Need CDI help
 

I’m having problems getting my 71 911T to start. Ran fine when it was stored last fall.
Now won’t fire up, seems no power to points or terminal 15 on coil.
I have 3.5 lbs fuel so that’s okay.

Checked the CDI box and it skweels when the key is turned on as it should, I have power to red on box but no power coming out of box to coil or points. Is it fried?
Or is there a way to check the box using std volt meter?

Also the coil, is this a special coil required for use with the CDI.

Check your points to be sure they are opening and closing.

Lots of threads on this topic. Here’s one:
http://forums.pelicanparts.com/porsche-911-technical-forum/449527-how-do-i-check-coil-timing-light.html

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 increause 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.

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.

Thanks Harry, I have the factory manual but is way over my head on this.
Your response is something I should be able to handle.
I think step 2 is where my problem is, the black that comes from the CDI box has 0 value on the voltmeter, thus no power to coil.

Thanks for your quick reply.
Larry

Glad to help. Look closely at the points to be sure the rubbing block and the contact surfaces are present. I have had the contact blocks fall off.

Not sure how much help a voltmeter is as the CDI power pulse to the coil is very quick. The points are a switch to tell the CDI to send a pulse to the ignition transformer.

Well I did item 2 and did get a spark but only when touching the moving part of the points to ground. So, when closed the points were not making contact . I checked gap and it was way too big.

Adjusted to .016 and well it almost almost started.
I did notice while checking things that the connection 15 there is a small crack in the surface around the screw connection. Is this enough to stop it from firing?

Lastly can any coil be used as a replacement to get this running or do I need a specific coil for CDI appliications?

Any will function, even an old VW coil.

Larry,

Any coil will do in a pinch. Many like the MSD High Vibration coil as an alternative to the Bosch Coil.

Put some new points in it.

I swapped out the coil and rechecked points, checked firing order, pulled a plug wire and connected to a loose plug and got spark.
Tried to start and again close but no cigar. When cranking the tach is moving.

Got some fresh premium fuel and we’re going to try again.

4 gals fresh gas, again sounds like it’s ready but not quite.
Gas is dripping from heater box on left bank. Pulled all plugs and all wet with gas.
Dried them reinstalled and propped open throttle to let evaporate overnight to see if that helps.

Sounds like you are flooded. Hopefully it will dry out. You may want to try a touch of starter fluid to see if it will fire (no pumping the accelerator pedal).

If it fires, you floats may be stuck and causing the flooding.

I propped open the carbs hoping to get it dry, tried this morning ..same..

Wants to run but not.

Getting very frustrated.

Mr. Walker’s advice is good. Replace the points. Then reset the timing. If you don’t have a timing light, buy one. Another option is to static time the distributor by finding top dead center, should be in the manual, make sure rotor is pointing to the notch on the lip of the distributor, about 4 o’clock position, loosen the distributor. Turn ignition on an slowly turn the distributor until you hear a click. Points making contact and should start providing the coil, etc is not bad. Tighten distributor. Also check the ground wire from the unit the CDI is attached to. Ground wires attach to a bolt to the right of the Cdi unit. Haven’t had to do this in some time so feel tree to correct me if I misspoke. Steve

So I replaced the points and no change. Timing seems in order..getting spark can hear the snapping.
Took out 5 gallons of gas and put in 5 gallons of fresh high test.

Nada.
You just have to know when your done.