Here is what I did.  I temorarily eliminated the fuel filter by replacing it with a barbed fitting and installed a guage at the regulator inlet.  The filter is clean so I don't fear removing it for this test.  I don't plan on driving it until the problem is fixed.

When cold the regulator inlet pressure was 7psi, outlet adjusted to 5.5.  As it was warming up the pressure on the inlet slowly dropped to 2psi.  I then unscrewed the gas cap.  Nothing changed so I turned it off.  I touched the pump and while it didn't burn me it was pretty toasty.  I held onto it for a few seconds and didn't get any burns.

So I think one of 3 things is happening.

1.  The tank configuration just isn't able to properly supply the pump.  Does anyone know if it is a syphon?  The line goes in the tank at the to of the tank.  I'm fairly confident that it is a syphon.  The Holley instructions say that it will work with a syphon feed.  The pump inlet is below the lowest part of the tank.

2.  The pump is defective.  It is rated to provide 7psi so it seems to be working properly when it's cold.

3.  The warmest point of the fuel line is at the fuel pump block off.  I wanted to bypass this with some rubber line but I don't have any fittings on hand to do so.  It can't be any warmer than it would be if a mechanical pump was installed.  Does anyone know the temperature at which it becomes a problem?  A friend of mine has one of those infrared thermometers.

So anyway, it looks like the regulator is eliminated as the problem.

I designed a fuel pump block off with a fuel line mounting tab built into it.  It provides a ridgid mount for the fuel line.  It is the engine heat warming it up in that area.

I found some stuff in the garage and was able to bypass the block off.  Still the same pressure drop issue.  So that eliminates the block off as the problem.  Now it's down to the tank or the pump.  I guess I could rig a gas can with a gravity feed to see if the tank might be the problem. 

             I've had lousy luck with Holley regulators. I am not sure that this is your problem, but the Summit brand regulators seem to cost less and work better.

I'm almost done.  I need figure out how to get the fuel from the door into the fuel cell, pump mounting, get it all painted, and that's about it.  I'm hoping to be able to try it out next week.

So, if the pressure is low when I'm done with this, the pump is all that's left.

Nice fabrication on that filler!  Where did you find that tank, & how many gals?

How big is the Mustang Tank? 

Kevin

The fuel cell is a 16 gallon unit that I got from summit racing.  It is 2 gallons less than stock.  That shouldn't be a problem as long as I achieve my goal of 16mpg city and 25mpg highway.

The mustang tank used in that article is available in two sizes.  I think 18 and 22 gallon.  It's in the tech articles section of the Ford Truck Enthusiasts forum.

I have one pressure gauge at the pump outlet, one before the regulator and one after the regulator.

I have 5psi at the pump outlet.  This is lower than it should be.  The wires are temproarily j-rigged so that may contribute to the low pressure.  However, 5psi at the pump outlet remained constant throughout the test.

The gauges at the regulator read 5psi to start and slowly dropped off.  I turned the motor off before it was able to reach 0 but it was getting there rather quickly.

If the pump remained at a constant pressure then it can't be the problem.  I think there is a problem with the pump because it is rated to put out 7psi and 5psi is the highest reading.  Again, this could be to do with the temporary j-rigged wire.

How do these non-return regulators work?  Is it normal that the pressure drops before them as well?  The two gauges at the regulator seem to indicate a pressure loss at the same rate.  This result corresponds with a previous test.

It seams to be heat related.  I can let things cool for a while, start it up and the pressure will be back up.

If the pump is faulty can it have a good reading immeditely after the outlet but drop off significantly 10-15 feet up the line?

I'm running out of ideas.  It's starting to look like this truck ain't going to be at Columbus. 

I installed the pump at the same time as the new engine about 3 months ago.  All lines from the pump to the carb were new.  The stock tank was being used.  The same sort of thing was happening.  I did some trouble shooting and narrowed it down to the pump or tank.  I did not have 3 gauges installed at this point.

Over the past few weeks I installed a fuel cell to eliminate the stock fuel tank from the equation.  I've been wanting to install a fuel cell anyway.  Now everything from the fuel cell to the flex line is new.  Still the same problem.

These two systems have used the same plumbing from the flex line to the carb.  It is the plumbing between the tanks and flex line that has changed.  The parts that are the same among the systems are the fuel pump, regulator, and all plumbing from and including the flex line, to the carburetor. 

I ran out to remove the hose.  I can blow through it easily with no indication of a blockage no matter how hard I blow, in either direction. 

Oh, It will die if it idles with the pressure at 0psi but it will run if I give it gas.  This doesn't make much sense to me.  The only thing I can think of going on here is that when it runs at about 600rpm the alternator isn't doing much charging and the pump is running slower.  When I give it gas the extra voltage speeds up the pump which kicks up the pressure enough to keep it running.  I haven't noticed any visual change in pressure from 12.8volts to 14.2volts, however.

We gotta get that truck to Columbus.  Here's what I see in my mind, and I know you have checked the lines.  Your pump can charge the entire system with 5 psi all the way to the carb when the engine is not running.  Now, when you start the engine, the pump outlet gauge continues to show 5 psi, which should be enough to keep it running.  After it runs a couple minutes, the pressure starts to drop at both sides of the regulator.  Why?  The needle valve in the carb opened, so that part of the line is now open at one end, so it can't get pressurized to 5psi.  Why can't it get pressurized to fill the carburetor and close the needle valve again?  Because somehow there is not enough volume of fuel getting through from the pump to the regulator.  The flow test mentioned above should show that.  If enough flow was getting to the regulator, then those gauges would show 5psi even when the float bowl was empty if the blockage was between the regulator and the carb.  Hope this is not too confusing.

John

I used the pump to empty the old tank.  I didn't time it but it was absolutely adequate for idling.  It's rated at 97gph which is 1.62gpm.  The can I was using is 2gal.  The time it took seemed about right.  I'll be sure to time it next time.  I'm going to go ahead and get another pump on order.  It's the only thing I haven't been able to bypass.  I hate to just throw parts at it but I feel like I've checked everything I can.

I spoke with Holley tech again today.  They did better but still not impressive.  They seem to think that it is possible that the pump is showing 5psi at the outlet but it is too weak to maintain 5 psi farther away from the outlet.  It sure doesn't seem common though.

Chuck, I'm in Norcross, GA - slightly NE of Atlanta.

John's explaination is clear to me.  If I've ruled everything else out and it's not getting enough volume it must be the pump.

One more thing.  Have you checked the screen in the Holley pump?  Since you ran it on an old tank, it could be full of junk.  However, I don't see how it could maintain pressure when the pressure drops of at the regulator with the screen clogged.

John

This is my first time running a pressure gauge and regulator.  I am assuming bythe replies of many of you that pressure that starts where I want and drops off gradualy is not normal.  It is not logical in my mind.  So hopefully I'm not trying to fix a problem that doesn't exist.  For about 5 or 10 minutes the pressure stays steady.  Then it starts to drop off slowly.  After 15 - 20 I shut off the engine and the gauges are very close to 0.

Can a problem with the floats or needles cause this?  The carburetor is the only part of the fuel system that I haven't done any kind of test or check concerning the fuel pressure issue.

You say after 10-15 minutes the gauges read close to 0.  Is that all 3 gauges, including the outlet of the pump?  If that is the case, the pump cannot draw fuel, because of a restriction in the inlet line or no vent in the tank.  What do you find in your flow tests?  Have you tried pumping 3 or 4 gallons instead of the common pint or quart?  Does the flow start to slow down after a couple minutes of pumping?  Does the pump change its sound?  You're right, the chance of two bad pumps is slim.  I have had problems with viton needles getting softened by the alcohol in the gas and sticking in the seat.  The carb goes dry, but fuel pressure does not drop off at all.

John

John, the new pump is putting out 6.5psi.  When the other two gauges are at or near 0 the pump is still at 6.5.  The other pump followed the same trend.  I haven't yet done the flow test.  I wanted to try the new pump in hopes that the problem would be solved. Plus, I haven't yet made the filler parts for the tank and therefore I cannot fill the tank without removing it.  Much easier to do with a friend.  I wil check it.  It doesn't seem to slow down or change sound.  I have 13.8volts at the pump and 14.4 at the battery when it's running.  The new pump seems to operate more smoothly.  The needle of the gauge would pulsate by a little more than 1psi with the other pump.  It only pulsates by aproximately 1/4psi now.  The pulses are expected because of the pump design.  I think I'll check the flow before running the engine and then after the pressure drops.  That way I'll have a reference in addition to the rated flow.

One thing I haven't done is run a rubber line directly from the pump to the carburetor.

It is possible that the fuel pressure is not the problem but I don't know what else to look for, given the symptoms.  Persuing the pressure could be a case of too much information.  One of my older buddies told me that having a tachometer is a bad idea because "you will try to see how high it will rev and break something".  Pressure gauges could be another way to find trouble.  I am only looking at the fuel pressure as the cause of the idling characteristic because the gauge was reading low the first time it died while idling.  It did run fine for a month or so before that with low pressure, which I had written off as a bad gauge at the time.  What else could cause it to die at idle, after warming up but run fine at a higher rpm?  I may be fighting the wrong battle.

Oh, something else I've noticed is if I stop hard the engine will sometimes die.  I wonder if that may indicate that the float level is low?

I'm going to try the old, reliable mechanical pump tomorrow. 

I've taken a couple trips around the block.  It's been idling well and hasn't tried to die.  I have a mechanical pump that I'll install to see if it changes anything.

It seems to be running fine.  A small amount of pressure loss is expected in the case of the electric pump because it is so far from the engine but it shouldn't for any reason drop to 0.  Pressure loss with the mechanical pump should not be measurable with my instruments because it is so close.

At this point, unless some miracle occurs, the truck isn't going to be at Columbus.  0 psi means something is wrong.  I'm not interested in breaking down in the middle of a 600 mile trip.

This is why you should use the absolute minimum number of gauges necessary to drive.  If you don't know there's a problem, there isn't one!

Have you done a 2 or 3 minute flow test yet?  I tested the system on my race car a few weeks ago, had a line on the line that I disconnected from the carb, with a 1/8" hole in a fitting.  It maintained 6 psi while pumping gas through that orifice.  That is about the size of the needle and seat.  Holley blue pump.  You said the mechanical pump did the same thing.  Was the electric pump turned off at the time?  If so, the mechanical can probably not draw fuel through the shut off electric.  Do you have a vacuum gauge that you can tee into the inlet line to the mechanical pump?  If the line is open all the way to the tank (electric pump needs to be removed or bypassed), you will see very little, if any vacuum.  If the line is stopped up, you will read full pump vacuum, probably around 10".

John

Pete, I appreciate your help with this.  I don't know if what I'm experiencing is a problem.  I have no prior experience with inline pressure gauges, regulators, and what is normal.  I haven't been told by anyone that what I am experiencing is or is not normal.  Apparently the stalling issue is related to something else.  It hasn't happened again on the past few trips around the block and to the store.  The engine runs great cruising, getting on it and so on. 

I measured the manifold vacuum at 13"hg, idling at about 700rpm.  I ran the engine with a gravity feed for 6 minutes with no problems.

          Another issue, when the fuel pressure gages get warm the readings will drop. I found that out on my Windsor powered Ranger. I am not certain why a bourdain tube would get stiffer with temperature, but it did. If you have that much volume, and the truck runs OK, then quit worrying and drive it.