Warm idle Lambda AFR

[Funracer]

Originally Posted by AndrewCologne

Then you should ask yourself why "on the other side" of the engine, the reading is different than Lambda 1, and here the options are a) AEM readings are off, or b) the mixture is different than on the other side of the engine.

b) From my previous post above:
“They are on separate banks. I have recently warmed up the car, unplugged O2 sensor so that FV goes to 50% and noted the O2 reading. Then shut off the car and removed the OE O2 sensor and put the AEM sensor in the OE cavity and restarted the car. Difference was only .4 AFR right side was higher.” I believe mixtures are fairly close between banks.

This leaves me with a). Currently looking for a used AEM 3.14” AFR gauge I can use to verify the custom gauge.

In the mean time I will set the mixture using the FV setting on the oscilliscope.

Thanks

[AndrewCologne]

Go to a service garage or emission check station where an official calibrated testing device gives you a credible reading

[Veeveessees]

Looks ok

[Funracer]

Originally Posted by AndrewCologne

Go to a service garage or emission check station where an official calibrated testing device gives you a credible reading

Florida stopped emissions testing in 2000. Really hard to find a shop to do that.

I have a Gunson and can set CO .8 myself.

I can tell you when I set mixture using AFR of 14.7 at warm idle, at WOT (closed loop) the AFR drops to about 12 and the car TAKES OFF. Like a turbo (admission: I’ve never driven a 930). If I set AFR with FV of 45% or use CO .8, WOT AFR drops to about 13.5 which is not as exciting.

[PeteKz]

When at WOT, the OXS CIS system goes to "open loop."

[AndrewCologne]

Originally Posted by Funracer

Florida stopped emissions testing in 2000. Really hard to find a shop to do that.

But this would give you the only true reference.

I have a Gunson and can set CO .8 myself.

And then?
The GUNSON is inaccurate – here btw in a ± range where you're within your off readings. So won't help you.

Second, an Initial CO seting of 0,8% does not equal to Lambda 1(ARF 14,7:1).
It's simply an initial setting where the ECU and its FV do pull the duty cycle up to match the final needed Lambda 1.
You can set it where you want, the ECU will compensate with its duty cycle to match Lambda 1.

I can tell you when I set mixture using AFR of 14.7 at warm idle, at WOT (closed loop) the AFR drops to about 12 and the car TAKES OFF. Like a turbo (admission: I’ve never driven a 930). If I set AFR with FV of 45% or use CO .8, WOT AFR drops to about 13.5 which is not as exciting.

See here PeteKz's comment.


Honestly, ... your approach won't bring you a satisfied result.
Go where a real Lambda gas analyzer exists, anything else ist just guessing, trying, guessing.

Good luck.

[Funracer]

Updates!

In order to absolutely verify my custom JBell made dual Voltmeter/AFR gauge was accurate, in early May I bought and AEM digital gauge compatible with my AEM 30-0300 controller. It showed exactly the same number as my JBell gauge, which eliminates the gauge as a source for my high AFR (lean) idle readings. Thanks to JBell for an awesome accurate analog looking gauge!


In mid May I bought an ECU wire harness from a fellow Pelican. This to verify my O2 wiring harness was not grounding somewhere. One of the many reasons a Cab is better than a Coupe is shown here:

Was able to run it through the unzipped window and leave my OE harness in place, unplugging the original and plugging in the test harness at each fitting.

Ran the engine and again, warm idle AFR was nearly 16 and the car ran otherwise as before. This told me the O2 wire harness was not causing these lean readings.

Pulled and cleaned and set the throttle position switch. The one between the throttle body and the air plate underneath the rubber “hat”. I had convince myself somehow this could cause a lean idle. Not fun to get this out and of course cleaning the contacts inside had no effect on my idle, but at least I know that now.


There is a happy ending, finally. See next post for the fix!

[Funracer]

In 2021 I had the motor out and on a stand, and added SSI’s at that time. Knowing that some day I would put in an AFR gauge had a bung welded into the passenger side at the local muffler shop. Never occurred to me that most folks put them on the drivers side. The welder did a hideous job on the weld, but functionally it worked so I pressed on.

After all was back together and AFR gauge installed I began trying to get the mixture numbers displayed to match the idle frequency valve and CO numbers in the Bentley manual. I could never do it or even get them to be close. AFR (with O2 sensor plugged in) was always way too lean compared to FV or CO. Why did I care about this if FV and CO were ok? I never felt comfortable running the engine hard with the AFR showing off scale lean at idle, even though cruise and WOT were good.

I had inquired a few times over the years on Pelican to those with O2 on each bank. My question was what is the AFR number difference between left and right sides. A few people said they were nearly the same with a spread of .1 to .5 between sides. This small difference would not account for the 15.8 on my car to the 14.7 I was looking for.
I verified this by putting the AEM sensor in the Lambda O2 bung on the drivers side and it was within .5 of the pax side readings, just as others had said.

Today I took the car back to the same muffler shop and had them weld a bung into the drivers side just behind the Lambda sensor. They did a better job this time:
.

Look here! Three years later and AFR is 14.7 at warm idle!!



Anyone with an O2 lambda system (SC 80-83) planning to add an AFR gauge, especially if you have SSI’s and a 2 in 1 out muffler, it needs to be on the drivers side behind the Lambda O2 sensor.

Thank you to everyone who had input on this over a half dozen threads since 2022. It was a frustratingly easy thing in the end.

I took my car out this afternoon and flogged the p*ss out of it.

Regards

[ahh911]

Fantastic.

Any insight into why L/R side report different readings?

Phil

[Funracer]

Originally Posted by ahh911

Any insight into why L/R side report different readings?

Phil

Not yet. I never found out much about the cars of the people that responded.
Could have been 2 in 2 out or some other setups that did not mirror mine well.

Or maybe I have an exhaust leak on that side. Actually just did another smoke test a couple of days ago by putting smoke up the tailpipe. Looking specifically for exhaust leak. There was a small leak from the SSI-to-muffler connection on that side so I will be replacing that gasket. Everything else looked clean.

Neil

[AndrewCologne]

Good report ...

beside checking the exhaust system on that side, ... did you check the fuel flow amount of all injectors so all do match?
https://nineelevenheaven.wordpress.com/adjusting-the-fuel-distributor/

[Funracer]

Originally Posted by AndrewCologne

Good report ...

beside checking the exhaust system on that side, ... did you check the fuel flow amount of all injectors so all do match?
https://nineelevenheaven.wordpress.com/adjusting-the-fuel-distributor/

March 2023:


Pretty close for popsicles test tubes!

Here is a pic of the pax side. Old sensor location now plugged and arrow shows the slight exhaust leak. About 10 inches away and also downstream of the sensor. May have had enough effect to throw off the readings.

[ahh911]

Originally Posted by Funracer

Not yet. There was a small leak from the SSI-to-muffler connection on that side so I will be replacing that gasket. Everything else looked clean.

Neil

The small leak might also expand at high temps?

Phil

[Funracer]

Yes good thought.

[Funracer]

Forgot the picture!