Check and compare your ignition timing. Also check the ect sensor, a common problem with them is if you don't change your antifreeze for a long time, a film of goo will form on the sensor. This will change the actual temperature it sees telling the ECU that its temperature is lower than the actual temperature of the engine, adding more fuel thus making it richer.

Also try to stay in closed loop as much as possible its better for economy.

 

Was this directed to me? It seems as such so I'll reply.

My timing is base line timing but advanced +3 degrees from stock. I guess I'll check the ECT, as the previous owner did a really bad job of maintaining the coolant. Did good with everything else though, thankfully.

 

The ETC might apply to me, it has been three years since the coolant was changed...[ducks rotten apples and vicious slurs]

I'm going to try and reground the manifold and see if I can't get the damn O2 working.

 

there is an earth strap on one of the cats or joins in the stock exhaust system to ensure that the sensor is grounded properly and its the cause ( when missing ) of many o2 sender issues

 

Weak thermostat will also hurt your fuel economy too.