Chevy s10 95 cpi fuel pressure problems

I am working on a friends 95 s10 with cpi injection. I found that the fuel pressure at ignition ON as 52 psi and maintain that pressure for a long time when turned off. When started it jumped to 85 psi and was overloading the injectors, running rough, with black ssmoke.The book says it should be 55 to 62 running. I traced the return fuel line and found that someone had taken a pair of pliers mashed the return line flat. I removed the crushed part of the line and bridged it with a rubber fuel line. When turned on the fuel pressure again went to 52 and when turned off help for over an hour. After an hour I started the truck and the fuel pressure went from 52 to 47 and now was running very lean I checked the regulator and spider for leaks and did not see any. I was told it had a new fuel pump but can't verify that. I put a clamp on the rubber line that I had installed in the return line and tightened it until my fuel pressure guage said i now had 60 psi. The truck ran perfectly. I should not have to do this. I changed the fuel filter with not change. At this point I am looking for suggestions on why the fuel pressure is low and the only things I have left is the regulator pump but all the test I have heard off they both pass. At this point don't know why I am loosing fuel pressure. Any help please.

Well we know the pump is capable of putting out plenty of pressure.I would open up the intake and take a look for leaks which are common on these spider web injections look at the lines from the regulator to each injector . Also check your pressure and return line that passes through the intake if you don't find any problems I would suspect the regulator. it's been a long time since I had to work on one of those maybe someone else will have more suggestions

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I agree with what Ben said. The CPI or "spider" units in the 4.3L Vortec engines are prone to fail. The most common issue is the regulator. The pump is clearly capable of producing the correct pressure so I'd say that is fine. The lines that run through the intake are also prone to dry rotting and causing issues. Some people have had good luck just replacing the regulator. I always replace the entire unit especially if it has the old style injectors with poppet valves. The newer units come through with electronic valves on the ends of the tubes, but unfortunately also carry a hefty price tag. Make sure to replace the gaskets as well! Internal vacuum in the upper intake plenum is what operates the regulator and if you don't have a good seal you will have driveability issues. Be careful with the big orange seal at the electrical plug portion of the CPI unit. Lubricate it with seal lube before trying to install the upper plenum....makes life a lot easier and if that doesn't seal it is a huge vacuum leak! Good Luck!

52 to 62 is normal on that. I don't like that is was only 60 with the return line pinched. What does fuel psi do during a WOT snap?
That pinched line may have damaged that pump.

And the bleed down numbers look great