GM LT Based 112mm throttle body (servo calibration)

Hello Experts,

I am planning to install a Granatelli 112mm DBW throttle, and I'm wondering whether the calibration under the name of (GM 1263 2172 BA.1.0 ) will work for this setup.

this is the throttle: https://granatellimotorsports.com/i-30499718-granatellimotor-sports-lt1-lt4-lt5drive-by-wire-throttle-body-gmtblt112.html

i assume I'll be connecting it as a UDIG hybrid signal with the position sensor on Hybrid B getting the UDIG input as decode resource.

Would appreciate if someone can give me feedback on this before I bite the bullet and make the purchase.

Reason I'm upgrading from 90mm LS3 type servo is that my throttle is facing this seemingly unfixable tracking aim fault at (5400+ RPM , 0.8 bar of boost) (tried adjusting the scales/offset), and I also gave it a try by removing the servo fault speed limit and the throttle would for some reason still close.

So my guess was that the best option is to just upgrade to a bigger TB for this PD supercharger setup (3L whipple).

And i'm considering the LT type Servo becuase it is available locally as opposed to ordering the LS3 type from overseas.

Thanks and apologies for streteching it longer than needed.

The correct solution is to have whatever DBW Throttle you wish to use calibrated by MoTeC in Australia. You loan them a throttle body, and they will do the calibration and then you know it will work correctly.

The alternative is to choose throttles that are already calibrated.

If you have having troubles with the stock LS3 throttle, my experience has been that it's not a genuine GM part (and you do say "LS3 type servo"), but it could be a wiring issue (bad crimp becoming intermittent at a specific RPM), which would not be fixed with any change in throttles alone.

Not knowing what your issue is, scale/offset is only one of the configuration issues to cause a DBW fault. Exactly what DBW diagnostic do you see -- tracking fault? Have you run the step tests and logged the results (basically all the DBW servo channels) so you can share?

You're right David. I will check the full wiring again.

I currently have a Katech DBW TB, and I would tend to believe it is genuine(i hope).

Unfortunately Level 2 logging is not available on this ECU, so I'll do my best to describe it.

The tracking aim fault I'm experiencing at first was very noticeable (Happens during WOT and several 0-100% throttle blips). I recalibrated the TB scale/offset ( manually fully closed/fully opened). Even tried to recalibrate it slightly before the mechanical stops.

That did not aid much, and the issue persisted. I attempted to manually adjust the scale of the main and tracking sensors as i noticed some discrepancy between the tracking and main sensors. (This only happened in 2-3 instances and could not reproduce it)

With manual adjustment i was able to slightly alleviate this issue but not fully fix it.

So i said why not just remove the servo fault limit and check, lo and behold for somereason the throttle still closes haha.

So yeah i will defintely check the wiring as per your advice. Would you say that even if a bigger DBW throttle is based off LT/LS variant the calibration would be different due to the bigger TB?

So you are getting a fault when at full throttle with no throttle movement? That has to be an intermittent connection (terminal pushed back in a connector, or bad crimp, or wire with internal break).

If you are using a PDM, do you see the current to the ECU / DBW servo increasing at full throttle? Are you trying to drive the blade to the stop? I would normally set the blade at parallel to the flow, often the stop is slightly beyond this point.

I didn't know there were any ECUs / firmware where you couldn't add Level 2 Logging. I find I need level 2 logging for DBW, Gear Shifting, Boost Control, Knock Tuning, Traction Control. Nearly every project has one of these, so it's pretty standard for my customers.

Yeah, actually trying to troubleshoot these issues without Level 2 logging is quite cumbersome. We will be making a new harness for the TB and re-testing it. I think I will also insist on Level 2 logging. If all else fails, then I have to welcome the sleepless nights of setting up the new 112mm TB haha.

Level 2 Logging can be added at any time -- have you contacted your MoTeC dealer?

There are a few things here...

GM has used more than one serial decode in it's time. SENT throttle uses udig hybrid A for the main and UDig hybrid B for the tracking.

SENT secure serial uses only hybrid A for the main and no tracking.

In regards to Granatelli throttles, unless their quality has improved, I would not advise to use them. Only one of their 103mm throttles has been sent to MoTeC AU for calibration and it was declined due to the mechanical stop of the throttle occurring with the blade at 90 degrees to the throttle bore - making it too easy for the 100% throttle position being calibrated against the mechanical stop.

In regards to SENT throttles and earlier serial number ECU's, there can be some compatibility issues. The signal processing of udig's was altered 7-8 years ago to increase compatibility with digital signal decode - such as the SENT protocol. If the LS3 throttle body is a later SENT variant and the ECU is early enough, you could have issues. Likewise if the ECU is old enough, fitting a SENT throttle end up with compatibility issues.

SENT signals do not do well with noise as well. If there is noise from the ignition system, or poor wiring practices in the harness construction, you could have issues with the throttle as well.

Thanks alot for the input Nathan, highly appreciate it.

If that is the case, I will not install the Granatelli TB.

Could you advise me on other large-bore TBs that would work well with any of the available calibrations?

I saw that the calibrations available for the Nick Williams TBs; is it possible to use an existing Nick Williams calibration with a bigger TB? (i.e. the available 103mm calibration on a 112mm TB?) OR would that mandate a different calibration?

In regards to the current LS3 type servo, I think the issue I'm facing is that under a seemingly high boost level and high RPMs (Supercharger at 0.8barg), it seems to sort of force it closed. That is the conclusion I have reached, as it even closes with the fault engine speed limit set above the engine speed limit.

It is the first time im seeing such an issue, as with turbocharged vehicles ive tuned running the same TB im not seeing this issue at all. I'm not sure if the way air passes through the tb from a PD blower as opposed to a turbocharger. Or i might be overthinking it, and it's simply a failing Servo motor.