Non starter

[DoubleHelix]

My 1989 318i (M40 engine) would not start this morning. It turned over but would not fire. I got a lift to work and tried to get it running tonight.

I did run for a short time (maybe 30 seconds) after a few attempts, but it would not idle and eventually cut out. We had squirted damp disperser on all of the ht leads etc and easystart into the air inlet. The plugs did not appear to be wet, so maybe no fuel is coming through, but we also seemed to be getting an intermittent spark. Strangest of all, when the ignition switch is in the on position, I can hear what sounds like a relay chattering under the inlet manifold, so I assume that must also be some sort of short.

What could account for all of these symptoms? - is the ecu knackered?

I am a relative novice in this type of business, so any advice would be most welcome, particularly on what to try next.

Thanks

[Brianmoooore]

Can be many reasons why an engine won't run. You have to go through them and eliminate them one by one.
BMWs are rarely affected by damp ignition, and ECU failure is rarer again, although running with a plug lead off can cause a flashover in the coil that has been known to kill the ECU.
Chattering noise is probably the idle control valve doing what they do.
Fuel pump would be my first guess.
Take the fuel hose off that comes from the fuel filter, and stick the end in a container.
Take the cover off the electrics on the bulkhead, find the orange relay, pull it out, and short together pins 30 and 87 of its socket. This should make the fuel pump go and pump fuel into your container.
If this is OK, put the pipe back on the engine, put the link in place again and try to start the engine.

Next test is to remove the wire link, leave the relay out and take a sparkplug out, put its lead back on, lay it sideways on the rocker cover, and crank the engine over. The plug should give a good strong spark once every two turns of the engine.

[DoubleHelix]

Thanks for the suggestions

I got my local garage to look at the car today. They checked out the fuel pump and it was okay. Also the ignition components were in good order. Their diagnosis was a problem in the ecu or sensors and to take it to BMW. This car has a borderline value and a visit to a main dealer could push it right into the red.

Any suggestions as how to proceed??

[Brianmoooore]

There's only one sensor that will really stop the engine from starting, and thats the crank position sensor.
A dud one will give no sparks or fuel injection. An iffy one sometimes gives a weak intermittant spark