Hey all, I just test drove a 2000 F-150 7700 2wd, supercab, 5.4, auto trans, Gas/LPG. It seemed to run alright, but when it was pulling hard(see floored) it seems a bit jerky, not smooth but not extremely bad either. When it is just maintaining speed on the highway it will start to jerk untill you let off the gas or try speeding up a bit, it will then continue to do it again as it stops pulling. It almost feels like it is slipping in lockup but I can't really tell. Anyone ever heard of this? This was running on gas btw, propane leaks fairly bad.

 

Even a small engine misfire will cause a stumble / jerk at highway speeds.

 

if it was a test drive, run.
is it LPG or Natural Gas?

 

This shudder was definitly not a misfire, it is somthing worse then that. It is a Gas/Propane system. I personally would never touch a CNG vehicle for the simple fact that you get pretty much no range from that type of fuel.