I have an 89 f150 with a 4.9L straight 6 and a 4spd manual trans. It has always "moaned" when I shifted into 4th too soon or going up hill. Just the other day I hit 45mh in a straight away and the truck started to shudder. It keeps shuddering and growling while I accelerate and once up to speed, when i let off the gas, it smooths out. Any time that I give it gas it shudders again. I pulled codes with a code reader to make sure that I wasn't reading the CEL wrong and I got 44 and 77 both seem pretty useless. I have relatively new plugs (maybe 10-15k ago). I as going to change the plugs before I started dealing with the torque converter. I have read a number of threads that deal with similar symptoms, but no real "fix". Any suggestions? You guys are awesome. This forum is how I have brought her back from the dead. Barn Find in Kentucky.

 

Think I'd check fuel pressure...sounds like it might be starving under heavy load.

 

Thanks. don't fuel pumps just die or do they slowly fade to death?

 

Just depends...I had a 91 that went slow, yours will have the high press pump on the frame an a low press pump in each tank.

 

Btw have you replaced the fuel filter?

 

just replaced the fuel filter in the fall. I was going to replace the tank in the spring. It has been patched and I get a whif of gas every now and then.