Hello --

I have a '91 F-800 dump truck with the 429 4v V8 gasoline engine. She has what I believe to be a Holley 4bbl carb and an electric fuel pump in each tank. Left side pump quit so I found what is supposed to be the correct Ford pump based on the truck's VIN -- big pain and big expense. Installed the new pump and the truck starves out of gasoline under any kind of load. The old right side pump runs the truck fine under all conditions.

Did some tests: Rt. side (works) develops about 1.5 PSIG max, flows 0.87 GPM (52 GPH) at about 4 inches water column residual pressure. Lft. side (doesn't work) develops 35 PSIG !!! and flows 0.55 GPM (33 GPH) at 7 PSIG residual.

Each pump's output goes through 3/8 fuel hose to a two tank valve, then from there via steel line through a spin-on fuel filter, then up to a device I'm not familiar with above the right side valve cover. From there it's more steel line into the carb.

I can't imagine that any 4 bbl carb could use more than a half gallon per minute of gasoline but it sure feels like insufficient fuel when trying to run on that side. And 35 PSI going to a carb sounds like a recipe for disaster -- makes me think the mystery device is a pressure regulator but I don't want to monkey with it without knowing, and especially since the right side works fine.

Does anyone know the correct fuel pump pressures and flow rates for this truck? I've been told by many that Ford didn't make a 429 in '91 but here one is. Manufacture date is Sept. 1990 so maybe she's the last one

Thanks,

Pete P.
Harborcreek, Penna.

 

wow, yeah 35 psi does seem very high.

I've got a '90 f700 with that 429 "4v". Which is not a 4 valve by the way. I have been through two of these trucks that claim to have 4 valves, and neither had 4 just 2? Whats with that?

Maybe the thing to do would be take the pump out of the left tank and put it in the right tank. See if the problem follows it around. Then you should atleast know the pumps to blame. Then you can either find out if its the wrong spec pump? Or it needs calibration?

Something is going on. Kinda strange problem. Too much pressure instead of lack of pressure. Low flow too? Hmm

Atleast you can still run the right side!

 

You got the wrong pump. 35PSI is fuel-injection pressure, I bet you got a pump meant for fuel-injection, not carb. One way to look at the difference might be California-versus-Federal emissions, CA might require fuel-injection, Federal was OK with a carb.

Have NO CLUE how to make sure you get the correct one.

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4V means 4 VENTURI - or 4 barrel carb. 2V means 2 barrel carb.

 

"4V" refers to 4 venturis in the carb as in 4verturis in a 4bbl Carb.
Ford did this for years and years.

429 2V would have been a 2bbl carb

 

I have seen the rubber lines collapse on the inside and restrict or completely stop fuel flow.

 

this one is for fuel injection !
1991 Ford F800 Fuel Pump 8 Cyl. 7.0L M.F.I. [TU205] - $170.84 : Fuel Pumps - FuelPumps.com, Buy a Fuel Pump Online

 

Ahh 4 venturi's. Thats some sneaky logo making. Dont know why I assumed it was supposed to be valves...

They were both 4 venturis..

 

"4V" and "2V" and even "6V" were used back through the 60's, at least. It's in all the Motor's manuals I have going back to the early 60's.