Two days ago I pulled out on the road with my '91 850i and nothing, well almost nothing. ping..safe trans fail. So I turned around and crawled home. I checked the forums here and heard that it could be just batteries. I had them both checked today. They are supposed to be load tested at 700CCA, my left was 700, but the right tested at 543. The auto shop didn't think that would be enought to affect the cars perfomance this much. Should I replace the battery or keep searching for the cause? Where should I look next? The car has just turned 90,000km. Appreciate shared wisdom.

The TRANS FAIL SAFE can occur for a number of reasons. Usually when you are in LimpHomeMode, it will trigger on occasion. Another possibilty could be the EGS (transmission Control Module - right rear above battery) could have gone out (been there done that). But it could also be not enough juice. These module do not like to be "underfed" and as many others can attest, the 8 is well known for its electrical gremlins.

It is more important to check the sustained voltage - you should be above 12 volts or better.

I would try a hard reset of the EGS module first (after determining that the batteries are ok). Remove the trunk liner panel on the right side and you will see a silver box mounted above the battery, remove the connector (looks like the one on the DME's and EML, and leave off for an hour or so - just to be sure. Connect everything up and give it a try.
Keep us posted

Thanks for the reply and I will give it a try when I go home in an hour. BTW, that is one heck of a collection of cylinders you have there.

I am in Canada as well (on the other coast) but have "some" experience in trans fail safe issues and troubleshooting thereof. As stated, there are many potential causes for the problem you are having and the majority have nothing to do with the transmission! As I am a 2 finger typist, its easier for me to chat than type so if interested, email me (wuffer(at)shaw.ca) your phone number and I will call you to discuss. Also visit my website (www.wuffer.net (http://www.wuffer.net)) and download repair manuals.

I have replaced te weaker battery, but no change whatsoever. It seems he car is only hitting on the six cyclinders on the driver's side. I also started to notice a gas smell for a few weeks before this major trouble happened. Anyway, more suggestions on how I can get back on the road?

Seems that the LHM (limp Home Mode) is most likely triggering the TRANS FAIL SAFE.
This has a whole bunch of possibilities as well.
First you have to isolate the problem, and that can be time consuming - just remember to do one thing at a time in order to positively identify the problem.
The first thing I would do is visually inspect certain elements, i.e, the distributor caps and rotors - do you see any scorch marks, or missing contacts? Are the vacuum lines hooked up to the fuel pressure regulators properly? (left FPR goes to right DK, and vice versa)
Next, find where the fuel smell is coming from. When the car goes into LHM, you usually do not get fuel to the side of the engine that isn't running, so I would imagine you have a faulty fuel line somewhere.
When was the last time the fuel filters were changed? Believe it or not a clogged fuel filter can trip all sorts of errors in these cars. Next you might want to check the sparkplugs, you can tell by the condition in what direction your problem lies. Are the plugs sooty, or oily?
After these things (probably missed something here), you will want to start swapping components from one side to the next and seeing if the "dead" side switches sides, if it does then the component you just switched will be the culprit (see why you only do one thing at a time?).

Do you have access to someone with an 8 that would be willing to let you see if your DME's are okay?

Try those things (should keep you busty for at least a day) and report back.

Good luck, and remember it always turns out to be something really simple, the trick is being able to pinpoint it.

Hi Wuffer and others..
I got back on the road today. Total damage $848. It was the ignition coils, which they charged $215 each plus, plus, plus. Labour was reasonable, but I got a motor vac $110 (not sure if this really helps, but hey it sounded good) and an oil change and the rest is taxes. Just happy to be back on the road, my friends old Nissan was great to have (beats walking) but just not the same as my 850i
Thank you for your phone call Wuffer, it was second on your list. Keith

Thanks for posting the fix, Where'd you get the parts from? Thanks!

Happy to help. That is what the E31 Community is all about.

I dont want to be the bearer of bad news but you paid way to much for the coils. They go for $66 each at autohaus Arizona.com They are bosch as well. Get your parts from them or Charlie at gault BMW 866 590 4252