From: Kurt Rottner [kurt.rottner@gmx.net] Sent: Thursday, January 20, 2000 3:40 PM To: 928 Cc: '928@list.928oc.org' Subject: [928] Brain failure: conclusion from received data Hi again first a collective thanks to all who helped to collect a reasonable set of data and also provided additional information. Since I can't post the curves, I'll put the summary in words: I feel that with all data at hand, including the information from those who sell new brains, the most likely conclusion is that indeeed BOSCH had a manufacturing problem: The LH brains from the 87-89 cars started to fail after 9 years. I have no report on 90 cars ("L") with a failure and only one 91 car whose LH brain failed already after 4 years (and was repalced by Porsche at no cost!!!!) so I consider this as an accidential failure, with a different failure mode. Thus, the problem was most likely fixed late 89 or 90. There was no report on failed brains on pre-87 cars, so, if they start to need new brains now, it is most likely a different failure mode as well. The symptoms of a dying brain don't show a clear pattern. They can fail with a sudden "death" as you would expect if a central control unit fails, but apparently it als can start with simple idle problems. It is definitely not mileage related, as brains failed between 20 and 140 k miles. This makes solder fatigue or bond wire problems less likely, as well as degradation of the semiconductors themselves, as both ususally is greatly enhanced by temperature/temperature cycles so the mileage should matter. Semiconductors normally don't die from just sitting somewhere. So my guess is that penetration of humidity and corrosion/ oxidation is the key. This can occur by bad sealing of the chips, or by using insulating material that turns out to be agressive to metals in the long run. Who knows ... It would be great if some of us had the know-how and the equipment to analyse a failed brain, or by some other means identify the failure - and meybe even find a "cure" ... (So don't throw away the failed units ;-) It is encouraging to see specialists are getting interested and share their knowledge to find the root causes and solutions. David, (thanks for the part numbers of the brains!) you mentioned that you saw IT in the micorscope, could you describe what was visible, maybe you already have the solution ? As I mentioned before, I try to get something out of the BOSCH people, but this remains to be done. I'll keep you posted. If anyone wants more details just mail me off-list. I'd be also highly interested in any ideas on the potential failure mechanisms and fixes. Keep those brains alive !! Kurt 90 S4 Euro Auto schwarzmetallic 928 OC >Kurt, >I assume no one reported two failed brains on the same >car? (i.e. do the replacement brains have the same problem or not?) >Glad I have an 86. :) Maybe this should push the value of it up a >little bit... >Mike >86S From: Kurt Rottner [kurt.rottner@gmx.net] Sent: Friday, January 21, 2000 7:37 AM To: 928 Cc: '928'; '928@list.928oc.org' Subject: [928] Brain failure: further discussion of received data Mike, you're right, I haven't heard of dead replacement brains. But all the replacements I have heard of were all bought in the last years, so if they also life for only 9 years, they will start to fail not before 2006. But I think its reasonable to assume that they don't have that problem anymore. AND beware of used ones - like some unlucky people who bought a used brain out of 87 cars ... Some other information I forgot to mention: From the data I've got, one out of three 87-89 cars have needed a new brain. Even though this is probably an overestimation, due to the nature of such a poll (people with problems tend to repsond with a higher probablity than those without) but it shows that there REALLY was (and is) a big problem built into the brains of that era. The question is now - how can you check if your brain is prone to fail? From the part numbers it seems not clear, but there might be a chance of narrowing things down. Here are some facts: Porsche part numbers for the LH brain: 928.616.123. xx xx = 87 10 88 11 89/90 13 (S4) 14 (GT) 91 25 (S4) 26 (GT) One question now is whether all 89 cars have the .13 or .14 brains if yes, the number can't be used to tell a "bad" brain from a "good" one, if no, it might be a starting point. But it would be only useful for original brains, as I suppose when buying a replacement brain, the part number e.g. for a n 87 hasn't changed, so I doubt that this is of much use to tell a original from a replacement brain. The individual serial number of each brain certainly tells a lot more, but since it is virtually impossible to get hold of that numbers of the failed brains, the only chance is to get something out of Porsche or Bosch. They certainly know... Kurt 90 S4 Euro Auto schwarzmetallic From: Tony Bryant [zot@paradise.net.nz] Sent: Monday, October 30, 2000 2:22 AM To: 928 Subject: [928] ECU failure On my 928S2 (with LH-jet) I recently experienced an ECU failure. The engine cut out during level cruising. It would not restart. One tow later (with the trusty Jag XJ-S :-) and its back in the garage. A quick check indicated that the fuel pump wasn't going. The relay checked out OK, but was not being turned on. I traced this back to a fault in the ECU. The ECU turns on the fuel pump relay with a transistor (which was OK). The transistor is driven by a TTL 7402 chip, which has a dead output.. I replaced it with a 74HC02, and it works again. Cheapest thing I've ever fixed on any car : cost all of 50c !!!! Moral of the story : Always carry a wire link around to replace the fuel pump relay if your ECU dies. Tony. '84 928S2 A/T