what is the correct fuel pressure for a 1994 f-150, 4.9 six ?

 

Engine Running 45-60 psi
Key ON Engine OFF 50-60 psi

 

That's what the manual says, but I've never actually seen one running that high, and they all run fine @ 35-40. Even mine. Look at the bottom of this diagram.

 

Mine holds right at 54-55 PSI KOEO

 

Mine runs right around 50 KOER, and about 55 KOEO.

 

that is the same as a 5.0 isnt it? or at least real close?

 

Not really, only the 4.9L is that high. The 4.9L requires more pressure because it uses 14 lb. injectors, whereas the 5.0L uses 19 lb. injectors. Fuel pressure specs for the 5.0L are 35-45 KOEO and 30-45 KOER.

 

It's my understanding that the 4.9L is higher because the fuel rail is trapped inside the intake runners directly above the exhaust manifolds, so the gas would boil at a lower pressure. That's why the first 4.9L EFIs ('87-88 only) had a fan to keep the fuel rail cool.

If it was just to get more fuel thru the injectors, they'd have just used bigger injectors.

 

That may have something to do with it, I don't know. I know they added a heat shield above the exhaust manifold to help with that problem, though. Regardless, the fact that it does have 14 pound injectors means they have to run a higher fuel pressure. In the same sense, you could say that because they have such high fuel pressure, they must run 14 pound injectors. Either way you slice it, they are still connected.

 

thanks to all . your information is very useful

 

I remember on dad's old '88 F150 a fan that would kick on after shutdown, but I was little then and might not remember right. Is that what your talkin about?

Adrianspeeder

 

It was cute. A lot like many of the early 80's Nissan's; a little fan under the hood aimed at the fuel system.

 

Adrian
Yes.

Pekkerwood
Actually, it was a large thin squirrel-cage blower mounted near the battery with a flexible duct (like an old heat-riser hose) going to the injector rail.

 

The one most Nissan's used was mounted by the firewall (FWD, so the fuel system was on that side of the engine compartment). Freaked me out the first time one turned on while I was under the hood. I never expected a fan from the back of the engine compartment. lol.