Wideband Accuracy: Facts & Issues

[BennyHHR]

To Greg: I agree about the lambda. With the variance in fuels today, i.e. E10 as in my immediate area, "regular" elsewhere and who knows what with "winter blends", we need to be thinking in lambda instead of "gas" AFRs anyway. I think it's the old school mentality that still wants to think in pure gas AFRs, which no longer hold true in reality.

ktoonsez: I've had a config file setup to log V from the AFX. I would need to dig up old logs to give any worthwhile feedback, though. I you have the HPT Pro, though, you can just make a little "bridge" wire on the green plug from the WB. On that input you can define the signal as voltage and log it, if that helps.

BTW, Happy New Year!!

[BennyHHR]

ktoonsez: Just looked up an old log. Saw a max of 4.8 V @ 16 AFR, if that helps any.

[ktoonsez]

Thanks BennyHHR, at least I am not the only one seeing the drop, like I said mine kinda floats between 4.86 and 4.88 volts at 16 AFR so I guess it might be the norm. Anyone else seeing this?

Happy New Years guys!!!!

[5_Liter_Eater]

It gets worse. I used to take ground differential into account by turning the ignition on (not engine) and comparing the WB gauge VS: HPT but this proved inaccurate because the voltage was ~12, not ~14. So I started using a digital camera and snapping pics of the gauge and HPT at idle. This seemed to work well. The other day I noticed that my WOT AFR (11.5:1 commanded) differed noticably at such a rich AFR. So now I'm debating taking a video camera to both and note the difference between the two at different AFRs. That or put it in open loop with a very small PE TPS value and command different AFR's each 500 RPMs (IE: 1000=11:1, 1500=12:1, 2000=13:1) and see the difference although this introduces another varuable (RPM/airflow) so I may try different tunes commanding different OLFA AFR's and see the difference at idle of each one.

Really starting to wish the serial output thing would materialize but it would have to be an EIO/Pro thing anyway.

[FastBlackTA]

It gets worse. I used to take ground differential into account by turning the ignition on (not engine) and comparing the WB gauge VS: HPT but this proved inaccurate because the voltage was ~12, not ~14. So I started using a digital camera and snapping pics of the gauge and HPT at idle. This seemed to work well. The other day I noticed that my WOT AFR (11.5:1 commanded) differed noticably at such a rich AFR. So now I'm debating taking a video camera to both and note the difference between the two at different AFRs. That or put it in open loop with a very small PE TPS value and command different AFR's each 500 RPMs (IE: 1000=11:1, 1500=12:1, 2000=13:1) and see the difference although this introduces another varuable (RPM/airflow) so I may try different tunes commanding different OLFA AFR's and see the difference at idle of each one.

Really starting to wish the serial output thing would materialize but it would have to be an EIO/Pro thing anyway.

Had same issue with my dynojet WB.

[ktoonsez]

I had questions as to the accuracy of my AFX when bought almost two years ago. Did a bunch of testing, including voltage issues, setting up average histos, without a confident solution. Even had exchanges with a NTK engineer on the issue.

First, realize that these and most others, compute lambda and convert that to a gasoline AFR value, even though you may be running an ethanol mix fuel. Stoic is usually considered to be 14.68, yet for some reason NTK considers it to be 14.57, so there's some of the difference.

After considerable testing with open loop tuning and seeing the resulting FTs when back in closed loop, looking at the histos for averages, etc., what I did was write a custom PID for the AFX. Their formula is: AFR = (V * 1.4) + 9. HPT's equivalent formula used in the supplied PIDs is: AFR = (V / 0.7143) + 9, which is the same. After doing considerable tests and some math, in the custom PID I used 9.33 instead of 9 for the adder in the formula.

From that point on, after open loop tuning was done switching back to closed loop always resulted on near 0 FTs, which tells me that the 0.33 "correction" resulted in accurate data. (The gage still reads a little low though.)

That seems to closely coincide with your testing, ktoonsez. You might want to try a modified custom PID for AFR and see what happens.

That 9.33 seems a little high, .33 is alot if your trying to maximize your AFR for 12.9. Just to make sure I understand you, if you were to tune for 12.9 AFR in your WOT area, HPT with your custom PID would read 12.9 but your AFX display would read 12.57? Or are you saying they are closer than that and you added the .33 to make up for the difference in stoich (14.67 real stoich to the 14.56 AFX stoich) plus your voltage drop?

[Rockrz]

So, the overall intention for using wideband is to help achieve a closer
to perfect air to fuel ratio mix, resulting in burning all of the fuel in each
cylinder making the vehicle as efficient as possible...right?

[proggod]

Here is a question for you guys that are using the AFX and I plan on calling them but are closed today I think. The max voltage I can get out of the yellow wire is 4.88V instead of the full 5 when the display is reading 16.00 AFR, has anyone else seen this? Suggestions?
I followed the recommendations and grounded the double black wire and the signal ground together at the battery and didn't extend the wires at all. My LC-1 had a little voltage drop, it always read 4.98 in air but 4.88 is a little too much of a drop and of course I had to adjust my formula to accomidate for the drop and did get the display and HP to match up, just want to know what is with the .12 V drop.

How long did you calibrate for?

[krunchss]

Was hoping someone might have had some feedback on this?

Thanx,
Krunch

Just curious,

Came across this one as well. Now, I have a gauge pod on my pillar with a worthless NB autometer A/F gauge in it. This would look cleaner in my application, and still be able to log the data to my tuner. Any comments on bang for the buck on this one?

http://www.egauges.com/vdo_ind.asp?T...mp&PN=ATM-3378

There is also a $50 rebate on the Autometer site right now if that makes it more worthwhile.

Krunch

[ktoonsez]

How long did you calibrate for?

A little over an hour.

[ktoonsez]

Just an FYI on a previous comment I made about the voltage drop (only reading 4.88 max at 16.00 AFR), I ended up bring the the controler/display into the glove box and powered it up thru the fuse panel below the passenger's feet. Then grounded it to one of the Bose amplifier mount screws (I knew this was an OK grounding point from my mild-to-wild install instructions) and guess what, I now get 4.96 to 4.98 volts at 16.00 AFR. Kinda bizzare since AFX says there prefered method of grounding is direct to the battery, anyway I am just happy I got closer to the real max voltage.

BennyHHR:
Please look at post #66, didn't want that one to get lost, and give me your thoughts, if you would mind.
Thanks

[proggod]

Just an FYI on a previous comment I made about the voltage drop (only reading 4.88 max at 16.00 AFR), I ended up bring the the controler/display into the glove box and powered it up thru the fuse panel below the passenger's feet. Then grounded it to one of the Bose amplifier mount screws (I knew this was an OK grounding point from my mild-to-wild install instructions) and guess what, I now get 4.96 to 4.98 volts at 16.00 AFR. Kinda bizzare since AFX says there prefered method of grounding is direct to the battery, anyway I am just happy I got closer to the real max voltage.

BennyHHR:
Please look at post #66, didn't want that one to get lost, and give me your thoughts, if you would mind.
Thanks

You want to ground both grounds to the closest ground point to each other. I gets the voltage by reading the differential in the ground voltage and actual voltage. Thats why I always twist both wires together and ground it into one

[ktoonsez]

Update to the AFX voltage drop:

Talked to one of the engineers today at NGK and they said it was completely normal to see the voltage drop I am seeing, so anyone that was worried like I was, there is not need to.

[5_Liter_Eater]

You want to ground both grounds to the closest ground point to each other. I gets the voltage by reading the differential in the ground voltage and actual voltage. Thats why I always twist both wires together and ground it into one

When you say both grounds what do you mean? In the EIO case I would assume you mean the EIO ground but if you're piping the WB signal through the AC or EGR I guess that would be the PCM ground?

[BennyHHR]

That 9.33 seems a little high, .33 is alot if your trying to maximize your AFR for 12.9. Just to make sure I understand you, if you were to tune for 12.9 AFR in your WOT area, HPT with your custom PID would read 12.9 but your AFX display would read 12.57? Or are you saying they are closer than that and you added the .33 to make up for the difference in stoich (14.67 real stoich to the 14.56 AFX stoich) plus your voltage drop?

Sorry, missed this post.

Please understand that I went through this issue about 2 years ago and don't have my notes any more, but will try to recall how I went about this.

When tuning part throttle, open loop, applying AFR error% was fine until I went back into closed loop and FTs were off. No WOT at this point. For power, seperate fuse off console block. Common grounds at instrument panel frame and voltages, resistances checked.

I set up custom histo PIDs for Commanded AFR Avg, Actual AFR Avg and AFR Error% Avg. (Just plot Commanded, Actual and Error on the X axis, nothing on Y, giving a single cell average.) Did considerable open loop logging, compared the results and found that the 0.33 "correction" eliminated the discripancy. Been fine since.

Also, even though the numbers jump around a lot on the AFX display, the "apparent average" reads lower than HPT by about the same amount.

I hope this makes sense and helps.

[proggod]

When you say both grounds what do you mean? In the EIO case I would assume you mean the EIO ground but if you're piping the WB signal through the AC or EGR I guess that would be the PCM ground?

Thats correct. Your best bet is to find the closest place where the AC or EGR grounds, and ground to that spot. Or at very least run a wire between the two grounding them together. The corvette has around 7 major grounding points. The resistance between them can cause the voltage differentials. Thats why if you use the pro hp tuners interface, its wise to run the ground directly into the plug. The ECM could be grounding from a different point to the one your wideband is grounding to.

[BBA]

So, the overall intention for using wideband is to help achieve a closer
to perfect air to fuel ratio mix, resulting in burning all of the fuel in each
cylinder making the vehicle as efficient as possible...right?

No, the purpose of a wideband is to monitor WOT PE AFR. The AFR at that point is no where near the point that provides the most complete fuel burning. That point only occurs at stoich AFRs, where the narrow bands are more generically accurate.

[Rockrz]

So, proper tuning with wideband should
get you better gas mileage, right?

Assuming one could keep his lead foot out of
the gas after getting it to run so efficiently...

[RWTD]

So, proper tuning with wideband should
get you better gas mileage, right?

Assuming one could keep his lead foot out of
the gas after getting it to run so efficiently...

As long as your O2 sensors are not reading improper, then you really don't need a wideband for CL fueling tuning, unless of course you are forced full time into OL.

[Rockrz]

OK, so what is "CL" and what is "OL" ?