Anyone know the V12 BMW M70 engine really well?

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unity

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I know is a long shot, but some of you have an extensive background in cars. Getting voltage at my injectors with key on and engine not running. If I crank her, she floods quick. Just a few sputters and its game over until it sits or until I pull the injector connectors and crank some more. I will give more details if anyone has some knowledge of this crazy V12 setup.

Thanks!
 
740 is very different than the 750. You guys would think this setup is weird. I sure do! I am getting spark, so both crank sensors works.

The way the engine is setup is that there are two 6 cylinder engines. Each have their own MAF, temp sensors, distributor, coil, crank position sensor and computer. In short, two engines that are synchronized by a bridge computer. One side can run fine while the other is completely dead. In fact, in limp home mode the system will do just that, kill the problem side. Cool, huh?

But the odd thing is that both sides dont run. I spend a lot of money (car was free) and time getting it this far just to be stuck with a problem it did not have when it entered my garage months ago! Frustrating!
 
sounds like a cool system. problematic, but cool.
so if both sides are dead, should narrow it down to something common to both sides i guess.
 
Cam position sensors all good too? I bet it's something simple that is being overlooked somehow. I had a 85 Jaguar Vanden Plas in 95 and 96 and that car drove me crazy when little things went wrong. Had a huge 6 cylinder but parts for it were outrageous. I had to sell it to a guy that collected them. Sometimes those types of cars just aren't worth having but are nice when they're running good and no problems are going on with them. Yours was free so that helps out a bit.
 
I know its gotta be something common to both sides. Which would be the EML (that bridge computer). There are even two fuel pumps!

As for cam, there are none. Just a cylinder identification sensor that monitors spark to know which phase ignition is in. A rather weird way to do things. If the sensor does not detect spark, the injectors will not even fire anyway. In my case, they ALWAYS want to fire (alway on voltage). And like everything else, there are two of those sensors.

And free is good, but after doing so much mechanical work I am frustrated to be held up by this new problem!

Im going to try a few more things. Might even have to pick up a new bridge computer - although that, in theory, wont do anything since I still have voltage when I pulled it out. And it does not control injectors, just makes sure both sides are in sync.
 
Do both sides have large tip plugs? I really can't think of much else that it could be unless there is some kind of relay that does control the injectors that may have possibly went bad. I'm sure you have swapped those around though, if that's even possible. Might be a grounding problem... I would definitely use big tip copper plugs, unless you already have them. I'm just guessing at different little things that it could be.

You mentioned checking the voltage for the injectors. What was the voltage when checked?
 
Silly thought.. Unhook the battery and set the positive cable on the neg, leave it for 10min or so... Let the computer reset.
Hook it back up and unplug one of the MAF sensors, it should go into limp mode. See if it runs.
Could be a bad ground or stuck relay like mentioned before. Relay is easy to check, grab your favorite screw driver and take a tour through the relay panel lightly tapping on the relays with the handle. Remember I said lightly.. Not like wack a mole.
 
^ been there, done that. More than once!

No logging options. "Stomp test" (where the display will show codes by pressing gtas pedal 5 times) shows nothing wrong.
 
Hmmmm.. It's broken!
I'd rather work on anything besides a BMW.
I wish I had something more productive to say.
If you unplug the crank trigger will it fire off of the cylinder position sensor when you crank it?
 
97MarkJA said:
Hmmmm.. It's broken!
I'd rather work on anything besides a BMW.
I wish I had something more productive to say.
If you unplug the crank trigger will it fire off of the cylinder position sensor when you crank it?
Click to expand...

No, like on a Mark they are separate. If no crank position is detected, it will not spark or inject fuel. Same goes for the "cam" position sensor (cylinder ID sensor). If it can not detect that spark is occurring, no fuel. And like others, there are two of those in play so even one side can run without the other.
 
Oh, and I agree. This is my first BMW. So far a big pain. But its a V12! :D GOTTA make it work!
 
I've worked on a friends 850 several times, once for a no start issue.
I checked every connection in that thing, by the time I was done I had half the car taken apart. I was almost ready to give up and had the car all put back together when I unplugged the maf's.. She fired right up, plugged them back in and it ran like a top. I haven't seen the car once after that. Which is a good thing considering after that car I was ready to unfriend him...lol
I can't say I actually did anything to fix it but he gives me credit for it, this isn't a good thing when he has friends with BMW's.
Dont get me wrong, I'd drive the hell out of a 850! The first thing I would do is jerk the drivetrain out and replace it with something I could actually stand to work on.
 
The 850 is a sweet car. Almost got an M engine out of one for my car.

Yup, on BMW forums. Been spoiled by the Mark and Mercedes forums. The BMW forums are just not nearly as active as you would think, especially with a car this rare. The V12 models did not sell well and I am finding many people dont work on them - for a reason!
 
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