I hope there are knowledgeable readers of this forum or owners who have had a similar problem. Problem began after nearly 5 years of ownership without any engine issues. The patient is a 2014 SL 550 US market with 86,000 miles problem started with the engine running a little rough and a check engine light. Plugged in the code reader and says random misfires on cylinder 2. Thinking spark plug, I replaced with new to no avail. Then I swapped coil 2 with coil 1, and error codes show now I have random misfires on cylinders one and two. Thinking I have a bad coil, I purchased a replacement coil no change, still random misfires on cylinders 1 and 2.
I take the patient to see a specialist at the local Mercedes-Benz service shop and perform some tests that include scoping three cylinders and compression checks reporting one cylinder was reporting 25 RPM higher but was within specs (I have no idea what that meant). The Doctor concluded that the injector cylinder 2 looked clean compared to others due to the injector in cylinder 2 had failed and was stuck in the open position, flooding the cylinder and causing the ECM to try and compensate and causing what was now misfires across the entire bank 1-4.
They offered me the opportunity to have them replace the failed injector, replace the aftermarket coil I just purchased and replace all 8 spark plugs for the paltry sum of $3,600. I respectfully declined. I purchased a Mercedes-Benz injector and seal kit. I made the mistake of pulling the retaining clips off of the entire bank only removing cylinder 2 injector from the fuel rail not realizing in so doing, I invited a fuel leak which places fuel into the engine rather than the engine bay. After replacing the injector and seeing that the engine was still running rough throwing misfire codes for four cylinders, I saw a video that explained, you can't simply swap out injectors for this motor and that the check engine light would not go away until this flow rate was registered with the ECM. Not knowing that there was a bunch of fuel mixed in with oil, I tried driving to the local MB service shop to have the injector flow registered with the ECM. I didn't get a 1/4 of a mile before the engine started running even rougher and died when I stopped the car and smoke came out from the engine bay and exhaust.
I had patient towed to the MB shop where they registered the injector flow with ECM and said injector had not been installed correctly and was causing fuel to be dumped into the engine through the valve cover causing white smoke. I spoke with the shop foreman and said that if I changed the oil and properly sealed the entire bank with new seal kits. The engine should run fine again after burning of sentiments and deposits in the exhaust systems for some time. As a result of having the fuel mixing with oil. A condition that would go away provided there was nothing else was wrong. I performed the tasks only to find out no change fuel system error codes are gone. Now I'm left with misfires that is cross banks and now occurs on all eight cylinders. What the hell's going on? and it sure doesn't sound like it's an injector problem!?
I take the patient to see a specialist at the local Mercedes-Benz service shop and perform some tests that include scoping three cylinders and compression checks reporting one cylinder was reporting 25 RPM higher but was within specs (I have no idea what that meant). The Doctor concluded that the injector cylinder 2 looked clean compared to others due to the injector in cylinder 2 had failed and was stuck in the open position, flooding the cylinder and causing the ECM to try and compensate and causing what was now misfires across the entire bank 1-4.
They offered me the opportunity to have them replace the failed injector, replace the aftermarket coil I just purchased and replace all 8 spark plugs for the paltry sum of $3,600. I respectfully declined. I purchased a Mercedes-Benz injector and seal kit. I made the mistake of pulling the retaining clips off of the entire bank only removing cylinder 2 injector from the fuel rail not realizing in so doing, I invited a fuel leak which places fuel into the engine rather than the engine bay. After replacing the injector and seeing that the engine was still running rough throwing misfire codes for four cylinders, I saw a video that explained, you can't simply swap out injectors for this motor and that the check engine light would not go away until this flow rate was registered with the ECM. Not knowing that there was a bunch of fuel mixed in with oil, I tried driving to the local MB service shop to have the injector flow registered with the ECM. I didn't get a 1/4 of a mile before the engine started running even rougher and died when I stopped the car and smoke came out from the engine bay and exhaust.
I had patient towed to the MB shop where they registered the injector flow with ECM and said injector had not been installed correctly and was causing fuel to be dumped into the engine through the valve cover causing white smoke. I spoke with the shop foreman and said that if I changed the oil and properly sealed the entire bank with new seal kits. The engine should run fine again after burning of sentiments and deposits in the exhaust systems for some time. As a result of having the fuel mixing with oil. A condition that would go away provided there was nothing else was wrong. I performed the tasks only to find out no change fuel system error codes are gone. Now I'm left with misfires that is cross banks and now occurs on all eight cylinders. What the hell's going on? and it sure doesn't sound like it's an injector problem!?
I had an R230 that had somewhat similar symptoms - CEL, rought running, failed into limp mode on wide open throttle and misfire codes,
My Indie chased the problem, much as you have - plugs, coils, injectors etc - without success. They were about to give up when someone suggested it might be a problem with the catalytic converters. Sure enough, two new cat's later and the problem was solved. IIRC they said the old cats rattled when tapped and were in bad shape.
Good luck
Gary
My Indie chased the problem, much as you have - plugs, coils, injectors etc - without success. They were about to give up when someone suggested it might be a problem with the catalytic converters. Sure enough, two new cat's later and the problem was solved. IIRC they said the old cats rattled when tapped and were in bad shape.
Good luck
Gary
