Big wiring problem (engine swap)

[danval]

Hey there. first of all, i started this thread in this section because it has to do with the engine harness most of all, so i wasnt sure if do it either in the electrical (stereo) section or engine swap (heavy duty stuff) section. So, i think is more general technical topic.. anyhow..

Ive been going through a lot of diagrams, my head is seriously about to explode. i have a 1975 530i and i did an m20b27 "i" head engine swap in it. i have the Motronic 1.3 (325i, 325is, 325ix) later model 173 bosch 0 261 200 380 ECU.

What im really trying to attemp is to tap the engine harness (e30) with the original (e12) harness.
So far ive tapped or connect the following
Start wire from ignition switch (black yellow e12)
start/run wire from ignition switch (green e12)
alternator (blue e12)
fuel pump (green/violet e12)
temp sensor (brown/white e12)

When i go to give it switch nothing really happens, i just hear a relay click in the power/relay/fuse box.
I guess my question is what is the very very basic that i need to connect to on the motronic (e30) harness so it can run/drive. I really dont need anything else than just being able to drive, the very basic.
Im not really that knowledgeable when it comes to wires and ecus, but im really trying here. I already went through the e30 harness diagrams, so is not that i havnt seen them, and the e12 diagrams are very very hard to find, a guy wanted to sell me a manual in german and wanted $150... hmmm no thanks..
Thanks in advance and hope to get a couple of pointers. Anything will help. :-?

[jlevie]

It sounds like the starter doesn't engage when the key is turned to start, which means that the starter isn't grounded, that it isn't getting primary power, isn't getting the solenoid control signal, or that the starter is bad. The first task would then be to diagnose that problem. Once that is dealt with the next task is to make sure that the DME gets all of the inputs it needs. The following will help:

For the engine to run the following conditions must be met:

Power on DME pins:
27 Start Input
18 Un-switched Power input
37 Power Input from Main Relay

Ground on DME pins 2, 14, 19, 24

Timing data from the CPS on DME pins 47 & 48 from a rotating engine

To have spark power must be present at the coil positive and ground pulses
from the DME's pin 1 must reach the coil negative. Power to the coil is
controlled by the ignition switch via C101. When checking for spark, use the
output lead from the coil to eliminate the distributor, rotor and plug wires.

To have injector firing power must be present at each injector and ground
pulses from the DME's pin 16 (Bank1) and pin 17 (Bank2) must reach the
respective injector bank. Note that the injectors are wired as two banks of
three. With cylinder 1,3,5 being bank 1 and 2,4,6 being bank 2. Power to the
injectors is controlled by the main relay. Injector firing is best checked
with a noid light.

The fuel pump relay must have power on pin 86 (relay coil) from the main relay
output (pin 87) and power on pin 30. The DME will ground pin 85 to turn on the
relay and power the pump(s) via pin 87. Of the above, only the fuel pump power
is fused. So if the there's power at pin 87, but not at the pump, check fuse
11.

The main relay and DME pin 18 receive power from the smaller of the two wires
that connect to the battery's positive terminal. That wire incorporates an
in-line fuse. When the DME is presented with a start signal, it grounds the
main relay pin 85 and furnishes power to the fuel pump relay, injectors, and
DME.

Troubleshooting:

Disconnect the battery and the DME cable. Then:

1) Disconnect the coil negative and check continuity from that connector to
DME pin 1. Also verify that from DME pin 1 to ground is an open circuit.

2) Check the resistance across DME 47 & 48, which should be 500-560 ohms. If
the CPS is dismounted, the resistance can be seen to change from about 500 to
540-560 ohms when a ferrous object is brought to the face of the
sensor. Neither pin should be grounded.

3) Check for continuity from DME 36 to main relay 85 and from DME 3 to fuel
pump relay 85.

Reconnect the coil, remount the CPS (air gap should be 1mm), plug the
relays back in, reconnect the DME, and connect the battery. Then do the
following checks:

1) With the key off, verify that power is present at DME pin 18 and main relay
86 & 30.

2) With the key on, verify that power is present at DME pin 27 and pin
18. Power to pin 18 is from the main relay and there should be power to the
injectors and fuel pump relay.

3) With the key on, verify that no voltage is present at the DME grounds (2,
14, 19, 24).

4) Verify that power is present at the coil positive and at fuel pump relay
pin 30. Those get switched power from the ignition switch via C101.

The engine will start and run (if poorly) with only those connections to the
DME in place. The other signals from Cylinder ID, AFM, temp sensor, etc., are
necessary for proper operation. But they won't prevent the engine from firing.

IMPORTANT:

A power check means seeing a voltage within about a tenth of a volt of what
you measure across the battery terminals, which should be at least 12.6v on a
charged battery.

A continuity check means seeing less that 1 ohm of resistance.

An open circuit means seeing a resistance of at least 100k ohms.

A good quality auto-ranging digital multimeter will make these tests much
easier.

[danval]

Wow! Great deal of valuable info! I checked the starter black/ yellow and ot was cut at some point. Checked the fuel pump pin at dme, then main, then pump relay and foumd that pump connections weren't good. Got the car to start. It runs like crap. I guess i have to check some other stuff. I got it to start by jumping the run and start wires. It wont start with the key. Im trying to through a wiring diagram for the e21 but its kinda hard. (Low resolution internet pic). I guessi. Just gotta figure out the start relay. thanks again man!