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2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
What scanner are you using? If it is generic, you may not be seeing everything.
Sounds like you may have low compression on cylinders 2 and 6. I would do a compression test first. With a proper Mercedes scanner, you can do a relative compression test that compares the speed for each cylinder. Slower speeds mean higher compression and faster speeds means lower compression. If the difference between cylinders is significant, the test will fail, and you know you have a mechanical problem, such as a blown head gasket, bad rings, or a cracked head, none of which are good news.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
I'm not familiar with Autocom 2020 but I assume it has Mercedes-specific software. If you think the MAF is bad, you can try to disconnect it completely and try to start the car. If the MAF is bad, the car will start but run rough. The Autocom 2020 should allow you to run a relative compression test since it appears to be a higher-end scanner.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Good explanation of a relative compression test. But the Autocom should have a function for you to run the test. You do not need the Snap-On tool. You may want to do a YouTube search for your location.
I tried a cold start again this morning. I still only have spark plug number 6 changed.
It's unbelievable. no engine light, no misfire. The outside temperature has been the same in the morning for 2 or 3 weeks, so nothing to change except the spark plug.
My son's C230 behaved like this when the intake started falling apart.
Initially it would run pretty well sometimes, and others it would barely run and would throw a code for misfires on the front two cylinders, and codes for lean bank one and two.
Then it started running crappy all the time. The hole in the front of the upper plenum where the arm is for the variable intake flaps to connect was falling apart and leaking vacuum badly. When we got the intake off, the whole assembly fell out.
As other have said, a good light and detailed visual inspection of the front of the intake is a good place to start.
Last edited by MaxxAction; Jan 21, 2025 at 08:20 PM.
Reason: spelling
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Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
