Advanced CIS questions

[Vereeken]

At least to me.

I only have experience with the non-lambda CIS on EURO cars.

1. CIS is continuous. So what happens to the excess fuel that is injected on the cilinders that are not firing when you turn off the engine?

2. Does the height of CCP affect in any way the CO setting when fully warm? I do not think that there is a relation but am wondering if start height of the bi-metal can affect the CO also when warm...

3. The residual pressure I see is the first 20 minutes higher then the opening pressure of the injectors (minimum 2.5 bar). Is it possible that fuel gets through the injectors when the car is turned off and residual is 2.8 bar?

4. Following from 3 would a leaking injector also not manifest himself in a quick drop of residual pressure?

Michel

[RarlyL8]

The injectors stop flow when the air meter plate closes, such as engine shut down. There may be residual run-on if you have a leaky injector.
Yes the pressures are a 3-way see-saw. All affect each other to some degree.
Injectors do not see control pressure. If fuel is getting through at less than cracking pressure you have a leaky injector.
Residual pressure is held by the accumulator and pump valve, injectors would have to be leaking badly to significantly drain pressure off the lines.
Symptoms of a leaky injector are rough key/engine cut off and long/hard cold starts. Idle will also "miss" or be irregular.

[ossiblue]

RarlyL8 has answered most of your question.

As far as your no.2 question, CCP has no effect on warm pressure nor mixture setting. The pin, which controls fuel pressure, is controlled by the springs beneath it. The bi-metallic arm, when cold, depresses the springs slightly, moving the pin downward from the diaphragm, thus lowering the fuel pressure. When the arm heats and bends upward, all pressure is off of the springs (if it's been adjusted correctly), and the pin's position is totally controlled by the springs alone.

Now, to fully answer your question, if one sets the CCP too low and the bi-metallic arm does not release all pressure off of the springs, even when fully bent upward, then the warm pressure will be too low and your CO will be affected. A properly set WUR will have the warm pressure set first with the bi-metallic arm fully warmed and disengaged from the springs. Then, when cooled, the plug will be tapped downward to adjust the CCP.

[Vereeken]

Thank you guys.

So to follow up. If the air meter plate at rest is maladjusted it is possible that the injectors continue to flow after engine shut down?

If the WCP is following specs between 3.4 and 3.8, is it safe to assume that the bi-metal is fully disengaged when the pressure reading shows 3.5 bar after 5 minutes engine running with 20 degrees celcius outside?

[T77911S]

i think starting in 78 there is what bosch calls a push up valve in the primary pressure reg.
this valve closes when the pump is turned off and pressure starts to drop.
this shuts off the return line to the fuel tank from the WUR to help with residual pressure.