Seeking advice... S54 odd situation

[Jsalicru]

Not really one to post much, but this one has got me stumped a bit.

I have a S54 Z3M and recently came across a no start issue. I sent the DME (MSS54) to Kassel and they found a blown capacitor. I ended up getting a replacement DME to install...

Now comes the weird issue. When I go to crank, it blown fuse F201 in the E-Box, which is the fuse for the coils. New coils, still does it. Changed the ignition harness with another one... same issue... except now that harness back in a E46 M3 won't start the car...

That tells me that it's likely blowing the suppressor capacitor... guessing here since it's completely sealed.

The car ran fine right before this all happened... I also have the Evap solenoid clicking and the throttles also are clicking.

So far I haven't found any shorts anywhere...

I am open to any suggestions to help figure this one out as it's certainly been a bit bizarre.

P.S. the capacitor part number doesn't pull up anything anywhere but if anyone has a lead on that... please share!

[ac427]

I think there are capacitors or inductors in the ignition harness. So perhaps they have been mullered. Ah, i just noticed your second picture.

Does the capacitor blow if you try to start the car with all the coil packs disconnected?

Depending on your patience threshold, it may be better to get an auto-electrician to investigate.

[stammc]

If F201 (coil power) is blowing immediately on crank, you almost certainly have a short to ground on the 12V supply side of that circuit. Since coils and harness have been swapped, I’d start isolating the suppressor capacitor they can fail internally and short under load. Try unplugging or removing it completely and see if the fuse still pops.

Also check the coil power wire for continuity to ground with the DME disconnected. If it shows shorted, you likely have a pinched wire in the E-box or loom. If it only blows with the DME connected, the replacement MSS54 may have an internal driver fault.

Given the evap and throttle clicking, I’d also verify your main DME relay and power distribution inside the E-box. Something is pulling excessive current on that ignition feed.