j0rdanisme

Hey guys,
I am having some troubles with my 91 pickup. It has a 3vze motor, and this is recently what happened.

My truck was sitting for 4 months in a dry area. When i started it back up it started, but died shortly after and could not be resurrected. I took it to the local shop and they said 2 things are happening.

1) Fuel pump is not pushing any fuel.
2) Ingnition Pulse is not active

So, after bashing my knuckles for a while i've replaced the fuel pump and can verify it is working, and is driving fuel up to the fuel rail.

Now, when i activate my ignition (not firing) i can hear what sounds to be an air leak from under the hood. Just from looking it sounds like its coming from under the throttle body, around the fuel rail area.

Any idea's? I am lost as to what it could be and just want to get back driving

Cheers guys and thanks in advance!

TNRabbit

If the ignition pulse is not active, I'm pretty sure that causes the fuel pump to NOT work.

Is it possible that mice chewed some of your wiring? Did you find any evidence of mice in the engine bay after the storage?

Also, I'd check for a crack in the intake tube running to the throttle body. Can't think of where else you'd get that sound on cranking...

j0rdanisme

I was told that the fuel pump and ignition are on separate circuits, meaning I had two different problems. The sound is happening NOT while cranking, simply when my ignition is in ACC.

According to the local shop it CANT be a vacum leak as the vehicle only builds vacum when its running. It would most probably be a stuck relay. Any idea on which relay we may we talking about?

Mice are not completely out of question, but it was stored in underground parking at my fairly new apartment building. Doubtful any mice got inside.

j0rdanisme

Bumpity Bump, any idea's?

j0rdanisme

Any idea's folks?
I am about as lost as a mouse in a corn field.

TNRabbit

So when the ignition switch is on ACC, or ON/RUN, you hear an air leak sound?

j0rdanisme

Yes, but the truck doesn't make vacum until its running. Which makes me think its a relay.

TNRabbit

I can't imagine what relay would cause an air leak sound......?

scope103

When I replaced my fuel filter, air ended up in the fuel line (of course). Before finalizing the job, I jumpered the FP connector (on the diagnostic plug) to run the fuel pump. To my surprise, I could hear an "air leak" sound for about 30 seconds as the air was being pushed through the fuel pressure regulator.

So first question: HOW did you verify your fuel pump is working? Presumably the FP jumper method? Next, have you tried starting it with the FP jumpered (to assure the pump is running)? The Fuel pump doesn't run "all the time" with the key on, it only runs while cranking, AND THEN runs when the air flow meter detects that air is flowing. So if your air flow meter stops sending a signal, you can sometimes get the truck to start, followed by dying a few seconds after you stop cranking.

So if you jumper the FP diag connector you will have fuel pressure no matter what the air flow meter is doing.

If that fixes the problem, DO NOT just leave it that way! If you are in a collision that breaks a fuel line somewhere, you want that fuel pump to shut off right away. Instead, fix the air flow meter.

j0rdanisme

The shop I brought the truck to had left the rear banjo bold on the fuel rail loose, so when I originally tried to start it it pissed gas all over my engine bay. Was very un stoked, but that informed me at least my fuel pump is working now haha.

To jump it i just do +B and Fp using a standard wire (or do i need a special jumper?) and see if it will fire?
If it fires look at the air flow meter?
Cheers and thanks for your help!

scope103

Yes, you need the special tool:


Before you go too far, jumper FP to B+ and listen. You should be able to hear the fuel pump running (you can't hear it with the starter cranking), but you shouldn't hear anything from the rest of the fuel system (and nothing should leak!) Then if it starts AND RUNS (when you turn the key in usual fashion), I would suspect the air flow meter

j0rdanisme

Ok sounds good, i will give it a try.
Any idea what the odd humming when its in ACC tho?

TNRabbit

You didn't say "humming", you said "air leak"....

Is your fan on low?

j0rdanisme

That would be too easy.. but i will check for sure haha.
I thought it was a air leak, but I was informed that the truck doesnt make vacum when its not running.

That makes me think its the hum of a stuck relay or something.

camo31_10.50

well is it a "Hiss" or a "Hum" or what?

i say jumper the fuel pump and see if that helps.

scope103

102.2FM KHMM

You left your radio on.

Get yourself a "Wide Band Stethoscope" to precisely locate the noise. (I always use a paper-towel core, but "Click and Clack" argue for a piece of heater hose.)

j0rdanisme

Quick update.
Jumped the fuel pump, same sound. The sound im hearing sounds like its an air lead and its coming from around the throttle body/fuel rail.
On the 3vze near the front of the fuel rail their is another banjo bolt, and just beside that is a T that leads down. Could it be possible said T is leaking?

scope103

The "front" of the fuel rail is where the fuel pressure regulator hangs out. It should make no noise with the fuel pump running, so you may have a dead regulator.

But the part is not cheap, so you want to be sure, don't you? There is no schrader valve on the fuel rail for an "ordinary" fuel pressure tester, but kits like the Actron CP7838 come with a banjo bolt adapter. (23802C on the drawing) $60 at Autozone, as little as $45 on eBay. If you have the correct fuel pressure (around 55psi not running), then it probably isn't the fuel pressure.

[When you remove any banjo bolt on the fuel rail, you need to replace the aluminum crush washers. Lots of folks do reuse them (even I have done it in extremis), but we're talking about gasoline here. They are a dealer-only item, but they only cost about a buck apiece. Don't use the copper ones; those are for brake lines.]

Before you do that, you could certainly localize the noise better. Use a piece of heater hose, or if you're really cheap, the core from a paper towel roll. You'll do a lot better than "throttle body hear the fuel rail."