Gentlemen - I have not posted in a few years, as both vehicles have been relatively trouble free. Between reading the posts and the archives, I have been able to keep them both in good running form. No more; I am in need of your assistance and guidance once again.

The 850 started first by intermittently falling into LHM mode. With past experience in mind (check the archives searching with my user name),I thought it was either the #6 or #12 spark plug being fouled. Upon changing all 12, I found this was not the problem. After a few incidents of this, it got where it wouldn't stay running for more than 5 seconds or so at a time. Cranks up every time, but dies almost immediately. Given time constraints due to work obligations, I put her on the battery maintainer and drove the 750 full time.

Last week, when I started the 7 to go to lunch, the engine fired fine, but all of the gauges slowly pegged and the read out on the instrument cluster started scrolling what looked like software build or version codes. This went on for about 20 seconds, then the gauges returned to normal. But when I put her in drive, it was immediately apparent that she was in LHM.

Finally had time to do some testing this weekend. Spent most of the day on the 8, as it had been laid up the longest. It has different symptoms than the 7. It has progressed past LHM. Instead of just running on 6 cylinders, it will crank, run for about 5 seconds, and then die. When I put a stethoscope on the injectors (all 12), they are all firing. Then they just stop and the car dies. While running, the exhaust is blowing a blue gray smoke that has a very strong smell. Not gas or oil, though. Just foul, like there is something wrong with the catalytic converter. Started testing with the fuel pumps. Both had fine pressure and delivery. The check valve on one pump is obviously bad, as it does not hold residual pressure at all. The other does, but not as long as it should.

Checked several other items - MAFs, coils, DKs, etc. All good. Finally got to the CPS. Passenger side reads well within specs, but the driver's side starts out at about 280 ohms, then quickly drops to around 2. Should read 540 +/- 10%. When I found this, I moved immediately to the 7 and checked its Crank Position Sensors and found exactly the same results - same side failed, same ohm reading.

Questions -

Has anyone experienced catalytic converter failure? The 8 does run a little rich, has Conforti chips installed. What were the symptoms? Can they get plugged up? Extreme back pressure would explain a lot.

Any thoughts on the lack/decreasing amount of residual pressure from the 8's fuel pumps? Is this a reason to replace them or something that can be lived with?

Any thoughts regarding the differing symptoms, when the only fault I have found is common to them both? The 7 is firmly in LHM mode, running on only six cylinders (my dumb [Oops!] didn't check which 6), but running nonetheless. The 8 won't run more than 3 to 10 seconds at a time, but will immediately start back up.

Any suggestions are welcome. I am posting this to both the E31 and E32 boards, I hope we all learn something from this PITA.
Paul

'91 850i (225,000 and begging for more)
'90 750il (159,000 and catching up fast)
'80 Fiat Spider 2000 (resident hospice patient)