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MB-Dude · #15 11-12-2007, 09:40 PM

WOW… Where do I begin? Great responses.

Brett – At the time of the thumping, I was thinking ‘old school’ and wrote the post as an EGR Valve. After a response or two, it became apparent I was not calling the part correctly. Nevertheless on my SL, the canister purge valve is within inches of the Air Pump Valve for Bank 1. Hence the confusion on my part. But… with all the thumping and such, I never got an error code. Strange.

Thanks lesrrt for the information on clogged passages. I’ll check it out in the next day or so. However, I do not think my situation is vacuum related or plugged lines. The car only has ~105K on it and currently is a very clean running engine with smooth idle, fabulous acceleration, and incredible top-end with no misfiring (except for the original problem). However, that’s not to say carbon can’t build up. The issue at the moment is no apparent output from the O2 Sensor, yet the engine runs real strong. With the observations made today, the vacuum leak would have to be massive; large enough to cause very rough idle. Probably similar for a blockage.

Also Brett, another observation… disconnecting a vacuum tube on either bank causes both banks to be affected. I tested this by disconnecting something coming off Bank 2 and watched as the Bank 1 O2 Sensor was affected. Repeating this on Bank 1 side also affects Bank 1, so I know my orientation was not wrong. Therefore, any vacuum leak should cause the same symptoms to both banks. They are not independent. On the V12, there are a number of interconnecting black hoses (~1/2” diameter) that provide cross-over between the intakes; especially at the rear of the engine. Any leak on one side is felt on the other.

Nicer try John! LOL!!! As a sidebar, I didn’t have the guts to tell you that I trashed my old ’94 SL500 wiring harness back in June… just before your first post on the subject. Sorry, dude! Seriously though, I am not discounting that an ECU may be bad. Perhaps good enough for computation, but bad on verifying ‘readiness’. I may come back to you, yet!

Brett – The vacuum line goes from the Brake Booster, through a dividing wall, curves around the #12 coil, and then loops to the upper-rear of Bank 2 where it goes into a three-line connector (?), or something. This connector (if that’s what it is) feeds directly into what looks like the bottom of the intake manifold. But in fairness, I am typing this from memory and only after a very brief glance. If you want, let me know and I’ll get a picture tomorrow.

Mike – Thanks for chiming in. I’ll pop the cover off the computer box on Wednesday and see if there are any different markings on the ECU’s. Also, thanks Mike for taking a look at the data. You may something there. Tomorrow, I’ll take another, longer data capture. Please e-mail me with the parameters you recommend I capture – this will reduce the data set by eliminating stuff we aren’t interested in. ProScan lets me capture any combination of data, for any duration of time. I’ll make a multi-minute run, which will also capture a couple of the random Bank 2, Sensor 1 events.

Just to recap, looks like Brett and I have the same issue – Bank 2 Pre-Cat O2 Sensor reports zero output. This would normally imply a very lean condition. However in my case, the engine runs very smooth and strong. This suggests the ECU is receiving O2 data, computing air-fuel mixture correctly, but not reporting proper O2 status. Thus, the ECU’s are not reporting a ‘Ready’ state.

Thanks again to all. I’m starting to get into areas I have no expertise; i.e.: ECU’s, etc. Any and all input would be really, REALLY appreciated. Thanks to all.

Cheers,
Jeff