Nicole

I hear that the '94 and '95 GTS automatic models were equiped with a dynamic kickdown function, that initiated a downshift on quick gas pedal movement. Apparently, this required addition of a throttle potentiometer and some other modifications. I hear that a 928 owner in Germany has retrofitted this to his S4, but have no detailed information at this time.

Has anybody of you ever done this retrofit? If so, can you describe what had to be done? Is it feasable to do?

Can anyone who owns a late model GTS or has this modification describe how well or not it works?

It sounds like this would make an automatic 928 much more responsive. In fact, it might be more valuable than adding power, as it takes better advantage of what's already there.

Jack '84 928s

This is going to sound like a flame but chevy makes there trucks with a very sensitive kickdown to make it feel faster. Not to be rude but thise sounds like the same

Steve Cattaneo

If you what part throttle KD, wire a relay to the KD solenoid, have it activated by a micro switch or the full load side of the throttle switch.

WallyP

If there is such a system, Porsche didn't show it in the wiring diagrams for the '94.

Steve Cattaneo

Nicole, Wally.

My WSM only have the 1994 electrical diagrams and it does not show any TPS wired into the KD solenoid. Or relay. The only MB Transmissions that have a TPS control KD, 5th to 4th are the 722.5, 5speed ( non electronic.)


Nicole
Can you get more information, pictures? Who has a 95 auto and is willing to take pictures of the out side of the transmission?


You sparked my curiosity

Rich9928p

I recall that the GTS sales literature indicated this was a feature even for MY '93. With my GTS all I need to do is make a quick poke 1/2 travel at the throttle and I get a downshift from 2 to 1st for off the line starts.

Gary Quayle

Here is what it says in the Service Info Tech for 1994. At the end, it mentions what would be needed to retrofit.
---------------------------------------------------

Dynamic kick-down
To make the 928 GTS with automatic transmission a
more agile vehicle, a dynamic kick-down has been introduced
for model year 1994.
The dynamic kickdown is connected in parallel to the
static kickdown. If the vehicle is travelling at more than
34 miles and the throttle valve is more than 24’ open,
the dynamic kick-down can be activated by rapidly depressing
the accelerator pedal a short distance angular
velocity > 240*/s).
If the throttle valve is less than 24’ open and the other
conditions are met, the dynamic kick-down is set to
standby. If the driver accelerates and the throttle valve
is opened to more than 24’ within 8 seconds, the dynamic
kickdown is also actuated.
After the kick-down has been actuated, this shift program
is held for about 8 sec. and then erased. The
dynamic kickdown is also erased if:
-the accelerator pedal is released until the throttle valve
opening is less than (24’)
-the throttle valve is closed about 50’ from its maximum
opening
-the vehicle slows to less than 34 miles
-the shift point of 4590 rpm in 1st gear or
5950 rpm in 2nd or 3rd gear is reached.
It is not proposed to retrofit older vehicles for economic
reasons. Apart from the throttle valve potentiometer, the
engine cable harness and the central electrical system
would need to be modified

Steve Cattaneo

Nicole you are right there is a dynamic kick down function in the 94/95GTSs


After searching thru the GTS wiring diagrams; the 94 cars have a different throttle valve switch and kick down relay then the other models, and yes the throttle switch is wired into the kick down relays solid state circuit.

From the description of operation it appears to be timed delayed and dependent on other engine parameters. Can it be adapted to other models we will see?


Thank you, Rich and Garry for the information

GoRideSno

Wow,
That sounds like a nice thing to have. It would be even better if it were able to work at around 15 mph instead of 34. If someone could assemble a kit I am sure it would be a popular upgrade item. Maybe Steve and John Speake could team up and build a kit.

Andy k

WallyP

I had not seen the tech write-up, and that sounds interesting.

I did see the additional wiring and circuitry for the kickdown relay in the '94 wiring diagram - BUT:

The kickdown relay does not, as I understand it, cause the transmission to kick down. Its function is, in fact, the opposite.

The kickdown relay is NC - that is, the contacts are normally closed. The power for the kickdown solenoid is routed thru the relay, and as long as the contacts are closed, the relay has no effect upon the kickdown.

When a specified engine RPM is reached (very near red-line), the ECU triggers the kickdown relay, opening the contacts. This drops the transmission out of kickdown mode, giving a very precise and very quick upshift.

Given this mode of operation, I still don't see any provisions for the throttle-movement-activated kickdown.

I can think of a way to do it, but it would require that the signal from the ECU (triggered by the rapid throttle movement) bypass the manual kickdown switch.

This wouldn't be the first time that the wiring diagrams vary slightly from reality!

Randy V

Just bumping this thread as it was a topic of conversation at Sharktoberfest this past weekend.

See the direct text from the Owner's Manual posted above - to retrofit earlier cars to this system requires much more than changing the throttle position sensor - see the last line from Porsche on retrofitting.

It is not proposed to retrofit older vehicles for economic
reasons. Apart from the throttle valve potentiometer, the
engine cable harness and the central electrical system
would need to be modified

https://rennlist.com/forums/684948-post7.html

GregBBRD

I, too, found this conversation very interesting, at Sharktoberfest.

Roger has a kit, which he says he has sold 20 of, that does this update.

Vilhuer

Its not too difficult to install if engine is out. Engine in the car but intake out hardest job is to get one extra wire from TPS to main relay board.

https://rennlist.com/forums/928-foru...-finished.html

Alan

There is a relatively easy path for this utilizing the firewall grommet behind/under the wiper motor in the cowl area - follow the vacuum line for the hot water valve to locate.

Room for a small wire bundle and easy to make it from there over to CE via the console.

Alan

ramcram

I had a 94 GTS for a number of years and this system was very nice and also a great fuel saver, allowing smooth downshifts without full throttle.

They also had an 'ignition retard' feature that is coupled to the up-shift. This reduced the force on the trans during full throttle up-shifts, so the engine at near red line power/torque doesn't smash the trans.