Expert: Josh Fields - 9/3/2006

Question
Hi Josh.
My '86 325i has served me well for 9years  without any faults until recently. About a month ago, i was travelling to work (about 3 miles) and the engine just died on me with a backfire and wouldn't restart. I walked to work and returned 30min later. Car started 1st time and has ran as smooth as always up until a few days ago. Same thing happened again, only this time the car won't restart. There is always a strong smell of unburnt fuel.

I assumed an ignition fault and sure enough, i have no spark at the plugs. There is also no spark directly from the coil centre when cranked. I have full battery voltage to the coil at the  15 terminal to ground. The Primary tests at 0.8ohms and the Secondary 5800ohms, which varies from my Bentley book (0.5/5000) so i replaced the coil with a used one but it's resistances match my original one. The car breaker is a family friend and the coil is a known runner as the vehicle it came off blew the head.

Next, i checked the Speed and Reference sensors. Both return 970ohms so seem ok. The main relay appears ok because i have 12v at the centre pin of the idle stabilizer valve which is 0v when i remove the relay. Now i'm thinking that the ECU has gone bad but want to be sure before spending more money.

What yer reckon mate?

Answer
Birchy,
 Sorry for the late reply, I was away for the weekend (U.S. holiday today).

 Well, it looks like you have done an exceptional job thus far on debugging the electrical system.  

 You are saying that you are getting full battery voltage TO the coil, but nothing is coming out of the coil going to the distributor cap?  This is confusing to me, because if you are getting power to the coil, then it should fire!

 The ECU is likely shot, as it should break connection in order for the coil to fire, it's probably locked in the "on" position all the time, like a DC circuit, when it should function like an A/C circuit.  

 I would borrow an ECU from a junk yard or something, but beware that after 1989 the ECU's were updated.  It might still work though.

 Good luck,
 Josh