ausgeflippt951

Just went out and checked my ign coil and plug wires.

I was reading 12.36 V at the battery.

Ignition coil:

Pos-to-ground: 11.7 VDC (should be 12 VDC)
Neg-to-ground: 11.7 VDC (should be 12 VDC)

Pos-to-neg resistance: .7-.9 ohms (should be .4-.6 ohms). I am using a cheapy multimeter to test this, so when I connect the pos-to-neg leads of the multimeter itself, I read ~.3 ohms. Does this mean I am really reading .4-.6 ohms on the coil?

Output-to-neg resistance: 5.4 kohms (should be 5-7 kohms). A bit on the low side, but well w/in spec.

Is my coil bad? When a coil fails, would it be possible for it to fail intermittently, or would it just go bad 100%?



Plug Wires:

The resistances are all over the place -- what is the resistance supposed to be? I have Magnecor units.

Plug 1 wire: 2.8 kohms (note, that's kiloohms)
Plug 2 wire: 3.1 kohms
Plug 3 wire: 4.7 kohms
Plug 4 wire: 4.7 kohms

Ign coil primary wire: 1.95 kohms.



WTF? Could this be the reason for my intermittent cutout?


Help! I need to know what parts to buy (if at all)! Thanks!

ausgeflippt951

Just found on the Magnecor website the wire resistance is "2.2 kohm ft". I expect they actually mean "2.2 kohm/ft? And this would make sense, given that #4 wire is longer than #1 and thus has a higher resistance.


So then still -- does it look like my ign coil is bad?

Spidey944

The longer the wire, the higher the resistance. Some Ign coils only fail when hot, and your values look to be in spec for the coil. What is the car doing?

ausgeflippt951

The tach will zero-out and the engine will die. The car will recover w/in the same second, but sometimes it'll just die. There is no discernible pattern for hiccuping as far as I can tell.

When an ign coil fails, is it possible for it to produce my symptoms, or would it just go completely?

Spidey944

normaly from what I have found in most coils, when they get hot, they start to faulter, but will restart normaly after they have cooled a bit. I would prob be looking elsewhere if your car restarts immediatly after stalling.

Start the car and do the old wiggle test on the harness. I replaced my harness due do the fragility of the wiring causing potential issues. Start it up, and follow the harness everywhere you can and just wiggle everything gently and see if she dies on you. You are more than likely looking at an intermittant loss of connection or break in a wire somewhere.

StoogeMoe

This is the key statement. A failing coil won't make the tach zero-out. This is most likey your reference sensor.

ausgeflippt951

yeah but I've replaced both the speed/ref sensors and the problem persisted...

944CS

why should those values be 12V? If the battery is only putting out 12.36, you have to account for the resistance in the wires running to the coil. You aren't going to get the same exact voltage at the coil as you are at the battery

Check your fuel injectors

Tom M'Guinn

Very good advice. Don't forget the connectors at the DME/KLR under the footwell.

When the tack zero's out, is it because the engine has died or does the tack go to zero with the motor running?

ausgeflippt951

Unfortunately it's too hard to tell. It all happens w/in a second, so it's much to hard to tell usually. The tach will zero along with the motor dying, nearest I can tell. I believe the tach will zero, which will cut ignition, which will then kill the motor. This is why the car will recover most of the time; the motor is still spinning and thus can catch itself.


Yesterday after replacing the fuel jumper line (which I replaced not a moment too soon, I might add), I started the car and wiggled everything. Every plug, wire, etc I could find, and I came up w/ nothing. And I wasn't very gentile, either.

However, I then started blipping the throttle lightly to hear how it would recover. As we all know, the fuel is designed to cut on decell, which is why the motor drops below idle for a bit, and then comes back up to idle. Well, as I'm listening to the motor do this repeatedly, the car suddenly drops below idle and then dies completely.


This caused me to think: can the ISV affect the car when it's not at idle? i.e. when driving down the road?

Alex Teela

Old thread, but I thought this might help someone in the future. I had a nearly identical problem (1987 944 na) and it turned out to be the ignition driver on the DME. There's a big resistor looking thingy (about like three stacked dimes) where the solder cracks over time. Just carefully pull the DME, remove the cover by bending back the tabs and reflow the solder on the ignition driver. I think there's a walk through on one of the e30 forums.