I am trying to find out if I have a bad O2 sensor on my '87 Max to fix my poor fuel mileage problem, which is 15 mpg city. I have fixed the cyl head temp sensor connection and the ECM now properly flashes the 44 code that is working OK. I measured the O2 sensor output voltage and get .23 -.77 V with crosscount cycle rate at about 1 sec. Unplugging a vacuum line to create a lean condition it gets .19 V and with a quick response under half a second. It's hard to get exact measurement because I am using a DVM and not an oscilloscope. For this year Max does the crosscount voltage and cycle rate look OK?

 

Put the ecu in mode II while engine is running and check the mixture feedback. If your green and red led doesn't flash at same time then you need to remove the plug on the maf adjuster and adjust it till both led's flash at the same time. Otherwise it should toggle at least 5 times in 10sec.

 

Thanks I check it out. I have a bad O2 heater circuit on the will this affect the operation in mode II ? I do not get a green flash in mode I that the O2 sensor is working correctly, I am guessing this might be due to the bad heater circuit.