My PLX vs. My AFX

Truck runs tremendously better than in the past with the changes to using stock bias table and converting WB results to stoich 14.47 for E05 for AFR error tuning of VE and MAF. That aside, with all the negative PR about PLX I bit the bullet and purchased an AFX WB with the Bosch sensor to eliminate further error or doubt about the WB.

In the stock Bank 1 bung I have a fairly new Bosch WB sensor simulating a NB hooked to the PLX M-300 controller (truck was tuned using this setup). Yesterday I added another bung in the same bank 1 right above the stock one. I put the new sensor hooked to the AFX controller in that one. I free-air calibrated the sensor for 45 minutes before installing it.

I recorded 40 minutes of driving including comparison between the two widebands. The averages adjusted for E05 for averages less than stoich commanded and at stoich commanded are in the attached pic.

Also attached is the scan log from the drive.

The question is do I believe the STFT averages are close enough to zero to say keep the PLX and send AFX packing or do I believe the LTFT averages keeping the AFX, installing a stock NB in Bank 1, and convert the PLX to a paper weight?

No matter which wideband you keep I would get rid of the simulated narrowband now that you have an additional bung. Since your trims are based upon the plx simulated narrowband output they are meaningless in the comparison (IMHO). If the AFX readings are accurate at least it looks like you are running richer rather than leaner using the simulated narrowband.

Thanks for the feedback. I agree with that observation, the PLX NB simulation would apt to prejudiced toward the WB reading. Physical driving observation of the truck it is not starving for gas. It is either near perfect or to the rich side if anything. It could be very well what I have now is a dirty tune happy with spark and fuel.

Trial and error method, I am going to unplug the PLX and put in a stock NB. I logged yesterday at 80 degrees and the weather is headed to the 40's today, so I will run another log with the cooler weather and see where I stand with the weather change and new NB. If the readings on the trims and the AFX still read rich, I will take one to two percent out of the MAF and VE tables across the board. Then I will watch the trims and KR as the tune settles in. If the truck still runs good after that, then I will retune with the AFX. If it goes to hell then I will put everything back the way I had it then toy with the AFX some more. One of the WB's is ultimately going away.

"I logged yesterday at 80 degrees"


Sure rub it in, we had -5 here today with a wind chill of -39. Painfully cold.

No violin music for me even at 36 degrees this a.m. (your summer is here).

With the stock NB in the number one bank again I have a big difference....but along with a drop of 44 degrees what is what. My log this a.m. after warmup and just highway cruise (no WOT) I had average -1 to 0 trims LTFT's and -0.5 to 0.5 STFT's. The AFX WB read an average of 14.28 (E05) vs. the 14.47 commanded. On another log with WOT commanded was 12.84 with the AFX reporting about 12.28 (E05). This appears to be leaner than before, but funny thing my gas mileage was noticeably down this morning....maybe attributable to the inefficieny now in substituting one NB sensor for the PLX simulated one the truck was tuned for or maybe just the cold weather. I will free air calibrate the AFX again (just in case) and then retune the truck somewhere through the holidays and hopefully be done with this error.

Happy Holidays

I too had a PLX and am now using the AFX. I never could get neither of them to come close to commanded AFR under 2200 rpm. This is probably due to the MS3 cam I am presently running. I had to tune with STFT in non PE. I had to do this in order to keep the LTFT from walking off. RPM over 2200, my AFX tracks with my commanded (non PE), but my PLX never would even in PE or in non PE. I have been trying to tune my WOT PE with the AFX, and have had to lower my VE table in that reigon so much, that I have stoped due to the fact I am finding it hard to believe the WB.

I am not going to finish my WOT VE PE tuning until I have my EGT sensors in place and working. That way I will know I am not going too far. Long story short I am having a hard time trusting any WB for WOT tuning.

I really hope the AFX will work out. I will set my WOT at 12.5 to be on the safer side (make it leaner later) since I will be taking fuel away and use the trims to check the stoich results. If I don't like the results, I can always go back to my PLX setup and tune.