DI Low Fuel Pressure - Pump or Regulator?

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WaarrEagle

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I have a 2000 GTX DI with low fuel pressure. Original OEM pump, new filters, cleaned in tolulol. Air pressure is 78psi and holds steady when I supply air with an external compressor. Air compressor puts out over 110psi when dead head. So I am looking at either the fuel pump or the fuel pressure regulator. I get 27 psi exactly when I insert the key. When I have the air side at 78 psi, the fuel side goes to 60 and just sits there, steady as can be.

How would I confirm which part is bad - the pump or regulator? From taking apart the fuel rail, I believe I should only be getting fuel recirculated back to the tank after the regulator releases - is that correct? So if I see 60 psi and fuel coming back to the tank, that means the regulator is bad (releasing too early)??

I am so close to getting this thing running again and believe this is my last hurdle!
 
I’m not exactly sure what for testing you have going on there. But it does sound like your fuel pressure regulator is doing its job because you’re getting 27 psi with the lanyard so you’re getting the 27 psi differential. Are you able to crank the engine? Just curious was your engine sitting for a long time and just happened to get some excess oil in the crankcase from a bad seal? I had some excess oil in my ski from sitting over winter and made sure I had pulled the plugs out and crank over the engine to get rid of the excess oil so it didn’t Hydro lock from excess “over winter” oil like it did the previous season. Well it did have excess oil in there and took a while to get rid of it and just for the heck of it I decided to check fuel pressure and I got 100 psi just putting on the lanyard!! After about a half a dozen more checks it incrementally came down to 26 psi with the lanyard. Thinking back on this I’m not really sure how the oil got into The fuel rail but it obviously affected the fuel pressure regulator. Oil would have to come up through the air injectors and the fuel injectors before getting to the fuel rail. Unless it somehow got in through the air compressor? Anyway I just figured I would throw that out there. Good luck.
 
Bought a needle valve at Home Depot this morning and put it on the fuel pump outlet. Squeezed it down and could not get anything over 60. Looks like a new fuel pump is in my future. Unfortunate but good to know definitively where the problem is.
 
Found some time to dig into this again. Bought a new OEM fuel pump from WSPS. Installed earlier today and getting the exact same behavior as the old one (runs rough, will not idle on PTO cylinder).

I disconnected the fuel discharge line and put a needle valve on it dumping into a cup. It only hits 60 psi before you can hear the pump struggle and start slowing down. Seems unlikely that I have 2 bad 60psi fuel pumps but what else can it be? Is my needle valve setup okay?

Edit: Scratch that. My gauge was bad and somehow maxing at 60 psi. I used another one and now see well over 100 psi when I clamp down on the needle valve. Looks like my problem is elsewhere.
 
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OK, starting over from scratch with diagnosing my issue. Below are videos of my good pressure gauge when cranking and running. It bounces quite a bit but stabilizes when the engine increases RPM. Does this look normal to everyone? Given it runs, I think the problem is elsewhere.
Cranking
Running
 
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