Fuel Injector Hoses replaced - fuel everywhere!

[Darrel]

Are you sure the hose is 5/16 and not 3/8"?

How easy was was it getting the fuel hose over the fuel rail fittings?

[twsutt]

I'm pretty sure that the hose that I have is 5/16"...to be honest, I don't think that I looked at the size on the hose - I just looked to make sure that they gave me hose for fuel injection. The hose fit snugly over the fittings, however I pre-lubed the fittings with a small blast of WD-40 to make the going a little easier. I'll check this evening when I get home.

[sblake01]

Stephen,

I thought that the fuel pump wasn't supposed to switch on until the key had been turned to the "start" position - which would also open the AFM flap, closing the fuel pump contacts. Is my AFM flap stuck open or is this normal? Do I need to lubricate or even clean/rebuild my AFM?

According to the FSM that's normal for a 75:

[twsutt]

Stephen,

Let me see if I've got this right. When the engine is shut off normally the AFM contact points are left on and the AFM flap is actuated (open at least 8%). If the engine stalls then the AFM flap will close (de-actuate) and the AFM contacts will be off.

I was under the impression that the AFM flap was closed whenever the engine was dead and only open while the engine was running. Thus leaving the fuel pump off until the ignition key is turned to the "start" position - opening the AFM flap and setting the contact points to on. Am I misunderstanding this?

[sblake01]

Your first paragraph explains it the way I've always understood it. My experience is with a 78 however which basically uses the oil pressure switch signal instead of the AFM contacts.

[twsutt]

Last night I stole about 15 minutes from the family and snuck into the garage to check a few things. First I had to check to be certain that I used the right size hose - 5/16" I.D. hose rated for fuel injection - check! Then, I proceeded to tighten the clamps all the way down (about 1 to 1.5 mm tighter.) After that was done I put the key in the ignition and turned it to the "on" position and brought the fuel injection system under pressure. After about a minute and not seeing any gasoline leaks I stepped away for about 10 more minutes. Upon returning I removed the key and checked all of the fuel hoses under the hood...no leaks anywhere.

Tonight, if I get the time, I'll push it out of the garage and start her up - with a fire extinguisher at the ready. If things look good I'll take her for a spin.

one question:

Will the pressure on the fuel injection system be higher while the engine is running or while revving at high RPMs than while just sitting, engine off, with just the (stock) fuel pump running? I'm assuming that the pressure regulator will keep the pressure at 36.27 psi, but I've been known to be wrong every once in a while.

Edited September 30, 2009 by twsutt
grammer

[sblake01]

The pressure should remain constant regardless of what the engine is doing as long as there are no leaks, vacuum or fuel.

[FastWoman]

Well, the pressure remains constant WITH RESPECT TO THE INTAKE MANIFOLD PRESSURE/VACUUM. When you suddenly stomp on the pedal, manifold vacuum drops to near-zero, and the fuel pressure rises in compensation -- with respect to the pressure of the surrounding air, that is (i.e. the pressure of the air you're breathing). So yes, there will be a pressure surge when you stomp on the pedal. Of course when the RPMs rise in response, manifold vacuum will be restored, and the fuel pressure will drop again.

That said, your fuel pressure will be at its highest (with respect to normal atmospheric pressure) without the engine running, as there is no manifold vacuum. If you don't see any leaks with the engine stopped and the fuel pump running, you're probably just fine.

[sblake01]

Atmospheric pressure? The fuel pressure regulators on there cars aren't that sophisticated. It sounds like you're describing a modern fuel pressure regulator. Let me take it directly from the FSM:

The pressure regulator controls the pressure of the fuel so that a pressure difference of 2.55 kg/cm2 (36.3 psi) can be maintained between the fuel pressure and intake vacuum. This constant differential pressure provides optimum fuel injection in every mode of engine operation. When the intake manifold vacuum becomes large enough to overcome the diaphragm spring force as combined with the fuel pressure at the pressure line, the diaphragm becomes empty on the intake side. This opens the return side port to allow fuel to flow to the tank for reducing tuel pressure. If fuel pressure is higher than the intake mainfold vacuum by 2.55 dg/cm2 (36.3 psi) the diaphragm returns to its original position by menas of spring force, and closes the return port. In that manner the pressure regulator meaintain the fuel pressure in the fuel line 2.55 kg.cm2 (36.3 psi) higher than the pressure in the intake manifold.

When everthing is working properly, watching a fuel pressure guage shows a quick needle movemt at the hit of the throttle that instantly returs to 36.3 psi. so the fuel pressure is about as constant as it could be. If it fulctuates for any longer length of time, something isn't right. Weak spring, problem with the diapragm, fuel or vacuum leak, etc. Edited September 30, 2009 by sblake01

[twsutt]

I pushed the car out of the garage and gave the key a turn. The engine started right up but now she's running very rough.

Before I replaced the hoses (and fuel injector o-rings) everything was running like a top, but now, not-so-much.

What could I have done to it?

I even put the fuel injectors back in the same order that they were in prior to their removal. I'm stumped.

I tried the "listening to the injectors with a screwdriver" trick and all of the injectors seem to have the rhythmic clicking that they should have.

Could something have gotten in the line? I hate to have a fairly simple job turn into a huge catastrophe.

I'm open to suggestions.

[FastWoman]

I'm not saying there's any regulation with respect to atmospheric pressure. However, there's a fuel leak, and the magnitude of the leak would depend on the pressure of the fuel with regard to atmospheric pressure. That is, after all, the path of the leaking fuel.

Terence, I haven't a clue what might be the problem. Can you isolate the problem to specific cylinders? Try unplugging your plug wires, one by one. If you unplug one and find it doesn't make any difference to the running of the engine, then that cylinder is dead, and you might have a clogged injector. Tip: Grasp the plug wires with a rag to keep from getting zapped.

Also listen to the exhaust. Does it have a rhythmic "chug-chug-chug" sound? If so, then it's the same cylinders missing with each revolution. Could be (a) clogged injector(s). If not, then the problem is most likely elsewhere.

[sblake01]

I'm not saying there's any regulation with respect to atmospheric pressure. However, there's a fuel leak, and the magnitude of the leak would depend on the pressure of the fuel with regard to atmospheric pressure. That is, after all, the path of the leaking fuel.

Generally, barring some type of mechanical problem, I think you'd agree that the pressure in the system would be higher than the atomspheric pressure. You're going to see the leak regardless of magnitude. No need to over think it.