E30M30: No Power at ECU pin 18

[AndrewGood]

Hi all,

I have a no spark & no fuel problem with my E30M30 swap project. The car is a 1987 325is, with a E34 M30, a '88 M20 harness, and a #173 ECU. In an effort to solve my issue, I went ahead and followed along with Jlevie's diagnostic test. Everything was looking good until I reached the step stating:

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

At this point, I ran into some trouble. I was using a multimeter, and to be perfectly honest, I wasn't exactly sure how to complete this step. With the positive cable of the multimeter "plugged" into pin 18, and the negative cable grounded to the valve cover I got around 0 volts DC. I then disconnected the main relay and plugged the positive cable of the multimeter into both of the Main Relay pins 86 & 30, with the negative cable again going to ground on the valve cover. Now my main question is this:

Is this an issue of human error or is there actually an issue related to pins 18, 86 & 30? Am I doing these tests with my multimeter incorrectly?
Any help is greatly appreciated, I have put so much time and effort into this project, and I just feel like I am so close!

Thanks,
Andrew

[AndrewGood]

Bump

[Digital]

You are using the multi-meter correctly, Have you tried any other grounding points, the one I use is on the passengers shock tower. If there is still no voltage there try locating the fuse-able link near the battery.

[AndrewGood]

Ok, phew!, good to know I'm using the multimeter correctly! I checked both fuse-able links by the battery and they both looked ok and I have been grounding my multimeter to the passenger shock tower at the same point the wiring harness is grounded to. It seems to me that the issue is that my ECU isn't getting switched on by the main relay, or isn't getting 12V from the battery. Faulty Main Relay perhaps? How do I test that? What else could I be testing for? I've read that when functioning properly and receiving power, the main relay and the ecu should "buzz" when the key is in the second position. Is this true? They certainly do not buzz in my car, so maybe this is another indication that they aren't getting power?

[AndrewGood]

Another quick update:

I double-checked the fusible link, and it is good. I used my multimeter to test the wire at the passenger-side firewall in the engine bay and got 12V. I also pulled apart the shrink wrap and used the multimeter to test both sides of the fusible link-- 12V both sides. What can I be missing? Headlights, windshield wipers, gauges, etc. all work. Engine cranks strong. Could it just be a main relay problem? I have two and have swapped both in. I appreicate any help! I'm struggling with this and feel that I'm so feaking close

[AndrewGood]

Just to help clarify:

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

Ok, I have 12V on Pin 27, and 0V on pins 18 and 37

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 to 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.

Ok, this all checks out. Multimeter read "0.2 Ohms".

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 540-540 when a ferrous object is brought to the face of the
sensor. Neither pin should be grounded.

Multimeter read around "500 Ohms" which falls within the acceptable range

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

Both read "0.2 Ohms", still looking good at this point.

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.

Here's where the trouble starts. All of these came back with "0V". I started looking for reasons why the ECU and Main Relay wouldn't be getting power and discovered the common issue of a blown fusable link. I thought my problem might be solved, but I'm getting 12V at the end of the wire in the engine bay. So now, I'm not sure what to check next.

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.

Curiously, DME pin 27 is getting 12V, while pin 18 has 0V.

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.

Coil positive has 12V, Fuel pump relay pin 30 has 0V.

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 batter 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.[/B]







I've done all of this in an effort to make my situation understandable to all you guys. I really am working so hard, but I am still in high school, so granted my knowledge has its limits. I really am hoping someone here can help me!!

[Digital]

you can try jumping your main relay, remove the main relay and insert a jumper wire that goes into 30 and then to both of the 87 terminals

[EatsHondas]

12V at the junction block and not at the main relay/pin 18 means you have something cut or unattached in between there and the ECU. As you can see from the diagram, pin 18 is connected directly to the battery through the junction block. There are no connectors between the fusible link, ecu, and main relay. You may be chasing a damaged wire.

G### are ground designations, S### are splices, and C## are connectors. The small numbers at the end of wires are pin numbers.

[AndrewGood]

Ok so maybe I am missing something here. Right now in my car, if I start from the battery, the wire runs from the positive terminal, to the fusible link, to the junction block at the engine bay. At the junction block, the wire is just bolted down to the block. I don't see where it continues on to the Main Relay. Now if I follow the wiring from the main relay, it seems to directly go to the ecu connector. I cut back some of the shrink-wrapping and the wiring did indeed seem to lead directly to the ecu connector. Is this correct?

[AndrewGood]

Quick Update:

While looking for a way to connect the battery to the main relay, I saw a connector that I had previously thought to have been a ground. I had it grounded to the valve cover, but upon inspection I noticed it did run to the main relay. After cutting back some shrink wrap, I saw that the connector was about 5 red wires bundled up. I thought it might have been the power connection for the relay, so I connected it to the battery junction with the smaller wire from the fusible link. When I went to crank the car, it cranked very slowly like it was struggling. When I stopped cranking I noticed smoke from the engine bay. I discovered that the wire running from pin 87 on the main relay had burned through all its insulation. I believe pin 87 is power output for the fuel pump relay right?

Regardless, thought I'd share this as it may help

[EatsHondas]

If I start from the battery, the wire runs from the positive terminal, to the fusible link, to the junction block at the engine bay. At the junction block, the wire is just bolted down to the block. I don't see where it continues on to the Main Relay. Now if I follow the wiring from the main relay, it seems to directly go to the ecu connector. I cut back some of the shrink-wrapping and the wiring did indeed seem to lead directly to the ecu connector. Is this correct?

Almost. When you arrive at the junction block, you're still dealing with constant (unswitched, always hot) battery voltage. Never ever ground a 12v source with no load (i.e. the component in the circuit you are trying to power). This is called a short circuit and will damage your electronics. If you saw smoke, that's probably what happened. Since there is negligible resistance in a short circuit, the amperage you draw is theoretically infinite (i.e. voltage = current * resistance) and will burn up your wiring.

If you followed main relay wiring that led to the ECU connector, you traced either pin 85 or 87. Your problem is no voltage at pin 18, and the two supply pins for the main relay, so I think your issue lies with connections at the junction block.

You know how to do a continuity test with your meter right? That's the best way to see what wires run where. When you hook both leads to the opposite ends of a wire, your meter will beep to tell you that there is continuity between your two probes.

Quick Update:

While looking for a way to connect the battery to the main relay, I saw a connector that I had previously thought to have been a ground. I had it grounded to the valve cover, but upon inspection I noticed it did run to the main relay. After cutting back some shrink wrap, I saw that the connector was about 5 red wires bundled up. I thought it might have been the power connection for the relay, so I connected it to the battery junction with the smaller wire from the fusible link. When I went to crank the car, it cranked very slowly like it was struggling. When I stopped cranking I noticed smoke from the engine bay. I discovered that the wire running from pin 87 on the main relay had burned through all its insulation. I believe pin 87 is power output for the fuel pump relay right?

Yes those bundled red wires are a splice that should be powered, not grounded. Red is never ground, brown usually is. Never guess though, always check. Can you post some pics of your junction block wiring? It's weird that your having this problem. The wiring that you are troubleshooting does not need to be modified between the M20 and M30.

[AndrewGood]

Ok, I'll post a photo of my junction block wiring later today when I get a chance. I have most of the shrink wrap removed from the wiring harness, so I'm hoping to figure out which pin/wire on the main relay is supposed to be supplying power, and then I'll trace that wire back to figure out where I'm losing the 12V from the battery.

[AndrewGood]

here are the photos of the battery junction

[AndrewGood]

Another update:

I decided to bolt the bundled red-wire connector to the main battery cable at the battery junction. I tried to start the car, but had no luck. However, when I went back to the engine bay, I saw fuel seeping out from the fuel pressure regulator on the fuel rail. Did I "jump" the fuel pressure relay by connecting it directly to the battery cable? At the very least, I now know that my fuel pump is good, but I'm not sure what to make of this.

[EatsHondas]

Fuel out of the FPR is bad. Replace her.

No you can run the fuel pump with the engine off and you should hear gas moving through the lines. In order to jump a relay, you must connect the high amp power and ground pins to each other. This lets power flow the way the relay would if it were in its socket and energized.

Your photos do not work by the way.

Did you make sure to connect all the wires to the starter (There are 4)? One of those smaller wires is to power the unloader relays, which are extremely important. Did you make sure to ground the engine? If you do not have a ground strap from the engine to the chassis, you need one.