Help with fuel pressure test

[hear]

On the new 2002 I've had the old hard start problem. Priming the fuel pump 2 or 3 times before a start fires her right up every time. Got a fuel pressure tester from Autozone and got to work.

Key on engine off, first prime gets it to ~22psi.
Key on engine off, second prime gets it to around 40psi.
Key on engine off, third prime gets it to ~50+ but it bleeds back down to 42psi almost immediately.

Running, it's at 49psi steady. No stumbling wavering or any other evidence of a fuel delivery problem.

When I turn the car back off it drops back to 20psi in about 30 seconds. The last 20psi will bleed off much more slowly.

I know the knee-jerk response is to replace the pump, but I would love to be CERTAIN it's not leaky injectors before I invest in a new pump (assuming I can even find a Bosch). So my question is how exactly do you test for injector leak down? I've heard of clamping a fuel line but I'm not sure which is the supply and which is the return, or if that is even the definitive test for such a thing.

 

[Jezza]

Check the injectors. The 2000 I bought earlier in the year had a leaking injector that was causing identical symptoms. You need to put the injectors under pressure while being able to observe the tip for leaks. I also believe that heat can be an issue as well. If you can pull the rail and keep the injectors in place that will work. I have seen everything from zip ties to a 2x4 cradle with holes drilled in it. As long as the injectors don't pop out under pressure.

 

[Jerry Bransford]

There's no return fuel line on a TJ. The fuel injectors aren't known for losing pressure nearly as often are the check valves in the fuel pump or fuel pressure regulator... both have a check valve that can leak down. The faster you get a no-start problem without multiple primes with the ignition switch the more it points to a bad fuel pressure regulator. For long leak-downs, like several hour or overnight that points more to the fuel pump.

 

[Jezza]

I do have an injector test bench at my shop in Plano if you need to test them. FWIW my current pump doesn't have a check valve period and the pressure falls to 0 instantly. It starts fine every time.

 

[Jerry Bransford]

I do have an injector test bench at my shop in Plano if you need to test them. FWIW my current pump doesn't have a check valve period and the pressure falls to 0 instantly. It starts fine every time.

Pressure failing to 0 instantly makes me think bad fuel pressure regulator check valve, not the check valve in the fuel pump.

 

[Jezza]

Pressure failing to 0 instantly makes me think bad fuel pressure regulator check valve, not the check valve in the fuel pump.

I don't have a factory regulator or pump, so it's a bit of an apples and oranges situation. It does go to 0 right away and back to 50 right at key on and starts instantly.

 

[hear]

I do have an injector test bench at my shop in Plano if you need to test them. FWIW my current pump doesn't have a check valve period and the pressure falls to 0 instantly. It starts fine every time.

I’m trying to buy a soft top from a guy in Plano, and would love to definitively know that it is or isn’t the injectors. What’s yiur availability? (And where in Plano? I’m off Preston…

 

[Jezza]

I’m trying to buy a soft top from a guy in Plano, and would love to definitively know that it is or isn’t the injectors. What’s yiur availability? (And where in Plano? I’m off Preston…

I will be back on Tues. I'm there most weekdays. 75 and Bush.

Send me a PM if you want