Misfire (M271) O2 Upstream Sensor reads 2 Volts - Is this a sign it is about to fail

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Aug 28, 2020 | 11:59 AM

Blackrock63

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Junior Member

Joined: Mar 2012

Posts: 15

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c180

Misfire (M271) O2 Upstream Sensor reads 2 Volts - Is this a sign it is about to fail

I have a C180K 2006 with over 100,000 miles on it
After taking off the cylinder head and putting the engine back together after replacing the cam adjusters and gears due to slipping 3 teeth i now have an engine misfire when hot.

Engine runs smooth on idle and drives fine while cold
One engine gets up to full temps it develops a misfire and throws engine light code for cylinder 4 misfire. It has also shown a misfire on cylinder 1
I have changed over the coil packs and plugs to see if misfire follows them but it doesn't
If i leave the engine to cool and restart then the engine runs smooth again until it gets up to full temp and then misfires again
The Short term fuel trim reads around 2.2 and Long Term fuel trim reads a constant 0.8
The O2 B1 S1 sensor reads 1.5v and goes upto 2.2v when the misfire begins
I have sprayed engine start around the intake to see if misfire disappears but it doesn't change the engine note at all so i don't think it is an air leak near the intake manifold or air b

I have searched high and low to find out if an upstream O2 sensor reading 2v is a sign it is faulty and about to fail but i have found nothing on this forum or on Google anywhere. Can anyone tell me if 2v is far too high?

I am thinking of taking the o2 sensor out and cleaning it with electrical cleaner to see if it makes a difference

Any ideas anyone?

Thanks

Aug 31, 2020 | 10:34 PM

slammer111

MBWorld Fanatic!

Joined: Dec 2003

Posts: 3,275

Likes: 236

From: BC, Canada

2003 C230K Coupe Orion Blue

When in doubt just change it out. They're not terribly expensive.

Have you tried swapping the ignition coils and spark plugs between cylinders?

Aug 29, 2021 | 04:45 PM

Pexen

Newbie

Joined: Jun 2021

Posts: 11

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C180 m271 2005

Quote:

Originally Posted by Blackrock63

Engine runs smooth on idle and drives fine while cold
One engine gets up to full temps it develops a misfire and throws engine light code for cylinder 4 misfire. It has also shown a misfire on cylinder 1
I have changed over the coil packs and plugs to see if misfire follows them but it doesn't
If i leave the engine to cool and restart then the engine runs smooth again until it gets up to full temp and then misfires again
The Short term fuel trim reads around 2.2 and Long Term fuel trim reads a constant 0.8
The O2 B1 S1 sensor reads 1.5v and goes upto 2.2v when the misfire begins
I have sprayed engine start around the intake to see if misfire disappears but it doesn't change the engine note at all so i don't think it is an air leak near the intake manifold or air b

Did you sort this out? I have the same problem. After driving 20 minutes misfire begins, if I let the car cool down it runs great again.

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