Re: Fuel Pressure... 7 psi cold, 1.5 psi hot(!)
Re: Fuel Pressure... 7 psi cold, 1.5 psi hot(!) -- Tracy Norris	Post Reply	Top of thread	Maverick Message Board

Posted by: Ken merring ® 2001/12/05, 15:43:00 Author Profile

:Hi everyone! : :Thanks for all of the previous help, been busy working on my '76 two-door V8 swap and its coming together nicely. : :But... : :I have a mechanical Holley 80gph pump, Fram clear fuel filter and a Holley in-line fuel pressure gauge. When the engine is first started (cold) the fuel pressure reads 7psi (the spec is between 5 and 7.5 so this is good). In addition, the clear fuel filter is chock-full-o-fuel. : :But after taking it around the block, popping the hood and looking at the fuel pressure gauge, it reads 1.5psi and the clear fuel filter is almost empty (maybe a tablespoon of fuel in it). : :Needless to say, it will idle fine like this but spits and pops if any load is placed on the engine (not enough fuel, I'm sure!). : :Any ideas why the pump isn't pumping well when the engine is hot? : :Remember that this is an inline-6 (250) to a 302 V8 swap with Heddman Headers. A friend suggested that the fuel line was getting boiled by the headers and causing the pump to suck air instead of fuel. I am inclined to believe this because the fuel line from the body on the inline six engine is just aft of the drivers's shock tower, whereas on the '73 V8 donor car, the fuel line rides the frame rail and exits in FRONT of the driver's shock tower (keeping the line cooler?). : :I would appreciate it if anyone else has any input on this. It's driving me batty! : :Thanks again for everyones help! :Tracy in Texas .................... ..Sounds like a servere case of vaporlock. As a test, find a sheet of metal to slip in between the exhaust and the line temporary and go through the cold-hot process and see if it improves. If so, there is insulating sleeve to use on the line or move the line to the out side like the V8 car. Also would run a little less pressure on the carb. The limit, if a Holly is about 7#, so if running the max in pressure, then there is no room for a needle seat problem before the carb floods over. Volume of fuel is the important factor (size of line)and pump GPH, over just the pressure. These cars even stock are often prone to fuel boil right in the bowl during summer and makes for hard starting when hot. Good luck.

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