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Mike
Mike, Technician
Category: Mercedes
Satisfied Customers: 38738
Experience:  34 years of in the Motor Trade as diagnostic Technician and general repair work.
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Mercedes-Benz C230 Sport: Suddenly my check engine light came

Resolved Question:

Suddenly my check engine light came on and the car began sputtering; it shakes at start up, in reverse, while idling, and is slow to accelarate. I have replaced the crankshaft position sensor and the spark plugs.
Submitted: 2 years ago.
Category: Mercedes
Expert:  Mike replied 2 years ago.
Hello and Welcome to justanswer..

With the shaking that you describe at start up / running - idling and accelerating... it sounds like you have a faulty ignition coil - but there are other things this can be ..such as a failed injector / circuit fault etc..

As the Check eng light is on, that means there will be fault codes relative to this fault, stored on the cars eng management computer (ecu )...

The proper way forward is to have the car plugged into a suitable diagnostic machine either at a MB dealer or local garage that has the equipment... and this will scan the fault log memory - retrieve the fault code/ s - and that then tells you exactly where the fault is / cause of the bad running....which can then be attended to.

That is the way forward on this one to take out all the guess work... its the proper/ cost effective way forward for you now to get your C230 fixed.

Im very pleased to have helped you - let me know if I can help anymore..

Please click the Accept button for me now - Thank You ...and if you do need / wish to get back to me after - you can do so just by coming back to this post and use the Reply button - your reply will then come straight back to me .. and Im always happy to help further.....

Please note , you need to press the Accept button even if you are a subscriber to justanswer - thank you again.

Kind Rgds - MIKE.
Customer: replied 2 years ago.
Also, there is no compression on one side of the engine. The generic computer scanners are saying random misfires and that there is a problem with the intake manifold runner position sensor/circuit, but I cannot find any information on what that part does. A friend told me that one bad sensor or component can throw off various error messages. I had all the fuel things checked and that seemed to be fine. My problem has been with getting an honest answer; the specialists for Mercedes want to charge $90 an hour to troubleshoot and say they need 2-3 days. I've been told everything from it's some type of electrical problem to I need a new engine.
Expert:  Mike replied 2 years ago.
Hello again, thank you for your reply / message..

Well, with no compression , that will certainly cause a misfire - and you will get codes for a misfire / multiple or otherwise.. ( I wasn't aware you had done any fault code / diagnostics, you didn't mention that )

When you say no compression "on one side"... are you saying any / all of the cylinders on that side - or just one..and if so, which ?

Have you checked that you are getting spark and fuel at the cylinders too?

Rgds - MIKE............................
Customer: replied 2 years ago.

One mechanic tested one cylinder on one side and said there was no compression while the other side did have it; he said I needed a new engine. Another mechanic disconnected all 3 cylinders on the side with no compression and the engine was still running; he said that I probably have an electrical problem and needed to verify the plug wires were receiving current.

Expert:  Mike replied 2 years ago.
Hello again.. thank you for your reply / info..

Ok.. well, the first didn't do enough at all and couldn't make a diagnosis based on compression test on only one cylinder..

Your second mechanic did right - but it needs to be determined if there is definately no compression on all 3 cylinders on that side or not.. If there is no compression on all three, then it has to be investigated further / deeper to see why. That would be unusual...

Its best to use MB test equipment but as you say , its not cheap - but a mech with a decent fault code reader will be able to extract fault codes as the EML (fault light ) is on on the dash that will point to the area of fault for you .

Random misfires can be for different reasons.. To explain..It could be yes, that there is no spark on the cylinders - 2 or more on that side.. if that is found to be the case, the coil/s are the first suspect that would need checking - with the ultimate suspect being a faulty Ecu.. as the drivers for the coils are in the Ecu.. but the wring loom would need to be checked back to the Ecu before condemning that. If its determined that its the Ecu at fault , I recommend locating an Ecu test specialist who can test / repair at a seriously cheaper cost than a new unit...

The other thing to check , if its determined that the sparks are there on all cylinders - and that there are no compression problems, is the fuel system - injectors etc.. If its not a compression issue or ignition issue - it will be the fuel system...injectors etc.

Proper equipment is needed to then test for faults there.

Working through as above, you will get to the bottom of this one way or the other..

Im very pleased to have helped you - let me know if I can help anymore..

Please click the Accept button for me now - Thank You ...and if you do need / wish to get back to me after - you can do so just by coming back to this post and use the Reply button - your reply will then come straight back to me .. and Im always happy to help further.....

Please note , you need to press the Accept button even if you are a subscriber to justanswer - thank you again.

Kind Rgds - MIKE.
Mike, Technician
Category: Mercedes
Satisfied Customers: 38738
Experience: 34 years of in the Motor Trade as diagnostic Technician and general repair work.
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