[W126 Coupe] Opinion on ignition parts & dust cover

Thu Sep 15 16:35:34 EDT 2005

This car has separate lights for check engine and 02 sensor, no? The O2 sensor light is activated by nothing more than mileage (at least on pre-86) and if it was ever replaced there is no more light bulb behind the O2 sensor light (that was part of the repair procedure,  apparently because as it turns out those O2 sensors do 120k before needing replacement typically, not 60k).  

-----Original Message-----
From: mbcoupes-bounces at mbcoupes.com [mailto:mbcoupes-bounces at mbcoupes.com] On Behalf Of Richard Hogarth
Sent: Thursday, September 15, 2005 3:24 PM
To: 'Mercedes Coupes Mailing Lists'
Subject: RE: [W126 Coupe] Opinion on ignition parts & dust cover

Tom,
I would bet that oil combustion products are getting deposited on the O2 sensor at idle and causing the chk engine lite to go on, then the hot gasses burn off some of that junk at normal temp or higher speed then the lite goes out. 
If you are burning that much oil and at that engine age, the egr valve is likely not sealing well and not operating smoothly, also prone to causing and being effected by vacume leaks causing the chk engine lite to go on and off. I'll get back to your plug issue later. Need to do some work. (lol) -Richard Hogarth

-----Original Message-----
From: mbcoupes-bounces at mbcoupes.com [mailto:mbcoupes-bounces at mbcoupes.com]
On Behalf Of Tom Oelsner
Sent: Thursday, September 15, 2005 2:14 PM
To: Mercedes Coupes Mailing Lists
Subject: RE: [W126 Coupe] Opinion on ignition parts & dust cover

Richard,
Always smooth on startup, don't recall if it is after hwy or city (I'll try and monitor over next few weeks), more prone to rough (not glass smooth) when hot.  I am burning a lot of oil...definitely seals based on mechanic feedback.  O2 was replaced about 20k miles ago.

Here is one for you...when driving at low speeds after car is first started and coming up to temp (in the 40 degree C range) or has been sitting for a period of time (but not necessarily cold), the check engine light comes on.
After a minute or 2 of acceleration, the light goes out.  Happens every time.  Since nobody outside of the dealer has the error codes for a non CA car and do not know the connector pinouts, they cannot access the code or read it.  I have not had the time to research building a small LED readout, connector pinouts and codes.
Tom

-----Original Message-----
From: mbcoupes-bounces at mbcoupes.com
[mailto:mbcoupes-bounces at mbcoupes.com]On Behalf Of Richard Hogarth
Sent: Thursday, September 15, 2005 11:47 AM
To: 'Mercedes Coupes Mailing Lists'
Subject: RE: [W126 Coupe] Opinion on ignition parts & dust cover

Tom,
Give us a little more,
Runs rough at startup, after stop and go,after being on the hwy, etc etc.
Does it run rough when the AC compressor cliks on? when it's hot or cold or whatever.  On that age of engine, inconsistent small vacume leaks that come and go with temperature and vibration changes are your biggest culprit. If you are using some oil, a little more of less build up on the oxygen sensor, or if the o2 sensor is not healthy may be the cause.
The ignition temp sensor in the intake manifold is also an item that can cause rough running and idling.
-Richard Hogarth

-----Original Message-----
From: mbcoupes-bounces at mbcoupes.com [mailto:mbcoupes-bounces at mbcoupes.com]
On Behalf Of Tom Oelsner
Sent: Thursday, September 15, 2005 1:16 PM
To: Mercedes Coupes Mailing Lists
Subject: RE: [W126 Coupe] Opinion on ignition parts & dust cover

I never tried it but will next time it acts up Tom

-----Original Message-----
From: mbcoupes-bounces at mbcoupes.com
[mailto:mbcoupes-bounces at mbcoupes.com]On Behalf Of Shayegan, Richard
Sent: Thursday, September 15, 2005 11:12 AM
To: Mercedes Coupes Mailing Lists
Subject: RE: [W126 Coupe] Opinion on ignition parts & dust cover

I'm using W9DC's in my 380 and the only mechanical issue I still have I is exactly the one you describe: sometimes it's perfectly smooth, but also every now and then it idles a bit rough. No rougher than a non-German engineered engine, but not as smooth as it is when it's running right. I don't have any fouling, and I'm using the proper plugs, so if we do have the same issue I don't think your plugs are at fault. Does yours also smooth out if you goose it in neutral a few times?
Richard

________________________________________
From: mbcoupes-bounces at mbcoupes.com [mailto:mbcoupes-bounces at mbcoupes.com]
On Behalf Of Tom Oelsner
Sent: Thursday, September 15, 2005 1:58 PM
To: Mercedes Coupes Mailing Lists
Subject: RE: [W126 Coupe] Opinion on ignition parts & dust cover

I'm using Bosch, Platinum 2, R3.  Sometimes the engine idles so smoothly that I am not sure it is running.  Other times it idles a bit rough.  This is in spite of the fact that I have major oil fowling on at least 1 plug (just checked one to confirm plug type.  I know I need the valve seals done.).  Oh yeah, for what it is worth, the car was not originally a CA car.  It was from Texas.
Tom
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