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32.000KMS Low compression in 2 cyl and carbon build up
Hey guys, I have a C63 AMG W205 (MY17) with 32,000 KMS, and last Friday I got a CEL and a misfire. Today, I sent the car to the workshop, and the scanner showed misfires in cylinders 1, 5, and 6. They checked the spark plugs and found that they need to be replaced. However, they also conducted a compression test and found that two cylinders have lower compression. Additionally, they discovered carbon buildup in 3 cylinders. What should I do considering the low mileage? Should I sell it as soon as possible, or am I overreacting and should keep driving it making sure to do proper maintenance?
Does your ECO Start/Stop button still illuminate? Or is it not allowing you when you get the CEL
It did illuminate after the CEL but I turned it off since I didn't want to force the engine to start/stop. So now I'm waiting for the ignition coils to be delivered in order to change them.
⏱️ 700HP Facelift converted C63 S Coupe with Drexler 3.06 plated LSD
Originally Posted by wkwong2
It did illuminate after the CEL but I turned it off since I didn't want to force the engine to start/stop. So now I'm waiting for the ignition coils to be delivered in order to change them.
Not yet, as I haven't taken the car to the workshop (waiting for the coils). Testing the injectors seems like it might be difficult. So maybe I'll try luck changing the coils first.
⏱️ 700HP Facelift converted C63 S Coupe with Drexler 3.06 plated LSD
Originally Posted by wkwong2
Not yet, as I haven't taken the car to the workshop (waiting for the coils). Testing the injectors seems like it might be difficult. So maybe I'll try luck changing the coils first.
If compression is low you have a leak, A coil can't cause low compression. A leak down test is in order. The leak down test will show where the cylinder is leaking. A cylinder can leak past the high pressure injector on direct injected engines. Past the Head Gasket, Past a valve or past the piston rings. A leak down test puts 100 PSI of air into the cylinder with the valves closed. The leak down receives 100 psi and blows that into the cylinder through the spark plug hole. It has 2 gauges attached, one measures the intake air pressure, (100 psi). the other measures how much pressure is in the cylinder. So if intake air is 100 PSI and cylinder pressure is. only 85 psi you know you have a 15% leak. For valves you listen to the Intake and exhaust for sounds of leaking air. For piston rings you can listen at the dip stick tube with the dip stick removed. If air goes past the rings it is in the oil pan and till try to escape out the easiest route, dip stick tube. I have never heard a Direct Injected injector leaking but I imagine you will hear it if that is the source of your leak. Might need a mechanic stethoscope. You also need to find a quiet way to get your air pressure for this test. You will never hear a leak if your compressor is running close to your car as you test.
I know of guys that test below 100 PSI but I think 100 is optimal, it makes all the math simple for measuring your leak down amount. If you test with 80 psi and your cylinder pressure is 68 psi you need a calculator to find the leak percentage but if you test with 100 PSI you always know your leak % at a quick glance.
If your coil is not firing but the injector is still spraying fuel it can wash oil off the piston rings and cylinder which could drop compression but also can cause piston and cylinder damage from lack of lubrication. New cars have the ability to shut off an injector if it see's misfire happening to avoid this issue so I think you are looking at the other possibilities.
Keep us posted what you find.
Mark
Last edited by Westlotorn; Apr 21, 2024 at 10:33 PM.
Just received the coils at my PO Box in Miami. Now, I need to ship them here (Chile). I expect to have them here by the end of this week or the beginning of next. The local MB dealer wanted to charge me $600 USD for each coil, but I found them at AutoNationParts for only $170 USD each, rather wait a couple of weeks than pay overprice parts.
If the CEL is gone and the car is working after replacing the coils, my plan is to perform a running-in period and use some injector cleaners. Then, retest the compression to see if the problem persists or not. I will keep you guys updated.
⏱️ 700HP Facelift converted C63 S Coupe with Drexler 3.06 plated LSD
Originally Posted by wkwong2
If the CEL is gone and the car is working after replacing the coils, my plan is to perform a running-in period and use some injector cleaners. Then, retest the compression to see if the problem persists or not. I will keep you guys updated.
Hey! So, they changed the coil packs today and the car is performing well. I did a roll test and reached 161 MPH with no problems at all. The only thing I noticed is that when I put it in reverse, the RPM increases a little, like a spike, and then goes back to 1000 RPM. I think that the cylinders and valves might require some fuel additive to clean them up. Any recommendations?
Hey! So, they changed the coil packs today and the car is performing well. I did a roll test and reached 161 MPH with no problems at all. The only thing I noticed is that when I put it in reverse, the RPM increases a little, like a spike, and then goes back to 1000 RPM. I think that the cylinders and valves might require some fuel additive to clean them up. Any recommendations?
my car has been doing this too since coil change , it jumps a little bit then stays regular it’s weird.
[QUOTE=wkwong2;8970332]Hey! So, they changed the coil packs today and the car is performing well. I did a roll test and reached 161 MPH with no problems at all. The only thing I noticed is that when I put it in reverse, the RPM increases a little, like a spike, and then goes back to 1000 RPM. I think that the cylinders and valves might require some fuel additive to clean them up. Any recommendations?[/QUOTe
Recently had CEL displayed drove to MB Dealership where it determined combustion misfiring
of cyclinder 5 and 6.
My car was at the Dealership fot 2 weeks. The ignition coils and sparks plugs (5 and 6) were replaced under MB Warranty for ignition coils till 100,000 miles.
. The Dealership did an overnight road test to log on miles to confirm the condition was corrected and it was.
I initially thought it was caused by filling up with bad gas but maybe not, just coincidence.
To appease me the Dealership supplied me a bottle of Valvoline fuel injector cleaner. I put it in with tank having about 65 mile range and filled up with fresh fuel at a station the Dealership uses.
. Photos above shows the detailed step by steps performed by mb tech.to address this issue.
So far no problems.
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