Dumb beginner questions...

[Rich Z]

I seem to have a lot of these, so perhaps I can just group them together here in one thread.

Number 1: I have electronic throttle control on my C5 vette, and notice that my throttle position doesn't go below something like 14 percent EVER. So I'm looking at various idle related tables that are apparently using throttle position as a trigger to select values in those tables, and they might range from 0.00% to 1.50%. Since my throttle position NEVER goes that low, what exactly does this mean to me? Are those tables NEVER used, or is there some sort of calculation done behind the scenes to produce a relative percentage somehow?

[Rich Z]

Number 2: I have a COS2 OS (I think) and am running in semi-speed density, apparently. When tuning the VE table, does the MAF need to be physically disabled, or can that be done simply by failing it in a table somewhere? Along the same lines, do I have to do ANYTHING about calibrating the MAF table? And do ALL fuel modifiers, including STFTs need to be disabled?

[ScarabEpic22]

1. Since it is DBW, the PCM uses the throttle blade to control the idle airflow instead of using an IAC valve on a cable throttle body. There is conflicting information about what the low TPS values mean, Ive heard they're absolute and that they're idle TPS minus desired TPS (so 14% TPS as idle and 6% of desired TPS = 20% TPS), I dont know for sure.

2. COS2 wasnt released "into-the-wild", so Im betting you have COS3. It depends on the MAF, sometime you can fully disable it in the tune and other times it will remain active even when you disabled it (in this case, you need to physically unplug/disable it). Yes, you need to calibrate the MAF curve at some point, unless you plan on staying full SD. The AutoVE (not Calc.VET) tutorial has the info on what tables need to be changed to disable the MAF. There are a few ways to tune the VE and MAF tables, AutoVE which requires DFCO, CFCO, LTFT, STFTs, COT, etc to be disabled and Calc.VET which doesnt need anything to be disabled. Those are the 2 most popular methods on here right now.

[joecar]

#1: GM.TP will show a minimum of 14% or so... try GM.ETCTP.


#2: If a MAF DTC is present, then you're running in SD (i.e. from the VE only)... you can make the MAF fail by editing the MAF low fail table (C2901-3).

If you want to run combination VE/MAF or MAF only then you have to calibrate the MAF table also (when calibrating the MAF you must disable VE).

If you're using a wideband for calibrating, then you must disable CL/LTFT/STFT/SOL (i.e. anything that corrects fueling ahead of your wideband).

[joecar]

More info: see posts #4 and #29 here: Summary-Notes

[Rich Z]

Arghhh.. OK, maybe it's COS3?

As for the MAF, C2901 and C2904 are both set at 13500, so I guess that means the MAF is failed then? I checked the P codes for the MAF and they are all set to "No MIL".

So CAN I disable the MAF input to the PCM merely doing it programmatically? Since I've got the combo MAF/IAT sensor with a 5 pin connector, it's not like I can just pull the plug to physically disable the MAF without my IAT's being crazy.

I'll try that GM.ETCTP and see if that looks better to me.

Thanks!

[ferocity02]

Check out the COS tutorial, it describes how to fail the MAF in the tune. I unplugeed mine as well, but I wired in a separate IAT sensor into the manifold.

[joecar]

Arghhh.. OK, maybe it's COS3?

As for the MAF, C2901 and C2904 are both set at 13500, so I guess that means the MAF is failed then? I checked the P codes for the MAF and they are all set to "No MIL".

So CAN I disable the MAF input to the PCM merely doing it programmatically? Since I've got the combo MAF/IAT sensor with a 5 pin connector, it's not like I can just pull the plug to physically disable the MAF without my IAT's being crazy.

I'll try that GM.ETCTP and see if that looks better to me.

Thanks!

Doesn't matter how you fail the MAF (physically, programmatically, other), the MAF is not considered failed until a scantool can read a MAF DTC as being currently present (regardless of C6002 being set to No MIL).

If you don't get an immediate MAF DTC, then look at C6001 (set to it to 1-Trip) and look at C2901-3 (set the threshold so that the MAF will fail).

[joecar]

The COS tutorial and the AutoVE tutorial both describe how to fail the MAF programmatically.

[Rich Z]

#1: GM.TP will show a minimum of 14% or so... try GM.ETCTP.

OK, so I used GM.ETCTP and I'm getting the same thing I did before. Foot off of the gas pedal shows a throttle position of 14 percent, MINIMUM.

What does this do for any PCM calculations that are based on throttle position? Seems that every table I recall seeing using TP shows MUCH lower percentages when referencing an idle condition.

Yeah, I've got to read over the tutorials again. Just too much to swallow the first few times through.

Thanks.