1986 S-15 4x4 stalling problem

OK i just bought a S-15 4x4 ext cab 2.8 V6 truck. I love it to death, but sometimes, it will stall and the service engine light is on. The guy i bought it from said they put in a bigger cam so that it would have more power, but it needs a computer chip. Does any 1 know which one it needs?