Strange AFR problem

[7MGTEsup]

I'm getting some funny things happening with my AFR at the moment, well here's the story.

I unplugged my O2 sensor the other day because it was causing a lean missfire. So I'm driving along with my wideband reading 12.6:1 which is about normal in open loop fueling when crusing (i.e rich). But I notice over a period of a day or so the the fueling is getting leaner soon my car is crusing at 14.7:1 WITHOUT an O2 sensor??? So I'm driving along thinking to myself what the fug is going on when the car has a stumble for about 1 second and all of a sudden my AFR is back at 12.6:1.

So my question is what the hell is the ECU doing and why is it doing it.

 

[clifftrail]

Why do you think 12.6 is normal for cruising? Its a good target A/F for max power in open loop (however, that may be a close to running it lean), but not needed when cruising. If just cruising and in closed loop and your wanting 12.6 your wasting gas. I don't think its possible for the car to be in open loop and cruising at the same time, sounds like the car is in closed loop and the ECU aims for 14.7. Sounds like the car is running normal. Also, sounds like whatever fuel programmer your running is fighting the ECU for control during closed loop operation which you really don't want.

 

[7MGTEsup]

I think you miss read what I put or I wasn't clear enough.

this is 12.6:1 OPEN loop crusing (My oxygen sensor is unplugged)

I have a stock ecu with no piggy backs, fuel pressure is 38psi static.

The car leans itself out without the oxygen sensor plugged in. Without feedback from the oxygen sensor the car will run open loop fueling hence the 12.6:1 I know that with the sensor connected it should be at between 14.6 and 15.2:1.

The car is not fighting (or shouldn't be) anything, the ecu is blind without the oxygen sensor so how and why is it leaning out the cruse fuel then resetting itself at random intervals back to 12.6:1.

 

[IJ.]

No 02 sensor would equal limp mode wouldn't it?

Ask JetJock he can tell you 100%.

 

[7MGTEsup]

No 02 sensor would equal limp mode wouldn't it?

Ask JetJock he can tell you 100%.

I'm not 100% IJ but I thought no O2 ment the car went to its open loop fueling tables.

 

[IJ.]

Limp would equal rich across the board and possibly pulled timing, can't be good for the Cat if you still run one. (It's been 10 years since I've run petrol)

 

[7MGTEsup]

Limp would equal rich across the board and possibly pulled timing, can't be good for the Cat if you still run one. (It's been 10 years since I've run petrol)

No cat so thats not a worry. Car seems to run normally under open loop conditions WOT AFR of 11.2 - 11.6 AF partial throttle on boost around low 12's.

 

[7MGTEsup]

Just to add a bit more to the story, got home from work and sat idling for about 30 seconds. AFR was reading about 14.9 - 15.2 then all of a sudden want max lean off scale for about 5 or so seconds and the car started to stumble then went back to 15.2:1 but had a bit of a missfire. This is confusing the hell out of me.

 

[Poodles]

from waht I understand,t he O2 sensor doesn't have much say in the curve...

the TPS, an temp sensors have more say IIRC...

 

[gixxer750]

The lean spots you see are misfires. A misfire equals a bunch of unused ox in the exhaust stream....

So, your wideband reads a little leaner for a second.

 

[CRE]

^^^yup, unburned fuel results in a leaner reading.


Gixxer, how's the car like a lean cruise of 17:1? PM me if you'd rather.

 

[gixxer750]

^^^yup, unburned fuel results in a leaner reading.


Gixxer, how's the car like a lean cruise of 17:1? PM me if you'd rather.

Sorry to thread jack, but...

It's great. EGT's come up just a HAIR, but not too bad. I also run around 46-48 degrees of timing in the cruise area. I have the accel pump set up to take car of acceleration. I only use the lean area for Cruise... it goes 14.2 under the slightest bit of accel.

I can go a good bit more in depth with it over pm if you'd like, just send me one.

Thanks

/end threadjack