1983 944: No power at coil.

[DeadPorsche944]

Hi all, another 944 that won't fire thread. :-)

I am not getting 12V at the coil, 2.8V. Consequently, no spark. I used the Power Probe to force 12V at the coil and I get spark. Where does the 12V at the coil come from? The ignition switch? Is there a fuse I could have blown?

I've jumpered the DME relay to make sure that is not an issue. A nice wiring diagram would help too.

[v2rocket_aka944]

The black wire runs from the ignition switch, through the Central electric panel and out to the coil from there. If the key is on there should be 12v at the coil.

Try running a new wire (or using jumper cables) from the battery positive directly to the + post on the coil and see if the car starts.

I was getting very low V at the coil (might have even been 2.8 or so) and it turned out to be my original black wire had burned its pin socket in the CE panel so was making spotty contact. I ran a new wire and all has been well...

[jcommin]

I'm presuming you check the coil. That would have been my first thought. I just had this problem over the winter-no spark. Using a multi -meter, the coil was bad.

[DeadPorsche944]

Originally Posted by v2rocket_aka944

The black wire runs from the ignition switch, through the Central electric panel and out to the coil from there. If the key is on there should be 12v at the coil.

Try running a new wire (or using jumper cables) from the battery positive directly to the + post on the coil and see if the car starts.

I was getting very low V at the coil (might have even been 2.8 or so) and it turned out to be my original black wire had burned its pin socket in the CE panel so was making spotty contact. I ran a new wire and all has been well...

Where did you run it from? I know it needs to get to the terminal" the coil where the black wire is, but where in the wiring harness, in the driver's footwell does it go? I'd like to make sure the coil is only energized when the key is in the correct positions.

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[DeadPorsche944]

On a side note, does anyone know the conditions that the DME uses for when to turn in the fuel pump and when to allow spark?
For the fuel pump is it: must see reference & speed sensor, & (fill in with what else must happen) and then the DME will turn on the fuel pump.
For spark, reference and speed sensors, & (fill in the rest) & you will get spark...

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[v2rocket_aka944]

the black wire starts at the plug on the ignition switch.
i removed the original wire/pin socket from that plug and put in a new wire which i ran all the way from that plug out to the coil, through the firewall and around the engine..

DME needs both speed and reference sensor signal working, once DME has power from the key on (via DME relay) and you start cranking the engine, when engine rpm exceeds 200 or 300 (dont remember which) rpm then the DME triggers the fuel pump side of the DME relay to close which powers the fuel pump. the "reference" sensor counts RPM (and tells the DME the engine is at top-dead-center) and the "speed" sensor counts flywheel teeth for accurate spark timing.

all that happens in milliseconds when you turn the key into cranking position.

[DeadPorsche944]

Originally Posted by v2rocket_aka944

the black wire starts at the plug on the ignition switch.
i removed the original wire/pin socket from that plug and put in a new wire which i ran all the way from that plug out to the coil, through the firewall and around the engine..

Excellent, thanks. I'll first just jumper the coil to 12V & see that it runs.

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[DeadPorsche944]

Ok, jumped the coil to the battery at the black wire and the car starts right up and runs.

I pulled the DME and probed the black wire as it leaves the switch. It reads 12V when in the start and run positions and ground when not. Does this wire go through any other connectors?

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[DeadPorsche944]

Note: I pulled the DME so that I would have access to the ignition switch.

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[DeadPorsche944]

One other note: the black wire that goes to the coil is in a harness that goes to the head light motor as well. If I shake this harness while it is plugged into the headlight motor, I hear a clicking in the car, some relay I assume. If I unplug the connector and shake the harness, no clicking. There is 12V on 2 of the pins in this harness.

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[DeadPorsche944]

Electrical Gremlins... I shook the harness behind the fuses and suddenly I was getting power at the coil. Hmmm. So I removed the jumper on the DME/Fuel pump and turned the key. Car started right up and ran. Then I turned the key to the off position and it would not stop...

I disconnected the battery to stop the engine.

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[DeadPorsche944]

I took the car for a drive and it felt like it was missing a lot of power. I didn't go much past my driveway because I wanted to make sure I could get back to my barn. :-) I once again had to disconnect the battery to stop the car. I hate 30 year old wiring...

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[v2rocket_aka944]

Key off engine keeps running should be faulty ignition switch.
Luckily on your 83 model it is a very easy swap and only about a $6 part.

The clicking you were hearing was probably the relay on the headlight motor, the little plug at the headlight motor doesn't "grip" very hard so it's likely the harness-shaking was making/breaking contact enough to click the relay.

Disconnect the battery.
Assume the fuse-panel position (head at pedals, ass in seat, feet in trunk).
Reach up behind the fuse block with one hand and feel for the 5 (or 6? don't recall) large electrical plugs at the back of the fuse/relay block. With other hand hold the relays and stuff still.

From the back push the large electrical plugs towards the rear of the car to try and re-seat all the pins/relays/etc...sometimes they can wiggle loose.

[DeadPorsche944]

I had some time last night to work on the car. I found that no matter what position the ignition key was in (or if it was even connected), there was power at the DME relay for turning it on. I'm going to snip this wire and run a new one from the switch.

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[v2rocket_aka944]

which pin had power no matter what?

[DeadPorsche944]

Pin 86. I snipped it at the relay and ran a new wire from the ignition switch. Everything works fine now.

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[DeadPorsche944]

Ok, I thought everything worked fine. Power is now properly getting to pin 86, but the fuel pump is now not turning on. Ugh!

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[DeadPorsche944]

I have power to the DME, but not to the fuel pump. The DME/fuel pump relay does not seem to work or the ground side supplied by the DME is not good enough to turn it on. With the DME/FP relay jumpered, the car starts right up and runs fine.
With the relay in, putting in the key and turning one click (run position), power goes to the DME, but not to the fuel pump. The voltage on the gnd side of the relay reads 7 volts (85b from relay diagram above). Turn the key and it drops to 0.4V. However, the relay does not turn on, supplying 12V to the fuel pump. With the key in the run position, grounding the gnd side of the relay (85b) turns the fuel pump on. Trying to start the car (turning key to start) while forcing the relay does not start the car. I may have not been supplying a good gnd, trying to do all this by myself.


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[DeadPorsche944]

I will try tomorrow to reseat the connectors at the back of the fuse panel. Is there an exploded view of that anywhere?

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[DeadPorsche944]

Bu the way, the lack of power turned out to be 2 clogged fuel injectors. Cleaned them out and she runs great again.

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