84' 6.9 no starty when Hot!

[Dieselguy123]

Hey all, I have a friend with an 84' f250 6.9, It will fire right up when it is cold and run perfect until you shut it off.......Then it will crank but no start.......unless you hold the accelrater to the floor and then it will fire up. I am thinking it needs an IP, have already checked the lift pump,replaced fuel shutoff solenoid.....all the basics. Any help is appreciated.

 

[Russ]

Sounds like the IP is on it's way out. Try the warm water poured over the pump trick. If it starts then it's the pump.

 

[Shadetreemechanic]

If the warm water trick works, he can get by by pouring anything in the tank to increase viscosity of the fuel, ie motor oil, veggie oil, fuel additive etc. Mines been that way for over a year now. I guess I'll have to replace it eventually.

 

[Andylad13]

ip's can get expensive. i would say if your friend is on a tight budget, start it when your foot is to the floor. kind of weird but my 7.3 has starting instructions under the drivers visor that actually instruct me to start it my holding the pedal 1/2 way when its above 32 degs, and fully when below freezing.

 

[smokin69]

All have those instructions. I notice mine starts a ton better with it the throttle held a bit.

 

[Dieselguy123]

What does the water do to the pump when you dump it on that makes it start?

 

[smokin69]

makes internals contract.

 

[MIDNIGHT RIDER]

makes internals contract.

Would not the warm water actually make the internals EXPAND ??

 

[Shadetreemechanic]

You use warm water to avoid catastrophe from thermal shock. The idea is that you cool the case causing it to contract. As long as the water is not ice cold its ok. Before I started adding veggie oil to my tank I just carried around a jug of water in my floorboard. It was generally tepid or warm from being in the cab.

 

[Agnem]

What your suffering from is called heat soak. When you shut the engine down, the flow of fuel stops going through the pump. The radiant heat from the engine expands the external metal parts of the engine faster than the intnernal parts expand. This results in increased clearances between the head and the rotor. When this happens, fuel that is supposed to pass between the head and the rotor, passes instead to the space between the two. Understand that the tolerances between the head and rotor are extremely tight. Probably on the order of 4 decimals of precision. If you get a .001 gap between the two, it probably doesn't work. So, pouring 12 ounces of room temperature water over the head causes it to shrink just a few thousands, but enough to reduce the clearances to the level required for operation. Once the engine starts, and fuel starts flowing again, the internal and external temps of the pump stabilize and clearances are restored. The problem with this lies in the fact that if the water shrinks the head too much, then when you go to start the truck, the rotor is siezed and the input shaft snaps. For this reason, I recommend trying this trick WHILE cranking the engine to reduce this possibility. Either way, if your having a heat soak problem, it is time for a new pump.

 

[Dieselguy123]

Hey guys, Great info, I think I will just be putting an IP on this unit.

 

[Mr_Roboto]

ip's can get expensive. i would say if your friend is on a tight budget, start it when your foot is to the floor. kind of weird but my 7.3 has starting instructions under the drivers visor that actually instruct me to start it my holding the pedal 1/2 way when its above 32 degs, and fully when below freezing.

I'll second that. One of my vans ran tons better with WMO in the fuel, presumably because the IP was well worn.