1998 GMC K3500 Sierra SLT 8 Cyl 7.4L
What could be causing the truck to run like it is missing out and smells rich?
2 days ago had left cat replaced and yesterday had right one
Nissan Technical Advisor 3/18/2011
There are many possibilities, like blown head gasket, defective ignition coil/s, incorrect ignition timing, bad O2 sensors, bad ECM. Did you already check the engine ,with a scan tool. That should be the first thing you did. Get the codes and post them here so that we can help you solve this.