From my days of long ago as an oil changer, we used to do fuel system cleans and it would result in this pretty horrible smell coming from the exhaust.
1997 F150 4.6L 4x4 215,000kms, when im doing bout 90-100km/h and i gun it to pass or just go, I can smell that smell comin from my truck, it kinda has like a sulfur kinda odour. at first I thought it was vehicles in front of me, but its there when im alone on a road.
Could this be a sign that my catalytic converters are plugging up? or any other thoughts