sudden acceleration and burst of power
 

I have a 1978 f150 with a 6.9 idi and randomly my truck will get a burst of power and accelerate on its own for a second. I just replaced injection lines and caps becuase they were leaking causing hard start. Am i sucking air? Could it be injectors, ip. I also just changed fuel filter. I dont know what it is im stumped also it doesnt matter what fuel level its at so i know its not rhe pick up lines cause know what the idis do when almost out of diesel. Please help

Sounds like air in the line, check your lines running to the lift pump. My 86 had a leak on the short hose between the frame mounted hard line and the lift pump. It wasn't until it got bad enough to drip that we actually noticed it. The truck had been surging for a long time and replacing that hose cured it.

I thought thats what it might be. I tried looking at all my lines yestraday amd couldn't find anything unusual. Ill look again though. If its not that could it be something else?

When i was in traffic today my truck started to sputter for a couple seconds like it was running out of fuel. Like when your running really low om diesel. Are these related do you think?

Ive also been getting some pretty horrible millege about 8 or 9 to the gallon and when i gotthe truck i was getting bout 13

That's how my truck acts when I get low on fuel. The pickup in my front tank is broken and starts sucking air about 1/4 tank and will surge and sputter and lope. If you can do that with a full tank then that's probably not your issue. It still sounds like you are getting air in somewhere. What does your fuel system look like, is it all the original gas stuff from the F-150 up until the lift pump on the motor?

It looks like a new tank and nee lines to the lift pump. The old f150 lines are there nut not in use.