The Stovebolt Site Forums The Shop Area Engine Shop fuel pressure zero

What would cause an other wise good running engine ie 235 with 2 stromberg bxov 26 to have zero fuel pressure? New fuel filter, adjustable regulator set 2+1/2 to 3 lbs. Manifold Vacuum is 21 at idle. It starts fine and holds pressure when cold, then when hot the pressure slowly drops to zero. When you shut off you can see the pressure drop real slow. I'm thinking maybe trash in fuel pump. The regulator is above the manifolds just before the guage and inline with the carbs. Pump is 3 years old. Will take apart tomorrow and clean. Any ideas.

Could be the fuel pump getting weak ?

Replaced the fuel pump today, still zero pressure when hot. Only thing left is the fuel pressure regulator itself. Fuel pressure works fine when cold.

You shouldn't need a regulator on a stock mechanical pump anyway.

It was a long time ago and I don't remember why but a mechanic in our shop had this same problem. As best I can remember it had somthing to do with the eccentric that opperates the pump arm. I think he modified his pump by adding some material to his actuating arm thus giving the arm more throw.

if you are useing a gauge after the reg install it before the reg and see what you have..check line from tank,,,pump should push around 4 lbs,,,remove line from carb and run in can turn over see what flow,,do same before reg check flow,,doc

I get the same exact thing on two of my cars, and it doesn't seem to have any effect on how they run whatsoever. And they're two totally different engines.

One's a 455 Pontiac, with a mechanical fuel pump, in a 1968 Firebird, and the other's a 427 big block Chevy in a 1968 Corvette with an electric pump.

I can only guess that when the fuel vaporizes in the line, it causes the pressure gauge to read zero. But why it doesn't run out of gas that way, that's what I don't understand. So I'll be watching this post to see if someone knows.

Last year with old fuel it did not read zero when hot, this year with new 10% alcohol its reading zero when hot. I think it may be vaporizing in the cheap dial pepboys regulator. Did a little on line research Saturday and ordered a better quality Holley 1-4 lb regulator. Stromberg carbs don't like fuel pressure over 2+1/2 to 3 lbs max. New Carter mechanical fuel Pump and new fuel filter. Wooden clothes pins next

52pu,

I ran three Stromberg BXVD carburetors on a 235 for several years and never had a problem.

The book I have says the mechanical pumps put out between 2 and 6 psi. I see these carburetors listed as factory items on many old cars with mechanical pumps, and I haven't seen any with regulators. I wonder what gives? :confused:

Stuart

The angle of the fuel pump lever has to match the camshaft lobe.
Camshafts had different lobes over the years.
You may have a different cam in your engine than was stock.

I have a 1962 235 which was rebuild at some point before I got it.
If I use the correct 58-62 fuel pump it gives me just enough fuel for all driving conditions, but doesn't always keep the glass filter bowl filled, mounted just before the carbs.
If I use a 55 fuel pump, the fuel gushes out if the glass bowl is not tight enough, it pumps so much.

But be careful, you can break a fuel pump with too much lever angle against the lobe.
Also only buy new fuel pumps - never remanufactured or NOS !!
And watch out - Vendors don't always sell the right one for the correct year.
It's 2006 now and people don't know (or care) about the subtle difference in fuel pumps over the years.
They always think everything goes and works with the old inlines anyway.

For those of you who have been following this story, here is the latest. This past weekend I eliminated the cheap dial regulator from the system. Started the truck with the new fuel filter and new fuel pump and the fuel pressure was 5- 5+1/2 lbs at the carbs when cold. As the engine got hot down went the fuel pressure to ZERO. The only thing left is crap in the tank. Its the original 1952 chevy fuel tank that I steam cleaned. Time for a new tank and blow out the lines. Any other ideas.