ROG100

Malcolm,
Did you check that all the injectors were working before pulling them?
Roger

FredR

Malcolm,

When sorting out my current 928 I had the injectors cleaned - witnessed the cleaning myself until I was satisfied I had a good set out of a total of two sets. Two were discarded so I had 8 plus 6 spare. We fitted 8 of these injectors. when we started the motor it fired first time but something felt wrong- it was not picking up correctly. One by one we disconnected the injectors then we found one that disconnecting made no difference- it had packed up evcne though it had fired OK on the test bench. I did not pick up any rough vibrations it just felt like it was running really crap.

Turn the clock back 12 years to 1999. I was driving my late S4 through a nice fast desert road running through the Hajjar Mountains, went to overtake a saloon car, pulled along side , kicked down- huge bang- no dirve. The drive shaft snapped just behind the splines and all kinds of delaminations had occurred. About $2k later the car was fixed along with new torque converter bearings/gearbox mounts etc. All was fine- for two weeks then a vibration at 3050 rpm. Hmm! Into the garage- followed advice from Rennlist that I had just joined- painted the area- released the flex plate- boing-jumped about 3mm. I am sure you get the picture. Vibration gone two weeks later back again- same thing. Porsche suggested replacing the flexplate bolt and overtorquing by 10%- did that- two weeks later vibration same thing. Then I implemented Captain Earl's loctite solution- still use it to this day. I theorised that the vibration had probably been there previously and given road speed of about 140 kph [nice speed that avoids being thrown in the lock up] the motor may well ahve spent time at that spot thus causing fatigue and eventual failure- the taper being a nice natural stress intensifier. Hence my suggestion to take a look in that area to if anything untoward going on. you would have to look very carefully as no torsion on the shaft in static conditions.

With the flex plate set correctly now the problem should not manifest but- if damage was done before you got to it or if it is slipping again since you released any tension? Not sure how failing torque converter bearings manifest themselves other than as a grating noise.

Thus why when I hear "Vibration at 3K rpm" I immediately think torque tube problems. I cannot believe my S4 is the only example that experienced this but I a very sensitive to mechanical noises and vibes maybe we are similarly cogniscent.

Of course for your owner's sake I hope I am way out here.

Regards

Fred

the flyin' scotsman

Unfortunately not......the batt was disconnected and I didnt have the key when I pulled the FIs.....the car is now 4hrs away round trip.

Lizard928

I had an 86.5 in here that vibrated like hell rough idle etc. turned out that someone had replaced one injector lead, their connection was only partially together, and on pin was all but pulled out of the connector.
Fixed those and the car ran much better.

the flyin' scotsman

Fred.....very much appreciate you sharing your TT experience. I too find it incredible coincidence that the flex plate was released and now theres bad vibration.......there must be a connection I believe.

A bad FI would be bad all the time and not just at a particular rmp range?

Im hoping to get the car back running then get it on a lift running and do a stethescope on the TT befoer full winter hits which will be soon.

To make matters worse Im currently 1300kms North of home in the NWT.

FredR

Malcolm,

When my fuel injector failed I had a 7 cylinder variant- not good! I did not even try to drive it like that so cannot comment on how it would feel running- bad I suspect.

I have seen two more S4/GTS TT drive shafts snap behind the splines. When mine failed I was told by a Porsche official quote "I can snap one of those in 5 minutes"- can you believe that?

I am convinced there is a linkage between TBF, drive shaft failure and examples where the clamp is known to let go to some extent. The flexplate is primarily designed to absorb small amounts of radial misalignment and it will also absorb a small amount of axial misalignment. However at some point of axial clamp slippage, I believe this translates to unacceptable magnitude at some point and this translate badly if a resonant vibration sets in at a given frequency. When my clamp slipped 3050 rpm was a clear "stay away from" zone. Whereas I replaced the TT with a brand new unit, the clamp was the old one.

Some 928's survive this slippage event- way too many do not and continue to fail to this day. It really is a scandal but of course with time comes plausible deniability [well its an old car isn't it? - yeah right!]. I was out of pocket by $3k not to mention two months whtout my car. Although I knew my current GTS motor was popped when I purchased it, morally I reckon Herr Ferdinand owes me a short block as well.

If you have not done so, clock the crank end float inspect behind the shaft splines. If you have access to a pal in the non destructive testing industry who inspects pipe welds, you might also consider checking the shaft for cracks with dye penetrant.

Whatever the root cause of your problem- hope you find it soon. Last thing we want to see is another popped 32V motor.

Regards

Fred

the flyin' scotsman

thx again Fred.

Not to long ago another 'lister posted of having severe vibration after R&R the engine for a head gasket issue........everything was inspected tofind litlle if anything wrong only to have the issue disappear. I PMd the poster but hes as in the dark as to what was his issue and why its now gone.

In my particular case the car is essentialy virgin since factory with less than 100k kms and unmolested other than Porsche shops until my work. I am confinced that the drivetrain was untouched from factory until my involvement and the fact the flex plate released a considerable amount the crank and drive shaft are now in a position they have not been in for 24 years.

I need to get the car back to runing condition and do much more investigation of TT and related systems.

FredR

Malcolm,

Good luck with your investigations when you get round to them.

My S4 was never touched by anyone except the local main agents- 84k km on the clock at the time- kerplonk!

The examples that I have seen bust their TT's [3] or suffer TBF[5] over the years here invariably seem to do so in the 80k to 120k km range. that may not seem remarkable but it is from a fleet that is probably no more than about 20 vehicles of the 32V auto variant that survived into this odometer range [quite a few were wrecked and a few exported]. Invariably there will be examples that have gone pop outside this range but it would be interesting to know what the statistics really are.

Regards

Fred