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S-Class (W140) 1991-1999: 300 SD, S 350TD, 300 SE 2.8, S280, 300 SE 3.2, 300 SEL 3.2, S320, S320L, 400 SE, S420, 400 SEL, S420L, 500 SE, S500, 500 SEL, S500L, 600 SE, S600, 600 SEL, S600L, 500 SEC, 600 SEC

S420 O2 sensor fault, no CEL

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Old Dec 31, 2015 | 04:27 PM
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1989 300E
S420 O2 sensor fault, no CEL
I'm working on a 1996 S420 for my dad, this was his dream car back in the 1990's and I'm hoping he will be able to drive it soon. The car has issues where it sometimes stalls, or near stalls, especially when the a/c is turned on, sometimes it's low on power when and bogs slightly off the line. So far I've changed the plugs (old gap was 2.5x spec) and toyed around with my obd2 interface. Oh yeah and it doesnt pass DEQ because nothing is ready even though I've put over 500 miles on it. So my friends interface said the car is running in closed loop but my elm327 says that it's running in open loop but with an o2 senor feedback fault. O2 readings vary wildly but usually stay around the 0.0-0.3 mark, sometimes one of the o2s goes up to 1.1v. My cheap readers refreshed rate is really slow so its hard to see how fast the are really fluctuating. Any idea on how to dignose the problem? I don't want to jump into changing out the o2s without making sure they are actually the problem. Keep in mind that there is no check engine light popping up and that the PO had one of the 02s changed to no avail. Any input would be appreciated.
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Old Mar 1, 2016 | 10:37 PM
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s280 w140 chassis and w140 s600sel
its coils - cheap on ebay and easy to install at least on my cars they are
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Old Mar 1, 2016 | 10:37 PM
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s280 w140 chassis and w140 s600sel
prob get a set for a good price
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Old Mar 1, 2016 | 10:39 PM
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s280 w140 chassis and w140 s600sel
i.e. coils break-up under load particularly with, brake lights on too long at lights, air-con and getting hot - yes?
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Old Mar 1, 2016 | 10:39 PM
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s280 w140 chassis and w140 s600sel
my V12 might get sorted with plugs but I know I'm in for coils I'll bet.
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Old Mar 1, 2016 | 10:40 PM
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s280 w140 chassis and w140 s600sel
ie I have a thread going about it
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Old Mar 1, 2016 | 10:40 PM
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s280 w140 chassis and w140 s600sel
coils
the S600
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Old Mar 1, 2016 | 10:43 PM
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s280 w140 chassis and w140 s600sel
My friend has a Singaporean built S400 V8 - same as yours?? Anyway he is having sluggishness when hot - nearly stalling at lights and running air!! Funny that - so there you go its not year of the monkey its year of the coil - i hear that my S600 eats coils and its very hungry! haha
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Old Mar 2, 2016 | 10:32 PM
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1989 300E
What makes you say its coils? I tested each coil and they the same resistance as a known good car.
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Old Mar 21, 2016 | 03:59 AM
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s280 w140 chassis and w140 s600sel
sorry been away - a few of us think its mass air flow sensor - cheap
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Old Mar 21, 2016 | 03:59 AM
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clogged air filter wouldn't help either
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