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    LHM issues 750il and 850i...thoughts requested

    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)

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    Re: LHM issues 750il and 850i...thoughts requested

    I think I would change those CPS sensors first. Reset both cars (remove batt negs) just for grins. Tested fuel pumps? Could you hear them running smooth? Do they get shut off with the injectors?

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    Re: LHM issues 750il and 850i...thoughts requested

    pumps tested good, other than residual pressure. new CPS units on the way. will follow up after installation. any thoughts regarding catalytic converter concerns? Paul

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

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    Re: LHM issues 750il and 850i...thoughts requested

    A possible cause would be bad gasoline. (water & crud in your tanks)

    Had this problem several times with my BMW's,
    they would buck, stall, and make all kinds of weird smoke.
    Hard to start, if at all.

    I drained the gas and switched gas stations!


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    Re: LHM issues 750il and 850i...thoughts requested

    this crossed my mind as well, but vehicles were fueled from different stations, months apart. not a likely cause.Paul

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

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    Re: LHM issues 750il and 850i...thoughts requested

    My 750 does the same thing with the gauges, different than the 8s. IIRC it does it after the battery has been disconnected for a while. I attribute it to the different DME systems; my 7 has the early M1.2, assume yours does too.

    You can live with the weak check valves, just takes an extra couple seconds to build up fuel pressure on restart.

    Got a vacuum gauge? If the CPS gets the motor running, you can check the cats by reduced vacuum at high idle speed. O2 sensors and fuel pressure regulators controlling the correct banks? Temp sensors OK?

    There is also an E32/E34 ETM Diagnostic manual on that site I listed the other day; it has LOTS of sections that are missing from the e31 manual, and will have M1.2-specific info as well.



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    Re: LHM issues 750il and 850i...thoughts requested

    Thanks for the reply, chrome. Yes, the 750 is using DME 1.2. But the battery had not been disconnected. May have been undercharged, though. Lucky me, commute is only 2.1 miles. Probably not enough to keep electrical system charged up to snuff with a 4 year old battery.

    Yes, yes and yes to the O2 and temp sensors and the pressure regulators. CPS units should be here tomorrow, will know more then.

    Thanks for the post on the ETM. Still wading my way through it, but you're right. Lot's of info I didn't have.

    Thanks for the reply. These boards seem a lot quieter than I remember. Unless, of course, I wanted to post my vocation.Paul

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

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    Re: Back pressure on the 8

    My 8 has 65k miles on it and had no usual signs of cat problems such as smell or rattle. Only indication I had was that it started to miss and run a little rich. Ufortunately I spent more than $4k on repairs before they found the cats to be bad.

    It had been gargaged for 5 years before I got it. It probably went bad from lack of use.

    Purchased 2 cats and two oh-2 sensors from Bavarian Auto and had them installed for less that the price of one cat from the dealer.
    '91 850i schwartz black on black
    '93 750iL schwartz II black on black
    '94 Dodge Dakota Magnum V8
    '00 Jaguar S-Type V8

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    Re: Back pressure on the 8

    how did they finally diagnose the cats as the problem?Paul

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

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    Re: Back pressure on the 8

    Unfortunately, by default. There was nothing else to fix. I am extremely disappointed with the shop that worked on my car.
    '91 850i schwartz black on black
    '93 750iL schwartz II black on black
    '94 Dodge Dakota Magnum V8
    '00 Jaguar S-Type V8

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