David L. Lutz

1987 S4
I have just finished replacing my kick down solenoid in the back of the tranny and now or maybe all along, I think I have a problem with the relay.

My kickdown switch is modified and working correctyly. When the kickdown switch is made I have 12+ volts at socket #30 on the relay panel. All ok. However when I break the switch and close the switch the relay does nothing.

I opened the relay and closed the contacts myself and blew a fuse. #10.

I had read somewhere I could jump sockets #30 and #87 and the tranny solenoid should activate. When I did this the fuse blew again. I unhooked the lead from the new solenoid on the tranny and again the fuse still blew when I jumped #30 and #87. Is is possible to jump these post.

Can anyone point me in a direction other that buying a new $100.00 relay?

Thanks in advance for the help.

jpitman2

Sounds like the line from the relay output is shorted somewhere on the way to the solenoid. You should be able to verify this by diconnecting the incoming wire at the solenoid, and get near zero ohms from the wire to ground/chassis. I would check resistance from each end. Depending on where this wire runs it may be fixable , or it may be a run a new wire job. It it runs along along the top of the TT and is hard to access, replacement would be the way to go. Have you looked behind the fuse board for signs of burning/shorting in there? If it produces any burning smell, you may have visual evidence there.
jp 83 Euro S AT 51k

ZEUS+

+1 with jpitman2. Try disconnecting the 6 terminal harness connector in the spare tire well and see if short is still there. Terminal 2 green and brown wire for kickdown. Might help to isolate short.

David L. Lutz

Thanks, I will check for the short today. I still don't understand why the relay doesn't close when I close the kick down switch. It does nothing. It's when I jump the #30 & 87 is when the fuse blows!
Thanks for your advise
David

ZEUS+

This doesnt make sense. How is your switch wired ? Many circuits using bosch relays can be powered by removing relay and jumping 30 @ 87. Terminal 30 is power supply and 87 is component feed. Not with the kickdown circuit. Terminal 30 receives power when switch is closed.

Alan

Looking at the kickdown circuit (like as posted) it seems odd. The switch is in series with the KD relay contacts which are normally closed. Activating the relay will open the contacts - so its more of a K-D disable relay by the looks of it... Driven by the LH

As Zeus says - jumping the 30-87a terminals should be no different than plugging the relay in - and it should be unpowered anyway without the switch activated...?

However having said this - the configuration seems basically the same for the '94 version. but this version has to be able to activate the kick down with the relay alone for the dynamic operation at < full throttle. The only way I coulod see that this configuation could work that way is if the relay and switch are both normally closed and either open opening and the solenoid losing power causes kick down...

In that case you'd need a series kick-down override switch not a parallel one...?

I thought I understood this relay operation but it seems all backwards!

The other option is the relay diagram is hopelessly wrong and the relay has switched contacts from both 15 and 30 to 87a... that makes more sense to me...

Anyone ...?

- esp. Schocki - how did you determine it worked?

Alan

ZEUS+

This should help explain kickdown operation.
http://www.nichols.nu/tip752.htm

jpitman2

I woudl check for +12V at one of the leads on the kickdown switch. If no volts, check the feeding fuse - 10? It would be odd for the swicth to open relay contacts, unless its opening one set and closing another...You could check the solenoid by running +12V directly to it, see if it clicks.
jp 83 Euro S AT 51k

ZEUS+

Exactly, but signal is from tach.

Alan

Yes you are right its the rpm signal - but on the 94+ dynamic kickdown version you also have the speed signal and dynamic override - but how useful is that if all it can do is disable the kickdown...

Alan

Z

Once the RPM reaches the specified point, the relay contacts open. That's what causes the 2-3 and 3-4 upshift when you're foot to the floor. Basically the upshifts occur the same way they would if you momentarily lifted off the gas pedal and the kickdown switch under the pedal was momentarily opened. RPM signal based electronic upshifting is more accurate and consistent than hydraulic pressure control, so no hitting the rev limiter.

borland

In the Nichols article, Wally's explaination is correct, except for the later GTS Automatics with Dynamic Kickdown Program features. Wally must have got this right out of the Porsche Service Guide "Automatic Transmission A28 Description and Operation". This manual refers to the kickdown relay as a "speed kickdown relay", as it serves to cause immediate upshift based on engine rpm. This Porsche document is included on the Morehouse CDs.

However for the later GTS (94'-95') with dynamic kickdown, the relay shown on the wiring diagram is incorrect, in that it doesn't show the second internal relay switch that feeds pin 30 power when the program detects fast throttle response.

At least my belief of that second internal relay switch is based on my own testing on my 90' S4 with the GTS dynamic kickdown mod installed, and with the front passenger floor carpet removed, I can hear the relay click when activating the dymamic kickdown downshift by fast throttle response.

Notice that, regardless of year models, power to the solenoid is directly from the kickdown relay pin 87a., and not from the throttle kickdown switch.

Alan

Yes thats what its fed directly from - but the other side of the relay contact (30) is shown series looped though the kick-down switch to ignition power via the fuse on all versions of the relay config. So per Wally's notes - both the kick down relay has to be inactive and the kick down switch active for the solenoid to activate.

I agree with you that the '94+ GTS models must have a separate relay switch - its not shown though.

Alan

ZEUS+

That diagram is for an 87, this is a 94.

David L. Lutz

Thanks guys for all the help. I had a short in the lead from 87 to the solenoid. Once repaired all worked exactly as you noted.

Thanks again, I am again kicking down as it should be.
David