Hi Bruce,

I guess I've been kinda preachy on the subject given my easy access to some better test equipment. Bricksters are always asking how to test the oxygen sensor. Or how many miles until it dies. There are simple answers to both questions, both mostly resulting in someone replacing a good sensor. The simple answers just don't cover all the variables in each situation.

Most of the time a do-it-yourselfer wants to get beyond parts changing as a diagnostic approach, especially when it gets expensive, so I try to lend my parts-cheap thoughts, like pulling a sensor and measuring its output while held in the flame of my soldering torch. Usually I assume too much and wind up helping only a very few.

So when you hook your DMM (1 Volt scale)to the oxygen sensor output on the LH system, you'll never "see" it at .55V -- unless it is dead or still cold -- and that voltage is coming from the ECU. The only thing the DMM can tell you for sure is it is switching from high to low. And there are so many variables there too-- the sampling rate of the meter, any autoranging delays, random synchronization between the switching and meter sampling... all adding up to what to many, depending on their familiarity with the meter, look like jumbling numbers. Yes, the swing. What it tells you is the system (ECU, sensor, injectors and motor) is in closed loop. If you're good with the meter and can time the transitions to get the 50% beat, you can fine tune the idle mixture - provided your sensor isn't lazy because it is contaminated. That is where the scope helps.

Now I haven't the foggiest idea what you'd see with Regina. Could guess, based on how I'd design it, but my track record for that is not good. Last time I tried to help someone through wiring on a Japanese car's lighting system based on guesswork --how I'd do it. Figured the relays would be switched by that skinny twist-on stalk from the column, but indeed the high current was run through that switch; the relays were there to save the ignition switch. I was way off.

So, until I have an opportunity to get Grandma's 940 into my driveway, my guesses about Regina's voltages and waveforms aren't worth the gamble. I suppose you could take some baseline readings, assuming the 93 you list is also a Rex-Regina. Knowing the titania sensor is a variable resistor, some voltage must be applied by the ECU to measure its resistance. This voltage would be modified by the varying resistance in response to the oxygen content of the exhaust. If the ECU then made corrections through injector pulse width, you'd expect to see some swing back and forth, at least during warm up. Guess I'd start out on the higher - maybe 20V scale first time. Hmmm- I don't think I've ever seen any posts on this regarding Regina...

The reason you see the sharp excursions with the narrow band LH (zirconia) sensor is its extreme non-linearity right where stoich occurs. I don't know if the titania sensor has the same curve, so the feedback may be much more stable instead of the on-off regulation in the LH. I doubt it, though. If it were the case, I could make a cheap air/fuel meter or poor man's exhaust gas analyzer from a titania sensor instead of springing for one of those 5-wire UEGO wideband sensors. All this just says I'm curious about what you will see with your meter, if you happen to try this before I do. There's probably no place to connect an LED on Regina like on the LH-2.2 models.