<VV> intermittent low fuel pressure

[djtcz at comcast.net]

snipped and bottom posted.  Original message string looks to be top posted, with newest at top. 

-------------- Original message -------------- 
> 
> Message: 4 
> Date: Sat, 4 Feb 2006 19:37:33 -0800 (PST) 
> From: Keith Onchuck 
> 
> OK I managed to get in the garage for a while today. 
> I put a fuel pressure gauge on the car and I have 
> narrowed down the problem. (I do not know why I 
> didn't do this way back when.) The fuel pressure will 
> hover around 7 but drop to 0 and then slowly build 
> back up. It seems to be a random pressure drop. 
> 
> I had replaced the fuel pump when this first started 
> so I am not sure that is the cause. I have a spare 
> electric pump from another car that I plan to test. 
> If it keeps steady pressure I may just convert to 
> electric. If it has the same symptoms then I know to 
> look into the lines and tank for a blockage. 
> 
> Keith 
> 
> --- Keith Onchuck wrote: 
> 
> > OK looking for a little more advice. I replaced the 
> > plugs, cap rotor, wires, points, condensor, coil and 
> > the problem still exists. Lets just say I took the 
> > shotgun approach on the ignition system since I 
> > haven't done anything in 9 years. The timing is on, 
> > I  have cleaned the advance weights to ensure that is 
> > working and the vacuum advance is working. I am 
> > going  to run a compression test next. Is it possible for 
> > the cam gear to have slipped enough to cause a 
> > problem? I think my diagnostic skills are suffering 
> > since the car has been running so good for so long. 
> > 
> > The only other possibility I see is blockage in the 
> > fuel delivery system. 
> > 
> > --- Keith Onchuck wrote: 
> >  
> > > The fuel line is not bent nor are there any holes. 
> > 
> > > I 
> > > was looking at this first. I did replace the fuel 
> > > pump so the only other fuel related issue unless 
> > > there  is a blockage in the tank. 
> > > 
> > then  but none the less probably to long. The parts 
> > > should  be here by Monday so I will post a follow up. 
> > > 
> >> 
> > > 
> > > I am having a problem diagnosing a strange problem 
> > > on 
> > > my 1964 110 4-speed car. On acceleration, normal 
> > or 
> > > hard, the car will intermittently stumble as if it 
> > > has 
> > > run out of gas. In some cases the car will 
> > > completely > > > die. This first started late this summer and it 
> > is  becoming more of a normal occurrence where I 
> > cannot 
> > >> > > 
==================================================
I'd try a fuel delivery volume test right away.  Ground the distrib end of the coil wire someplace safe while cranking the engine for 10 seconds and catching the fuel pump discharge in a clean measuring thing . The flaw in a pressure-only test is that a 95% tank side restriction will not prevent an otherwise healthy pump from bravely developing full pressure against a teeny tiny flow requirement (idling). The real  requirement is simultaneously being able to develop 7 psi and more than 1/2 pint/minute (to sustain 200 HP) at the carb inlet(s).  The best test would be a fuel delivery through an orifice sized to produce 7 psi back pressure, or through a fuel pressure regulator.  I think even a tank-side pinhole air leak would have a hard time hiding during that test, if someone was wiggling the lines.
I love fuel pump pressure and fuel delivery tests.  Combined, They pretty conclusively prove the condition of fuel system, including filter, fuel pump, tank sock, fuel lines, all connections, and even if there really is some useful amount of liquid in the tank.  With no disrespect my fellow Corvarians and other car loving humans, two weeks of chatting about anecdotal symptoms and subsequent hopeful parts-swappin' is effectively trumped by 1/2 hour of pressure and delivery testing.  If I had a fuel pressure gage or even a warning lite in a car (like 70s AlfaRomeo with mechanical fuel injection) I would probably not even change the fuel filter until the gage told me to.