m20 no start - cranks and has fuel

[frontin540i]

Maybe someone can help me out here.

I just swapped an m20b25 top end into my 87' 528e. I used and modified an "i" e30 wiring harness. Now here is the issues:

Car cranks but no start
Checked for fuel at the rail, it's getting fuel.

There is no spark, the ignition coil heats up, and i mean hot, too hot to touch.

Going through Jlevie's no start post i checked pin 1 on the dme (the coil pulse wire). According to him it should be an open circuit and the dme pulses ground on ignition to send spark. Well pin 1 on my dme is constantly grounded, no pulsing, makes sense why the coil is heating up like that.

Does anyone know what tells the dme to trigger pin 1? i checked my cps, reads 520 ohms so that is within spec and ok.

I'm thinking the dme is fried, but hoping otherwise.

[jlevie]

Because it is hidden in PM's I'll repeat what I said earlier today for the general benefit.

The coil negative being grounded all the time could be a shorted coil, a shorted output section in the DME, or a short in the wiring harness. If the ground goes away when the coil is disconnected, the coil is bad. If the ground goes away when a different DME is swapped in, the DME is bad. If neither of those have an effect, the harness has a short.

The DME briefly grounds pin 1 based on data from the CPS when the engine is rotating.

[frontin540i]

Just so the solution is posted, when i extended the ignition coil wires i neglected to cut back the shielding wire. This caused the circuit to stay grounded at all times. Cut the shield wire and it was fixed. Big thank you to jlevie for the help.

[Digitalwave]

Bringing this back from the dead as I had the same issue. I did an M20 swap and extended the coil wires from the harness (to relocate the coil). I was not getting spark. Sure enough, I had soldered the shielding wire as part of my connection. Redid the connection and the car fired right up.

The thing that tipped us off was the coil was getting REALLY hot.

Hope this helps someone!