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ballcock
Sepang


Joined: 21 Jul 2008
Posts: 2959
Location: Dublin

1996 Porsche 993 Carrera 2

PostPosted: Wed May 01, 2019 8:41 am    Post subject: 996.1 Tip Woes .. Sorted Eventually! Reply with quote

Ive been slow to put this up as I’ve seen a few tip problems apparently sorted but returning after a few weeks of use.
I’m hopeful I’m over my woes, it’s been a month and 2,000kms since the ‘fix’.
Huge thanks to DeMort for all his patience and help along the route to recovery!

Original symptoms, gears jumping randomly, going from 4th to 3rd to 5th at intermediate speeds, flashing D light , and then more alarmingly, a feeling of gear ‘slippage’ when accelerating from second.

First port of call was a gearbox service .. ATF and filter change.
This SEEMED to clear the problem. Gear slipping sorted, gear changes much much smoother. And all was well in the world for about a week, when the gearbox suddenly refused to go into fifth, even when motorway cruising at 120kms. This also brought on the dreaded flashing D light again. However, it did shift to fifth in manual....

Drat!!!

Back to my trusted indie.
Now here’s the freaky part.
He diagnosed four potential problems.
1) I’d a very slow puncture front off side.
2) My steering angle was off
The two above would mean that the tip box was getting info that the car was in a constant turn, and apparently it would hold gear rather than increase to fifth in these circumstances..
3) I’d developed a significant oil leak from the AOS (see pic of old knackered AOS!)
4) My Varioram had been messed with some time in the past and wasn’t functioning properly.
Now the two above (in layman speak!) meant the gearbox was getting confusing info from the engine ECU, and apparently this was enough to cause gear change problems in itself.

So a few days later, all sorted, including AOS and hose change (which he did with engine in situ, the bloody genius), and the transformation of both engine and gearbox was unbelievable!
As said , I’ve been slow to call the tiptronic problems sorted, but I’m very hopeful they will not return after 2,000kms of happy motoring.

I’ve posted the above in the hope that someone may sort a tip problem by reading this. I have to also put my hands up and say I don’t understand any more than the above. If you guys with more technical background/knowledge can explain the solution (especially the AOS/Vario) in more detail I’d love to hear...
_________________
'96 Iris C2 vario manual coupe, Koni FZD's/M033's RSR's and HID's.
‘98 Ocean blue 996 C2 Tip pressed into daily service.

Ex '83 W460 LWB G Wagen updated with OM602 engine and 6 speed 'box
Ex. '99 996 C2 manual coupe.
 



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Robertb
Long Beach


Joined: 01 Sep 2003
Posts: 6978
Location: South Oxfordshire

2002 Porsche 996 Carrera 4S

PostPosted: Wed May 01, 2019 9:06 am    Post subject: Reply with quote

Good that its sorted!

AOSs are the devils work, your guy is indeed a genius to fix it in situ, or perhaps missed his calling as a keyhole surgeon...

Its amazing how unconnected things cause issues. I was reading the other day of a 996TT owner who had problems with PSM, and was on the verge of needing a new PSM ECU at ££££.

Eventually traced to a short in a sidelight bulb...
_________________
"911- the guilt-free supercar"

Current: 2003 C4S Coupe, seal/black

Ex: '02 C4S Coupe, '96 993 Targa, '88 Carrera Sport Coupe
 
  
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deMort
Long Beach


Joined: 21 Mar 2015
Posts: 6485
Location: Brighton


PostPosted: Wed May 01, 2019 7:01 pm    Post subject: Reply with quote

I'm no expert here but ill give it a go and this is as i understand it ..

The tip box needs to know the engine load at all times and this info comes from the Dme ( engine control unit ) , most of this info is related to the signal from the Maf sensor .. air flow into the engine basically .

If you have an air leak the Maf will give incorrect readings .. too low , it will be inside the range the car expects to see so no fault code generated but its the wrong signal for both the engine AND the tip box .

The engine will try to adapt via the lambda sensors and correct the mixture but with your problems young man i would expect the engine to .. er .. not be running that well shall we say Smile

For the tip box its getting the wrong info and trying to react to that info .. hence incorrect gear changes etc .. it thinks there is a low load so may shift up a gear when it shouldn't .. then depending on the throttle position it may shift down and hold a gear when again it shouldn't.

This is one of those .. i kinda understand it but cant really explain it situations Sad

For me .. i look at fault codes for All control units regardless of the fault .. its not uncommon to find the actual fault stored elsewhere from the actual fault .

Its also the downside of remote diagnosis .. i look at the fault and don't often think of secondary systems whilst when i have the car in front of me i do things differently .. instinct and just how we work in a garage .

there is no better way of finding a fault than just driving it i'm afraid . we all have a feeling for want of a better word and it leads us in a direction ..

I always have a chuckle when someone tells me .. you just plug in a laptop and it tells you what's wrong don't you Very Happy

Ref control unit faults as per the PSM comment .. we cant see software .. to prove a CU fault you have to test every single wire and what signal or voltage should be on that wire .. its often either not possible or so time consuming that it isn't done and a mechanic will go with the obvious .. its the control unit guv comment .

he will be right some of the time .. but he will also get bitten with this approach .. some jobs are a bitch to find , it takes far .. far longer to find the fault than we are ever going to charge as a garage .. mechanic will be jumped on as well for the time taken ..

But i'm afraid .. some jobs just aint easy and i can say this as someone who specialises in this kind of fault finding ..

Sometimes .. i think .. id rather be a brain surgeon .. all brains are the same !
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ballcock
Sepang


Joined: 21 Jul 2008
Posts: 2959
Location: Dublin

1996 Porsche 993 Carrera 2

PostPosted: Wed May 01, 2019 10:16 pm    Post subject: Reply with quote

Love it DM! Great answer, and to be fair you did a fair bit of teasing out of the prob from afar, more than you’ll take credit for, knowing you!

I have to laugh at your comment re “you just plug in the laptop and it tells you the problem” , I get this constantly.. “ you just let the computer fly you to America don’t you” ..
Ammm .. well alrighty then!! Cop Razz
_________________
'96 Iris C2 vario manual coupe, Koni FZD's/M033's RSR's and HID's.
‘98 Ocean blue 996 C2 Tip pressed into daily service.

Ex '83 W460 LWB G Wagen updated with OM602 engine and 6 speed 'box
Ex. '99 996 C2 manual coupe.
 
  
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deMort
Long Beach


Joined: 21 Mar 2015
Posts: 6485
Location: Brighton


PostPosted: Thu May 02, 2019 7:02 pm    Post subject: Reply with quote

We don't do the same job .. but we have the same issues Very Happy

Always a pleasure and glad you have some happy motoring in front of you !

worship as you deserve it .
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Now At An Indy.
 
  
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