duckstrat

Hi,there.

I wanna know about the signal of the O2 sensor on the 24 pin DME.

I saw the signal by the oscilloscope.
It' was repeating about 0.7V and about 0.1V frequently.

But the time period was changing
Idle is low frequency
Accelarating is High frequency.

Is it normal?

I wanna know the relation between A/F ratio and the voltage of the O2 sensor while the closed loop operation.

Please let me know about that.

Thanks.
Masa

Dan Martinic

What you are observing is normal operation. It's like the exhaust pulse: every cycle produces an alternate reading as the closed loop system compensates to reach an average AFR (IIRC, the ideal 14.7:1 is aprox. 4.5v)

Obviously, the faster the engine operates, the quicker the pulses (cycles)

Dan Martinic

Here's a quick tutorial that covers the basics http://www.autotap.com/techlibrary/u...en_sensors.asp

duckstrat

Dan san

Special thanks!
I'll check that.

Best

Adker

The O2 sensor is part of a system, the catalytic converter, the engine ECU and the O2 sensor. The cat is a chemical reactor, it has two fundamental chemical reactions, reduction and oxidation. The O2 sensor is part of the system that swings the AFR around the 14.7 ratio to run the cat slightly lean and then slightly rich to support these chemical reactions. This swing is controlled by the ECU using the O2 sensor to determine if it needs to add or reduce fuel in the closed loop operation.

Video is a bit silly but accurate



More technical read:
"To operate efficiently, catalytic converters need an air/fuel mixture that alternates between rich and lean. When the air/fuel mixture is rich, it reduces the amount of oxygen in the exhaust. This allows the reduction catalyst to break down NOX. But to burn HC and CO, the oxidation catalyst needs more oxygen so the air/fuel mixture has to go lean. This allows the catalyst to momentarily absorb oxygen and trigger a reaction that burns up the HC and CO.

"The powertrain control module (PCM) flip-flops the air/fuel mixture when the engine is warm by monitoring the rich/lean signal from the oxygen sensor in the exhaust. When the O2 sensor reads lean, the PCM makes the fuel mixture go rich. When the O2 sensor sends back a rich signal, the PCM shortens the on-time of the fuel injectors and leans the fuel mixture. The O2 sensor then send back a lean signal, and the PCM increases the on-time of the injectors to make the fuel mixture rich again. By rapidly changing the air/fuel mixture back and forth, the overall mixture averages out and keeps emissions at a minimum."


This is how the 944 DME monitors the O2 signal to control a AFR.
https://redirect.viglink.com/?format...otronic.lambda.

Dan Martinic

Adker

No chip update required. The DME will still run in closed loop but no cat means no chemical cleaning of the exhaust gas. If we had a post O2 sensor, the ECU would detect that the cat isn't working and throw a code. The 944 slid in before the post O2 sensors and check engine lights became common on cars. I would guess ROW just doesn't use the closed loop code in the DME, it uses the fuel maps.

The FR Wilk web pages do not appear to be maintained anymore, just a matter of time before they go away...too bad.

Cleaning the cat isn't something that I think would ever work, they are very refined chemical reactors. Most cat failures I am aware of are because the closed loop had issues (bad O2 sensor or a rich mixture) and damaged the cat by overheating it or coated the honey structure.

Did you notice the video is filmed in his kitchen? Must have a very tolerant wife. Maybe I could clean my aluminum parts in his dishwasher.

Dan Martinic

Sorry should have wrote 'gutting' the cat as in punching out all the crap in my old cat so I can install it as a "test pipe" with WB02 sensor and new chip.

As for asking the cat or no cat details when ordering chips, I just checked Lindsey's A-Tune site and don't see that option (I can't find the order page on Vitesse's pages (?)). Funny, I could swear that ordering option was there before.

Too many times starting the car first in the closed tent garage lol

Adker

The sweat spot for mounting a WBO2 sensor is in the down pipe near the starter. The exhaust there is hot but not too hot like in the factory O2 location which is pre-turbo. Gutting the cat just messes up airflow, the only time I could see doing this is if it was overheated and clogged but replacing it is a better choice. There are lots of aftermarket cat converters out there that are affordable, the factory one costs an arm and a leg.

Dan Martinic

Interesting.. haven't heard about that downpipe WB02 location

I failed emissions and replaced my old cat (crumpling stuff came out) with a like-new original: this thing looks like it was immediately removed from a delivered car and stored in a warehouse. Only $200USD iirc. Didn't change the emissions test though; that turned out to be something different. Now I have the old complete cat unit with worn out inards yet a solid outer. Figured I could use that piping... but.. will investigate the downpipe solution thanks

gruhsy

WBO2 location

https://www.lindseyracing.com/LR/Par...2LOCATION.html

Dan Martinic

Well.. that was a quick investigation lol

Yes, that's the usual recommendation and probably easiest

fast951

We never offered any tune chip or MAF on an "ordering page" . Most of our software and performance are customized to the person's needs. Not a one size fits all as found elsewhere. If you need to order you can email me.

fast951

You want the Wide band O2 sensor after the turbo, where the exhaust pressure is lower than in front of turbo. The Factory Narrowband O2 sensor can live in front of turbo.

The DME reads the O2 and will try to reach the target AFRs. The time interval on the rich side and lean side is not the same.

Gutting the cat or no cat does not affect O2 readings. However the AFRs may change some.

To increase your chances at the emission station, drive the car on the highway for 20-30min. No boost. When you arrive at the test location keep the car running, do not turn it off. You want the cat to remain as hot as possible.
Of course the tune must be emission friendly, good plugs and injectors....

Dan Martinic

Not anymore! As of this year, emissions testing is gone here in Ontario! That's why I'm considering using my old cat piping to go 'cat-less' and finally go for a chip. That, or continue fixing the AC. Or replace the severely pitted windshield. Or.... ...at least we never tire of choices with this car