Idle tuning for larger TB with ETC.

[DrX]

I have installed the 90mm LS2 TB on my Radix. In trying to get it to idle in gear before any learning takes place I have found that B4349(ETC Throttle Area Conversion) is the only parameter that seems to have any effect on this with ETC. From the units, it looks like the PCM multiplies the desired throttle area by this factor in order to determine the required % throttle opening. So for a larger TB you would expect the factor to be lower in order to yield a lower % throttle opening for the same throttle area. Correct?

The value was .0208 for the OEM 78mm TB. According to my calculations, something like .0157 would make sense for the 90mm TB. It turns out though that it actually required a value closer to .0300 in order to run properly! Am I misunderstanding something here?

[Delco]

I have installed the 90mm LS2 TB on my Radix. In trying to get it to idle in gear before any learning takes place I have found that B4349(ETC Throttle Area Conversion) is the only parameter that seems to have any effect on this with ETC. From the units, it looks like the PCM multiplies the desired throttle area by this factor in order to determine the required % throttle opening. So for a larger TB you would expect the factor to be lower in order to yield a lower % throttle opening for the same throttle area. Correct?

The value was .0208 for the OEM 78mm TB. According to my calculations, something like .0157 would make sense for the 90mm TB. It turns out though that it actually required a value closer to .0300 in order to run properly! Am I misunderstanding something here?

What did you have to do to get the LS2 throttle body on , I tried to do it the other day on a car here and rewired the throttle but couldnt get it to work properly at all on our Aust cars.

Kept throwing tps corollation codes

[Doc]

THROTTLE BODY
If you have a bigger throttle body (FAST 90, or Nick Williams) you want to multiply your Effective Airflow Area by 48%. (put in 1.48, select the whole row, hit 'multiply')
or 1.44 (44%) if you go by straight math
You get this # from Circle Area
Pi * Radius Squared
(Pi*45*45)/(Pi * 37.5*37.5)
which = 6361.725123/4417.864669
which = 1.44

90mm area/75mm area

same thing goes for any different size Throttle body
just do the math and scale accordingly

[DrX]

What did you have to do to get the LS2 throttle body on , I tried to do it the other day on a car here and rewired the throttle but couldnt get it to work properly at all on our Aust cars.

Kept throwing tps corollation codes

As recommended on performancetrucks.net, I used GM TAC module # 12574221(shows as for a 2002 Avalanche when I looked it up, but I believe it was used on some other ETC trucks as well). The other significant difference is that the wiring for the dual TPSensors is switched around. Here is a copy of my last post on this topic from performancetrucks.net :


Had to figure out why the high/low ref wires appear to be crossed going into the LS2 TB according to the truck/LS2 wiring diagrams. Didn't make sense unless the TP Sensor signal wires were also switched, which they weren't. So I looked at the operation of the sensors. According to the behaviour of the signals, sensor 1 in our trucks = sensor 2 on the LS2 and vice versa.

Truck:
"The TP sensor is actually 2 individual TP sensors within one housing. Separate signal, low reference, and 5-volt reference circuits are used to connect the TP sensors and the TAC module. The TP sensor 1 signal voltage increases as the throttle opens, from around 1.0 volt at 0 throttle to above 3.5 volts at 100 percent throttle. TP sensor 2 signal voltage decreases as the throttle is opened, from around 3.8 volts at 0 throttle to below 1.0 volt at 100 percent throttle."

LS2:
"There are 2 individual TP sensors within the throttle body assembly. The TP sensors are used to determine the throttle plate angle. The TP sensors provide the ECM with a signal voltage proportional to throttle plate movement. The TP sensor 1 signal voltage at closed throttle is above 4 volts and decreases as the throttle plate is opened. The TP sensor 2 signal voltage at closed throttle is below 1 volt and increases as the throttle plate is opened."

So for anyone doing their own wiring or checking an install, this is how the OEM wire colours should match up to the LS2 connector as shown above(this was accomplished in my application by simply plugging in the Speartech adapter harness ):

Black OR Black/White(C) Yellow(B) Brown(A)

Purple(F) Light Blue OR Grey(E) Green(D)

An alternate arrangement that theoretically should also work would be to keep the high/low reference wires as per the OEM wiring and switch the Green and Purple TPS signal wires. This would look like:

Light Blue OR Grey(C) Yellow(B) Brown(A)

Green(F) Black OR Black/White(E) Purple(D)

[DrX]

THROTTLE BODY
put in 1.48, select the whole row, hit 'multiply'

Which table are you referring to? I tried modifying the B4403(IAC Effective area table) -the values would have to be decreased/shifted down for a larger TB. Tried all kinds of changes to this table. This didn't seem to have any effect with my ETC setup. Not sure if any of the IAC stuff is relevant. Logging the GM.IAC PID always shows the park position and there is no actual IAC motor as on cable style TBs.

The value of B4349 seems to be all that is required for effective area calculations with respect to throttle opening. But it seems backwards to increase rather than decrease it according to the units. Or perhaps I am just looking at it from the wrong hemisphere.

[jfpilla]

DRX,
You're correct. ETC is the value to change. As you said lowering it reduces airflow and raising it increases airflow. If you're not cammed I'm surprised it doesn't idle fairly well without changes. No leaks?
If your IFR's, VE's and MAF are correct then when you log Dynair gms and IACDES gms they should be close. Raising ETC lowers IACDES and viceversa. Lowering IACDES tells the PCM that less air is coming in (or more fuel if you lowered IFR's) so it opens the blade and the opposite. You may then need to set IDLE/DESIRED AIRFLOW. When that's right you may also need to use STARTUP FRICTION AIRFLOW to get the startup RPM's where you like them.
Joe

[DrX]

DRX,
You're correct. ETC is the value to change. As you said lowering it reduces airflow and raising it increases airflow. If you're not cammed I'm surprised it doesn't idle fairly well without changes. No leaks?
If your IFR's, VE's and MAF are correct then when you log Dynair gms and IACDES gms they should be close. Raising ETC lowers IACDES and viceversa. Lowering IACDES tells the PCM that less air is coming in (or more fuel if you lowered IFR's) so it opens the blade and the opposite. You may then need to set IDLE/DESIRED AIRFLOW. When that's right you may also need to use STARTUP FRICTION AIRFLOW to get the startup RPM's where you like them.
Joe

So, then I actually should be decreasing B4349 to compensate for the larger TB as I had thought. Since I had to increase it, something else must be messed up. It started up and idled OK in P/N before I changed anything. But would shake, rattle and stall if I shifted into gear. If I waited for it to warm up to learn enable ECT(80*C), I could get it to learn and recover. Don't want to have to do that after every reflash. I changed everything at the same time-trans and converter, TB, and fuel system, new intake gaskets. I would think that a leak would cause a lean idle condition causing me to have to close the throttle with B4349 rather than open it. AFR is looking good at part and WOT. Seems to run great other than the idle in gear issue. No MAF.

[jfpilla]

DRX,
I only pointed out the affect of the changes. I don't know enough about your car and tune to be sure of whether you need to go up or down. I did know you are mafless. I slipped, but it's the reason I indicated Dynair and Iacdes should be close. This is more important than thought and helps keep the tune from changing when done right. You will probably have to find the ETC value by trial and error. Fortunately there are not to many possibilities and EFI is fast.

[Doc]

Jfpilla,
Thanks for the explanation. I hope I didn't mess anybody up. I just felt that first cup of coffee and threw my hand up in the air as fast as I could.

[DrX]

I appreciate everyones input. Helps get the gears turning. Never know what is going to set off a Eureka! moment.