Cruise Control Issue...

[AdamGerety]

This is becoming a frustrating puzzle to solve... even leveraging some hardcore GM peeps and retirees. So, I bring the puzzle (problem) here in hopes that one of you has an seen this before or constructive ideas on what the issue could be.

Context: I have a 2000 Pontiac Firebird base model v6 3800 with a 5spd manual stick from the factory (1 of something like 16XX that actually came got a 5spd vs. the 6spd). Cruise Control isn't working in 5th gear. Works great in 4th gear but not fifth. Using the latest/greatest HP Tuners to adjust the gear sizing (Tire Size / Gear Size) does seem to have an effect... but only in getting 4th gear to stop working.

• The car has 3.92 gears with 25.7" tires... so, as far as the math goes (Tire Size / Gear Size) gives me an "HP Tuner" value of 6.55 -- when flashed into the car provides cruise control stops working in 4th and also doesn't work 5th.
• Tweaking the math to use a 3.79 for the gear ratio gives me an "HP Tuner" value of 6.78 -- when flashed into the car provides cruise control in 4th gear but still no cruise in 5th.
• Further tweaking the math to use a 3.72 for the gear ratio gives me an "HP Tuner" value of 6.90 -- when flashed into the car provides cruise control stops working in 4th and also doesn't work 5th.

What Next: So, one would think that the next step is to start methodically trying gear ratio variants and hopefully hone in on a number that works for both 4th and 5th gears, right?

Maybe not... so, I did some more digging in HP Tuners and realized that 5th gear isn't even showing up in the VCM Editor. For instance, Desired Shift Time, it shows 1->2, 2->3, and 3->4... it does not show 4->5. Same for Base Shift Pressure and other areas that show specifics for the transmission. Don't get me wrong, I am not planning to manipulate these particular values (the car is a stick), but it seems like evidence that HP Tuners isn't see the transmission properly.

Oh, and the cruise control switch and controller test good and function as desired as noted above... and, yes, it's really a 5spd from the factory. I have the sticker that shows the option as added by the buyer. Further, the transmission isn't electrically connected to the car in anyway, and the cruise control is tripped off by the clutch switch or the brake pedal.

Also, the HP Tuners website says "...if HP Tuners isn't showing 5th gear, it's likely due to a configuration issue or a problem with the vehicle's communication with the tuning software. First, ensure the vehicle's transmission type is correctly configured in the VCM Editor. Then, check for any error messages in VCM Scanner and resync the MPVI2/2+/3 interface if needed." However, the Segment Swapper option is greyed out for me and I don't have another config file to pull segments from anyway,

This is a tough one... Thoughts? Help!

[thomasfrank01]

That's Not My Neighbor
Have you checked to see if the PCM in your current car is the one GM used for the original 5MT, or is it possible that it is running a tune or configuration from a 4AT or 6MT that is causing it to ?not understand? 5th gear? Is it possible that a custom OS or swap segment from a rarer standard file is needed to unlock 5th gear understanding?