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1984 500sel
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13 Posts
Discussion Starter #1
Hello everyone, my 1984 500sel has been acting strange lately, with the temperature gauge rising more than usual when sitting in traffic and the needle also jumps occasionally. There’s a new loud buzzing noise coming from engine bay so I took off the air filter and found the source. It’s a part that looks like it’s in dire need of replacement but I’m not sure what it is/called. Any help would be appreciated
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84 500SEL AMG, 90 560SEC AMG, 85 500SEC AMG Widebody
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1,757 Posts
Fuel Frequency Valve
 

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Outstanding Contributor
350SDL, '17 GLS450, "Grandpa's Roadster" Project Car
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3,084 Posts
I'm sure HD will give you a better explanation, but, in a nut shell, it varies the control pressure in the fuel distributor to adjust the mixture based on the O2 sensor reading.

(You might want to give that cracked hose a good looking over as it carries fuel pressures in the 15-45 psi range.)
 

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1991 500SEC sub 50K mi. 1987 560SEC Now 150K mi. 2018
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4,207 Posts
Hi there,

It's a Frequency Valve as others have noted, and is NLA now.

As it is in operation, its buzzing can be somewhat loud, judging from my experience as a Volvo line tech all those years ago, as it dumps excess fuel back to the tank....

I did find a NOS one for your car, should you wish...... It would need a fuel line & fitting to install. I think that should be pretty straight-forward to do..


OR:
Cheers,

MBL


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1985 MB 500sel (Euro)
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184 Posts
Concur that cracked hose looks bad Understand NLA, but what does NOA mean?

Looked for the fuel frequency valve. Couldn't find it, then remembered I don't have an O2 sensor either. My guess is that my GenI euro model makes do with the WUR to vary fuel mix.
 

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Outstanding Contributor
350SDL, '17 GLS450, "Grandpa's Roadster" Project Car
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3,084 Posts
NOS, not NOA... New Old Stock.

If you don't have an O2 sensor then there's no feed back and no frequency valve. The Warm up regulator adjusts the control pressure during warmup, after which it is fixed.
 
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