HEGO Voltage ...

[Coz_KB95]

Ok Folks ... been working on the car and the calibration over the last several weeks. Made a bit of good progress, however I'm hoping some of the knowledgeable folks here could help me confirm something I'm seeing that doesn't quite make sense to me.

Background: I've been chasing down an annoying Fuel Error Variance issue. I've smoke tested multiple times and ruled out vacuum leaks ... also ruled out any exhaust leaks upstream of the O2 sensors. The car behaves really well in CL during 'normal' driving but I was having declutch & return to idle stalls along with Fuel Error variances >10%, mainly during decel driving conditions. Seems that in the 175-250 MAF AdCount range ... as I let off the accelerator the O2 sensors start to act a bit strange. No x-pipe on the car, and I've confirmed the O2 sensors are connected properly and not crossed over.

I am running longtubes and have read many posts in the forums around how they can really mess with CL fueling particularly at idle and lower RPM/low exhaust flow driving conditions. Seems some people do have issues, some people don't ... but to get some drivability in place ... I have the tune set up to idle in OL. With that change ... my declutch and return to idle stalls have completely disappeared. Which is great ... however I don't want to mask the issue and the variance on decel is bothersome.

As I'm trying to rule out the HEGO circuit as a potential issue, here is my question. When I start my logging in TunerPro ... I start recording with Key-Off in the ignition. The log records HEGO1 Voltage at 0.038 and HEGO2 Voltage at 0.067. Not sure where those numbers come from, as the Key is in the off position ... and (I'm guessing) the sensors should not be getting power. When I move the key in the ignition to the 'On' position (Sample 126 in the attached log) both HEGO1 and HEGO2 go to 0.053 volts ... which is normal based on my online searches. However ... they only remain at the same value for about 3 seconds, at which point HEGO2 voltage jumps to ~1.3 volts (see sample 147 in the attached log), while HEGO1 voltage remains at 0.053 volts. This is just sitting with KOEO, not having started the car ... engine cold. My searches around expected behaviour for HEGO at KOEO is that the 1.3v reading on HEGO2 is not normal and could indicate a problem with the circuit or ground. Looking to validate with the folks here that know their stuff before I dive into back-probing and wiring harnesses. If there is a problem with the HEGO circuit or ground, It might explain the skewed readings and variance as HEGO2 would seem to be continuously reading inaccurately higher voltages ... skewing fueling corrections toward rich on that bank and throwing things off.

Posting up my last drive_log and bin for anyone interesting in having a look.

07_14_2027_Drive_Log2.xdl

(2.46 MiB) Downloaded 2 times

Coz_KB_95_260714A.bin

(56 KiB) Downloaded 1 time

Thanks in advance ...

Coz

[danielt]

Since the output range on a HEGO is 0-1V, if you are seeing a negative value, something is definitely wrong. Double checking the grounds would be a good first start. You can also switch the 2 HEGOS and see if the behavior flips sides. That would isolate the issue between the harness and the hego