I have an '86 f250 6.9 that I recently purchased from a somewhat neglectful PO. I was out with it yesterday (the third time that I have had it out on the road for any distance).

When it's cold, it stumbles and hesitates when accellerating in 1st (3 sprd auto). It acts like it's running on just 4 cylinders and produces lots of white smoke. Within an 1/8-1/4 of a mile, it clears up, shifts to 2nd, then takes off.

Even when warm accelleration is not great, but acceptable. When it gets up to speed on the flats, I can do 70-75 mph without any issues. However, on the slightest uphill I start to lose speed. Romping on the accellerator does not cause the tranny to downshift, but does produce a lot of white and black smoke, sometimes hesitating/stumbling. On longer uphills (3-5% grade), I can only manage about 35 mph.

When it's warm and I shut it off, I have to crank for 10-15 seconds before it will start. When it does start, it produces a big puff of whiteish smoke.

When I first purchased it, it had an awful time starting it when it was cold. I replaced the glow plugs (all 8) and it seemed to clear up most of the problem. However, if I let it sit for a few days, I have to crank it for a few minutes to get it to start. Even if I only let it sit a day, sometimes it will start right away, die, then crank for 30-60 seconds to get it going again.

I suspect that I have old cracked fuel lines allowing fuel to drain back to the tank. I know the return lines off the injectors are old and are starting to crack, but would that allow fuel from the primary fuel line to drain back? Or are there other lines I should replace as well.

I know that:

black smoke = fuel (rich)
white smoke = air
blue smoke = oil

Anything other suggestions?

Thanks.

 

You are on the right track. Cracked fuel lines will allow air to get into the system. It won't leak fuel out because the fuel is thicker/bigger than air molecules. Replace all hoses and clamps also check the steel fuel lines to the tanks. if they are rusty they can leak also. I've had to do both and my 93 purrs right along and fires right up.

 

I would first suggest you check the water separator on the firewall by the booster. If it still the original one then you may want to drain it then plug the drain hole with a bolt/clamp as they are notorious for not sealing and air enters the lines causing exactly what you have for a problem. Now if the water separator has been bypassed you may have water in the fuel at the IP unless the fuel filter has a drain on it. If it has try draining water from it too.