1990 Mack em-6 injector pump troubles?

Just spent about 10 hours in this new to me mack. Left Illinois with it yesterday, seemed okay for the first while, further I drove the worse it got, now its almost all the time.

Engine seems to surge/ hunts. Started in the middle areas of the throttle, seemed to go away when wide open, or totally out of the throttle. Got worse and worse

I first thought it was tires or driveline, but tires wouldn't make any difference in and out of the throttle (it stops doing it as soon as you let...

1990 Mack em-6 injector pump troubles?

1990 Mack em-6 injector pump troubles?