detroitdiesel

is a 2003 2500 express van w/ a 4.6 or 4.8liter. exhaust smells like unburned fuel and stalls when at low rpm. has erratic rpm. cylinders cut-out at random, feels like engine is in neutral. not sure if the transmission has anything to do with the engine stalling but the transmission makes a loud clunking sound when engaging all gears. is the loudest between 1st and 2nd. sometimes while traveling at 60mph feels as if transmission goes into neutral, then rpms increase for a second or so, then returns to gear. took it to dealer and they could not figure out.