CIS 02 sensor voltage okay?

[aigel]

1981 SC with CIS: When I bought it, it came with the 02 sensor disconnected. I wasn't aware of that fact, and not knowing what I was doing at the time, I had it smogged just like that - without a problem!

Since the last smoggin we now have treadmill dynos that give the car an actual workout (instead of just idling it and running it at 2500rpm with no load).

I figured I'd put back the 02 sensor to run cleaner. The car runs okay, a bit less power, as expected and I had to adjust the idle set screw. Idle rpm had dropped a few hundred after the O2 sensor install.

The voltage reading I get (it depends on the quality of the ground I find) is in the 0.5-0.7 range. I read in earlier posts that .48 or so is ideal. Would you go smog the car with a reading in the range I see?

I think I may be able to get a pre-inspection. They could tell me where I am, so I won't fail and make it into the DMV's blacklist.

Whaddayathink???

Cheers, George

PS: I have the innovate a/f meter, however, the only place to plug it is into the stock O2 sensor location! I don't want to start playing with this, just pass smog and go on with life...

[Noel]

George,

I would use the Innovate meter to reset the mixture to the stock level of .40 - .80% CO (I think that is around 14.7:1 Air/Fuel ratio, but confirm this first). Per the Bently manual this is set with the O2 sensor disconnected anyway. Then reconnect the sensor, drive down to get tested and then home to reset the CO to 3.5% and leave the O2 sensor unplugged. You should pass, no problem.

[aigel]

So, you think the O2 sensor output is within the range of where I'd think it is working properly? Does it reflect a slight rich idle setting?

I think right now it is at 13.8 a/f at idle. That may be a tad rich to pass smog, however, it passed idle test like that last time. At higher RPM the O2 sensor should regulate it to 14.7, so I am not sure if I should even bother?

Anyone can confirm that .4-.8 CO is equal to 14.7 A/F?

Any other opinions if I should just give it a shot as is?

Thanks!

George

[Noel]

George,

I know I have seen a chart here on a Pelican thread that translates CO to A/F ratio. I copied it onto my home computer, but will not have access to that computer until Thurs evening. If no one else posts it, I will.

[klatinn]

Hi George,

According to this chart:

AFR to CO conversion

You should set your AFR to 14.2 to 14.4 at idle. The 1-wire O2 sensor of the CIS system does not get hot enough at idle (it's heated only by exhaust gases). Above idle it's hot enough to go to closed loop, but then you will run at 14.7, which is a little to lean for good throttle response.

Regards,
Klaus

[aigel]

Klaus:

Thanks a ton.

I checked again today coming back from work. I goofed. The voltage is 0.06, not 0.6. I think the O2 sensor is shot. May be the reason why it was disconnected in the first place. It sure runs very different with the 02 sensor connected. I will get a new sensor and see where that gets me.

Thanks guys, I will keep you posted!

George

[911Mac]

George,

Here's a graph showing both wide and narrow band o2 sensors plotting voltage and A/F ratio. You have a narrow band sensor.
One thing to remember, because the voltage curves are so flat on both sides of 14.7/1, you can't really tell anything other than you're leaner or richer than 14.7/1. It also sounds like the voltage can vary considerably on either side of 14.7/1 depending on the exhaust gas temperature.
I'm running Tony's EFI conversion kit on my SC, watching the o2 sensor output on the laptop shows the narrow band o2 voltage varies on both sides of .5 volts. The EFI controller richens the mixture if its below .5 and leans it if above .5. Sound like you may have a bad sensor if you're seeing a steady .06 with little or no variance.

Mac

[Lorenfb]

"Sound like you may have a bad sensor if you're seeing a steady .06 with little or no variance."

Or a shorted O2 wire.

[aigel]

Got the new, correct (not generic) sensor today. Everything is the stinking same! I read about 0.06V at hot idle with some fluctuation. If it weren't a factor of 10 off, I'd be happy!

If I disconnect the O2 sensor and read just the sensor lead, it acts exactly the same than if I plug it to the wire going to the controller?

What's going on???

Cheers, George

[aigel]

Just out of despair, I tested the lambda brain relay under the pass. seat (which turns the lambda ctrl. unit on). It is functional.

George

[aigel]

And one more thing. The voltage increases dramatically if I rev the engine. up to 0.2!

I am starting to think that my system may have gone lean on me since I tested it the last time. Off to see where I am at A/F at hot idle when using the innovate o2 sensor and meter.

George

[aigel]

Ilde A/F is 15.2! This may be the problem, why the 02 sensor reads zilch?

I will richen it up. Looks like I won't be back on the car until late tonight. I you guys have any ideas, let me know!

George

[911Mac]

George,

Sounds like you're on the right track. Once you richen the idle, it'll be interesting to see what the A/F ratio is at higher RPMs. The 2.0V reading on your wide band sensor looks like it is in the best power range, the lean A/F at idle could work to your advantage for the smog test.
Don't expect the stock o2 sensor to vary the mixture at idle speeds. Most systems ignore the 02 sensor at idle because the exhaust gases aren't hot enough to get a meaningful reading. My controller is set to start running in closed loop mode at 1200 rpm. They also run in open loop during acceleration.
Is there any chance you have a small vacuum leak? That might make it run lean at idle, but richer at higher RPMs.

Mac

[aigel]

Ok. I had the A/F meter hang in there for quite a while. It did go down as far as 14.9.

I stuck the new o2 sensor back. Seemed like the idle was a tad bit higher than what I'd like. It was right above 1k rpm. It may have crept up, because the engine was nice and hot at this time, almost into the second 1/3 of the temp gauge.

So, I adjust the idle back down to 950 and sure enough, my 02 signal (with lambda box attached) now reads between 0.1 and 0.6, fluctuating very nicely.

I am unsure what to say. I think that Mac may be right. I may have never gotten the stuff hot enough in all my fiddling with it, including a test drive late at night when things didn't heat up enough.

I will go to the smog check tomorrow. I won't richen up the idle mixture before. I am pretty sure I'll be fine. I will report back.

Thanks for all the input.

Cheers, George

[aigel]

Hurray!

Passed!

The CO and HC were very very low, the NOx were 2/3 of the allowable. All points towards it running lean and a hot day in the mid 90s. I am sure, on a cool day, the NOx would have been lower. I drove the cobwebs out of it before I got there, so that may have contributed to the heat...

Thanks all.

George