Hi Y'all,
I just had my injectors cleaned and replaced the fuel filter. Now Im testing for fuel leaks using the jumper wire in the diagnostic port. Well, right when I start the test i hear a hissing sound somewhere in the fuel rail vicinity (can't pinpoint) It sounds like air escaping somewhere and this lasts until i turn the ignition switch off, then the sound dies off in no time. I can't see any fuel leaking so I was wondering if this air leak is normal. Anyone out there have any advice for me? Thanks in advance, Karl

 

Shouldn't have an air leak. I'm wondering how you check for fuel leaks with the diagnostic port.

 

So when you're ready to test for leaks, you put a jumper wire between Fp and B (if i remember) then turn ignition switch to on. This should pressurize the fuel lines and then you just inspect for fuel spraying out. My problem is i hear air hissing out but no fuel. Im gonna have to put it all back together and test it again bc/c maybe the air is coming out of one of the hoses that are still unattached

 

That will pressurize the system. I don't understand why you would hear air leak and no fuel leak. I would look real good at the fuel rail, each injector and the cold start injector and see what is there. If you think it is down low I would look at the fuel filter. I wonder if it is one of the brass washers on the fuel filter or on the cold start injector that isn't tight enough.

 

Jumping FP > B+ only turns the fuel pump on. If you're hearing noise around the fuel rail it's probably either the fuel pressure regulator or pulsation dampener... but since the engine in question is from an 1990, the PD is probably not involved.


So the problem is that the sound of fuel circulating within the system is bad, right?

 

Using the fuel pressure test as you describe, I can hear the return fuel running through the Fuel Pressure Regulator. It's noisier at first because air is getting pushed through, but that's only about 3 seconds and for me it quiets down. But it's still audible in the quiet with out the engine running.

To localize the sound, you can use a fancy stethoscope, or the core of a roll of paper towels works pretty well.

 

... or a sufficiently long piece of tubing and serve well as a stethoscope....


It might be worth noting that the FP shouldn't run at all until the key is turned to start, as in the engine is being cranked to start running, so any noise in the fuel system before the engine starts cranking is suspect. Everything I've read and my own experiences confirm this too.

 

Unless he has jumpered FP to B+, in which case the fuel pump will start with Key-On. This is the case I believe he is referring to.

[Might be worth mentioning here that you shouldn't drive around with the jumper in. The reason the fuel pump won't run with key-on alone is to protect you from suffering a horrible, fiery death. If a fuel line breaks in an accident (causing the air flow through the VAF to stop), you want the fuel pump to stop immediately.]

 

Yeah, I think I covered that in my post prior to the one quoted, but it's worth mentioning that the jumper should cause the fuel pump to run despite signalling from the VAFM and the ignition switch being in "start" position.


Nutshell:
Fuel pump on with the engine running (controlled by VAFM).
Fuel pump on with the key turned to "Start", (controlled by the key).
Fuel pump off any other time.

 

thanks for all the input everyone. So after paranoid searching for fuel leaking again and again, I double checked my FSM and it stated that there will be noise from the fuel pressure regulator during this test in one of the write-ups. I accepted the noise and got on with the job. So far so good. we're running again and * knock on wood* no engine fires!!