Porsche Enthusiasts Club Forum

When I accelerate normally in my S4 it soon changes into fourth and sits at just over 1,000rpm at 30 mph. If I accelerate fairly gently it seems reluctant to change down, so overtaking I can end up with my foot almost right down and while not slow to increase speed, it still seems to be in third or fourth.
If I boot it, that is put my foot down sharpish, it changes down rapidly and even (at low speeds) into first very briefly, producing massive acceleration.
It does seem to me a bit lazy, I've not had an automatic before, is this normal? You have to pretty much floor it quickly to tell it "yes I want you to change down and give me some real acceleration here, not just a steady rise in speed"
Should I be using the shift lever more to change manually instead of just leaving it in "D"?

There are two stages of kick down, one is triggered by manifold vacuum ("load") and also by the kick down cable to the gearbox. The second stage of kickdown is triggered by a solenoid from the kickdown switch under the throttle pedal (via kickdown relay).

First make sure you have the correct engine vacuum at idle 22inHg as measured on the vac feed to a fuel damper. Then check the vac line to the 'box from the union under the engine airfilter is actuually connected. If all's well there, then check for slack in the kickdown cable, tighten it to take out slack. When operating correctly you should be able to trigger the first stage (i.e. not actuating the kickdown switch) up to 75mph in 3rd gear. At lower speeds, you will need much less throttle to get it to change down a gear from 4th

Thanks for the advice. I'll check it out. I did test it last night and it will change down without flooring the accelerator, but you have to press the pedal quickly. If you ease the pedal down the transmission tends to stay in 4th. likewise the kickdown, if you stamp it down there's no problem otherwise it's slow to respond and does not use first gear (from a standing start)

Sounds pretty normal. You may still need to tighten the kickdown cable, and also check vacuum at idle.

The main check is the one when kicking down at 75mph. Keep tightening the kickdown cable until you achieve that without getting to the point at which the kickdown switch is activated.

Personally I always drive around in 3rd gear in town, I don't usually need to go more than 120mph

You should be able to activate a 1st gear start by selecting "2" from rest

Is the vacuum system connected to/part of the heater control system? I recently repaired my HVAC system as the heater distribution controls were very slow or did not work at all. The main problem was with the non-return valve under the air filter, which was blocked. Now that's all OK but I am aware that there is some kind of vacuum control line that goes to the gearbox.
I assume this part of the gearbox control is OK as the heater controls work properly now. Nothing is simple on the 928 is it!! Oh wait a minute, not quite true, replacing the number plate lamps only took 5 minutes.

The vacuum line to the auto-box comes from the throttle body via the 'spider' connector to rear of fuel damper.

It's not affected by any problems with the hvac system which takes its vacuum via the check valve.

Thanks for the advice I will take a look at that on Saturday.

I was looking at some of the S4's on ebay and there's one with a very long description. In it the seller says that a "small vacuum failed in the car and made a bit of a noise" and it was "removed by the garage as it seemed to serve no useful purpose in the car". I'm not sure there are any parts that serve "no useful purpose" in a 928 S4.

How about the rear seat passenger visors?

Take your point though about dubious eBay claims. I see in the Q&A section that Brett approves of the ad's honesty, but for me it seems frankly overpriced given that sunroof has been painted over or something (it seems to gloss over some drastic short cut in the respray), there is a potentially frustrating door lock/alarm problem, driver's window doesn't work, there's an undiagnosed battery drain and the inevitable "aircon needs re-gassing" (which I thought was one of Brett's pet hates!) followed by "I wouldn't bother" (why on earth not?). Reducing the reserve by £100 is not really compensation for bodywork costs. The reserve is arbitrary anyway.

The reference to the appendix-like uselessness of the "vacuum part" tells us quite a bit about the credentials of the Mercedes mechanic who has been looking after this car but "really knows his stuff".

As you say Lightning there are a lot of S4s for sale, so I think this one has strong competition for any buyer's wallet.

Hi

I just liked the guys honesty and it makes a pleasant change to see an actual 928 "owner" selling his car and not a dealer or a "friend" of someone...

For the price it looks pretty reasonable 928 as well.....

I read every 928 ad on Ebay and I may be wrong but I "think" prices are starting to rise for the good ones...

I just hate the dealer/scrappie ads where they insist on breaking them

To be honest I think that will stop soon as well as there are not that many cars needing major parts considering how many were originally imported...and some of those "reserve starting prices" are really silly....

On principle I would rather buy new from Roger in the US or from Paul A....

All the best Brett

Yes I think the advert is very honest, and he seems to really like the car, a proper enthusiast. In regard to the vacuum part I think it's the fault of whoever "repaired" it for him for giving bad advice. Probably why he says the aircon "still works but needs regassing".....with the vacuum system not working the aircon will still work but will blow hot air only through the vents!
The respray sounds like a good one, it cost him a further £3,000 on top of the £3,000+ for the new bumper. But why paint over the sunroof?

Oh I sorted out the "lazy auto transmission shifting" (the original subject of this post) I never knew about the kickdown switch on the accelerator pedal! Pressing the pedal against the stop to engage the kickdown switch certainly produces results that are anything but "lazy".

Hi Everyone,

I have had a problem also with recently the autobox in my 1991 S4 shifting harder than it used to. I tested the vacuum today as John specifies above at a fuel damper, and found the car is down on vacuum. It is at about 19inHg when warm at idle.

Is there any way apart from finding a pressure tester to use to find the leak? I am assuming that to find a leak with an appropriate tester, I would go to the vacuum spider to the rear of the engine bay, remove each line one by one and see if they hold vacuum?

Cheers!

Hi

When you get hard shifting..the first thing to do is..CHECK the auto fluid level......next is CHECK the auto fluid level....lol

ITS ALMOST ALWAYS THIS...you MUST check it the correct way...car up in the air and LEVEL, after a 15 minute run to make sure fluid is HOT....then put into ALL gears at least twice for 10 seconds on EACH gear....then WITH ENGINE RUNNING...check the fluid...if its low (very likely) top it up and see how it shifts now...

All the best Brett

Sorry I should've added that the fluid was topped up after the last service. It did help slightly, but now we've found a loss of vacuum aswell, and to be honest it still isn't smooth like I'd want it!

Cheers!

Hi

Was it "topped up" PRECISELY as I described above ??? you cannot just "top up" a 928..the auto fluid level is not designed for that way....

If not as above....try it and see.....

All the best Brett