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The STRANGEST Ignition System IN THE WORLD BMW V12 M70

Timm's BMW Repairs and Information

13,756 views

It could have been all so simple - but BMW decided to go with a half-baked system on the new flagship engine, the BMW M70 V12. The new engine came with electronic ignition and fuel injectors - but they forgot to join the two together in a sensible way - and that brings us to the DOUGHNUT.

Technically known as the CIS - Cylinder Identification Sensor, this is the weak link between the ignition system and the fuel system. It was as though one team didn't talk to the other and they ended up with a system that was so fussy that something like changing sparkplugs would stop the whole engine running. This engine was used in the BMW E31 8 Series and the E32 7 Series.

This video shows how to fix the system, how it works and what to look out for.

#BMW, #Ignition, #CIS,

Hello from Timm 00:00
How a normal Ignition System works 01:21
Electronic Ignition 03:08
The CIS Cylinder Identification Sensor 05:29
How the CIS Works 06:01
The right Sparkplug is NGK BKR6EK 10:01
The MSD Blaster Coil helps 12:31

20 Comments

@markhoult599 4 years ago (edited)

You Sir are a lifesaver .11 years owning a E31 850 and the reason i have kept it running is down to your forums. Cannot thank you enough !!

@jasoneyes01 4 years ago

OMG this sounds like something Jaguar would do back in the day.

@kevinconstantine5244 4 years ago

Everydays a school day learnt something new today.

@Tango_Alpha_Charlie 3 years ago

My tech and I are trying to get an M70 to behave on both banks, not just one .... this was very informative. Thank you !

@rileyandikeysplaytime5936 1 year ago

This is my 2nd 1991 base e31 and on the 1st car I did 100% of the service on it.
I knew nothing about the M70 motor back in the beginning. YouTube, Timms e31 info & online forums gave me all the info I needed.
Here I am again realizing ir forgotten 80% of the tricks and shortcuts from before...

@andrewthompsonuk1 4 years ago

So that's why those cars can be a nightmare to start if flodded?

@killer1963daddy 4 years ago

Only square heads can take something so simple and make it complicated.

@CarLos-yi7ne 3 days ago (edited)

Funny thing is that the Alfa Romeo Busso V6 Turbo (used in 164 & Gtv) has exactly the same ignition system. The distributor is identical with the M70.

About same era and both Bosch systems.

On the Alfa V6 all six injectors are fired all together on one output.

@ianmcwilliam1753 3 years ago

Recently acquired a 91 850i 6speed LHD and I’ve been watching your e31 vids to get familiar with the oddities of this magnificent vehicle. Many of your videos contain exactly what is needed for this 850. The first and perhaps most important piece of advice was DO NOT JUMPSTART so I purchased new battery and went with the single battery setup… car maintenance and small repairs can wait until my 2000 m5 is back on road (rod bearings, T.chains&guides , clutch/flywheel are installed)
But i didn’t want to damage the windows when opening doors with old drained batteries. Looking forward to seeing all the other videos you’ve made over the years. I also have the m62b44 in my 97 540i/6 daily driver and your inpa diagnostic overview has been eye opening. My 540 has a rough cold start , idles smoothly , tons of power but has some vibrations when revving up 900-1600 rpm’s. No doubt You’re m62 advice will also prove helpful. You deserve to be one the top YouTubers in your area of expertise.

@oldgtstrokers 4 years ago

Highly interesting, very pleasantly presented! Looking forward to new topics!

@topdawg1692 7 months ago

wow, wow wow, amazing information, well done, see you on the forums!!

@marioduran7913 4 years ago

Tim, thank you so much, I got the job done, I couldn't do it without your response. Best
Mario from Raleigh nc

@funfun5656 4 years ago (edited)

Exotic ignition setups like this is actually quite common with V12s (or at least as "common" as any component can be in a V12 considering how uncommon it is to have 12 cyls)

Check out the DB11S with the AE31. It reminds me of the same way an M70 is just a pair of siamese M20s as it were.

@synthwavegarage 3 years ago

Thanks for all the useful information. I have been following your channel for years. I saw all the videos.

@alioral1358 4 years ago

Never heard about it before Timm. Thanks.

@drewmurray2583 4 years ago

They should have had cam sensors, not a hard thing to design into the front timing cover. Nothing wrong with batch firing the injectors either, carburetors do the same thing with pooling fuel on the closed intake valves and I have never had idle or running issues from setting up EFI that way.

@midik123 2 years ago

Learned something again. Thanks!

@bargla 4 years ago

What I absolutely love about Bmw and what really bought me into these cars was fact that you can have a certain type, symbol and part number of a spark plug throughout a huge variety of bmw engine models, and it will be the correct one. For example M40 4-cylinder and M62 V8! Isn’t it just genius? Wow.

@woocash2139 4 years ago

Small correction, the ht leads are copper in the m70, the resistance is in the end connectors which is how they all have the same resistance but different lengths