byrdman454

I was looking into doing this mod on my '88, but Borland alerted me to a problem with the '87-'88 that might not allow this to work "as is".
Here is his PM.

I was looking at the wiring diagrams for 1988 and it looks like it may not work without further modifications that are required for 1989-1993 cars. The 1988 uses a different kickdown relay which doesn't require a speed signal; the mod uses a GTS kickdown relay that does require a speed signal as well as a throttle position sensor.
The digital instrument on 89' and newer provide the 'digital' speed signal to the kickdown relay's used on 89'-95 cars.
The speedometer signal for speedo and cruise control may not be at the right voltage or wave form. There may be another speed signal from another controller, like ABS, but I'm unaware of the any.
There is a speed signal relay for 91'+ cars that no longer get speed from the differential sensor. Just haven't looked into that yet.

Does anyone have any further info on this? Does anyone have any ideas on how to make this work on the '87-'88? A big thanks for Borland for finding this before I sunk a load of $$$ into the mod.

borland

I've had a chance to drive my S4 a few times since finishing this GTS dynamic kickdown modification. It’s everything that Schocki says about the car being more “agile”. And in my mind, a “well worth it” modification.

Installation is relatively easy, requiring only a few hours. Removing/reinstalling the S4/GTS intake manifold is actually quite easy. Even better, if your going to do manifold powder coating or replace knock sensors at the same time.

Hope my write-up eases any concerns about the costs and sourcing of necessary parts.

borland
90’ S4, Slate Metallic

Schocki

Good to hear that you like the modification.

To bad that Porsche never offered a conversion kit....

Alan

Mike - Schocki and I have been kicking this around. He has documented his project and in looking at the relays - it appears that for '85-'88 there is a good possibility this could be made to work - are you game to be the test case? I would say the probability is certainly better than 80% that this will work - but no guarantees...

The earlier cars use the impulse sender to feed the cruise control module speed signal in place of the digi-dashboard output on the later '89-'95 car.

Because of this its very likely they both have the same characteristics and that it can also be used to drive the newer relays kick-down speed signal.

The CE panel on 85+ cars is the same and can directly accept these new relays. The only difference to Schocki's previous implementation would be 1 more wire to run from the Cruise Controller brain to the CE panel as another connection to the relay. If this works it may be possible to retrofit this change to '83-'84 cars also - though some investigation of the different relay socket in the earlier CE panel would be needed to confirm.

Anyone interest in being the test mule(s) here?

for Ref:

The kick-down relay sequence is like this:

1994-'95: 928.618.108.01 (w/ min speed signal & dynamic I/P)
1989-'93: 928.618.108.00 (w/ min speed signal)
1986.5-'88 928.618.109.01 (no min speed signal)
1983-<'86.5 928.618.109.00 (no min speed signal - old CE panel through '84)
<1983 (No Kick Down Relay)

Alan

borland

Alan,

If it's a "minimum speed" signal from the digital cluster, why would it need to be a pulsed? A pulsed signal would requre the logic circuits in the kickdown relay to be more complex.

You might want to investigate at a possible mod to the above mod, that overrides the "minimum speed" programming of the later kickdown relays.

byrdman454

All,
I am for sure game for this. The car is going on jack stands in the next seek or two. I am rebuilding to TT, changing the transaxle for lower gearing, plus doing a Tbelt job and intake refresh. This is a perfect time to do this mod, if it is possible. Please let me know what I need to do.
Thanks
Mike

Alan

Borland - I agree it would be nice if it were not pulsed - but I believe it is. On earlier cars e.g. <1989 it was fed to the relay from the pulse sender.. also on the later cars this exact same signal now from ths digital dash was fed to the Cruise Control as a speed signal. Its the only speed reference to the cruise the only other inputs are the Cruise stalk switches, clutch switch (MT only) and brake switch inputs... so it must be pulsed.

(<'88 cruise brains are different but '88 was the same as '89-'95)

Not so easy...

I do still wonder though if feeding a permanently low signal would work (the pulse sender switches to ground).

Borland - I agree with you - I was also thinking that being able to disable the min speed speed limit might be interesting - presumably this was added to ensure 2nd gear starts unless you select 1st?? did this only start in ''89??

Seems that with dynamic kickdown this would give the option of first gear start just with a little quick stab at the gas... and 2nd if you go gentle...

Schocki - did you consider this?

Alan

Alan

Mike - I'll see if Schocki responds here - we could check out if it could also work on your 84 too...?

You will need some new parts... - in case it doesn't work out - is there anyone out there who has a '89-'93 (this will for sure work on those years) who would also like to do this mod? - then you can buy Mike's parts if it doesn't work out for him... insurance policy...

Alan

borland

If I still had my handheld digital o-scope, I'd try recording the speedo "A" digital output signal by tapping it at...

CE panel, Connector "N", pin 25 (BL/RE wire).

Same location on your car Alan.

byrdman454

Unfortunately, my '84 Euro is a five speed, so there is no kickdown option to try.

Keep me informed on what I might need to do or buy for my '88. My car is a permanent resident in the garage for a few months now, so unfortunately I cannot test anything out by driving. My plan is to pull the transaxle and TT in the next week or so. Then after the TT is rebuilt, and the LSD from my '88 is transplanted to the new '91 transaxle I have, I will then start working on the engine (TB, intake refresh).

Alan

Mike perfect timing if you are to be refreshing the intake anyway.

Schocki has the update on his project details - hopefully he will send you those details - meanwhile you will need:

1) 928.618.108.01, Relay Kickdown, $57.07
2) 928.606.157.01, Throttle-Valve Switch, $101.38
3) A new 6 pin MAF connector & terminals - you can get one from john speake www.JDSPorsche.com or www.eagleday.com
4) 2 x terminals for the small relay slots - I can send them to you

Alan

byrdman454

Alan,
I actually already bought the MAF connector from John Speake last year before I found out the mod would not work on the '88. Are the prices you posted from the big 3?

I have never driven a properly runnning GTS before, especially a '94-'95. Is there going to be a way to check if the dynamic kickdown is working on my car prior to driving? I am worried than as many changes as I am doing to my car over the winter, I will not know my car well enough to verify it is working correctly? I am changing the gearing and I already have my extra TC stall increased.

byrdman454

Just checked the prices. Those are Sunset Porsche prices. I think the big 3 are a little higher on those for some reason.

Alan

They were the prices Schocki posted - I have a manual GTS so its moot for me - I plan on including Schocki's project in an electrics book I am putting together - the more years it can be applicable to the better!

Alan

Schocki

Quick reply before I'm off to work.

I'm pretty sure that the dynamic kickdown relay needs a pulsed speed signal. The kickdown can't be activated below 30 mph and the signal comes from the speedo on the instrument cluster.
Hopefully the older cars use the same frequency...

What is so fantastic about a permanent 1st gear start???