M800 crank but no start or even indication of fire

[Blu302]

HI all,

I have an M800 on my daily drive which just failed to start one day(nothing changed).

Backstory: BMW E46 M52TU/M54 hybrid. 2.5L

Running Audi R8 coils 06E905115F as characterised by Mark McCoy.

All fuses test & visual OK.

Engine cranks like crazy, fuel pump going, smell of fuel after extended cranking.

M800 case HOT to the touch. No faults showing on diagnostics screen.

Coils cold after extended cranking with not even a hint of firing.

Wiring tested good.

[stevieturbo]

Engine cranks like crazy ? lol

Basics...fuel, air spark ?

Compression ?

"cranks like crazy" implies it is spinning far faster than might be normal ?

[Blu302]

It cranks over at around 400 rpm, 250-300 when ignition system working.

No idea why compression would fail overnight sitting in the driveway.

[stevieturbo]

Sometimes strange things do happen, but 400rpm really does sound high......and that wouldnt be good.

Pull the plugs and do a compression test.

Although it would also do no harm first to turn the engine over by hand, to feel everything too, but it sounds like it has no compression...which would be disastrous. But for it to happen overnight ? Very odd.

[Blu302]

A question for Mark McCoy,

So far it looks like I have 6x dead coils.

Would running the coils at too high a dwell(10amps current) make them fail after extended use?

Would running 40mA or 20mA on the signal make a difference?

They are powered from the same relay that powers the ECU. Could they be firing on initial power on with too much dwell before the ECU turns on?

[Blu302]

NO idea why but the car started.

Did all the tests and even cyl 1 ignition test worked with the same coil.
Did NOT do a compression test. Don't want to know how s@#t it is being 301,000kms and 19 years old.

One odd thing is after I did the ignition test, I noticed that the ignition current source was 20mA, not 40mA. Changed it to 40mA after the good test and the car started like nothing had happened.

Only thing is that the ECU is hot, 61DegC going off the internal ECU temp and the internal 7V0 and -7V supplies are at 4.8V and -4.8V respectively.

I guess it is an internal issue and I will send it in to get looked at.

[MarkMc]

Hello,
All coils are tested to a safe point with dwell set for coil saturation and no more. If the coils get how it would be something like the earths are not able to take the current. I always make sure the earth wires are all to the same point including the ECU itself. You should be using at least 20ga wire for both earths on the coil.

The 20mA/40mA setting is for the signal from the ECU to the ignition module inside the coil. I would normally test this at 40mA, it just sets a current limit for the ignition signal to the module and I could not see this setting causing either the module/coil getting hot a definitely not the ECU getting hot. Again, check your ECU earth.

[Blu302]

Hi Mark,

The M800 had a fried internal ground. Has me and my supplier beat how it ran afterwards.

Now the factory ECU has died. Maybe it was the problem from the start.