system pressure leakdown

Ben Swann bswann at
Tue Apr 16 14:06:45 EDT 2002


No, not too late as I am still having problems.

Perhaps total leakdown both control and system sides is normal, but there
was something seemingly flaky going on with the control pressure.

I wanted to verify system check valve not leaking, which Probst alludes to
checking first.
I put all new O-rings on the system pressure regulator check valve.  Did
this 2X because I had gotten the inner and outer mixed up the first time,
ruining the outer.

Now I get about 85%system pressure(was 90 PSI) on both sides(same with the
correct o-ring placement as with the previous botched job), so I attribute
this to something I did wrong, but can't figure what exactly.  The outer
O-ring is a sloppy fit and tends to slip out of the seat on the shaft when
inserted.  Anyway, now  I am sure the correct o-rings in the right spot,
but it is screwed up worse than before I touched the check valve.

Maybe the system is totally blocked now at the c.p. regulator. Pump on ->
system pressure.  When the pump is off,  pressure still equal on both sides
and drops to about 50 PSI.

I am going to check the screens on the c.p. regulator this afternoon.  How
much insanity is disassembling and cleaning it.

Probst also suggests a blocked return line.  where might it get blocked?

What else should I be looking at?

Thanks for the support!


On Tuesday, April 16, 2002 6:02 AM, Graham Thackrah
[SMTP:gthack at] wrote:
> Hello Ben,
> Sorry if this is a bit late, I took a look through Probst's FI book and
> shows a plot in there with system pressure rapidly falling to c. 3 bar
> after shutdown, which it is supposed to hold for a few hours, but then SP
> drops off to zero after a prolonged period of time "through various minor
> leaks in the fuel system." I'm not sure if total leakdown overnight is
> undefined behaviour for CIS systems. One place it did say to check on CIS
> systems suffering fast leakdown is the system pressure regulator, it has
> O rings in it and you can buy a kit from the dealer with new ones in.

Right I just got 2 kits today.  Used/abused the one I had last week.  Of
course the Bently blowup does not show detail, and the kit has no
instructions.  Almost lost that tiny c-clip that retains the shaft which
has the outer(control pressure?).

> Dodgy O rings in there could cause both control and system pressure
> leakdown, one O ring seals off the return from the CPR and the other
> system pressure return to the tank.
> hth,
> Cheerio,
> Graham.
> P.S. just in case - and sorry if this is teaching you to suck eggs! - but
> when testing cold control pressure you did disconnect the CPR heater
> didn't you?


 I got that wrong a few times when I was checking my own car
> out but I think if you jumper the FP relay it also sends a feed to the
> heater so you'll be testing warm CPR operation even though the engine is
> not running.

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