I recently decided to test the o2 sensor on my 740 with a handheld voltmeter - didn't have any noticeable drivability problem but I knew the sensor had not been changed for at least 125K miles (could be 250K - dont know if the first owner ever changed it or not). I've been able to pass the emissions test without any problem (every other year - last time was a year ago.) Anyway, not to my surprise, the senor was dead (voltmeter indicated the sensor had a constant output of .6 volts). I grabbed one on my next trip to the boneyard from a wreck that had passed the emissions test within the past year and got lucky, the first one I tried was good (fluctuates between .3-.8 volts). The reward has been an increase in mileage with mixed city/hwy driving from 20 to 22.5 mpg. This has gotten me thinking of installing an accessory air/fuel mix gauge to monitor the o2 sensor function. Has anyone installed one of these - if so, what brand? It looks like they aren't too expensive (egauges.com). I have a 87 745 and a 87 244 and I think I might install one in both. On the 240 it could go right in one of the accessory gauge slots and on the 740 I'm thinking of using the two gauge accessory mounting cluster that egauges.com sells and mounting it on the flat center section of the dash (it would cover up the worst cracks in my dash too) alongside a transmission oil temp gauge. (I pull a trailer with the 740 occasionally). Has anyone installed one of these either? I'm thinking I could Tee a small block into the transmission line right before the radiator for the sender and maybe even adding a stopcock to make flushing tranny fluid easier at the same time.

Jim