Fuel Distributor Issues

[Bitsyncmaster]

You can not set the idle mixture to compensate for a need for more fuel at a higher RPM and vice versa. The Lambda system will compensate at different engine loads though.This has nothing to do with the mechanical base setting. Mechanically though it is not possible. with just the screw. Proving this is also difficult because if you jack it hard rich the car will not even make it into higher rpms off idle and will foul the plugs etc.

Yes the working lambda system will keep the mixture set to 14.7 AFR within it's range of control. But if you disconnect the lambda (run open loop), I'm pretty sure the mixture adjustment will give you full mixture control at any engine speed. I could put my tailpipe LM-2 system on to check this but that's how people run open loop and adjust the mixture.

[DMCMW Dave]

Let's try something else.

The fuel distributor is a calibrated mechanical valve. The plunger is the valve. A certain deflection of the metering plate which pushes up on the plunger will meter a fixed amount of fuel to the injectors. That's all it does. The injectors don't "fire" per se. The injectors spray whatever is sent to them once the pressure is high enough to open them. Regardless of any other parameter (other than plugged injectors).

The warmup regulator and the frequency valve affect the resistance to air flow of the plate by adjusting the fuel pressure on either side of the plunger (i.e. the plunger is easier or harder to move). This in turn modifies the relationship between air flow and deflection of the plate, but not the relationship between the deflection of the plate and fuel flow.

The range of the ability of the frequency valve to change the mixture, and therefore the lambda system, is very limited. The early turbo control sytems that ground the O2 sensor during boost are simply cranking the frequency valve to go as rich as possible without any attempt at reacting to load, knock, temperature etc.

So - back to the adjusting screw. The problem is that the adjustment screw action is non-linear with fuel flow - it simply sets the position of the metering flap relative to the plunger on the fuel distributor. Visualize graphing fuel flow relative to the flap position - it's a linear relationship with a fixed slope. As you adjust the screw, it does NOT change the slope of the line, only the point where it crosses zero. Therefore a large adjustment at idle (when the fuel distributor is very nearly closed, i.e. fuel flow off) is a tiny, inconsequential adjustment at, say 3000RPM under load.

If you adjust the screw to richen the mixture very much at load, it will foul the plugs at idle - if it will even run at all. Another analogy for the EFI people - picture an EFI map where you can only raise and lower the whole map, and not differently at different air flow rates/temperatures/RPM. You can't change the slope.

The range of the warmup regulator is fixed and only changes when cold to richen it up during idle. It is also has a somewhat limited range. There are aftermarket versions of the warmup regulator that can be electronically controlled to change the mixture based on other parameters, but it's much more complicated than a screw adjustment.

The only other way to modify the slope on a K-Jet (without re-inventing the regulator and/or lambda systems) would be to redesign the fuel distributor internally, which is why there are dozens of Bosch part numbers for what appears to be the same fuel distributor.

[Bitsyncmaster]

The FD holds a pretty good mixture adjustment for our engine even without the lambda. You can see how good it is by reading the FV duty cycle at different RPM settings.

So what your saying is running open loop, (say 13.0 AFR at idle) the mixture at other RPMs would not be close to 13.0?

[DMCMW Dave]

The FD holds a pretty good mixture adjustment for our engine even without the lambda. You can see how good it is by reading the FV duty cycle at different RPM settings.

So what your saying is running open loop, (say 13.0 AFR at idle) the mixture at other RPMs would not be close to 13.0?

Can't say I've ever tried it, but on a stock engine it might not be terribly far off. The Lambda system is not making gross adjustments, as has often been mentioned it was added to keep the catalytic converter happy. It's more of a fine-tuning than a comprehesive electronic control.

The problem comes in when you mover further from stock and do something to the engine that wants more fuel at a given RPM in the higher ranges, i.e. forced induction, high compression etc. but doesn't need it at idle.

This is all pretty far off the original post now.

[Elvis]

...

So - back to the adjusting screw. The problem is that the adjustment screw action is non-linear with fuel flow - it simply sets the position of the metering flap relative to the plunger on the fuel distributor. Visualize graphing fuel flow relative to the flap position - it's a linear relationship with a fixed slope. As you adjust the screw, it does NOT change the slope of the line, only the point where it crosses zero. Therefore a large adjustment at idle (when the fuel distributor is very nearly closed, i.e. fuel flow off) is a tiny, inconsequential adjustment at, say 3000RPM under load.
...

Dave - thank you for that good explanation.
mathematically spoken: y = a*x+b
the only thing you can change with that screw is "b", not the slope "a".

So there is no spring or whatever that makes it change only at idle.

Thanks, time to grab a beer :-)

[Ron]

...it's a linear relationship with a fixed slope.

Thank you very much!

[TonyDi]

Well I have gotten the adjustment to a point where the car will start but then immediately die. The plugs get fouled before the car even warms up to check the dwell. Any ideas?

[Ron]

Try unplugging the cold start valve.

[TonyDi]

Try unplugging the cold start valve.

It won't start at all that way. If I have the pedal down when I hit the ignition it won't start either. When I try to start it it revs for a second then if I am not immediately on the throttle it dies. If I can keep it going response is sluggish & I have to constantly work it to get it to run. I have tried movin the screw a full turn in either direction (in small increments) & it is the same through the whole range except maybe slower stumbling to death. It never matures into a stable idle.

[Elvis]

is the piston in the fuel distributor stuck ?