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Wideband reading off?

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2gGSX

15+ Year Contributor
1,956
30
Feb 15, 2004
St. Louis, Missouri
Cliff's notes: is it possible for a wideband to be reading too rich?

So, while my old turbo was in the process of dying and spewing out black smoke, I at one point noticed some coming out of my flex section. With that being said, the place I took my car to to get the bung welded on for my wideband decided to put it in BEHIND the flex section due to concern for exhaust temperatures being too hot.

Now, at idle, my wideband is reading 17:1-18:1. With ANY throttle and during closed loop operation it will settle around to oscillating 14.7 like normal.

At WOT, however, it seems to be reading more rich than normal. My estimated A/F Ratio and the wideband match up very closely. At WOT after reaching full boost however, the wideband starts to read consistently more rich than my estimated A/F Ratio.

What could be causing the wideband to be reading so rich? The exhaust leak is small enough to where it's not sucking air in at anything other than idle, and I don't know of any condition where the wideband sucks in extra fuel from exhaust leaks.

For the record, this is a PLX-M250. Power is tapped from the cigarette lighter (green/black wire), and the ground is off of the vertical bracket for the ECU (a chassis ground, I think). My airflow is reading correctly (just look at BoostEst vs. GM3Bar). Fuel trims are within 4% of each other. Both pulls were made at 100% throttle albeit not logged (I check it before startup fairly often).

In the first log (run11112007-1 3rd gear pull 1.dat) I was aiming for an AFR of 10.5:1. The estimated A/F ratio is very close to this, but the wideband is rich off the scale.

In the second log, I tried leaning it out to 11.3:1. Surely enough, the estimated A/F ratio looked like it was heading the right way, but then the car started knocking. The PLX also hits rock bottom just before I lifted as well. Something's messed up with the logs and you can't see the fuel/timing panels. For the record, 6000-8000 is at -18%, 4000-6000 is at -16%, and the rest is scaled back to zero so it's not a sudden jump. Timing is the same as in the first log, as is global fuel.
 

Attachments

  • run11112007-1 3rd gear pull 1.dat
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  • run11142007-1 3rd gear pull lifted.dat
    12.8 KB · Views: 50
Have you calibrated the O2 sensor or s yours adjustable? one quick test to see if it's on would be to take it out, Get it warmed up and use a butane lighter to do some "basic chekcs"

hold the sensor in teh yellow part of the flame , this should be about 14.7...the blue part of the flame should read about 13.5 and holding it about 1/4 inch above the flame should read 19:1.. don't clean it with anything other than blwoing it out with comressed air..and do that with the sensor cold

My sensor has an "open air calibration screw" so that when it's warmed up the decimal will blink if it;s out of cal and then you turn it till it reads 25:1 in open air and the decimal is solid

Or are you thinking it's the sensor, or something in the actual fuel system and burn associated with your car/motor?

the only thing i can think of right now ( being that i'm on the edge of passing out ) is that you may have an injetor sticking under WOT due to being dirty and or a combination of too much fuel pressure

The sensor should be accurate across the entire scale if it's accurate in more than one of the "tests" it could be carbon build up as well. How many miles are on your sensor and how much leaded gas have you put through it? also oil burning out the exhaust can effect them..they are more sensitive than alot of people think to contamination, but seeing how you said it reads the 14.7:1 when it "should" i would say the problem lies in your car's fueling system or fuel control...

feel free to call me tomorrow if you need some more ideas or just want to pick some one else brain in case you're over looking something ( i know that helps me a lot of times ) PM me for my #
 
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