CDI problems
 

My '83 sc quit on me last Friday 200 mi from my home.

I initially thought it might be a fuel pump but after having my local shop check it out they tell me that they feel the hall effect switch in the distributor is bad , AND the CDI unit is toast.

I've sourced a replacement (rebuilt) Cdi unit but I'm not too sure about the distributor and the parts needed to be replaced.

Can anybody offer help or suggestions?

Thank you,

Hugh

There is not a switch. There is coil in the distributor that is dirt cheap. It has to do with picking up the collapsing magnetic field which is created by the reluctor which spins inside the stator. This field change (ask the electrical guys) somehow spits out a little charge from the coil and sends it to the CDI via that green wire that comes from you distributor.

If you have an ohm meter you can check the resistance in this coil from the wire harness end that plugs into the CD box. I am searching for the ohms value. (right around 600)

http://forums.pelicanparts.com/porsche-911-technical-forum/744535-sc-distributor.html

Coil is not so dirt cheap - time makes a difference. Search on distributor pickup coil.

If the shop is correct and there is a trigger signal interruption the connections from the coil to the CD box are also suspect. I don't read much about the dist and CD going south at the same time.

That wire harness that runs from the three pin CDI (is your's three pin?) can loose resistance over the years. They do make a replacement wire harness that connects to the coil, distributor and CDI unit that is an easy R&R.

Bob

is this a Porsche shop?

bob is right, about 600 ohms for the coil inside the dist.
not sure how they determined the CD was bad if they say the dist is bad.

the CD should make a whining sound. if it does NOT, then it IS bad. if it does it COULD be good.

the green wire from the dist to the CD can cause problems. its best to measure the dist coil resistance thru the green wire to verify that is good too.

he has the 6pin.

could also be the ign coil. this is one of those deals where you ohm the dist, then check the ign coil. you can ohm it out but it can still be bad. if it ohms good it may try to fire but just wont catch.

heat usually kills the coil and/or the CD. if that's the case then when it cools it may start up,.

if they try to measure 12v at the coil it will NOT be there even though everything is good.

Contact Bob Ashlock at Ashlock Tech. He's kind of a CDI whisperer. He took great care of me when the CDI on my SC died.

Green wire......

Green wire directly to distributor seems to be the weakest link. Other Bosch ignition cars have the same problems with this.
However if you have the original Bosch black & brown coil, they are very tough & reliable so dont discard it.

I had a CDI unit go on me - it whistled but didnt work. Replaced it with a MSD but you will have lots of choice for repairing yours & staying original.

I'm on the road again. The shop that originally diagnosed the problem replaced the coil in the distributor and I sent the CDI unit to Bob Ashlock for refurbishing.
Meanwhile I had the car towed to my garage rather than leave it outside at buddy's garage.
I tested the coil removed from my distributor and it measured 585 ohms, so it seems the replacement was not necessary.
The repaired CDI was installed Mon evening and the car fired right up.
So other than checking the timing everything seems to be OK.
The tach however is all over the place, much worst than previously, so I guess that's another problem for another day.
Thank you all for your assistance.
Hugh

Tach all over the place can be an indicator of a bad alternator Voltage Regulator.
Check your idling voltage and at 2000 rpm and 4000 rpm at the battery with a meter.

Make sure it remains almost constant around 13-14 volts and isn't spiking.
Could be what killed your CDI if it was spiking up to 16-18 volts.

And will kill your new or refurbished one....