M20B25 Ignition Problem

[priddin]

Alright i bought my 325ic taken apart and have been putting it back together based on what the Bently has told me. I purchased all new wearable parts from pelican to rebuild it right. I have a new timing belt that has been timed correctly and put on. New Water pump, New V belts, New Cap, Rotor, and Plugs. Took the head to the machine shop got it all cleaned and reassembled and All new gaskets for everything above the block, including head-gasket.
Well now i am at the point of starting it and i cannot get it to catch. Now i know you only need 3 to get an engine to work so lets start there.

1. Compression, this is fine getting power from each cylinder.

2. Fuel, I pulled the fuel pump relay and saw that this was bad so i then jumped it and can hear the pump running and feel the fuel hose and return hose coursing with gas.

3. Spark, Here in lies the problem. So at first there is no spark at all coming from the wires. I then traced that back to the Cap, I pull the feed line from the coil, no spark at all when cranking. I was told by a buddy to jump the coil itself, when i do that there is an interesting humming coming from the interior almost like the car is starting with the key on but not cranking though slightly different. Then when i crank the car with the coil jumped i get spark from the feed wire. So i can deduce that the coil is at least somewhat functional enough to start the car at least. then i plug everything back in and try to crank the car but no spark from the wires. Im thinking maybe the wireset is bad since i didnt replace that new. But what could be causing the coil not to spark on its own to begin with?

[MTechnikII]

how do you jump a coil?
if you did what I think you have , (connecting a + wire to the coil), you might have fryed the ECU,
also check the timing gear for the spark and the sensor on it, the gear is the one that goes behind the crank pully and there is a sensor close to its teeth.
Henry

[CorvallisBMW]

^ agreed. The pulse sensor on one of the spark plug wires (#6 I think) and the crank reference sensor both plug in near the diagnostic port. It isn't hard to get them mixed up and plug them in wrong. Check those connections.

[Cabriolet]

^ agreed. The pulse sensor on one of the spark plug wires (#6 I think) and the crank reference sensor both plug in near the diagnostic port. It isn't hard to get them mixed up and plug them in wrong. Check those connections.

did this exact same thing when i put my engine back together.

[priddin]

^ agreed. The pulse sensor on one of the spark plug wires (#6 I think) and the crank reference sensor both plug in near the diagnostic port. It isn't hard to get them mixed up and plug them in wrong. Check those connections.

Yes they use the exact same plug and plug in the same port, and i have been trying everything to start it then switch it and start it again, it seems to me that something has to be off cause its not wanting to give spark.

And you can hook up a positive and neg to the coil and it will not fry your ecu that is how a coil is run, you're just cutting out the trigger.

[Jean]

The spark plug id/impulse wire is not required for the engine to fire/run.

Confirm CPS and DME are ok.

[jlevie]

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.

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 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 0.040"), 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.

[BronzitCab90]

^ Jlevie and his start guide to the rescue! Actually to test the coil all u have to do is ground the neg side for a moment to fire it. That's how the DME fires the coil.

[priddin]

you guys are awesome i will be checking this all out here in the next coming days

[Jean]

jlevie should be a mod of the technical section :)