Air valve problems ??? - Mercedes-Benz Forum
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#1 (permalink) Old 12-22-2008, 12:41 PM
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Air valve problems ???



I'm experiencing a strange new problem on the SL. In the last month I've been stranded 3 times. Also, the sometimes the engine refuses to fire and then 30 minutes later it's as if there never was a problem.
I've replaced the overload protection and fuel pump relays. I just replaced the plugs and wires as well. today it started and ran fine. After lunch I tried to start it and no joy. I took the air cleaner off and the air valve (that's what I call it but I'm sure there is a real name for it, see pic) just hops up and down and the motor will stall. It's just starting to do this now as it's getting cold but I don't know if thats just a coincidence of related.

What would cause this plate to jump? Is there a relay that controls it? Is the cold a likely related factor?????

Thanks all and may you and yours be happy and safe over the holiday season
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#2 (permalink) Old 12-22-2008, 01:23 PM
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That is the 'metering plate' or 'air flow sensor'.

The amount of deflection of the plate caused by the volume of air that passes over it determines the quantity of fuel delivered by the fuel distributor.

Changes in operation with denser cold air may indicate adjustments to the rest height and or plate centering are needed.
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#3 (permalink) Old 12-22-2008, 02:29 PM
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Changes in operation with denser cold air may indicate adjustments to the rest height and or plate centering are needed.
What other phenomenon can be observed when cold air passes through the intake, especially if said cold air also happens to be moist?

Felicita e un bicchiere di vino con un panino.
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#4 (permalink) Old 12-22-2008, 03:41 PM
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Thanks guys for the rapid reply.

Here is the situation. When it won't start the air flow sensor will slap up and down rapidly and sound like a bad rattle. You might get a momentary start but it will stop almost instantly. I've notice a cloud of white smoke form the exhaust if I really try and gun it. It's not oil color or smell. It is very intermittent and will happen cold or hot. It will happen when first started or after being driven for a while. The last time, before this one, it happened it started fine then about a mile into my trip it stalled out several times and then would not restart . I tried restarting it 10+ time and nothing, just bad rattling smoke and stalling. After about an hour, my wife came and got me and we went to several shops, we returned and it started right up and we drove it all the way to the shop. That is when we replaced the plugs and wires. The previous time it died on the parkway and I had it towed. That time we replaced the overload and fuel pump relays.

Could it be the black relay, below the fuel distributor, showing on the left center of the picture? If so what is it one called and is there any adjustment of it?

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#5 (permalink) Old 12-22-2008, 03:52 PM
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Ike, if you have something to contribute, please, carry on....
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#6 (permalink) Old 12-22-2008, 03:57 PM
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I'm thinking a stuck valve. This would let compression return to the underside of the metering plate and cause it to do what you described.
One the other hand, it you had no fuel pressure, there would be no counter pressure from the WUR and then plate might move more freely.
I'm just thinking out loud here.

Timing has a lot to do with the outcome of a Rain dance.

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#7 (permalink) Old 12-22-2008, 04:01 PM
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Ike, if you have something to contribute, please, carry on....
Well, I can't very well be doing`all your thinking for you guys, but I can help you along. C'mon, everyone, cold, moist air that's accelerated through a venturi-like opening. What could be happening?

Felicita e un bicchiere di vino con un panino.
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#8 (permalink) Old 12-22-2008, 04:15 PM
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NASCAR -- Fuel pressure seemed fine, at least when it was running. I'm thinking you're right about pressure but it's not constant. Since it's intermittent then I was thinking a failing relay. Since the relay, circled in the photo, is under the distributer I thought maybe it was related to a flow problem as well as the fact that the fuel pump relay was just replaced. What is it called so I can look it up in the EPS. It's not shown in the engine or fuel system sections

Ike -- thanks for the support.
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#9 (permalink) Old 12-22-2008, 04:29 PM
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Quote:
Originally Posted by miked56
What is it called so I can look it up in the EPS. It's not shown in the engine or fuel system sections

I'm not that familiar with your KE. This post refers to a potentiometer.....



http://www.benzworld.org/forums/w116...ml#post1719873
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#10 (permalink) Old 12-22-2008, 04:29 PM
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Ike -- thanks for the support.
Let's forget about all those relays for a second. Let me ask you this: does this happen after a long trip(s), by any chance? Like you drove a lot the day before maybe and then the next day it will start doing that?

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