Have you tried pulling the injectors after a short run? Pull them and look for drips. As the injectors age they don't close always and they'll stay open pouring in fuel.

BTW...your oil is going to be needed of changing soon....gas in oil sweeps off all the years of build-up inside your engine all the while diluting your oil... this then causes your oil pick up screen to get clogged and by that time, you' F'ed! Change your oil OFTEN until you fix this!
-Andy
1991 740 had same problem once...new injectors fixed this.

Thanks for the input guys! This, by the way, is a NA engine. I'll go back over it again looking for leaks etc and I'll swap the ECT sensor from dads ot see if I get any difference. Appreciate the ideas as always!

bruce

Since it's unlikely to have 2 bad fuel pressure regulators, I'd look for a bad ECT sensor- that's engine coolant temp, on the head under the intake manifold.
If it's failed, or the wire is broken, the computer thinks the engine is stone-cold all the time, and runs like a carbureted car with the choke stuck on.

I'd buy a couple new sets of spark plugs too, to get you through this till it's fixed- you must be fouling them left and right.

I'd also inspect your connection at the Air Mass MEter just to be sure that's not part of the problem. Don't plug or unplug it with the key on.
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Rob Bareiss, New London CT ::: '87 244DL/M47- 228K, 88 744GLE- 212K, 91 244 183K-SOLD! Also responsible for the care and feeding of: 88 745GLE, 231K, 88 244GL, 146K, 87 244DL, 239K, 88 245DL, 246K

You don't mention if you are driving a turbo or not. If you are check the turbo hoses carefully by removing them and inspecting for any thin spots. You will probably find they are leaking especially when under boost. The same thing might happen with a normally aspirated engine but it is more crucial with a turbo. Its a shame the hoses aren't available from anyone but the dealer (be sure you know your turbo make) cause they love to charge an arm and a leg for them. The only good thing is that you can fix it yourself.

Since the Oxy sensor seems to check out, possibly a leaking/clogged fuel injector.

I have been chasing a similar condition in my 240 for a while now and still haven't licked it. But my solution might not be yours anyway. Yours doesn't sound lack of air or spark, which can both mimic rich mixture. Your problem could be a leaky injector (as could mine), but I don't know how to test that. It could also be your cold start injector and I hit on a way to exclude that as my problem. I pinched off the fuel line between it and the fuel rail and it made no difference for me, but it might for you.

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Andy '91 745 184K, '89 244 134K, '87 245 lost the rust battle at 225K mi