Help! 13:1 AND 16:1 while cruising in between normal AFRs

[Hotwire]

Here's the rundown:
64 chevelle
02 LQ4, stock bottom end, stock heads
LS6 intake w/ 02 LQ4 DBW throttle body, 33lb flex fuel injectors, returnless fuel system
Elgin E1839P cam (220/224, 112 LSA, .575" lift), PAC1218 springs
dual AEM 30-4100 widebands acting as narrowbands for o2 readings to ECM
2005 0411 ECM green/blue
T56

Car runs good, I still need to tune the fuel, had tuned for a bad fuel pump earlier and haven't had a chance to get back into it.

Cruising down the road the car will go to ~16:1 AFR for a little bit, then switch back to toggling 14.7, then drop down to ~13:1 for a while. I cannot figure out what's causing this to happen the ecm is actually commanding this AFR.

In the scan it starts to show the behavior around 6:43

Attaching tune, log, etc. Any help would be greatly appreciated.12-Salty-33lbinj-injectortuning.hpt9-6-tune12-home2WORK.hplsalty4.Channels.xml

[5FDP]

Easy, you have the P59 and not the P01/411 computer like you typed.

The P59 trucks have a cat test you can not disable with HP Tuners. Because you have likely removed the rear o2 sensors from the harness this test will happen. Dealt with this issue more than once on vehicles like this. It will command leaner then richer or vise versa to try and make the rear o2 sensors see a change and to do a test of the cat converter itself.

The only way I could fix this was to disable all the codes and leave the rear o2 sensors plugged into the harness so there was no open circuit. I zip tied the sensors to the frame.

This is likely to be your issue, not sure of anything else on those computers that will make it do this.

[kingtal0n]

Hi , I was wondering how you are setting up that wideband as a narrowband?

[Hotwire]

Easy, you have the P59 and not the P01/411 computer like you typed.

The P59 trucks have a cat test you can not disable with HP Tuners. Because you have likely removed the rear o2 sensors from the harness this test will happen. Dealt with this issue more than once on vehicles like this. It will command leaner then richer or vise versa to try and make the rear o2 sensors see a change and to do a test of the cat converter itself.

The only way I could fix this was to disable all the codes and leave the rear o2 sensors plugged into the harness so there was no open circuit. I zip tied the sensors to the frame.

This is likely to be your issue, not sure of anything else on those computers that will make it do this.

Thank you for the reply and explanation. Thought I was loosing my mind missing something. I'll have to somehow get the o2s back in, wondering if I could just mount a resistor under the dash to give the ECM something to see? I've seriously went through this harness and it's way far from stock.

Hi , I was wondering how you are setting up that wideband as a narrowband?

As 5FDP noticed, I'm a little lacking in the details. Went back and checked, I'm running AEM 30-4110 sensors. The displays show AFR but I've got them set to P04, so the output is Nernst Cell 0-1V. I have the 02 grounds (return) of the o2 sensors on the ECM going to ground, grounded the AEM sensors to the same point, then ran the output from the gauges to the 02 sensor signal wires of the ECM. I'm getting good 0-1v readings @ the ecm, am able to see complete wideband readings throughout the RPM range (but they are in the 0-1v setup). There's a conversion chart in the instructions but I've yet to do the math to calibrate the datalogging to actual AFR. Just winging it and watching the gauges.

You can see the gauges mounted, and you can see the output in the original post's datalog:

[5FDP]

There might be o2 simulators out there but you'd still need the wires/connector for that.

Some people will just tune the vehicle in open loop with their wideband to get all the fueling under control and just live with the cat test happening once they go back to closed loop. I think the test only happens a few times per drive cycle and then stops but I can't remember for sure.

[kingtal0n]

I always drive in open loop. I dont even have narrowbands. I dont like the oxygen sensor's target of 14.7 anyways. When I am driving around light throttle and cruising I checkerboard 14.9 though 15.3's to me 14.7 is 'needs tuning still too rich'

[Hotwire]

There might be o2 simulators out there but you'd still need the wires/connector for that.

Some people will just tune the vehicle in open loop with their wideband to get all the fueling under control and just live with the cat test happening once they go back to closed loop. I think the test only happens a few times per drive cycle and then stops but I can't remember for sure.

Thank you again, I used to make 555 timers that toggled 0-1V a while back for people that needed simulators, might just rig one up and put both sensors to it. It doesn't bother me so much now that I know what's going on. Just before when I'd get to steady cruise I could feel when the test would start as it felt like a small pull on the car, I glanced over at the o2s and saw the weird AFR, then saw the ECM was actually commanding it, and had no idea where it was coming from.

I always drive in open loop. I dont even have narrowbands. I dont like the oxygen sensor's target of 14.7 anyways. When I am driving around light throttle and cruising I checkerboard 14.9 though 15.3's to me 14.7 is 'needs tuning still too rich'

I agree, getting out of the car after driving around and I reek, running turn downs right now. When I retune the fuel tables I'll try a leaner combo in my cruising RPM to see how it acts.

[kingtal0n]

If convert to 1 turbo it gives 1 downpipe which simplifies things to 1 side. Then, you could use 1 cutout to have both quiet full exhaust and loud reeking potential