91 gmc sierra

I have a 91 sierra 4x4 that started running really bad all of a sudden. I thought it was the fuel filter and changed it out, but that did not help. Plugs are good. It will run great for a while and then starts acting like it wants to die and the exhaust smeels really strong. It will act up for a while and then run good for a while. It has a 350 engine. I have ran the tank empty and put fresh gas in and also added additives to the fuel to clean system. It has a new engine with only about 2500 miles on it. Any suggestions.

Welcome to AF, many things can cause this, look at the fuel pressure, must be 10-13 psi.

sound like the MAP sensor is Bad, did u change the fuel filter, IT can also be the module going bad.

What temp is the engine coolant temp sensor reporting to the ECM? If this is wrong, it can run rich.

//2000CAYukon