Still Fighting Fuel Press. Problem

[Russell S Southerlin <Russell.S.Southerlin@lmco.com>]

All,

I'm sitll having fuel pressure problems and was wondering if anyone has any 
suggestions. Here is a sequence of events:

Car originally died and would start when cold but after a hot soak it 
wouldn't start. I had good spark and no error codes so I determined it was 
fuel.  I found the fuel press. reg. o-ring was torn and tried to 
re-position it. The o-ring then crumpled up into hundreds of tiny peices. 
After getting a new o-ring (junkyard) I still had low fuel press. I got a 
complete set of injector, warm up reg. and cold start valve lines and used 
the end fittings to make my own fuel press. gage. I am measuring the press. 
at the cold start valve line (replaced cold start valve line with the 
gage).

Thinking the o-ring peices in the dist. might cause a problem I then took 
the fuel dist. apart. I knew better but I think it was a case of temporary 
insanity. After getting the dist. sealed up with Loctite it was all screwed 
up. It flowed fuel continiously out #3 injector.

I still had low fuel press. When the fuel pump is turned on the press. 
comes up to 70psi and then you hear kind of a squirting sound when the 
press. then drops to 55-60psi. If I shim the press. reg. the initial press. 
goes up to 75-80psi but I hear the same squirting sound and the press. 
drops to the same 55-60psi. It seems like the shims affect the high limit 
but not the low limit.

Since my fuel pump was noisy I went ahead and replaced it. I found that the 
check valve was also junk so I'm sure this was money well spent. I still 
have same press. problem even with new fuel pump.

I now have a new/used (junkyard $130) fuel dist. I got the entire fuel 
dist. with air plate assy so hopefully the plate rest position and CO are 
close.  Well I still have the same press. problem.

If I do the OXS F/V output code test the pressure fluctuates between 55psi 
and 75psi on about a 2 second interval. When trying to start the engine it 
fires and tries to idle but dies out exactly as the press. drops below 
70psi. I would expect this since the injectors will not deliver fuel below 
70psi. I also checked this with all injectors removed and sure enough they 
only deliver when th press. is above 70psi.

I tried isolating the warm up reg. by removing the line on the top of the 
fuel dist. and putting the press. gage in place with same results. I also 
replaced the warm uo reg. with junkyard unit with same results.

I then tried isolating the OXS F/V by removing the line to the dist. and 
replacing with the press. gage. This caused the same initial press. drop 
but the OXS F/V output test didn't cause the press. to fluctuate (I would 
expect this since the OXS F/V isn't in the circuit). When trying to start 
the engine I got the same.

I think my press. accumulator is o.k. because when you break open the fuel 
system alot of fuel comes out before pressure drops to 0psi. The system is 
holding good residual pressure for at least 30 min.

The only thing I can see that might cause a low pressure like this is the 
reg. valve. itself (I now have three of them (junkyard units) and they all 
do the same) or the OXS F/V. I'm thinking that the OXS F/V is the only 
other device that is between the pressure side and fuel return. 

Has anyone ever seen this type of problem? Any suggestions? 

Russ 
87 5KTQ