Non starting

Re my 1975 3.0si. A few weeks ago i was just coming off the motorway when the engine cut out,i tried to restart it ,it cranked over but would not fire.I took out one plug and it was dry ,no fuel .10 minutes latter it re started ,drove another 5 minutes to a petrol station filled up and drove off for anther 5 minutes and it cut out again.I then waited ages for a truck to take myself and he car home.Of course once home the car restarted and i drove it into my garage.At this point i thought maybe my 2K fuel pump relay might be faulty so i swopped it for my old one ,the car drove ok for about three weeks ,then i went to take it out and the engine cranked over but would not start.Im not good at car electrics,but upon checking i have power the the centre of the relay ( when the ignition lights are switched on ) but the pins 87 are dead.ie the ones which supply the cold start and pump.Ive tried a brand new original relay and nothing on 87.Being one of the last Djet cars ive noticed unlike in the factory manual there is no separate earth wire running to the pump relay fixing screw.Ive also just seen hidden high up behind the fuse board a small relay Bosch 0332014406 This for sure has never been replaced ,could this be the issue ????? Look forward to your knowledge to sort this hopefully .

Hi Unknown,

would be great if you could sign by firstname so that we can address you.

A 3.0Si is very rare these days. Mostly only 3.0 CSIs have survived. Did you hear a hissing sound from fuel pump when you turned your key to ignition? And if not, can you measure pin 19 to +12V by a voltmeter and tell us what happens when car stalls and if you apply gnd to this pin 19?

Hi from Nigel,No there is no hissing as there does not seem to be a supply to the pump.Where is pin 19 ? What is that relay for i mentioned?

Hi Nigel,

pin 19 is on the ECU contact plug. There are 24 contacts, contact 25 is free. Contact 19 is for fuel pump control. It sends ground to fuel pump relay. When fuel pump relay is active, it sends +12V via contact 87 to fuel pump and to the relay for activating cold start valve. The relay you mentioned is a general 30A relay. It should be the one activating cold start valve after starting engine.

BMW has a specialty: Cold start valve is used for after start enrichment. Other cars handle that via longer injection pulses. BMW uses cold start valve. In detail: Normal cars activate cold start valve only while cranking engine and if thermo time switch is active. In BMW cold start valve keeps ativated as long as thermo time switch is active, even after engine has already started.

Now you should find out what happens in your car exactly. By the way you first should verify whether the separate cable from battery plus to main injection relay is tightly connected to battery plus pole. You will see that on contact 16 and 24 of ECU. ECU should activate fuel pump via relay via applying ground to contact 19.

Thank you,sorry but how do test pin 19 ? i cant connect onto the long block which joins the ECU,So is this cable 19 on view going to the pump relay ? Same pin 24 ? sorry as i said electrics are not my skill.Yes my SI is rare its been on display twice at Techno Classica Essen.The battery connections are very good.I forgot to mention i did try my spare ECU which i last tried maybe three years ago .I did not drive the car but just to compare the CO readings on my drive .The car ran ok with it.So with my spare the same problem.

The small 30 amp relay seems strange as there is already a cold start relay in the engine bay next to the main relay!

Hi,

contact 19 goes to contact 85 of fuel pump relay. If you do not know how to handle a multimeter: Then you cannot diagnose D-Jetronic.

If you say that this fault does not happen with another ECU: Then you know that your original ECU is broken. But you can also diagnose the way I showed: Connect ground to contact 19 and see if that lets your fuel pump run continuously.

Hi from Nigel.The white cable marked 26 going to pin 87 on the pump relay ! I pulled the plastic connecter down slightly and touched 87 pin with a test light and nothing ,this is with the ignition on.Note pin 30/51 is live. I then tried a bridging wire between 30/51 and 87 nothing again ,no sound from the pump..The main relay is new and the cold start has has only covered low miles.The pump i fitted March this year a new and original bosch version for these cars.