Control Pressure Problem

[ydrogs at gmail.com (Gordy Stedman)]

On 6/3/07, Cris Carpenter <housecall55@xxxxxxxxx> wrote:
>
> CIS-E and plain CIS are not the same, and an 81 will have only one fuel
> pump. If the control pressures are indeed as high as the system pressure,
> something is blocking the return through the control loop. Are you simply
> substituting one bad WUR for another? If the control pressures are that
> high, it should have a real hard time running at all, but especially cold.
> If you are sure you are using a known good WUR, the problem must be the fuel
> distributor. The control loop uses some fuel pressure to hold the fuel
> distributor plunger down. The air flap of the fuel distributor has to
> overcome the control pressure to raise the piston and let more fuel to the
> injectors. The control pressure is lower when cold by virtue of the WUR
> bleeding it off through the return circuit back to the tank, allowing the
> piston to ride higher and let more fuel to the injectors until the engine
> starts to warm up. But both the feed and return side of the warm-up loop on
> an 81 goes through the fuel
> distributor. If you are acccurately testing the control pressures (I've
> seen people set it up wrong), have tried a known good WUR, and you still
> have control pressures that high, the problem must be the fuel distributor.
>
> Cris

That was what we were coming up as a conclusion also. Thanks for the
detailed explanation.  It does run badly when cold and would not start at
all until we fixed the cold start injector circuit.  We will be swapping out
the fuel distributor, maybe complete air box assembely sometime this week.
Hope it works.
-- 
Gordy
MK1 x 5