[svxistentialist]

Originally Posted by rmjjensen

Sure ...it's not necessarily sending +5V to the TCU that initiates power mode. It's the theory that power mode is engaged when there is a sudden charge in throttle (TPS). Pulsing +5V to this wire will make the TCU think you keep flooring the gas pedal ...then letting off ...flooring it ...letting off. Now, if you physically do this in the SVX, you'll get the TCU in power mod, but you'll also be driving like a moron and get engine surges and wouldn't make any sense.

The 555 Timer does the TPS blips into the TCU while you maintain control of the engine by way of the physical accelerator pedal (TPS signal to the ECU).

Blipping the TPS wire to the TCU with 0 -> 5 -> 0 -> 5 -> 0 -> 5 does not cause the transmission to kick down gears. It depends on the length of which +5V is applied. If it's for 250 ms (for example) there's not enough time to kick down gears. Now if you maintained constant (or long period of time) +5V to the TPS input, the TCU will kick down ...it will think, "what the heck? this guy is flooring the car, but the RPMs are barely increasing - let me kick down a gear cuz this guy wants to MOVE."

Gear changes are determined more by the RPM signal input into the TCU (which we are not changing).

Does this help?

Yeah. A lot. Thank you.

If the 0-5v break is short enough, then the TCU circuitry decides that Power mode is required [because of the sudden-ness of voltage rise] but because the 5V is not maintained, it does not cause kickdown to a lower gear.

That is magic in a way.

You are then saying that the shift map uses rpm and road speed to assign gear changes. But these changes are assigned from the Power mode shift map, not from the Normal map.

The key or trick to it is keeping the 0-5V interval very short, using the 555 switch, that presumably has a variable interval.

Thanks Mike, that seems to solve the conundrum.

Joe