'75. No spark, no power to coil.

[Last911]

Help! I drove my '75 911 into the garage, ran and drove perfect. Then I randomly decided to start it (it's kind of cold). And no start. It smells like gasoline so I'm not messing with that right now.

1) Grounded a spark plug (on wire) and no spark.
2) No power on either side of coil.

How do I check for power or get power to the coil?

(I also hooked up power from a battery charger to one side of the coil and it didn't run, also no spark was generated).

[T77911S]

there is no power to the coil.

make sure you have power to the CD unit
make sure the points are providing a ground and removing the ground.
removing the ground is what fires the CD unit.
it can also be the wire from the dist to the CD. you can test the CD by grounding and removing the points signal at the CD unit.
check the grounding from the engine to the CD unit

the CD should also make a whining sound. if it does not it is bad. if it does it can still be bad.
the problem can also be a bad coil.

about the only other thing I know of to do after this is swap in a good coil and CD

[Last911]

Thank you! Did more reading
"no power at the coil with the ignition on, it gets the voltage (450+!) from the cdi unit, i would advise not checking voltage at the coil as your tester will fry and you will be propelled to the other side of the garage (with the engine running) se note on cdi box. power at the cdi box and a good trigger (points) is all you need. you can check if its working by using a induction timing light, that is the safest way. if you have spark you can move on to air and fuel and timing."

OOPS!

1) I can check for power to CD unit.
2) How do I check points? Remove dizzy cap and see if they are opening/closing (they should spark right?) If they don't... then?
3) When I ground the wire to the CD what should happen? (Sorry newbie!)

CD unit is making a whining sound (but I understand it can still be bad). I can easily get a good 12V Coil, the problem is getting a good CD unit up here.

[ischmitz]

When the points close or when you short the points with a screwdriver or short the trigger wire directly to GND the box should release a spark.

And yes, please be very careful as there can be high voltage at the coil output once you disconnect the coil primary while the box is whining. Even with the coil connected (and internally broken) there can be up to 400V present. The coil primary essentially serves as path to GND to charge up the internal main capacitor. Once the spark is about to be released the other side of that internal capacitor is momentarily connected to GND and this makes the voltage of the capacitor appear at the CDI box output. At that point the primary "sees' up to 450V and the secondary of the coil transforms this pulse into the HV pulse that generates the spark. Under no circumstances touch the output from the CDI box while it is powered (whining)

Last, you are correct. Even if a box makes the whining sound it isn't proof that it is fully functional. It can still have an issue internally.

Ingo

[Bob Kontak]

Originally Posted by Last911

CD unit is making a whining sound (but I understand it can still be bad). I can easily get a good 12V Coil, the problem is getting a good CD unit up here.

You are at square one. You have identified nothing as a genuine culprit except that the CD unit is more than likely good. (It's all good. Just troubleshooting).

Pull you cap and look at the points. You can spread them a little with a screwdriver. Do they look like crap at the contact points? A mountain on one side and a crater on the other? If ok, put the car in 2nd gear and push it (the car) until the points are at the top of a lobe. Measure the gap with a feeler gauge. Adjust if necessary. Better yet, replace the points and condenser as preventative maintenance if scruffy.

For $20 you can buy a coil for a 67 Chevy. Use that as a test mule.

Get a multi-meter and test continuity from the distributor to the CD box. Test continuity from the CD box to the coil. You need to learn how to do this as a Porsche owner that may only have one left nut ($$) to give to professional mechanics, if you know what I am saying. Forget about a spark at the points (for now). Set it and forget it, assuming continuity is present.

The CD system does not "juice" the coil constantly with 12V. As T77 says there is no power to the coil. However, when your points open and the stored energy in the condenser is released to the CD as a trigger signal, the CD box sends the big voltage signal to the coil. The coil ramps it up further and sends it on down the line through the secondary system (distributor/spark plug leads).

You just have a break in the system. Annoying to find, but on the upside, worse for a noob.

Also, you will not be knocked across the garage. You will only experience massive involuntary muscle spasms in your arm and chest. You will pull away and drop a huge sustained F bomb followed by a "Jesus H Christ, that effing hurt". Nothing to worry about.

Edit: Just read ischmitz's post. He's smarter than me on electricity. Take your time.

[Bob Kontak]

Keep us posted.

[Last911]

I didn't give up! It doesn't start but I am learning alot. I didn't know what continuity was or own a multi-meter. But I do now and now I do!

Please bear with me, in return I promise to help other newbies if I get this thing started (plus my eternal gratitude of course!).

I feel as though I have some 'strange' wiring in my car. I will post photos, but remember the car was running when I drove it in.

1) Continutity; I traced the wires and I believe they all have continuity where they should. I will post pictures to confirm which wire leads to where.

2) The problem is, not all of my wires are 'wires', some of them are just 'shielded cable'. In particular from the CDI Box ('D') to the distributor. Spliced along with this wire was the 'green' wire (which was a ground wire). Is this correct?

3) The wire (shielded + normal wire) + green wire if it is touched, or grounded, makes the coil 'chirp'.

4) I could never get the points to spark. They are beat up, I used a very fine sandpaper on them to clean them, but no go. I ordered new parts.

Pictures to follow!

[Last911]

1) These wires lead to a plug at the bottom of the dizzy. (I cut the connector off)


2) Same wires closer up.


3) Close up of grey wire. Notice how it is shielded? If I turn key on, and touch shielding to normal part of this wire, the coil 'chirps'


4) The grey (shielded) wire has continuity to here;


5) The 'green' wire has continuity to the CD box (labelled 'D') shown both here (well just the connector on the CD box)


6) The connector on the CD box (shown above) has shielded wires (not regular wires) and they lead to this thing?? (Confusion)


7) CDI Box wiring. (The wrapped female connector; I took the wiring apart on it, expecting normal copper wires, but it had two braided shielding type wires leading into the female connector).


8) Close up of the wiring. The CDI box side, you can kind of make out dual 'silver braided wiring'. The mass of wires at the other side of the picture are what I thought should be all connected to (how it was previously but I added a new wire to the distributor).

9) Took the cover off the box (for no reason)

[Bob Kontak]

Originally Posted by Last911

2) The problem is, not all of my wires are 'wires', some of them are just 'shielded cable'. In particular from the CDI Box ('D') to the distributor. Spliced along with this wire was the 'green' wire (which was a ground wire). Is this correct?

Great job on nuttin' up with the MM.

I am seat of the pants talking here because I have yet to look at you electrical diagram. On my 81, there is a different trigger mechanism. It has a stator, reluctor and a coil of copper wire. It creates a magnetic field with the iron parts spinning near the copper coil. Stuff aligns at the right point and a tiny charge is sent to the CD box.

That said, I think you need voltage sent to your condenser to charge it.

I said in an earlier post you need check continuity from the dist to the CD box and then CD box to coil. I think you have an added step of making sure there is voltage going to the distributor to charge the condenser.

It sounds like there are two wires. A green shielded wire and another. The center of the green wire is what sends the trigger to the CD box (I think). The shielding is for radio interference suppression. The second wire may be the power wire for the condenser? If so, this needs to be tested for voltage but I can't confirm exactly how.

There are hundreds of members here with point distributors and CD boxes. One will help.

EDIT: Just saw your picture post. I'll stand down as I don't have experience with your car.

[Last911]

At least someone is listening Bob I was going to shy away from the electrical stuff but then I was, 'eeeh, what's the worst that can happen? It's not running now anyways.'

I am thinking of just going with MSD, but I don't want to add on to the problems. I am thinking it is something simple in the wiring. But the MSD search lead to this info from timmy2;

On the original 3 pin connector:
The middle red terminal is switched power.
The black wire is to the points.
The blue/yellow wire is to the coil positive.

I can confirm middle does have power. Should I just run my own wire from black to points (I assume this is to the distributor) and then a new wire from blue/yellow to + on coil?

Edit; crap. Of course there would be 2 identical white wires Oh well.

[Bob Kontak]

Originally Posted by Last911

I can confirm middle does have power. Should I just run my own wire from black to points (I assume this is to the distributor) and then a new wire from blue/yellow to + on coil?

Patience. There are a handful of guys that will help. Well worth the wait.

What you need to understand is the function of the wires. Then it gets easier.

FORGET MDS right now. Get you car running well, then switch. If you tie it all in and nothing, maybe the CD box is toast? It can also be fixed.

I run an MSD box. This is after buying a P-Tune to replace the P-Tune that came with the car. Installed MSD. No problems, 12 years.

[ischmitz]

If you short the wire going to this terminal to GND the box needs to produce a spark. It's what is getting grounded when the points close.

[Last911]

Nice! There is 2 wires that are white on that plug. The red wire is power, where should that wire (with the arrow) go to? Will it make a spark even if points are bad?

And where should the other wire go to (not red arrow side)?

I searched but I can't find a wiring diagram, just a picture of the wires themselves.

[timmy2]

Porsche changed from individual wires to the coil and points with a seperate shield Ground for each to shielded white cables on the '73.5 to '77 models, so ignore my colored wire info for 73 and earlier cars.
One shielded white wire is for the coil, the other is for the points and splits off near the 3 pin to connect to the tach signal with the CDI switched power red wire.
No green wire used at all. That is a PO Hack...

[ischmitz]

The box will have to release a spark when the terminal with the arrow is shorted to the housing of the box (GND). Regardless of the condition of the points. The points are a switch, one side at GND, the other side goes to this terminal.

The other terminal on the other side goes to the coil primary. Be careful, there can be HV present even when there is no spark.

And as you said correctly, the center wire is +12V switched by the ignition. And GND goes to the spade on the housing.

Ingo

[Last911]

Good stuff! I know a few things to do. Ideally, I would like to run new wires myself.

Where do I run these new wires? (I want to use normal wire vs shielded wires).

[Last911]

I want to do something like this. I messed up the shielded wires a bit, can I use regular wires as grounds?

[ischmitz]

12gauge braided wire works for me, even as HT wire from coil center to spark plug.

[Last911]

Found some wiring diagrams and I plan to re-create/fix the wiring from scratch.

[Last911]

Except this diagram shows 2 spots on the distributor, whereas on mine there is only one place for the wires to go.