WB Ground Offsets

[minytrker]

I have a dual WB Fast setup in my racecar, the fast is showing almost 3 numbers off from the scan tool. With that big of difference whats the easiest way to get them in sync?

[mr.prick]

Which mode is it set to, simple or hi res?
Hi res seems to match the PIDs already defined in the software.
The manual doesn't give the minimum or maximum Lambda or AFR values so it hard to
figure out the slope & intercept to make a custom PID.

Is serial connection an option for you?

[minytrker]

HI RES. There isnt a serial option for the fast that I know of. I ended up pulling out the fast and putting in my LM-1 with serial to fix the tune. But I need the fast to work.

[mr.prick]

Can you get it to output a set voltage?
If you can measure it with a DMM and see if there is a difference from what Flashscan sees.

If the signal ground omits .1v then don't plug it into the AD-
a low reference ground wreaks havoc with the AD inputs.

[minytrker]

Back to the top, I need to get this working ASAP.

[minytrker]

Can you get it to output a set voltage?
If you can measure it with a DMM and see if there is a difference from what Flashscan sees.

If the signal ground omits .1v then don't plug it into the AD-
a low reference ground wreaks havoc with the AD inputs.

I dont think you can adjust output voltage.

[5.7ute]

Can you go low tech. Command 3 different AFR's, compare the log to the gauge at the 3 different AFR's & see if it is a common offset. If so just add or subtract the value in the V2 or calc pid.

[swingtan]

Confirm the ground offset by placing a DVM between the ground of the V2 and the ground of the Fast. Given that most analogue WB controllers provide a 0-5v signal, you can estimate the impact any ground offset will make.

• 0.5v offset = 1% at full range but closer on 2% at half range. Assuming stoich. is around half range, that's nearly 0.3AFR difference.
• 0.05v off set = 0.1% and 0.2% respactively.

The problem is though, that if you do consecutive corrections, you may end up being way out on the commanded AFR as the you chase a skewed reading. to make matters worse, the DC offsets are not normally "consistent" as they will change depending on electrical loads. Also,because the WB is reading off "by some unknown amount", it's very hard to try and work out a correction factor.

The solutions are not particularly easy either. Normally, you would ensure that all devices are physically earthed at the same place, so there can be no DC offsets. But it's a little hard to earth the WB on the ODB-II plug and adding an addition earth to the ODB-II plug may introduce an earth loop on the PCM.

I run a TechEdge WB controller and it actually has an earth reference on it's analogue O/P. You tie the signal -ve wire in to the earth on the V2 and it will compensate for any DC offsets. This "may" work on the Fast, but I would not know. I just used an additional connector on the V2 to run a wire from the earth pin of the 12V switched I/P to the -ve WB input. In back to back testing against the serial signal, there was no difference.

The easiest fix, is to get a serial WB controller, but it's also the most expensive. You could try joining the signal earths and hope you don't fry the V2 or the Fast, it might work..... If you are handy with electronics, you can build a buffer circuit to convert the WB signal into a true differential signal on the Fast, then convert it back on the V2, but it's getting pretty complex now.

The most practical fix will be to take the DVM and start testing around the car to find a point where you can earth the Fast and have the lowest possibly earth off set on the V2. Connect the DVm to an earth on the V2 and with the car on and running, test places around the car to see where you get the lowest voltage reading. In theory, it should be on the PCM, but you never know.

Simon

[GMPX]

Lorenz, this is the very reason why serial WBO2 support was implemented.

[minytrker]

Ross, I think the serial WB is truly top notch and I use it every time I tune with my LM1. I sold my shop and dyno and just do mobile tuning again. Every time I rent a dyno and there tuner uses another software and they see my wb setup with the serial cable they are blown away. So I usually rub it in and tell them about hooking efi up to the dyno also, lol.


Thanks everyone. This is in my personal race car, I got a deal on a brand new dual fast wb setup from a customer so I figured why not just install it in my race car and leave it. I installed my LM1 with serial cable and tuned the car with that but I want to use the fast setup for data logging as a reference. Since I have a big nitrous car I data log and pull my plugs after each pass anyways but it would be nice to know the a/f ratio. I am really only concerned with the a/f at wot.