Weird CIS behaviour

[Russ Southerlin <russell.s.southerlin@lmco.com>]

Phil,
I was catching up on some older posts:

On 3/22/1998 Phil wrote:
>I've been having a hot-start problem intermittently for a few months.  I 
>thought that replacing the check valve in the fuel pump had cured it, but it 
>happened again last week.

>So I decided on a comprehensive day on the fuel injection.  I'd noticed several 
>times that the residual pressure falls too quickly when the engine is turned 
>off, so I decided to put the gauge on and start swapping bits.  Swapping out 
>the frequency valve cured the slow leakdown, so I was fairly happy.
 
>But something odd happened when I was running the diagnostics.  On two 
>occasions, fuel pressure fell like a rock when I turned the ignition off.  All 
>the way to zero in five to six seconds.  Turning the diagnostic back on, 
>waiting the usual four seconds, and then turning it off gave me the approved 
>behaviour - pressure retention above 2.8 bar for over an hour.

>Has anyone ever seen 'intermittent leakdown' before?  Any ideas?

Correct me if I am wrong but I think there are only 3 ways you can get
leak down on residual pressure.
1)FP check valve.
2)OXS F/V.
3)The system pressure reg. could cause leak down. The spool piece inside
the bore could be getting stuck or the O-ring on the end of it may not
be sealing well. You might also want to check the reg. internals for
dirt, crud and o-ring condition.

There is also the fuel press. accumulator. I suppose if it was not
holding any volumn of fuel you might get an intermittent leakdown.  When
you open the fuel system do you get a fairly large volumn of fuel?

My 0.02, hope this helps.

Russ
87 5KCSTQ
Littleton, CO