XGauge coding: My data is wacky

[theholycow]

I'm trying to create XGauge codes for my GM VPW system (2002 GM 5.3 engine, 4l60e transmission) on my ScanGauge II, but I'm having trouble interpreting my data. When I try my codes as CMNDS, I look at the response, pull out the data, and put that through a Hex-->Decimal converter; sometimes what I get could make sense but while driving it doesn't follow driving conditions properly, other times what I get makes no sense.

Everything I read implies that the last two digits of the response are to be discarded. (Edit: The last two digits are a one-byte CRC.) I've found a few lists of PIDs that I think are correct beacuse every PID they share matches.

I sat idling and entering CMNDS to see which PIDs work and which don't, and to gather sample data. Here's a few of them:

1192 Desired Idle Speed. Response is 2cf4. 2c = 44 (presumably to be multiplied x10). Actual idle tends to be well over 500, so either "Desired Idle Speed" doesn't mean what it sounds like or the truck never gets near the desired speed.

1141 Ignition Voltage. Response is 8d0b. 8d = 141. Is "Ignition voltage" the voltage at the ignition wire in the dash (which would make this data '14.1', which would make sense) or is it the voltage in the spark plug wires (which I guess could mean it was 14,100 volts; I thought spark plugs run a lot higher voltage than that).

1212 Rich/Lean to Lean/Rich Ratio Sensor 1. Response is 188f. 18=24. What could this sensor mean?

1212C: Average O2 Bias Voltage. Response is d39a. D3=211. Another one that I'm not entirely sure what it means.

1172: IAC. Response is 003d69. 003d=61. This could be percentage of IAC opening, not really sure.

The ones that I really want the most:

125a and 125b: Fuel Injector Pulse Width, banks 1 and 2. Responses include 00bff3 (00bf=191), 00c465 (ooc4=196), 00c5f7 (c5=197). Does that sound right? What units might it be? How do I convert pulse width to duty cycle so I can know if this is accurate (compared to my direct measurement of duty cycle)?

1970: TCC PWM Duty Cycle. Response is 002d (00=0) at idle, but is all over the place while driving and rarely seems to make sense.

1991: TCC Slip Speed. Response is 114c55 (114c=4428) at idle. It should be zero or very low at idle, right? This one is also wacky when driving.

I want to know when my TCC is locked, and either of those last two should tell me...if I can get them working right.

[Jay2TheRescue]

As a followup to our conversation the other day I was not able to get any meaningful information out of my Scangauge on my drive to Florida as far as lockup status on the torque converter. I did get some other info you were looking for. After driving for a few hours @ 70 MPH my transmission temp was 132 F, where it stayed for quite some time, until towards the end of my trip it was 143. I think the only reason it went up was because of the rise in ambient air temp. It was 12 F when I left Virginia, and today it was 70 F here in Florida.

-Jay

[theholycow]

I think I need to undo some grille block or relocate my tranny cooler, I'm leveling out at 170.

I've been working fervently on learning how XGauge codes work. Every time I went to post a question I'd learn a little something while writing the post and cancel it. Finally I posted this one just in case anyone could help.

In the meantime I learned in leaps and bounds and have a great understanding about how to make codes. All I lack now is documentation about the data I'm trying to query, some of which I may be able to figure out myself. I'm pretty sure I have a few codes working, and I'm working on a bunch more.

[Jay2TheRescue]

Remember, on my grille block I have a 4" hole right in front of the external tranny cooler.

-Jay

[theholycow]

Ok, I concentrated on some XGauges that seemed like they might be working right. Specifically, Input Shaft Speed (ISS) and Output Shaft Speed (OSS). They looked good testing in my driveway after dividing OSS by 10.

This should tell me without any doubt what gear I'm in and (comparing ISS to engine RPM) how much TCC slip I've got.

The good news is that they seem to work right -- they pass sanity checks (not reading 20,000 rpm or 2 rpm) and change as expected (following speed, gear changes, and eachother). The bad news is that they're both reading too low by ~400 RPM.

I've calculated what my OSS/driveshaft RPM should be at 70mph and at 2100 engine RPM. It should be reading 2800-2900, but reads 2350.

There are 3 ways ISS should compare to engine RPM:
ISS < engine RPM: TCC unlocked + engine applying power
ISS = engine RPM: TCC locked, and/or transmission in Neutral
ISS > engine RPM: TCC unlocked + engine braking
In all conditions it reads lower than engine RPM () but the amount varies based on which condition is in place; it appears that it will read correctly if I merely add a few hundred RPM before displaying it.

The only thing that makes me doubt that is that I read ISS of 800 at 580 engine RPM...but maybe I was confused when I wrote that down.

[Ford Man]

theholycow if you're not a member on cleanmpg.com you might want to become a member there just for the purpose of Scan Gauge related information. There are a coulple people on there that seem to be pretty good at figuring these things out.

[theholycow]

Yeah, I did a lot of reading there, looks like CarlD could help.

I'm starting to figure stuff out, though. Here's the update after my commute home:
I changed the MTH on my ISS and OSS codes to add 300 before displaying, and everything looks right, except at a dead stop when both read 300. By the time the ISS reads 900 it's accurate and I assume the OSS is accurate by that time too. It stays accurate up to 70mph.

The issue of the ISS reading higher than idle when it shouldn't seems to have explained itself once I fixed the numbers. ISS reads as if I'm in gear when I'm in Neutral. Theory: ISS is not measured between the TCC and the transmission, it's measured somewhere between Neutral and the gears...or there is no sensor and it's calculated.

The TCC Slip Speed XGauge code I tried (which I may have not mentioned above) just needed to be divided by 10 and it seems to be correct now. However, it reads 5000-6000 when I'm in Neutral. WTF?

[theholycow]

Ok, upped the ISS/OSS addition from 300 to 400 and I think it's nearly 100% accurate now. I still don't know why it's like that, nor do I know how to deal with at low speeds (or for that matter, exactly where it becomes inaccurate).

I figured out why the TCC Slip Speed XGauge was reading 5000-6000 in Neutral. It was also doing it sometimes under engine braking, and what it's actually showing me is negative slippage, as happens under engine braking (and maybe in Neutral -- or maybe that info comes from the ISS, which has the theory I describe above). When it goes negative, the ScanGauge flips around from 0 to 65535, as computer programs often do. I don't know how to fix that, but I guess I'll figure it out eventually.

[Jay2TheRescue]

Originally Posted by theholycow

Ok, upped the ISS/OSS addition from 300 to 400 and I think it's nearly 100% accurate now. I still don't know why it's like that, nor do I know how to deal with at low speeds (or for that matter, exactly where it becomes inaccurate).

I figured out why the TCC Slip Speed XGauge was reading 5000-6000 in Neutral. It was also doing it sometimes under engine braking, and what it's actually showing me is negative slippage, as happens under engine braking (and maybe in Neutral -- or maybe that info comes from the ISS, which has the theory I describe above). When it goes negative, the ScanGauge flips around from 0 to 65535, as computer programs often do. I don't know how to fix that, but I guess I'll figure it out eventually.

I know it can display negative numbers. When in DFCO my ignition timing reads -10.

[theholycow]

Yeah, I've seen negative numbers from other stuff, I don't know why that one won't show negative.

Are you going to try any of the codes I posted in the XGauge Codes thread?