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Check engine light

Tiny
LASCRIBE
  • MEMBER
  • 2002 MERCEDES BENZ CLK430
  • 4.3L
  • V8
  • 2WD
  • AUTOMATIC
  • 44,000 MILES
At speed (65-90 mph) in L.A. Traffic, a perfectly-kept car listed above Coupé experienced a CEL illumination. The car was running perfectly, though the weather was cold (~44-50^ f).

Note: The vehicle seems to always encounter engine-issues during Southern California “winter months.” It’s normally (78-117^ f), and the Benz runs smoothly.

I wouldn’t think it was a MAF ‘because the “big cat” part of the exhaust was replaced with new 2.5 years ago (and the offending issue causing the unburnt fuel to f/u the cat was repaired), unless the “old” MAF was reinserted and in need of new, I’m at a loss. This seems to be an “at-speed” issue, as there are no idle-issues and no malfunctions listed. It just happened and I haven’t inserted the OBD-II, but it seems this is a vacuum leak or MAF issue.

Thoughts, anyone?

Thanks.
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Sunday, January 13th, 2019 AT 12:57 PM

2 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,164 POSTS
Hi and thanks for using 2CarPros.

If you aren't getting codes, I question if the MAF or a vacuum leak is the issue. Have you checked the coolant temperature sensors output reading? If it's inaccurate, it can create a problem with fuel mixture. I would put a live data scanner on it and see what it says.

I attached a picture of its location.

Let me know what you find.

Joe
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Sunday, January 13th, 2019 AT 3:26 PM
Tiny
BMDOUBLE
  • MECHANIC
  • 1,139 POSTS
Being that it is happening in cold weather, I would do a thorough vacuum leak test or smoke test. One way that I test for this super quick and easy is to let the vehicle cool down, preferably first start in the morning. Connect a scanner, pull up live data of the upstream oxygen sensors and carefully (away from alternator or hot engine parts) spray the intake where it mates up to the engine and also around the intake hoses while watching the oxygen sensor data. A leak will show up as a positive spike in voltage and will stand out like a sore thumb.
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Sunday, January 13th, 2019 AT 3:55 PM

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