Fresh rebuild, car wont start. (no spark)

[ODIN3030]

A little bit of back story: Bought this as a project car while the engine was completely disassembled and put everything back
together with some newer pistons cam and head 177k on the odometer. (Previous owner said it drove and ran before dis assembly)
Dropped the engine in and tried to crank and it wouldn't.
Took the car to a bmw shop and had timing checked and was informed my fuel pump was bad and something was going on electrically
and that’s about all I got. And so replacing parts began…

Replaced: starter, fuel pump, main relay, cps, distributor cap, ignition coil.

Now the engine turns over but it is not getting a spark.

As the car stands right now I have taken the dash out and am trying to figure out what to do next.

I am in school and this is just a hobby but I will keep the thread updated if I can get a good direction as to were to start looking next. Thanks for reading.

[jlevie]

Here you go:


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.

[paperplane94]

After a rebuild, make sure you didn't reverse the fuel feed and return lines.

my post is a smidgen compared to ^

[ODIN3030]

After a rebuild, make sure you didn't reverse the fuel feed and return lines.

my post is a smidgen compared to ^

The fuel lines are good and in the proper positions.


I am having a little trouble following the troubleshooting for the DME.
How do you check if the pin is working properly? Do you trace the specific wire?
Would I be better off swapping a DME? Or is this more of a wiring issue?
Thanks for the helpful responses thus far.
:D

[jlevie]

A continuity check means putting the meter into resistance mode, placing one lead on the pin of interest, and the other lead on the other point of interest. If the wire is good you should see close to zero ohms. The CPS test is intended to prove that the connections to the CPS are good. Those is really just a check of the wiring. Other tests in that writeup are prove that power and ground are present when/where they should be.

If all of the wiring checks out, the CPS is good, and power/ground is preset where it should be no spark when cranking has to be the DME.

[Myster-E]

Have you tried swapping the crank sensor with the impulse sensor?