So i figured out I have a 1991 engine sitting in my 1994 chassis. I'm getting really bad MPG, like 150 to the tank. What else, besides the O2 sensor regulates the fuel/air mixture? I can smell that it's running rich. I overheard someone talking about the coolant temp sensor has something to do with it. Is this true? Any suggestions to fix this problem?

 

Are you running an OBD0 or OBD1 ECU? But both should be similar - A/F ratio is determined by the ECU, which takes inputs from multiple sensors, including MAP, O2, ECT, IAT, TPS, etc.

Any CEL codes? Is the thermostat stuck open? Is there an exhaust leak? Is the fuel pressure high? Is a fuel injector stuck open?

 

there is no map on a 1991 honda engine. IACV replaced. TPS good.

 

My stock 1991 has a MAP mounted on the firewall. Please don't start new threads about the same problem.