I don't have an air fuel ratio gauge yet and wanted to check how the car was running lean/rich wise. I've seen some digital a/f gauges that just read out the o2 voltage and stated .5v as stoich. So I hooked up a digital voltage meter to the o2 wire feeding the ecu, postiive wire on ecu lead and negative to ground. Before I started her up the meter read a steady .03 v with just the ignition on. When I started it, the readings just went all over the place. Immediately it shot way up ot .98v and stayed there while the car was on the fast idle. THen as the engine warmed up and it droped down to normal idle speed the readinds slowed dropped to about .7v, then all of the sudden the reading went crazy. Numbers just jumped all over from .03 to .85 or so. Never steadied out at idle even at operation temp.
I gave her a little gas and held it at 2.5k for a min or so and still numbers were all over the board.

Is this at all normal? I figured the o2 numbers would osicllate from the ecu correction the mixture, but I though it would eventually even out. In the end I had absolutely no clue was to what the mixture looked like. THe only consistency I got was inconsistency. I'm running a stock 94 p72 ecu with all stock fuel system into a del sol S.

 

It's not supposed to even out eventually. It should pretty much continually scroll back and forth. Even with a needle gauge the sensor itself is just as inaccurate. At WOT you should be seeing a rich mixture - can't remember if that's nearer 1v or 0v... while revving the computer is still trying to keep things at stoich. Try this instead: Give it a big blast of throttle up to about 6k, then let off entirely. The readings should go full lean - whatever that indicates on the gauge. When driving when the engine's under load at WOT - it should be the opposite.

 

rich = high voltage
Lean = low voltage

 

IMO all a/f gauges are crap except wide band 02 sensors that come with an extra o2 sensor and bung to weld in...they run well over 200 dollars...all the cheap ones give you a round about guesstimate...it all depends on the purpose of the gauge to monitor or for looks...

 

Thanks guys. The purpose of the gauge was just to get a general idea of the mixture. I just rebuilt it with some .20 os forged pistions and some stainless valves. Just want to know if ecu was able to adjust for the slightly larger displacement while runing on stock fuel system