Easy and safe method to temporarily disable one engine bank on the 850?

Interesting question. I think that it's not so simple. You need to find a way such that the EML or ECU will not detect a problem and make the engine go into limp-home mode.

If fuel pressure is monitored (?), then fuel-pump disconnection may not be the thing. Disconnecting the ignition coil will trigger a fault from the ignition coil sensor. Perhaps unplugging the injector wires and connecting them to some spare injectors (so that an open-circuit is not dtected) may do it. But, you don't want unburned fuel in the engine as this will remove the oil-coating on the cylinders causing wear and it may also overheat the catalysts when the bank is re-enabled.


Mercedes at one time had some V8 engines that would disable one bank on the fly for greater economy when cruising, but I don't know why they went away from that.

I would assume that pulling the fuel pump relays (DME box) is the easiest method and should not do any harm. Disconnecting the coil might go unnoticed and if injection of fuel continues, over time wash out the oil in the combustion chamber.

I am pretty certain that some error will be logged in any case, so from that point of view be prepared.

My hunch is that the engine ought to run smooth - I do remember people not detecting which bank was out and scratching their heads until they dared touching the headers.

Cheers
Reinhard

I have had only one bank runnig a few times due to engine washing and failed distribution cap.

Engine was running smooth and with a bit deeper voice probably due to running a bit more on the 6 remaining.
Actually hard to tell if all 12 are running or only 6

Regards
Terje

A bit of OT, sorry:
I have been told time and time again from people who either know cars or have sold cars over a longer period of time that the 850 V12 disables one bank (or runs on 6 cyl) under 3000 rpm.

But despite everyone telling me so i can't find a single piece of proof on it, other than other people on the internet saying its true.

Get those people here to receive the flogging they deserve

Disabling a bank is a sign of something going wrong. That´s all there is about it. Everything else is "internet lore", ie rubbish talk.

Cheers
Reinhard

Zitat von revtor;90315

But I'd like to test and measure some items on each bank individually where I don't want the other bank to influence the test.

I know I'm probably jumping the gun 'cos you're gonna tell us anyway but what is it you are hoping to test and measure

That is what I call dedication to the cause and I love reading all this stuff even if it is mostly over my head.

The debt of gratitude we owe people like you is almost incalculable

If you want to disable one bank, it would be best to make sure that no fuel is entering the engine on that bank (otherwise you'd ultimately flood the cats and thereby killing them when that fuel ignites).

Disabling one bank is not bad for the engine as it's still lubricated and cooled. But I'd advice not to go full throttle at high speeds (it should still do aroung 90mph) as the engine block would heat unsymmetrically - and I have no idea if that would be harmful.

What I don't understand about this is that the firing order must have a sequence that spreads the load across the banks, therefore taking out one bank is going to cause asynchronous firing?

Pulling the fuel pump fuse for one side or the other would seem the neatest solution. You can do it while running with no more than the fuse puller and the change should be immediate.

As for the firing order I believe that the V12 is two complete inline sixes electrically independent of each other but melded onto a single crankshaft.

Fascinating - hence the exceptionally smooth running (when all cylinders are firing!). I love the Euro coin video posted by a German enthusiast on his website dedicated to the 850 Csi - it was that website that first got me to want an 8!

I had my CSi go into limp-mode once when I had a faulty ignition lead. It felt a lot less power than a 2.8 Litre! I think that the EML reduces power in other ways too.

However, Revtor is correct that the engine will still run perfectly balanced as a 6 cylinder. In fact, a straight-6 and a V12 are the only perfectly balanced configurations for both 1st and 2nd order forces.

With all 12 cylinders working, there is a power-stroke every 60 degrees of rotation of the crankshaft. With only 6 of the 12 cylinders working, this reduces to 120 degrees.

Obviously, there must be a good reason why manufacturers do not implement this shut-down system as part of normal engine operation at low load, although, as I previously mentioned MB did have it for a while about 10 years ago. Maybe the uneven thermal expansion is a problem or the cooling of the cats requiring time to get back to operating temperature again.

Here is some background information on how the Mercedes "ZAS" system work(ed).

They gave up on it but AMG is said to revive the idea and hopes to save significant amounts of fuel. As if AMG customers would care

Use translation engine on the above texts - all German, most of it can be understood using Googles translation services.

In a nutshell: 1990´s DB V8 engines shut down cylinders 3,4,5,8. In the V12 engine - one bank. All with closed valves.

Cheers
Reinhard

Doesn't one of the GM V8 engines do something similar? I seem to remember the Chrysler 300C has/had this feature to save fuel when cruising.

It's been done a long time ago. Like with many things, Cadillac was the frontrunner bringing innovative ideas on the road (or, the US car industry as a whole.. yeah yeah.. we don't like to hear it.. but they did it anyway).
http://wardsautoworld.com/ar/auto_two_four_six/
Back when I lived there, unfortunately, my 1982 Cadillac Coupe deVille did not have the cylinder deactivation feature. But one of my friends' Cadillac did - and it did work.

Just to remind us of the time... it was 1981.

And that wasn't the coolest feature of these cars. They automatically turned the headlights (low-beam) on and off, depending on light conditions (a feature you just find in reasonably newer cars, today) plus they turned off the high-beam headlights when a car was heading towards you (not to blind them) and then turned them back on when that car passed...

Yeah.. features that you just barely find in modern cars nowadays.

Oh.. and who invented the standard way to manually shift a car (clutch as the left pedal, brake in the middle and gas on the right) ... that's right! Cadillac, again.

The the US boys also invented the airbag.

Alltogether, that leaves just the petrol and diesel engine invention in Germany.. and ABS, and ESP of course. But.. that's almost it..