No voltage to the coil, PermaTune box checks out OK...

[BottleNose]

Hi All,

I'm not getting spark on my '70 T Targa. First thing I always check on longhoods is the PermaTune box as that is usually the problem. But the Permatune box checks out OK. There is no voltage going to the coil when the ignition switch is on. What should I check first?

Thanks for any help.

[Flat6pac]

Your old dry wires are grounding out to the shielding..standard proiblem on the pre 78.
If you ohm the wire to the coil you ll find it ohms to the ground wire too.
Bruce

[BottleNose]

Does the positive wire to the coil come directly from the ignition switch (no relays or control box in between)? Easiest thing to try would be the ignition switch...I have a spare. If that doesn't work, I'll try to ohm it to the ground wire to check for a short (good idea).

Thanks for the advice!

[BottleNose]

The wire does ohm to ground. Finally got around to trying a different ignition switch...same problem.

Where does the wire go that comes from the ignition swith to the coil? I don't see any colored wires at the ignition switch that match the ones at the coil +

[john walker's workshop]

center wire on the p-tune gets 12V w/key on. the coil does not.

[BottleNose]

I see...so does the coil get voltage only when the engine is turning? If that's the case, then I'm guessing the voltage to the coil + comes from directly from the alternator. I do get 12V at the Permatune center wire...what should I investigate next to solve the lack of spark?

I'm a bit confused as to how this all works...is there a resource that does a good job describing how the CDI/Permatune, alternator, and coil work together?

[HarryD]

The P-tune provides a brief pulse of power to the coil. Unless you have an ocilliscope, you will not be able to see it.

Check this thread out for how to check out your ignition: How do i check a coil with a timing light??

Originally Posted by HarryD

To get a spark to the spark plug in the engine. Several things need to happen. First, you need power to the CDI. Next you need to have a way to trigger the CDI (the points do this by opening and closing). Then the CDI will then send a pulse to the coil which will increase the voltage and send it through the high tension lead to the rotor and to the selected spark plug. You need to verify that each step in this chain is working.

1) Verify that the CDI is getting power. Do you hear it wining (if it is a Bosch unit)? (ed. if it is a Permatune, you need to check for power on -- see below) If so, you are good to go.

2) Verify that the CDI is producing power to make a spark. You can do this with a "telegraph" test. Take the high tension lead off of the center of the distributor and put a spark plug on it. Ground the threaded part. With your plug attached to the center lead, open the distributor, remove the rotor, place your key in the run position, and manually open and close the points. Each time you cycle, you should see a spark from the plug. If you do not, you may have a bad CDI.

3) Verify that the coil gets a signal when you crank. Replace the rotor and distributor cap. Leave the plug on the center high tension lead. Crank the engine. Do you see a spark? If so, you are getting spark to the distributor. If not, your point gap may be off or there is some other problem with the connections.

4) Verify that the spark goes to the spark plug wires. Reattach the center lead to the distributor. Attach you spark plug to one of the leads going to the cylinder spark plugs and ground. Crank engine. If you see a spark you may have a timing problem. If no spark, you have a problem with your rotor or distributor cap or your wires are improperly seated.

Do a search here as there are many threads on this topic. Look especially for the ones by early_s_man. Warren (RIP) left a great deal of knowledge on troubleshooting this problem.

From http://forums.pelicanparts.com/porsche-911-technical-forum/364174-cdi-box-troubleshooting-help.html#post3448932

Originally Posted by HarryD

Doug,

You better check your wiring diagram. Per Permatune (http://www.perma-tune.com/T-ignition-Porsche-911.html):
A = + or 15, coil hot primary terminal ( - or 1, coil ground primary terminal is connected to the engine ground).
B = Power from ignition switch.
C = Distributor breaker points.
D = Ground

BENCH CHECK OF THE IGNITION BOX (Perma-Tune only)

PIN A TO D = 3,300 Ohms +/- 100 is normal . Zero Ohm or lower than normal resistance indicates defective ignition coil damage to the box.

PIN B TO C = 100 Ohms, +/- 1 is normal. Open circuit or higher than normal resistance indicates ground loop or over voltage damage to the box.

PIN D TO MOUNTING FLANGE = Zero Ohms is normal. More than 0.2 Ohms indicates ground loop or battery terminal reversal damage to the box.



But, I hate to burst your bubble but AFAIK, Permatune boxes make no sounds, ever. You are thinking of the Bosch CDI.

If Cameron looks for Warren's posts, he will find a weath of trouble shooting advice that will help him track down his problem.

And, yes, I can easily post the thread I am thinking of, but it is better to teach a person to fish then to give him the fish. Since Cameron has indicated he had difficulty finding theappropriate post, I offered some hints where to look.

[HarryD]

Originally Posted by BottleNose

I see...so does the coil get voltage only when the engine is turning? If that's the case, then I'm guessing the voltage to the coil + comes from directly from the alternator. I do get 12V at the Permatune center wire...what should I investigate next to solve the lack of spark?

I'm a bit confused as to how this all works...is there a resource that does a good job describing how the CDI/Permatune, alternator, and coil work together?

The alternator is only to provide power to operate the car and charge the battery.

Go to http://www.howstuffworks.com/ and poke around the automotive section. It can be very helpful.