Is the DME toast?

[fatsooo]

I put in my subwoofer system, and tried to power it off the power distribution block in the engine bay (behind where the battery would ne if it was in the bay, I couldn't figure out how to branch power off the actual battery due to lack of connectors and the fact that terminal nut is stuck. I've tried everything)

Anyways, got it connected everything worked great then the car wouldn't start. No power at the coil. Also tested battery, full charge.

What makes me think it's the DME, the check engine light doesn't illuminate when then key is in the "on" position. I tried resetting the DME using a method I read on another forum by turning the key to position one and disconnecting the battery. Still no dice

Another side notes: I did disconnect the battery while doing work and I did try starting while the sub system is disconnected, nothing
Checked cap and rotor all good


Cliffnotes:
Installed sub system
Car cranks but doesn't turn over
No power at coil
No check engine light when key turned to ON position

89 325is (only running a week after being worked on for 9 months!)
173 red label if it makes a difference

Thanks in advance!!!

[jlevie]

Did you tap power off of the lug where the small wire from the battery connects? That wire powers the engine management and the wire has a fusible link. The audio stuff may have overloaded the circuit and blown the fuse.

[fatsooo]

Did you tap power off of the lug where the small wire from the battery connects? That wire powers the engine management and the wire has a fusible link. The audio stuff may have overloaded the circuit and blown the fuse.

At first no, later yes. Where is the fuse located so I can check that?

[jlevie]

The fusible link is a bulge in the small wire close to the battery. To see if it has failed. check the voltage in the engine bay at that point with the ignition on. If you don't see battery voltage, the fusible link could be bad.

My fix for a bad fusible link is to cut it out, splice the wire, and mount a lug type 60a fuse between the wire and the lug in the engine bay. Use a solder splice and heat shrink to eliminate the fusible link.

[fatsooo]

The fusible link is a bulge in the small wire close to the battery. To see if it has failed. check the voltage in the engine bay at that point with the ignition on. If you don't see battery voltage, the fusible link could be bad.

My fix for a bad fusible link is to cut it out, splice the wire, and mount a lug type 60a fuse between the wire and the lug in the engine bay. Use a solder splice and heat shrink to eliminate the fusible link.

Off the top lug pictured I got 10.5 volts
Middle lug I got something like less than one volt
Battery at 11.25 volts

[reelizmpro]

Why wouldn't you just put the amp in the trunk and get power directly from the battery?

[fatsooo]

Why wouldn't you just put the amp in the trunk and get power directly from the battery?

Amp is in the trunk, couldn't take apart the battery terminal because the nut on it is stuck against the terminal itself.
I've tried for atleast an hour hour and a half over the past year to break it loose but it won't budge
Haven't found the need to place it until now lol

[jlevie]

Reading 10.5v at the DME power lead could mean a bad fusible link, but reading 11.25v at the main power lead suggests a bad connection at the battery. Well that or a dead battery.

[fatsooo]

Reading 10.5v at the DME power lead could mean a bad fusible link, but reading 11.25v at the main power lead suggests a bad connection at the battery. Well that or a dead battery.

took my battery in to get recharged at vatozone, defective battery.
will put back in car tonight and update

EDIT: will put NEW battery back in car**

[fatsooo]

New battery results

12.4 volts at the battery
12.3 volts at the junction box
Still nothing at the coil

[jlevie]

The new battery isn't fully charged. It would show 12.7v if it were, but it should still start the car. coil power is provided by the "Hot in Run and Start" circuit from the ignition switch. There are no fuses in that circuit, but on cars with the 13 button OBC the code relay is in the circuit. And if the car has a aftermarket alarm it will usually be in the circuit.

[whodwho]

Sounds like you are close, if it turns out to be a bad DME I will trade it out for a good one. ;)

[fatsooo]

The new battery isn't fully charged. It would show 12.7v if it were, but it should still start the car. coil power is provided by the "Hot in Run and Start" circuit from the ignition switch. There are no fuses in that circuit, but on cars with the 13 button OBC the code relay is in the circuit. And if the car has a aftermarket alarm it will usually be in the circuit.

Hm what about the no check engine light illuminating with the key to the on position ??

I have the 13 button OBC but I didn't put in a code before working on it
And no aftermarket alarm

[fatsooo]

Any ideas people?

I want to start testing to see if I'm getting power to and from the DME
Anyone know which pins I should be testing?

[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. 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.