77 Turbo Ignition Problem

[Adidas]

77 911 turbo with a 85 turbo engine won't crank. Not gettting any spark at spark plugs. The 6 pin CD unit will whine when switch is on. Could the problem be in the pickup unit in the bottom of the distributor. Any easy way to check tach, coil, cd unit, the ignition unit in the bottom of the distributor before I start plugging new parts in? Would this car have a muiltpin brain or control unit as well? Didn't see one under either seat. Thanks in advance. William

[NathanUK]

You could check for a resistance in the Dizzy with a meter.

[spuggy]

"won't crank". This would imply (to me, anyway) that it doesn't turn over on the key, yet you're saying no spark at spark plugs?

Assuming that it's turning over and not firing, is the tach needle moving when it's cranking over? Mine does...

These are CIS motors, there's no brain and thus no DME relay. There might possibly be a Lamba O2 system that regulates warm, part-throttle running and can be largely ignored for the purposes of starting the car (and complete removal in non-emission areas is common).

Check coil and dizzy connections, and that there's 12V to the coil would be my SWAG.

[JFairman]

probably the coil or the green co-ax signal wire.

[timc]

Just because the CD "whine's" with power does not mean it is good. Mine failed, but still "whined" when I turned the key on. When I checked it for power, was very weak, and did not produce enough power to fire the engine.

[JFairman]

Electronic flash units for camera's make a rising whine as the capaciter is charged.
The whine is from the thyristor which charges and controls the output of the capacitor and duration of the flash.

I would guess the whine in a CDI is also the thyristor.
so if it still whines and doesn't put out the 350+ volts to the coil that it is supposed to do, then the capacitor is probably shot and leaking voltage internally.

Take out your upside down mounted coil and see if any brownish oil has leaked out between the aluminum housing and plastic tower and stained it there.
That is what mine did recently and the dead bosch coil was only a few years old.

[NathanUK]

I'm happy to take resistance readings of everything for you from my car. Let me know if you would like them. I had a problem with my 3.2 recently and having these readings saves a lot of time diagnosing what's wrong. They may come in handy for me in the future.

[Adidas]

Nathan. Sure your readings would help me. Everyone else who responded thanks I'll look into it further. Bill

[A930Rocket]

Tim,

Did you ever get your CDI fixed or go to a MSD?

Jim

Originally Posted by timc

Just because the CD "whine's" with power does not mean it is good. Mine failed, but still "whined" when I turned the key on. When I checked it for power, was very weak, and did not produce enough power to fire the engine.

[timc]

Yes I finally did, sent you a PM. Actually wishing I did go with the MSD, as I'd would of liked to try the ign retard unit.

Tim

[NathanUK]

OK, here are the resistances

At the CDI connector with it unplugged

Coax to dizzy (green cable) is 570 inner to outer wire.
Brown to White (coil primary) is .7

Coil secondary (coil HT to either + or -) is 649

At the CDI box

31/1 to 31d is 0 (closed circuit)
31d to 15 is 672
31d to TD will charge briefly and then go to infinity (open circuit)
31/1 to TD also charges briefly and then goes to infinity (open circuit)

My CDI is a 930.602.702.00
Bosch number 0 227 300 004

[Adidas]

Made a basic check. Not getting 12 volts to the coil. Thanks Bill

[JFairman]

If you have CDI you should not be getting 12 volts to the coil. You would get pulses of 350 to 450 volts instead, depending on the make of the CDI box.

Now if you have simple points and condensor ignition with no voltage amplifier like a CDI you would have around 10 volts to the coil.
In that ancient type of ignition you should not have 12 volts either because that would burn up the points quickly, so they put in a ballast resistor to drop the 12V down to approximately 10V to keep the points from burning up too fast.

356's and early 912's had simple points and condensor ignition, and I'm not sure if the very first 911's had Capacitive Discharge Ignition or just points and condensor.

The points and condensor ignitons worked by grounding the coil when they close and letting 10-11 volts flow through the coil which created a magnetic field in the primary windings of the coil and when the points opened the magnetic field drops and induces a higher voltage in the secondary windings (which there are much more of) and that higher voltage jumps the plug gap and makes your spark.
The condensor is there to act as a buffer for the points so they last longer.

[NathanUK]

I added a pic to my post I made up in Paint. Anyone who wants to use it in the future is welcome.