Vac leak question.

[Fett]

The vac line going from the tree, across the firewall, and into the reserve cannister was broken, so I replaced it. Could that broken line cause any fuel pressure issues? My car has always run rich, even with the adjustable regulator set at 39lbs. It seems to be running richer, so I wonder if that broken line could have had an effect on the vac going to the regulator. I haven't checked my pressure since fixing the line, so I don't know what it says now.

This is just something that came to me last night, and I wondered if that line being broken could have thrown off my fuel pressure.

 

[Daggar]

I presume what you mean is that you suspect that the line was broken when you last SET your fuel pressure. If so... yeah, I could see how that could affect the rgulator now that you think the system is sealed.

I would probably lean towards their being one or more OTHER vac leaks. The EEC should be able to correct for minor variation in the fuel pressure regulator so long as the vac system is tight and able to run in closed loop operation.

 

[Fett]

It is possible, but I don't think I have any more vac leaks. The reason I found this one was when I was removing all my EGR vac lines. I don't have many vac lines left, and when I found the leaking one, I checked all the rest. This wasn't as much leaking, as it was almost split completely in half. It was such a bad leak that my brake pedal is stiffer, and my idle was horrible to the point where I needed to reset it. So this vac leak has been there for a while, it was obviously there when I originally set my idle. The problem was that the break in the line was hidden, I didn't notice it until I went to actually relocate it.

Last night I started thinking about how I had to reset my idle after replacing the line, and then I started thinking that I never rechecked my fuel pressure. Granted when I set my pressure I removed the vac line from it in the first place....but at idle it is horribly rich. So I will recheck it Monday and see where it is. I will check it with the vac line removed, then I will put the vac line back on and drive around to see what the pressure is doing.

It should be set at 39lbs with the vac line off, where should it be while driving? Between what and what?

 

[jrichker]

Fuel pressure will vary with altitude, barometric pressure and manifold vacuum. Vacuum line disconnected, sea level, 29.92 barometer, and idle will get you 39 PSI when it is set right.

If you really want to get a headache figuring it out, here's some thoughts:
For every inch of barometric pressure below 29.92 inches, subtract 1/2 PSI from 39 PSI.
For every inch of manifold vacuum greater than 0, subtract 1/2 PSI pressure from the above result.

Now that I have thoroughly confused you, did you really want to go through that mathematical exercise?

 

[Fett]

Well technically, some of the places I drive are actually below sea level....so that really throws things for a loop.