snoz

I was working on my 86.5 today and decided to measure the output voltage of my O2 sensor while driving. I looped a thin wire around the terminal at the O2 connector and reconnected it. During idle and driving the voltage varied quite a bit at times. During cruise at about 60 mph it would sometimes settle to mid .7v to .8 volt range. At times it would go as low as .1v and sometimes spike to 1.3 to 1.5v. This is a stock bosh sensor with about 4K miles on it. Should a stock sensor have spikes to above 1v? If the reading at cruise is accurate, I guess I'm running a bit rich. I'm running @PorKen's S300s chipset with an S4 FPR. I'm thinking about replacing the O2 sensor but am not sure if what I'm seeing is out of spec. Let me know what you think.

Thanks,

-Ethan

jcorenman

Ethan, the factory O2 sensor is basically a binary device: a lean mixture is around 0.1v, rich is around 0.8v-- both plus/minus a tenth or two. If the LH senses lean then it adds fuel, if rich then it reduces fuel. So cruising down the highway it should be alternating between rich and lean, i.e. switching from 0.1 to 0.8v and back once or twice per second. If it sits at 0.8 then it is rich all the time, which usually means the LH is out of adjustment range.

If the sensor only has 4K miles on it (and it is a Bosch sensor) then it is likely fine. I think the 85-86 cars have a manual O2-adjust which can correct idle and light-load (i.e. cruising) mixture. What you are looking for is the rich-lean-rich cycle at idle.

FredR

Jim,

If the NBO2 sensor is a two position control device then that would explain why such cannot be directly controlled by a WBO2 sensor that is modulating.

Historically I was a bit puzzled by this- not any longer!

snoz

Thanks @jcorenman and Fred. I guess I could lean it out a bit at the MAF adjustment. I haven't messed with the adjustment on this MAF as it is a rebuilt unit. I may go the Blink'r route or add a wideband to get it dialed in a little better.

I've been checking through things because I've had a slight intermittent miss at idle ever since I got the car running again two years ago. Last weekend I found that one of my coils had nearly twice the secondary resistance that it should. I replaced both coils with some used ones I had that tested within spec. The miss is much less frequent now and can barely be felt. I haven't checked it with my ignition analyzer since replacing the coils. I'll be doing that soon. Here is a video of what I was seeing before I replaced the coils.

Engine analyzer showing miss

Thanks,

-Ethan