MyE28.com

Hello.
need your help before i send car to the scrap yard. bad joke..
SOO swap from 1.8i m10 to 528i all. good. lot of work but worth it
after few days came the starting day .
12 v on injectors on both wires .no ground ,no click, no open injector.. have fuel, have spark..runs 1/2 seconds and then stop. start again.. run again 1/ 2 seconds and stop and soo on
i use start fluid... works as long as u give him fluid..
i ve read on forum... but mostly have same problem on original m30 cars from factory.this one is swap and could have something i dont know
i changed 5 computers. nothing. fuel pump new. pressure regulator new. injectors cleaned and tested. still nothing
my question is... is there another relay on the car that 518 dont have it and it s controlling the ecu??
i have put the engine with all original wires from donor car.. just plug in the original 518i fuse box. could be one wire that is not corect or is another relay that comands ecu ? soory about my english.hope you ll understand
thank you very much

This is not specific to your car but... Normally the injectors get grounded by the DME when it pulses them. There should be constant 12v on one side and the 12v you measure on the other side is present because the injectors are relatively low resistance. So ONLY when the DME pulses the injector will there be some voltage approaching 0v (not quite the same as ground) on one side of the injector. The DME is in the path to ground and I believe is what is called a current sinking device. Energy flows or gets pulled through the injector to the DME. The coil works similarly. This pulse of current is very rapid and cannot be easily read with a basic meter. You need a scope or a noid light to see it.

So best guess is that the ground path between the battery, engine and DME is not so good. Perhaps the DME is trying to complete the circuit to fire the injector but not enough current will flow. Most of these cars had an extra ground strap from the engine to the firewall near the DME (glovebox are) but even that might not help if the DME is not well grounded to the body. Maybe put a ground jumper right on to the DME and it's ground strap if it has one. There is also normally a whole batch of ground wires that get attached to intake manifold stud or similar on the engine.

You should be able to find the schematics for your specific car on Wedophones and see how it is all wired and works. If you have a cold start injector it may be running that 1/2 second just on the fuel supplied by the cold start injector. That injector is NOT grounded through the DME and simply finds it's ground path at the engine and the 12v is supplied when key is in start.

thank you. will try find and fix the ground.. next week wii do that and write back to let you know.