All:

Can the frequency valve in a CIS system (I have an 84 380SE) be serviced. I mean either taken apart or cleaned with a fuel injector cleaner etc.

Reason I ask is I want to fix the flutterring/pulsation/vibration of my Air Flow Sensor Plate at idle. When I disconnect the frequency valve, the vibration dissapears. Reconnecting it back does not return the vibration. Except if you rev up the engine and return it back to idle - when it starts vibrating again.

Thanks,

Amit

I don't know what you mean by "frequency valve". Do you mean electro-hydraulic actuator (EHA).

Duke

Duke

Join the club ! I do not know what the EHA does.

But in Bosch CIS systems, the Lambda Control Cycles the Fuel Frequency Valve and tries to maintain it at a 50% Duty Cycle to achieve correct A/F ratio. The frequency is kept constant - but the on-off duration of the frequency valve is varied to correct the A/F ratio. Lambda controller ultimately gets its signal from the Oxygen Sensor and maintains closed-loop control.

Thanks,

Amit

I believe you are referring to the EHA. The duty cycle will vary depending on how much time the EHA is lean biasing versus how much time it is rich biasing the mixture to maintain and average stoichiometric mixture. (I think a higher than 50 percent duty cycle is an average lean bias, but I might have it backwards.)

The mechanical adjustment on the air flow meter should be set to achieve a duty cycle in a range of 45 to 55 percent at idle and 2500, no load, which places the EHA near the middle of its working range. It then will adjust fuel flow to maintain stoich. for varying air density, varying oxygen quantity in the fuel, etc.

Frequency and duty cycle are not the same thing. I'm not sure if the EHA frequency is constant (I don't think it is.), but the value we test from the X11 connector superimposes the postion of the EHA (rich or lean bias) on a 100 Hz signal generated by the ECU, which tells us on average if the EHA is biasing lean or rich.

I do not believe the EHA is serviceable. If defective MBZ says replace it, but enterprising individuals can sometime open up "non-serviceable" components and repair them.

There is an excellent writeup on testing and adjusting the duty cycle at:

www.landiss.com/mixture.htm

I highly recommend that all the DIYers print out these pages and file them with your service documentation or maintenance records. I sure did!

Duke

A frequency valve is not the same thing as the EHA although it accomplished the same task. The frequency valve is supposed to make a buzz when it is working normally. You have other problems with the sensor plate probably not associated with the frequency valve. I would look for loose or worn components associated with the air flow sensor plate, like pivot points, linkages etc.

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I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k

Does anyone know where to get the corresponding X11 male connector?

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Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

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Not part of the in-crowd since 1952.