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JFairman JFairman is offline
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Join Date: Jul 2006
Location: S. Florida
Posts: 7,289
The lambda valve is an inline fuel injector that is opening and closing in pulses. Thats the buzzing sound and it's returning fuel from the lower differential chamber or bottom half of the fuel head to the gas tank.
System pressure fuel feeding the lower chambers has to go through an orifice so returning some of it faster than it can be replenished will lower the pressure.

Removing the lambda valve and plugging the inlet line to it line on one end and installing a shorter banjo bolt on the return line side of it will stop the return of fuel and increase lower chamber fuel pressure little and that will push the diaphragm that seperates the upper and lower chambers upward.

[The control pressure regulator is a seperate circuit that shares the same small 10x1mm thread return line banjo bolt.
The fuel is returned there so it goes through a small fuel pressure valve in the middle of the system fuel pressure regulator valve so it holds system fuel pressure after the fuel pumps are shut off.]

As the diaphragm flexes up a little it closes off or restricts the opening of the bottom side of the 6 final fuel metering orifices that lead up to the injector line fittings.
That will lower fuel flow and fuel pressure to the fuel injectors.
There are also 6 little springs - one around each final metering orifice pushing down on the top of the diaphrahm with 3mm allen head adjustment screws that adjust the spring pressure.

Failure mode of the lambda valve inline injector could be stuck open letting too much fuel return to the tank instead of the pulsing open and closed action it usually does (the buzzing sound) or stuck closed and then it would not be returning any fuel to the gas tank.

Stuck open would drop the lower chamber fuel pressure lowering the diaphragm a little which would let more fuel by the clearance between the top of the the diaphragm and the bottom of the 6 final metering orifices and stuck closed or unplugged so it isn't buzzing or pulsing and returning fuel to the tank from the lower chambers will raise lower chamber pressure pushing the diaphragm upward a little closing off the clearance between the top of the diaphragm and the bottom of the 6 orifices and that will reduce the amount of fuel going to the injectors a little leaning out the AFR a little.

This is all happening after the airflow meter has moved the control plunger up or down in it's cylinder exposing more or less of the 6 vertical fuel metering slits in the control plunger cylinder wall leading to the upper differential chambers in the top half of the fuel head.

If you could see a cross section diagram of the inside of the fuel head with arrows showing the orifices and fuel flow through the inside of it, it would be easier to understand whats going on.
Old 11-18-2014, 07:42 AM
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