gbgastowers

I have had the engine out twice in the past year and have addressed any rubber deterioration issues. Anything is possible with this old thing though.

gbgastowers

I can press the air metering plate down and it revs like a formula 1 race car. Perfect. I think this being able to happen eliminates timing,vac leak and compression questions among others.

Dennis Wilson

Air and fuel have to be tied together to get the correct A/F mixture. If you have too much air due to a vacuum leak, pushing the air sensor plate down increases the fuel without adding more air to correct the A/F ratio. This indicates there is a vacuum leak or your A/F is set too lean. Common areas for leaks that aren't readily apparent are:

1. Rubber boot between the lower plenum and the throttle body
2. The gasket that separates the two halve of the lower plenum (air sensor plate housing).
3. Leaks at the bottom of the boots connecting the spiders to the upper plenum. These typically get blown out during backfiring due to the bottom of the boots getting brittle.
4. A large leak in the brake booster.
5. A leak in the decel valve.

If those are OK, try resetting the A/F ratio.

Dennis

dogleg

finally another believer in the vac theory

Glenn Evans

Dennis,

I apologise for upsetting you by not repeating exactly what you said (which I'd quoted above my own statement). The substance of my post was that injector pressure is constant and unrelated to control pressure or sensor plate deflection ie I disagreed with you.

To quote from "Bosch Fuel Injection and Engine Management" by Charles O. Probst, SAE (Robert Bentley inc, Publishers, 1991), page 5-16:

"Fuel flow to the injectors is influenced not only by the size of the exposed slit [in the control plunger], but also by the pressure drop at the slit. Think of it this way: the pressure drop at the metering slits is the pressure differential between system pressure inside the slit pushing fuel out, and the lower pressure outside the slit in the fuel distributor. If the pressure drop changes for a given air flow and plunger lift, fuel flow through the slit also changes. For example, increased pressure drop forces more fuel to flow through the slit; fuel delivery increases.

"Changing pressure drop at the slits causes problems with the linear relationship between air flow and fuel flow. When the control plunger rises, a more open slit changes the pressure drop and upsets the basic proportional relationship between air flow and fuel flow. So while increased air flow produces a linear increase in plunger lift, it does not necessarily provide a linear increase in fuel flow. At a certain point the change in pressure will cause the air-fuel mixture to be incorrect.

"To hold constant pressure drop at the slits for the entire range of plunger lift, all continuous systems have something called Differential-Pressure Valves in the fuel distributor.

"The differential-pressure vavles maintain a constant pressure drop at the metering slits of the control plunger by reacting to the increased fuel flow that comes with a larger slit opening. There is one differential-pressure valve for each injector. They are mounted in chambers in the fuel distributor, and have a flexible metal diaphragm that separates the upper and lower halves of the chamber. "

Figure 4-6 is a cross-section of a K-basic differential-pressure valve. The upper half of the chamber, from which fuel is delivered to the injector, is labelled "System pressure minus constant 0.1 bar spring force".

I do agree with you that if control pressure is too high or system pressure too low, the piston will not meter enough fuel to the injectors.

Regards,

Glenn

Glenn Evans

gbgastowers,

Do you have a vacuum gauge? I pull off the brake booster hose and plug the vac gauge into its port on the intake plenum body.

At idle, the manifold vacuum should be between 17 and 21 inches of mercury (17 to 18 is fine). If it is significantly lower than that, you have a leak.

Also, the control pressure is adjusted by vacuum. The hose which goes to the top of the control pressure (aka warm-up) regulator should be at atmospheric pressure (ie zero on the gauge), and the one which fits to the side, low on the regulator body, should see manifold vacuum.

Does the vacuum advance diaphragm on your distributor have one vacuum hose attached to it, or two? Euros should have two. The one on the front (not connected to US or Australian-delivered K-Jetronic 928s) is the vacuum advance line, and should see manifold pressure. The one on the rear is the vacuum retard line, and should see manifold vacuum when the throttle is fully closed and zero when the throttle is cracked open.

gbgastowers

I have a Mityvac that has a gauge. Thanks for this info I will check it out and report back. Gunar

Glenn Evans

Any update?