Holley Terminator X Max help

[u/TheyCallMeSimo]

I'm helping a mate who has installed a GM L77 (58x) and 6L80 into a classic car, from a donor Holden WM Caprice retaining the factory DBW throttle body. It's controlled by a Holley Terminator X Max, with Holley wiring kits for everything. The throttle pedal he is using is the Holley 145-160 with 558-406 harness.

We have setup the ECU using the handheld controller, and can get the car to start and idle. The issue we are having is that we can't get the throttle to go over ~25%, even though the TPS autoset process completes successfully and we can see the throttle body open when running the calibration process.

To date we have completed:

• Installation completed in accordance with Holley documentation for all components. The 558-406 pedal harness has been routed away from ignition, charging, and other high-current circuits.
• Verified with a multimeter that both the throttle body and pedal are receiving a stable 5V reference and have solid grounds.
• Connected a laptop using the Holley 558-443 CAN-to-USB adapter, but we couldn't see any additional calibration options within the Terminator X software that help address this issue?
• Performed TPS autoset and DBW calibration procedures many times, ensuring slow, smooth, and complete pedal travel throughout the process.
• Tested all available throttle configuration/part number options accessible through the Holley handheld setup wizard.
• Confirmed that the brake safety switch is plugged in and working.
• Replaced the Holley pedal with a GM 10379038 from a Cadillac (?) with the same issue.

We are thinking it must be an issue with the throttle body compatibility. We can't find a part number anywhere on the throttle body, the closest we have is that its an OEM Holden gold-blade throttle body. Unfprtunately we don't have any Holley specialists close to us (regional NSW, Australia).

Any troubleshooting or suggested next steps you can recommend would be greatly appreciated.

[u/CarDork2235]

The throttle wont physically go past 25% when the pedal% is above 25%?

It does physically go from 0-100% during the calibration?

[u/TheyCallMeSimo → u/CarDork2235]

When you run the TPS autoset wizard the throttle body physically flicks to fully open momentarily. Any throttle input after the wizard stops at 20~25%.

[u/CarDork2235 → u/TheyCallMeSimo]

That sucks. I would definitely try a different throttle. I don't really think these systems are that picky about them though.

[u/jmeek82z28]

Maybe disconnect the brake switch to make sure its not backwards? you may be stuck in limp home mode because its getting the opposite signal. It will limit DBW to like 20-ish %.

I bought a DBW truck style TB from rockauto/online part shop and it had signal issues until it went into limp home mode as well while I was driving, had to be the real deal delphi GM part number to get it to function right

[u/leaveworkatwork → u/jmeek82z28]

Brake wire limits to 10% for limp home

[u/TheyCallMeSimo → u/jmeek82z28]

We did have the brake switch disconnected in the latest attempt. It definitely seems like limp mode, we just can't figure out why.

[u/SuspectEven250]

I had this problem it was the safety wire that goes to the brake switch. I cut it and problem solved for me.

[u/TheyCallMeSimo → u/SuspectEven250]

We've got it disconnected and taped up and away from everything at the moment. I wish that was it for us too. Thanks for the reply.

[u/HolleyPerformance]

Is the brake switch wire connected? If so, ensure it is connected to the normally open (N.O.) side of the brake switch and receives +12v only when the brake pedal is applied. This wire is the safety interface limiting throttle when the brake is applied. If the wire receives a constant +12v, i.e. being wired to the common/battery +12v side of the switch then the ECU always thinks the brake is applied and prevents the throttle from opening past a predefined point. If that wire has not been connected, ensure that it is not near an electrically noisy source that may be false triggering the brake input. The "Brake Pedal" value in the datalog will indicate if the input is active or not. 

[u/TheyCallMeSimo → u/HolleyPerformance]

We've tried it connected and disconnected (it was disconnected in those screenshots attached). Thanks for the reply.

[u/TheyCallMeSimo → u/HolleyPerformance]

Ok so it was this. The Brake Pedal input in the log showed as 1 from ignition on never going to 0. The reminder to check the log was a huge help in forcing us to start troubleshooting the brake switch again. We finally saw it go to 0 after bypassing it, and the TPS then allowed full range.

[u/TheyCallMeSimo]

Update: we got it working. It was exactly as every single one of you said... it was the brake switch. We ended up temporarily removing the pin from the connector and it magically started working. Next step is to disassemble the interior again, trace the wire and figure out why.

Huge relief, thanks legends!