1986 325i mtech1 manual no spark!!!

[DJT]

ive got no spark (also cant hear the fuel pump when the ignition is turned on),theres power to the coil.ive changed the ecu(off ebay,so it might not be any good)! i even got a auto electrician round to look at it,he checked the reference and speed sensors on the bell housing and said they are OK.he said its the ecu!i then went and brought a cheap running 325 and changed the ecu,still nothing.
id be very grateful if anyone can help!
thanks Dan

[eko]

Brianmoore will be along soon mate,hell get it going for you(so to speak)

Welcome to the zone by the way!

[Brianmoooore]

How do you know there's no spark? At a plug lead or at the coil?
If at a lead, the spark could be going AWOL in the distributor.
Lay a plug on the rocker cover, and connect a lead from the coil centre connector to the plug. Don't run the coil without a plug connected, as it can flash over and spike the ECU.
Having said that, ECU failure is very rare. I've no experience of pre facelift stuff, but on the later cars, crank position sensor failure is not uncommon, so I would expect the same to apply to the flywheel mounted type as well, in spite of what your mechanic says.
Seem to recall that it's possible for whatever triggers the sensor on the flywheel to come loose, but don't rely on that unless someone else confirms it.

[DJT]

there's no spark from the coil lead,
he also said it could be what ever triggers the sensor on the flywheel as he's come across that before!

i will have a look at the flywheel at the weekend!
cheers

[Andyboy]

The early ECU's were very prone to failure and it also happened to the 525e with the same basic ECU (but different chip). There are two sensors on the bellhousing, one for TDC so the ECU can get a reference on when to trigger the coil and the other one is for speed so the ECU knows what speed the engine is doing and can advance or retard the timing as needed.
Job one; find the ECU and check for power at terminal 35(ignition on!). This is a red/black wire at the end of the ECU. If there is no power there, check for 12v at the 5 pin DME relay on the inner wing. It's next to the four pin fuel pump relay. You are looking for power at terminal 87 - also red/black. There are actually 2 87's but one is 87b. You want the red black wire - the white black one powers the injectors. Test for power with the reley FITTED! If there is nothing at the DME relay red/black wire terminal, test again at terminal 30 (red wire) which is the main power feed. If you have 12v there, the DME relay is shagged - pretty common. If nothing there, you have a break somewhere and to test this, run a lead from terminal 30 to battery plus - it should power up and run. Also run another earth wire from terminal 85 (brown wire) to battery earth as there could be an earth fault. DO ALL THESE TESTS WITH THE RELAY FITTED!!

If you DO have power at T35 on the ECU either the ECU is shagged or one of those sensors is down. To test quickly, locate where the sensor leads plug into the loom on the inlet manifold side of the engine side by side, and swap the connectors over. Thus the speed sensor will now be a TDC sensor albeit a few degrees out and the engine should run (badly) or at least try to fire up. If this happends you've found the problem. The TDC sensor is the bottom one with a tie wrap - remove them both and swap them over and it should run and idle okay. The resistance (if you have a multimeter) is about 80 ohms at room temp. The engine will run with a speed sensor failed (but won't rev) but not a TDC sensor. At this stage it's a good idea to buy two new ones anyway as if they haven't failed, they will.

As for the trigger on the flywheel - there is a steel tang that is very noticeable on the flwheel and you'll need to look for this. Yes, they do fall off and if it's still lingering at the bottom of the bellhousing you'll need to MIG weld it back on again!

[Gunni]

Also to note,

Check for 12v at the green wire on the coil, it is the power supplier to the coil.