and cant find any solution for the problem. no fault lights come up on the dash and also no faults are read by both dealers equipment. anyone any ideas or suggestions

thanks 

Comments

Profile picture for user MercedesMedic

There are a couple of things that come to mind.

One is that one of the ignition coils is causing the missfire. The second is that small amounts of coolant or oil is getting into the cylinder.

To go further we need some more information.

  • What codes come up?
  • If there is a missfire code, is it the same cylinder all the time?
  • Do you have to add coolant or oil on regular bassis?
Profile picture for user AMRIT

No codes come up, I haven’t had to top up oil or coolant on regular basis 

 

thanks

Profile picture for user AMRIT

Comes and goes, mainly noticeably when idle at traffic lights. Also sometimes car even at cruising speed feels rough running 

Profile picture for user MercedesMedic

My first guess is that one of the coil packs is acting up.

Another possibility is a fuel pump or fuel injector issue.

And the last thing that comes to mind that is unlikley is a head gasket issue.

What I would do is keep an OBD2 scanner with you all the time. When you notice the car act up, plug into the obd2 port under the dashboard and see if there are any pending codes. It's ok, even if the check engine light is not on, there may be a pending code.

You want to try to isolate the cylinder that is acting up.

Then other tests you can do is swap the ignition coils, perform a fuel pressure test and also a compression test.

First things first, scan for pending codes when it missfires and let us know what you find out.

Profile picture for user AMRIT

Thanks for all your suggestions. I am not a mechanic but I will get a scanner and will try to get some more information and post back the results. 

Profile picture for user AMRIT

would you recommend any particular scanner that I could plug and leave in while car is running to see how engine is running etc

Thanks

Profile picture for user AMRIT

BlueDriver Bluetooth Professional OBDII Scan Tool for iPhone, iPad & Android

any good?

Thanks

Profile picture for user MercedesMedic

BlueDriver is great and offers a lot of options on American cars. On MB it will be a simple code reader and show you some data from the ECU. 

Haha no diesels do not have a coil. Just ignitor and no need for spark. So I guess with the diesel engine you don't need to worry about coils and spark plugs. 

Check the fuel pressure. Has the fuel filter ever been changed?

Profile picture for user AMRIT

Yes fuel filter was changed at last service 

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