How do I test a Carrera coil?

BGCarrera32 · 05-15-2003, 05:28 PM

Hi-

Can't start engine, no spark. Pretty sure its the coil (let's just say I wouldn't be suprised). Changed DME relay, checks out o.k. I won't list all the other details, I just want to hit the coil next.

Black wire to coil is getting 12v when engine in run and /or cranking. Not sure how to check green wire or check the coil in general. What does the green wire do?

Tips appreciated...

Thanks!
BG

Jeff · 05-15-2003, 05:37 PM

BG,

The green wire goes back to the DME unit.

The simple way to test your coil is pull a spark plug and have someone crank the engine. If you have spark your coil is working.

Jeff · 05-15-2003, 05:41 PM

Just re-read your post. No spark. I think you have it (thinking it is a bad coil).

Do you have an alarm? Could it have been set.

BGCarrera32 · 05-15-2003, 05:49 PM

I have an alarm, but the performance dropped off yesterday during the course of the engine idling for a few minutes, then she wouldn't restart. Its acting just like my wife's Mazda did when her coil went bad- unable to increase in rpm's etc. But I'm getting absoultely zip...I just want to double check the green wire to make sure its not something back at the DME brain...which I don't know why it would be but I like to cover the bases...

I jumpered the fuel pump when I got home today, that is all good. Definetly fuel back there too after pulling a plug.

Jeff · 05-15-2003, 06:14 PM

BG,

The wiring diagram I have shows the green wire going into the DME unit And another green wire coming out, going to the O2 sensor. My diagram doesn't show if they are "connected" or if they both just happen to be green.

To bad your not in Phoenix I have an extra coil here you could try.

Did you see my post in your previous topic about testing the reference and speed sensor? If they are not functioning properly you will not get fuel (even if your fuel pump is working properly). The sheathing on mine was cracked and needed replacing. They run close to the exhaust and are subjected to multiple heat cycles.

BGCarrera32 · 05-16-2003, 05:00 AM

My speed and ref sensors are hooked up correctly, because the car was running the other day. I checked the connections to them and did a quick continuity test through each sensor but will get more specific today.

I'm thinking maybe I can place my sweep style meter or a test light inline with the green secondary wire at the coil, and make sure that it is pulsing or flickering. If its not pulsing, then I'd guess the coil is fine and that the ref sensor is belly up as nothing is telling the DME to pulse the secondary trigger (green wire).

I pulled a plug yesterday and there's fuel back there. Probably doing an oil change after I get this resolved...

-BG

Tim Polzin · 05-16-2003, 06:43 AM

A couple of places to start:

http://www.pelicanparts.com/911/technical_specs/911_DME_troubleshoot.htm

http://www.pelicanparts.com/techarticles/911_carrera_start_troubleshoot/911_carrera_start_troubleshoot.htm

Good luck...Tim

Lorenfb · 05-16-2003, 09:06 AM

Check out this website (systemsc.com).
It has some good diagnostic info for Porsches.
They rebuild ECUs, if that's the problem and not
the coil.

Good Luck

See ya
Lorenfb@aol.com