No spark

[yetta]

I broke down for the first time after 20 years ownership of my 1990 E30 320i SE. There is no spark, the RAC checked and changed the coil temporary to no avail. The petrol pump works on cranking. I have checked the coil and tomorrow will remove the distributor cap to inspect any issues there, any help as what to check next would be appreciated Thanks.

[Brianmoooore]

Exact model of car?

[yetta]

1990 3 series 320i SE 2 door saloon M20 engine Motronic system

[Brianmoooore]

Right, that rules out it being any of the weirder, and more primitive, earlier versions of an E30 engine.
The first thing to do is to connect a spare spark plug directly to the coil king post, to see if there's any spark there, which, if there is, would imply a distributor fault.
Assuming there are still no sparks, connect a small 12 volt lamp between the + terminal of the coil and a good body earth, and check that it remains lit while cranking the engine. I would have expected the RAC man to have already done this, but I can't assume that.
If all is good here, the chances are that it's the crank position sensor at fault, unusually putting out enough "noise" to activate the fuel pump, but not enough distinct pulses to produce sparks.
Failing that, it's likely to be an ECU fault. Very unusual, but it's not unknown for the coil driver FET to be 'spiked' by a high voltage pulse from the coil.
Could also be worth checking for continuity of the lead from the - terminal of the coil (disconnect it) to pin 1 of the ECU, and to check that it's not shorted to earth (it's a screened wire, with an earthed screen around it). This wire also branches to pin 1 of the diagnostic socket.

[yetta]

Sorry for delay in getting back to you on this issue. I am about to check the cable from ecu but cannot work out how to remove the connector plug without causing damage. There is a lever that I have pulled and the plug has started to come out at an angle. There looks like clips on the right hand side does the plug pull straight out or pivot on the corner clips?

[Brianmoooore]

Plug come out at an angle. Release lever, lift plug clear of pins, then pull towards the end the cable goes in - there's a plastic lug projecting from the fr end that fits into a slot in the socket. It's easier to remove if you unbolt the ECU from its bracket.
The pin numbers at the ends of the three rows are marked in the socket of the ECU.

[yetta]

Thanks. Plug removed and tested continuity on cable okay. No short to earth. thought it may be the aftermarket immobiliser but first look at the cables they seem to isolate the starter motor and ignition lights and they all work when operated. No sign of shorting out the neg side of the coil.
So far all tests carried out, replaced rotor arm, dizzy cap, plug leads, new coil, fitted new pulse sensor, cleaned and checked all spark plugs. Just out of interest one of the cables connected to the immobiliser is a black/yellow cable and is the only one that I dont know where it would go if I removed the immobiliser,

[Brianmoooore]

Just one black/yellow connected to the immobiliser?? Black/yellow is the start signal from the ignition switch to the starter motor solenoid.

[yetta]

Now I have pinned all wires, and its not the immobiliser it may be the ECU. I did buy one on e - bay but when it arrived over a week later it wasn't the one I picked and bought which matched my faulty one. Had to send it back. What numbers have to match to be compatable with my 320i ECU. ie Bosch white numbers on green lable and large numbers and small numbers under scan codes white lable. Thanks

[Brianmoooore]

The first thing to do is to connect a spare spark plug directly to the coil king post, to see if there's any spark there,

Have you done this?

[yetta]

Yes did all tests you suggested. Couldnt see a good spark so tested coil on bench all ok but fitted replacement coil , ignition leads ,rotor arm dizzy cap & Pulse sensor pinned out cable to coil replaced main relay. Still no spark at plugs so I am not sure of what next. ECU is still out of car at moment have to pick my time to work on it as car is outside in the drive.

[yetta]

Success ! I just got my replacement ECU after a lot of delays, went out in the snow plugged it in, first turn of the key and she started first time. What a delightful moment. Many thanks Brian for your patient help with something that was out of my comfort zone. Best wishes Yetta

[Brianmoooore]

A faulty coil, sending a few thousand volt pulse back the lead from the ECU, is one of the few things that can damage an ECU. Very unusual, but since you've changed the coil. I'd leave the replacement fitted.