Hissing from fuel pressure regulator

[77Datz]

With the ignition "on" and the AFM flap pushed in, I can hear the fuel pump relay click, fuel pump come on, and an immediate hissing sound coming from my fuel pressure regulator. If I hold the AFM flap in for a few seconds/minutes, my car will start and run for a few seconds then sputter out and die. I'm thinking I need a new fuel pressure regulator, I pulled the vacuum hose off the bottom, it was totally dry. All connections on it are tight, shouldn't the fuel pump stop running when the fuel pipe is up to pressure?

[Zed Head]

Everything that you described is normal except for the dying part. The fuel pump should run continuously after it starts and they do hiss as fuel passes through. Since you've shown that the switch in the AFM works, it might just need adjustment by bending the rod that actuates it (take off the black side cover and you'll see) or you might have a vacuum leak allowing air in past the AFM or you might just need a higher idle speed. Normally the AAR would give a high idle speed for a little while after starting. That could be your problem. Try turning the idle speed screw out to keep it running.

[77Datz]

I thought the plate on the AFM wasn't removable? it looks like a sealed unit to me.

[77Datz]

I bent the little rod in the AFM so the pump would activate sooner, and i adjusted the idle speed screw out, still not luck

When the key is in the "on" position, should I hear the fuel pump running?

[Zed Head]

The pump should run when the key is at Start or when the key is On and the AFM vane moves, like you showed with your test.

It sounds like your pump is operating correctly. Can you keep the engine running by giving it throttle? Or by using starter fluid?

You should give more details. You might be trying to start a car that has sat for five years and has a gas tank full of old rusty gasoline.

[77Datz]

The car sat for two years without any gas in the tank, the owner put gas it in about a month ago when i first looked at the car. I've been trying to get it started for about a week now, I pulled out all the injectors and cleaned them, they all work. The injector connectors are in rough shape though. It'll start with starting fluid, and if you hold the AFM flap open for a minute or two it'll start and stay running for about 20 seconds, then the engine stutters and dies completely. I think its starving for fuel, which makes me think the fuel pump isnt putting out enough pressure, and I don't have a fuel pressure testing tool.

Either that, or theres a bad wire or connection somewhere in the harness, or theres a vacuum leak. All fuses and fusible links are good (at least the ones that I can find are) I'll be replacing the starter this week, being sometimes the starter drive works and sometime it doesn't. I have a new fuel pump coming as well, but I'm not sure thats the problem, I'll have to clean the contacts on the pump and see if that fixes anything.

Everything I've been trying hasn't really changed much, I replaced the fuel filter, fuel lines and a few vacuum lines here and there, new battery terminals and wiring connections there. Ive been going through and cleaning whatever electrical connections I can find as well. I just don't know what else to do to get it running.

[Zed Head]

The fact that you can generate enough fuel pressure to start the engine by letting the pump run suggests that it might actually be a flow problem. A clogged inlet screen/sock in the tank seems like a possibility.

You could check flow by removing the fuel line from before the filter and putting it in a bottle. Then move the AFM vane and see how much flow you get. You should get a pretty good stream of fuel out of the hose.

The fuel pumps go bad pretty quickly though if they get rusty inside. Either way, a flow check will give a clue.

[77Datz]

Already did that, the fuel flow was good and steady, but im not sure of there was much pressure behind it. The fuel that came out wasn't really rusty or have any sediments in it at all, I've also heard that the fuel tank needs to be completely full for the pump to work properly after running the car out of gas, but that doesn't really make any sense.

[Zed Head]

Your local auto parts store might have a loaner pressure tester. If you measure pressure then you'll know. Fuel pressure is key to proper EFI operation. Many have guessed their way around actually measuring and spent lots of unnecessary money.

I think the full tank thing is if the pump runs completely dry, with a factory pump (maybe). I've run a 78 out of gas with an aftermarket pump and had no problems with just adding another gallon.

[ZCurves]

Don't forget the tiny screen in the Fuel Pump inlet itself. As for running the tank down, you can "prime" a '78 model by putting the key in the On position and unplugging the Oil Pressure sender. Let it run for 30-45 seconds and plug back in. When I cleaned out my tank, I put a 3/8" clear filter between the tank and the Fuel Pump - to catch any crap that was left behind. You might try that if you are working on that area anyway....