Crank, no start - DME coil without ground

[jnreves]

After being stopped for a while, when I started my E30(318i, Motronic), after a few minutes (~15) it suddenly stopped.
The main "symptom" I first noticed was the pump no working when I tried to start it.
After following this video: https://www.youtube.com/watch?v=AjOHHBVaBqY and this post:https://www.r3vlimited.com/board/for...i-master/page2 (and following the appropriate diagrams) I noticed that something was wrong with my DME relay. I tested the relays with a battery and a multimeter to verify they work.

In the relay's coil, I should be getting 12 V between 85 and 86 and in order to trigger the relay. Although I do have 12 V in pin 86 (straight from the battery) I don't have ground in pin 85 - I have around 6.5 V.

I also tried to bypass the relays, by bypassing both DME and Fuel Pump relay with a piece of wire. The fuel pump works this way but the car still doesn't start.

Could this mean my ECU is not working properly? Can I perform some extra test to verify before I buy a new one?

Thank you for your help in advance!

[venerated]

Which book/page did you get that diagram from? I don't think it's the right one for a 318i.

In that diagram, 86 is not coming from the battery, 30 is.

There's lots of other tests you can do, but let's first make sure you're looking at the right information for your car.

[jnreves]

I used the BMW Electrical Troubleshooting Manual for 318i/is/ic and this diagram is found on page 1360-1 (the first one on Fuel Injection). I am fairly new to car's electrical diagrams so you might be right regarding the manual!
Pin 86 in fact comes from the connector, what I meant is that it should be the battery's voltage, right?

[venerated]

I'm not 100% sure if 86 should have the battery's voltage.

The relay should be triggered by connecting 30 (+) and 85 (-), it seems. So have you measured for voltage across those two? When you checked 85 for voltage, what did you use as a ground?

Are you 100% sure the fuel pump isn't working with the relay connected and trying to start the car? Have you tried disconnecting one of the fuel lines and cranking the car to see if fuel is being pumped?

Have you checked for voltage at the ignition coil? Asking cause these are probably easier tests to start with rather than going straight for troubleshooting the electronics.

I've been chasing a crank/no start issue in one of my E30s for the last few months and have made many mistakes/thought I found the issue multiple times, only to realize I didn't, so I'm trying to put you on the easiest path forward.

[jnreves]

Since pin 86 is connected to a junction block and a connector, I assumed there wouldn't be any voltage drop or logic to switch in the voltage supplied by the battery, but again, I might be wrong...

From what I gathered, in order to have the switch on pin 30 and 87 switch ON (thus connecting the Battery Junction to the Fuel pump pin 86), there should be 12 V between pin 86 and 85.

The fuel pump is working with the relay bypassed, I have removed the fuel hose and gasoline shoots out of the tube. But with the relays in the car, the pump doesn't switch on. What I haven't had the opportunity to test is if the injectors are working...

Yes, there is voltage on the igntion coil and also spark.

This has been a frustrating journey but I am also learing quite a lot!

[ADEN]

Just a tip that might help you: The car won't engage/prime fuel pump nor pulsing injectors if ecu didn't see a crank sensor signal.