rough rough 6.9 when letting off accelator

[fugenay]

my 87 f250 4x4 just started running running like sh-t. so I put in new injectors and return fuel lines. the inj. pump only has about 50k on it. Its smoking like crazy especially when cold and most of the time when it's idling. Also when I let off the gas it runs super rough. It's also missing quite a bit when accelerating and fades out at about 3000 rpms. It still seem to have pretty good power. I'm not sure what to do next. A friend told me it might be a loose or stretched timing chain. Any help would be great. Thanks Ted

 

[FordGuy100]

What color is the smoke?

I'm not the smartest when it comes to diagnosing these things but start with changing the fuel filter. If that doesnt work bleed the injectors, it could be air in the lines, though air in the lines the roughness will usually go away as the rpm's increase. Maybe lift pump?

 

[fugenay]

thanks. I'll try to give it a try this weekend.

 

[Petri317]

Yea, take a look at the lift pump as well as the lines from the fuel filter header to injection pump. Couldn't be a timing chain, as these engines have timing gears, not a chain. Also check the fuel lines at the tank selector valve (left side on the framerail at the front tank) for leakage. For that matter, check all of the steel, plastic, and rubber fuel lines that you can for any obvious wear or leakage. The fuel lines, if the cause may,however, be damaged enough to suck in air but not leak. A clear piece of fuel line placed at varying points will show any air bubbles (indicative of an air leak) and where the leak may be originating.