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Stan, Mercedes Technician
Category: Mercedes
Satisfied Customers: 3526
Experience:  Technical support engineer
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I have a 1997 Mercedes SLK 230K auto with what I believe is

Customer Question

I have a 1997 Mercedes SLK 230K auto with what I believe is a system controlled missfire.
Car starts first time every time, will rev with no issues up to approx 1800 rpm before it misfires on cylinders 2 & 3. Turn off the ignition & it re sets itself.
You can also floor the accelerator & the car revs perfectly & sounds sweet but when you let the RPM drop to around 2200 RPM the missfire appears again. This happens while driving or stationary. There is no warning light on dash. Error codes are obviously multiple misfire / misfire cyl 2 / misfire cyl 3.
So far I have replaced Coil packs, Ignition leads, spark plugs, Cam adjustor magnet, cam sensor, MAF, battery, Had ECU sent away for inspection, had injectors refurbed, checked exhaust / cat for blockage, compression check, checked for vacuum leaks & had electics checked. I have put in an addative to release sticking valves.
Ive had 2 x auto diagnostic guys out who can find the problem & 2 local garages One says its the head gasket, the other says its the ECU but neither garage can say 100% they are correct & I cant afford a £800/£900 bill on their guess!
The only other thing I can think of, because this car is a "weekend toy" it didnt get used for about 2/3 weeks before the fault started. The battery was totally dead. Before this the car has had no faults at all since I bought it 18 months before.
Submitted: 3 years ago.
Category: Mercedes
Expert:  Shantal-Mod replied 3 years ago.
I'm Shantal and I'm a moderator for this topic.
I've been working hard to find a Professional to assist you with your question, but sometimes finding the right Professional can take a little longer than expected.
I was checking to see if you had already found your answer or if you still need assistance from one of the Professionals.
Please let me know if you wish to continue waiting or if you would like for us to close your question?
Thank you,
Customer: replied 3 years ago.

Hi, No I dont have an answer but its a bit late now. Can you close & refund please?

Expert:  Stan replied 3 years ago.
If the gasket has failed, there would be exhaust gasses present in coolant. This is checked very easily with a special test kit at any garage. I suggest to check the cylinders with a leak-down tester as well. The valve seats might be burnt, and this will not show with a compression test.
Another thing to check is the valve advance mechanism. If it is faulty,engine timing will be wrong. It is easily done with Star Diagnosis computer.
And lastly, engine timing might be wrong due to timing strech.