96 SL600 Exhaust Air Valve - PeachParts Mercedes-Benz Forum

MB-Dude · #1 11-12-2007, 05:21 PM

Please refer to the attached picture (Bank 2 MAF has been removed for clarity) from a '96 SL600. If this is the Air Valve that feeds air into the exhaust, what would be the effect on engine performance and, more specifically, O2 Sensor operation if the valve were to be stuck in the open position? Arguably, this would be a rare case as (I presume) the valve is normally closed and requires vacuum to open. But it could get stuck open, maybe.

The reason this is important is that in troubleshooting this problem…
V12 ECU's Reporting 'Not Ready'
…the symptoms seem to suggest an overly lean exhaust out of Bank 2. Yet the engine must be burning the correct, or close, air-to-fuel mixture, because the engine runs awesome!

QUESTION: How does one test for proper Air Valve operation? More to the point, how does one remove the valve from the engine (my R129 Repair DVD is unavailable)?

Cheers,
Jeff

Brett San Diego · #2 11-12-2007, 07:48 PM

Yes, it is the air injection valve. But, I don't like this as a possible cause to our problems either. It's not enough for the valve to be stuck open in my opinion. For air to enter the exhaust system and lean out the exhaust, more things have to happen at the same time. The clutch on the air pump has to be energized so the pump turns, and the switchover valve (another valve between the air pump and the air valves) has to be opened. Now air can be pumped through the opened air injection valve. Perhaps it is possible for air to be drawn into the exhaust if you have a break in the air supply line between the switchover valve and the air injection valves, and I suppose this should be ruled out as a problem, too. But, overall I just don't think that is it. Just my thoughts.

Quote:

QUESTION: How does one test for proper Air Valve operation? More to the point, how does one remove the valve from the engine (my R129 Repair DVD is unavailable)?

I don't think you need to check operation. The car does it for you regularly. Well, it checks that air injection occurs when commanded. The computer cannot specifically identify a stuck open valve. It would be inseparable diagnostically from all the other vacuum leaks causing lean running, as you surmize. I think you're right that you'd have to remove it from the cylinder head and apply a vacuum to it and see if you can blow through it. And check that you can't blow through it when the vacuum is removed. I haven't looked closely enough to see how it is removed. I will look.

Brett

MB-Dude · #3 11-12-2007, 08:48 PM

Quote:

Originally Posted by Brett San Diego

... It's not enough for the valve to be stuck open in my opinion. For air to enter the exhaust system and lean out the exhaust, more things have to happen at the same time. The clutch on the air pump has to be energized so the pump turns, and the switchover valve (another valve between the air pump and the air valves) has to be opened. ...

Yes, your response makes sense. Guess I was just brainstorming possibilities, given the problem set.
Cheers,
Jeff

Brett San Diego · #4 11-13-2007, 01:23 AM

My bad. I seem to be full of misinformation. I've looked at so many diagrams in the last few days, I'm getting my wires crossed. There is no additional valve between the air pump and the air injection valve. The switchover valve is the device that routes vacuum to the injection valve to open it up. So, if an air injection valve is stuck open, perhaps it would be possible for air to passively get drawn into the exhaust stream, but it would have to get sucked through the non-running pump mechanism, unless as I mentioned before, there is a break in the air supply lines between the pump and the injection valves.

Brett