Heading south 275 miles between Marshall, VA and Greensboro, NC yesterday afternoon with a full tank to visit kids/grandkids, mama and I had traveled 150 miles to Lynchburg, VA where we stopped at Advance Auto for replacement wiper blades. Attempting to continue, the S4 would start okay but then stall. Each effort produced the same result; start - stall, start - stall. Given enough throttle, she would run roughly for 15 - 30 seconds then stall After 5 or 6 attempts, she began to smooth out and eventually ran and idled well.

Given the rain and for reasons of safety, we drove 2 miles down the road to an Enterprise Rental Car agency where we picked up a Ford Fusion for mama to drive as I would follow in the shark. 30 minutes later out of the Enterprise store to continue, the S4 displayed identical symptoms; start - stall, start - stall. ENOUGH! It was getting late. Both of us into the Fusion and on to Greensboro.

About two years ago, we had a similar problem although that time, it was strictly start - stall. With renn listers' guidance, it was determined to be an LH brain failure. John Speake at JDS Porsche in the UK rebuilt and returned it. All AOK until now. Could this be the culprit again? Other suggestions/tests?

So, the S4 sits cold, wet, lonely and sadly at an ERC store in Lynchburg... not a happy situation especially if she requires a rollback ride back to Marshall.

Thanks for your usual perceptive insights.
Bob

 

temp II sensor?

I just replaced mine and it solved similar issues, especially when it was cold. Does it smell very rich?

It very well could be the LH again. Do you have anyone near you that could swap theirs in to test?

 

Had a situation similar to this and it ended up being the ignition relay, worth a try.

 

Brett - No rich smell. Temp sensor II? Where is it located? I had 2 kind offers to swap test in the 3 years ago event but had concerns that something nefarious may have resulted for the kind donor.

Sean - For testing purposes, is the ignition relay interchangeable with another?

Although 5 months out of its 3 year warranty, John Speake, at JDS Porsche has offered to repair/replace the LH brain if it is defective - a generous offer considering the $500 rebuild.

Further mysterious connector questions in following thread.
Thx guys,
Bob

 

so once the engine gets beyond the stalling does it drive ok?

the idle has many sensor inputs and requires all to be tested and the simplist method is to use a diag tester through the cpus......someone close by can perhaps run your car through all the multiple checks

 

Relays are always first suspect, but of the trio of injection, ignition, fuel the fuel pump is most likely failure.

All are interchangeable with a '53' spst standard relay like the horn

Temp II as you face engine on LHS of water bridge. Pull off the bosch 2 pin connector. Test each terminal of sensor separately for resistance between the terminal and ground (not between the 2 terminals). There are 2 thermistors in sensor body - 1 sends signal to ignition ecu and one to injection ecu. Check the readings with hot engine, and one that's cold.

 

This introduces an interesting concept especially so if the if the rebuilt LH has gone.

In days gone by a fried LH brain resulted in one of two possibilities- new unit from Porsche or a s/h unit from a wreck. When John introduced his service this created a third option. Now, as in your case several years on, maybe we will start to see a new layer of degradation starting to manifest itself. Realistically John can only do so much with his brain refreshment and maybe we will start to see new problem layers occurring that previously would never have been seen or known about. It is all about component half life.

When he refreshes these units John replaces the components he knows from experience to be suspect. An 87 model is now 24 years old and needless to say, so is a good chunk of a rebuilt brain. How many pieces of kit containing printed circuit boards remain in use in the home after 25 years? Not too many I guess. My daughter has an old CRT telly purchased in 1990 in her bedroom that I want her to throw
out but that is about it.

It will be interesting to learn what has happened here but realistically, 928 owners really need to have spare modules for critical items like the LH and the MAF. If I remember correctly the S4 has 4 computerised modules: LH, EZK, anti lock brake system and one more I cannot remember? Realisitically owners need spares for all these that by now must be getting tired. One good thing that happened when I lost my 90 S4 was that I was able to collect these up. My spare LH is currently in my friends S4 pending arrival of the rebuilt LH John has just done for him.

Good luck- hope you recover soon from whatever the problem is.

Regards

Fred

 

I would be checking the CE panel for water,
look above the panel after you open the wood panel,
look for tell tale drip stains.
If you find them then the relays are all suspect as are the fuses. remove every relay and inspect it for corroded pins any that are corroded should be opened and smelled for burning,
inspect the fuses as well.
Check the battery connections and clean every connection.

check the 14 pin connector above the hot post and fit a cover if you dont have one the 14 pin has current flowing through it all the time.

Also remove the connectors to the computers and see if they have gotten wet or corroded

Pull off both of the coil wires and check each end for corrosion

 

My rebuilt LH ECU have a replacement "tile" that is much more rugged than the original. So I expect them to survive at least anouther 75k mile/10 years. My rebuilds from 10 years ago are still going strong, in fact no returns.

I did have a small batch of failures from about 3 years ago when the encapsulant I used on the "tile" caused problems after a year or two in service. Maybe Bob's LH came from that small batch.

Although I give a 3 year warranty, I will always replace a faulty unit due to my workmanship, well after that time, if the unit hasn't been obviously abused.