Funny issue with O2 sensor and Transmission

I have 2000 Accord 4cyl ULEV (ultra low emission vehicle) model and been having transmission slipping issue for awhile now. I have tried cleaning and swaping solinoid of the tranny and etc and doesn't seem to completly fix the problem.

Two weeks ago I decided to mess around with the emission system. I set my car to limb mode by putting a dead O2 sensor (pre cat), and I get CEL (engine checklight) on my dash. Now my car runs really rich and exhaust smell really nasty, BUT surprisingly my transmission doesn't slip as bad as before. I only get a few hickups but overall 95% of the time it doesn't slip from complete stop.

Anyone has a clue of what's happening?

Note: ULEV model doesn't use O2 sensor, it uses Air Fuel Ratio sensor instead for precat which cost like $200+ to replace. Normal O2 sensor will fit but will not have long enough wire to connect to the harness and unfortunately O2 sensor fits and look just like A/F sensor.

All I can think of is that forcing open loop operation is committing the TCU to a different shift strategy that isn't affected as much by whatever the root problem is...like an earlier downshift to first gear when decellerating, so if the tranny was hanging on the downshift to first, it'd have more time to complete the downshift before the vehicle actually stops or something...

Good question...I'll have to think more in-depth and get back to you...

I agree with jeffco- maybe being in open loop bumps line pressure up, which masks root problem.

The car still run very good with loop mode but I ordered a new A/F sensor. I also found out that I have been using SULEV model A/F sensor on my car for the last 2 years... Hope ULEV A/F sensor will give me the same smooth ride. Not sure what's the different between ULEV and SULEV A/F sensor, maybe SULEV A/F sensor was driving my ECU nuts?

Update: Ok so I got the OEM Air Fuel Sensor that is designed for ULEV model, installed it, reset the ECU, and the car runs noticibly slower.

I have to step on gas more than before to accel from a complete stop but the tranny runs so smooth. Still little hickup on uphills stop signs, but rarely does it now. The exhaust has deeper sound also.

Overall feels like a brand new stock car. Everything is tight and smooth.

I'll drive it for couple of weeks to see if tranny will slip again.

Did you reset your ECU after installing a new sensor (idle without touching gas untill your fan comes on twice)? It may clear the old memory.

Sam

or driving it in limp mode (real rich) fouled out the spark plugs and you now need a tune up to get back to optimum performance

Ah I didn't know that I have to wait til fan comes on twice. I left it idle for 5 mins and started to drive for 15 mins at 80mph. Do I need old memory for a reason?

I just got new sparkplugs installed a three weeks ago while I was on loop mode for 2 weeks, do I need a new one? I'll take it out and look at it.

I am getting great gas milage right now without adjusting anything since 99 when I bought it... I know I need to adjust the valve very bad but the car runs very quiet, no tics sound.

I'm getting 320 miles per tank on unleaded 91 city and freeway mix.

It has been discussed many times that Hondas like 87 octaine gasoline. That might be your another problem. ...even thought your milage is great for Honda!

Sam

A friend of my that tune cars, he told me to use octain 91 since I have 4-2-1 ceramic headers and exhaust system, but anyhow I use both mixed and I get same result.

with those mods, octane wont do anything.