I just bought a 96 f-150 with a 5.0, 5 speed standard. It starts great cold and great when it is hot up to a couple min after you shut it off, after about 1o min it cranks over a little longer and then starts if I wait about half an hour it cranks over for about 5-10 sec then starts and puffs black(over fuel?) I checked the fuel pressure with the engine cold it is 38 psi and 34 psi while running.Fuel psi increases to about 41 psi with the fpr unplugged. The fuel psi bleeds off about 6 psi in 1 min, and in 10 min it bleeds off about 25 psi, eventually it will go to zero, Is this normal? I have changed the ECT, new plugs cap and rotor and wires. Cleaned the MAF, new airfiler.I have no codes, if i do a koer test it comes up with a p0411 ( air pump). Any ideas? Other then the hard hot start the truck runs great.

 

It sounds like the injectors are leaking the fuel into the combustion chamber. Strange it would start good cold with the fuel pressure going to zero. I would try adding some fuel injector cleaner to the gas tank. Hopefully someone else will reply.

 

As soon as I turn they key on the fuel pump cycles as nornal and gives me instant fuel pressure. I was also thinking leaky injectors but would it not start hard when cold as well ?

 

A cold engine requires more gas to start, and I suppose some of the gas evaporates and a little may get past the piston rings into your motor oil. That's the way I imagine it. Hopefully you will get more replies to confirm or deny what I'm saying.

 

Sounds like that could be fixed with a tune-up. My truck used to do the same. Found it was a combination of the coil giving weak spark when it's hot, and a weak old starter

 

I had the warm hard start issue a while ago. Does it start quicker if you start it with full throttle after that 1/2 hr delay? (this shuts the injectors off) If so, then check codes. I had an ECT sensor issue that told the computer to run rich as in a cold start but was too rich for the warm engine and basically floods the engine. Code 118 was my problem. Changed the sensor and it instantly ran perfectly and no more warm start issues.

 

I have changed the ECT, but I will try holding the pedal to the floor. I changed the coil out but still the same problem ( after about half and hour it cranks a long time before it starts)

 

I would put some fuel injector cleaner in the gas tank. It may not help, but it shouldn't hurt anything.

 

So i figured out that after it hot I can shut it off, then bleed the psi off of the fuel rail. When i come back in 30 min there is about 10 psi of pressure that has built back up, when I go to bleed this off there is a bunch of pressured air/fuel. I have to cycle the pump numerous times to get all the air out(and yes it's pressurized air/gas ). Even if I dont bleed the initial psi off when I shut it off, when I come back there is all this pressurized air/gas that comes out ????

 

I think that may be the gas in the line expanding due to the heat of the engine...not something to worry about I think...I would go with a tune up, check the air filter too

 

i have this same exact problem with my truck but its a 96 f-250 with the 351 keep us posted if you find the answer

 

any updates yet, my 96 is doing the same thing. I was thinking fuel pump is getting hot and not pumping enough. Starts great when cold and fuel pressure was ok according to my shop (but they did not drive it long)

 

I ordered a set of injectors, just waiting for them to come in and i'll let you know. I clamped off both fuel lines after i shut it off and my fuel psi still dropped off in about 10 min , so I think I have some leaky injectors.

 

Maybe, but from what I've read those injectors very seldom ever go bad.

 

I got my eBay reman injectors installed today. So far so good. It starts great and has way more throttle response. Hopefully my fuel mileage goes up.