URQ fuel pressure......(LONG)

[Frederick Smith]

>If one finds that the fuel pressure is not to spec, what are the ways of 
>controlling it other than the FPR, and the fuel pump itself.
>I see constant references to fuel pressure causing problems, but never a 
>curative procedure.



Dennis

The "system pressure" is regulated by adding or removing shims at the
regulator port of the fuel distributor.(Bosch calls it the "primary
pressure regulator"). On the urQ it's on the rear of the FD head,
near the base. You can identify it by the "hex nut" on the end of the
valve. The hex is 16mm??, or close to that size anyway. I am pretty
sure that's the only pressure that's adjustable per se. Although I
have heard of some folks "adjusting" the control pressure by way of 
the large disc on the rear of the warm-up regulator. 

System pressure that is higher than spec. can be caused by 
restrictions in the return line (bent/crimped) to the tank.

Problem:
Cold control press (ccp) low
Warm control pressure (wcp) normal
System pressure (sp) normal
Rest pressure (rp) normal

Check control pressure reg. (cpr)
-----------------------------------
CCP normal
WCP low
SSP normal
RP normal

Check CPR
--------------------------------------
CCP high
WCP normal
SP normal
RP normal

Check CPR
------------------------------------
CCP low
WCP low
SP normal
RP normal

Check CPR
-----------------------------------
CCP high
WCP high
SP normal
RP normal

Check for restriction in return line from CPR,
run the open end of the line into a container.
If the CP drops replace the line,if not check the CPR.
----------------------------------
CCP normal
WCP normal
SP a little high
RP normal

System pressure regulator misadjusted (shims) or defective.
--------------------------------------
CCP normal
WCP normal
SP very high
RP normal

Restricted return line to tank
Bad Fuel Dist. Connect a fuel line to the return port
on the FD and run fuel into a container. If the pressure drops
look for a restricted return line. If not, suspect the FD.
---------------------------------------
CCP normal
WCP normal
SP normal
RP drops below spec.

Check the following:
FP check valve
Leak atr cold start inj.
Leaking System pressure regulator
Bad FD
Bad CPR

The only way to check the above components is to
isolate each one working forward from the fuel tank.
Pinch off the line from the FP to the accumulator and
see if the pressure holds. If not move to the cold start valve...
If you plug the return port from the FD and it still doesn't hold
then you need to replace the FD (or the "D" shaped o'ring in the
pressure regulator.
----------------------------------------------------
CCP low
WCP low
SP low
RP normal

Do a FP volume test. If the volume is low replace the Fuel Filter (s).
If the volume is still low run the test with the gas cap removed. If
it's still low, replace the F Pump.
----------------------------------------

A fuel pressure tester with a shut-off valve is necessary to do the
above testing since it enables you to isolate the CPR and read
system pressure. Closed = system pressure, open = control pressure.

While this doesn't cover all the possibilities, it does cover the
majority and certainly points you in the right direction. Happy
hunting.

Smitty