Fuel pressure leakdown...can I pick your brains?
 

I hate to be the guy who posts another fuel pressure issue- I know there are 100 and 1 threads on this, but after going round and round with this issue, and doing a ton of research and parts replacement, I'm still having an issue on my 2000 blazer


I tested my fuel pressure leakdown right out of the filter. It was around 95 psi, and held above 55psi for 16 mins.... which checks out as acceptable- the fuel pressure thread said it has to hold above 55 psi for 10 mins....this confirmed my issue is forward of the fuel filter.(I have new rear lines, and new pump anyhow)


Testing at the Schrader valve on my upper fuel lines, my pressure is 62psi with truck off, and fuel pump running. But it bleeds down to between 15-30 psi within seconds of when the fuel pump relay clicks off, then very slowly loses pressure from there. While running, pressure fluctuates slightly but hangs around 55psi at idle
I pulled the upper intake manifold and hooked my injectors back up to look for a leak with the fuel pump running. I found nothing. Since I have a spare, known good injector assembly (the old poppet valve style) i pulled my mpfi off and dropped that in its place. Despite my fuel pressure regulator being pretty new, I decided to throw a new one on just so there weren't any doubts about it. Put everything back together, and still have the exact same leakdown issue...

My only thought is an external leak in the fuel line from the filter to the injector somewhere but I'm not seeing any leaks or smelling raw fuel- would it be possible the leak is small enough that the fuel is evaporating before dripping down?

at this point i feel like it either has to be that or somehow both of my injector assemblies are shot, and leaking down in an identical way, which does not seem likely. I visually saw no leaks in either of them, and the poppet style worked perfectly when removed a few years ago.

Also, is there any possibility I could have an electrical issue that is causing the injectors to allow fuel to bypass into the return line? I hear a relay click, and it immediately leaks down(I'm assuming it's just the fuel pump relay clicking off, but I'm trying to explore all options at this point)

Any insight or suggestions would be appreciated!

Your going to need a real pointy finger nail to pick at my brain but it sounds like it's in your spider or regulator to me. There's very little chance it's leaking in the line without being able to see the fuel some where around the leak but I suppose it's not impossible.

I've been filing my nails to a point just for the occasion lol.

I tried both regulators I had, plus the new one with no change, so spider does seem more likely.. I powered it up with the Injectors sitting where I could see them and didn't notice any fuel leak... could it be allowing the pressure back out the return line? Or could that only happen if the regulator wasn't working properly?

I won't let you pick on such delicate parts as my brain.

But - What is the issue with the engine? Not running?

As for the fuel pressure leakdowns. I can't tell about the 99's but you would need to know exactly what the factory tells about the leakdown testing. Every fuel system has it's own set of rules. Some keep the system pressurized after the fuel pump shuts off, some have an internal bleed restrictor which bleeds it off, some simply de-pressurize immediately such as the TBI's on pre 95's.

Some pulsating fluctuation can be normal but it will depend on how much as the system has to keep the pressure constant to be able to inject the correct quantity.

Try to get a hold on the factory troubleshooting manual.

The engine runs, my issue is hard starts, and sputtering when taking off at low rpms.

At the service port fuel pressure is supposed to hold above 55psi for 10 mins after pump is primed, mine is leaking down to 15-30 almost immediately.
55psi is supposed to be the minimum psi to keep the engines running, and should be around 58 or so while running, mine is running at 55

When I had my blazer I too had some issues with pressure dropping off, just as u describe..the problem for me was the orings inside with the plastic pieces that are in the injector assy itself, problem was initially I didn’t unbolt the fuel lines from the main line coming from tank when I took apart, because I didn’t have a stubby box end wrench..Instead I had bent the lines up , so I could gain clearance needed... I’m willing to bet this is your issue......