'83 CDI Issue?

[GaryDG]

Lots of posts on this one - is there anything I missed in evaluating this No Spark issue?

No spark at sparkplugs when cranking

Removed coil wire from distributor. Connected sparkplug to coil wire no spark when cranking.

Removed two wires from coil tested each for high voltage when cranking - no high voltage.

Continuity exists across all fuses

Resistance across coil terminals (with wires on, ignition off) is 300-400 m ohms
New fuel pump relay

Fuel pump works

Starter motor engages

Input to CDI are marked 31/1, TD, 31d, A, 15, 75

With ignition on: 15 is 12V, TD is 5V, all others zero, voltage at either coil terminal is .34V

I've never listened to the "normal" CDI sound so I have no basis for comparison but I hear a faint squeal.

The following is from Mikko Kosinin's tech article
Ignition box (CDI/CDS)
• First thing to check is that the ignition box is making squeling sound while power is on, this indicates that the high power voltage is produced.
• If there is no sound check that the ignition box is getting correct voltage (Check the manual which terminal) If the voltage is much under 12V the ignition box will not sound "healthy". If you have heard the sound while its working, you know the difference.
• High voltage terminal should be reading 4-5V, and when measured with oscilloscope there should be this 400-500V spike when terminal C is connected to ground.
I have attached the wiring diagram associated with the CDI & Coil.
I am not sure what Mikko is referring to about "Terminal C". Also, based on the tests results above, terminal 15 (my reading of ~5V) seems to go to the Heater Ventilator Relay on the diagram.

Here's a diagram from a different post.




Any other ideas or tests that should be performed?

Thanks again.

[Porboynz]

Yours is a 6 pin CDI, the article seems to be describing the simpler 3 pin CDI. The wire to the points is your #7. All the points do is earth that wire when the points close. The #15 wire should be a solid 12V, if you have just 5V there is your problem. The squeal a healthy CDI makes is hard to miss. TD goes to your tachometer, ignore that for now. The 31/1 should be a good earth. The A connection is the high voltage dump from the CDI to the coil, be careful there and make sure the coil is always connected when the CDI is powered up, plus never short the coil terminals or earth them, bad things can happen.

[GaryDG]

Thanks Porboynz

I've corrected the diagram from a pretty comprehensive post on repairing 6 pin DCI by Warren hall, et al, see link below

And also, I had my test results incorrect the results were 15 = 12V and TD = ~5V, I corrected that in my original post as well.


6-pin SC/Turbo CDI unit repair documentation

[schumicat]

check green wire. do a search for it and you will find lots of info.

[Porboynz]

12V in, OV out, its broken. If the whistle is low pitched or muted then the high voltage section is faulty, if the whistle is in good song then its the SCR/thyristor probably defunct. Either way, plug in a known good unit if you can so you can prove it in or out.

[T77911S]

make sure its not the dist.

at the very least ohm between 7 and 31/d. your diagram says 600ohms. i did mine just recently and i think that is what i got. i will check mine again now that i have seen something that says what it may be.

if you have power at 15 and sginal at 7, thats all thats needed for it to work.

there is a picture on my coil bracket that says not to put a MM across the + and - of the coil, with it cranking i presume.

[GaryDG]

Thanks Guys

I'll check out your suggestions!

OSI930 has offered to send me a working Permatune to see if it's the CDI. I should get it soon and I will post results

Poorboynz wrote "If the whistle is low pitched or muted then the high voltage section is faulty" that would characterize what I heard. Anyway swapping out my CDI with a good one should isolate it.

[GaryDG]

I received the Perma-Tune CDI from OSY930, swapped mine out, started right up!

The real story here is OSY930. He just shipped it to me, didn't ask for anything up front!

Now that's a great guy!

[James Brown]

great troubleshooting process

[Arne2]

OK Gary, so now you have 2 running P-cars. What next?

[Porboynz]

Originally Posted by GaryDG

I received the Perma-Tune CDI from OSY930, swapped mine out, started right up!

The real story here is OSY930. He just shipped it to me, didn't ask for anything up front!

Now that's a great guy!

Kudos to both of you.

[GaryDG]

Poorboynz

I do intend to fix my CDI. There's a post out there, I think it's the one I referred to above, that discusses the testing/repair process.

Your comment on the CDI diagnosis seems to indicate you have dealt with this circuit before. Can you easily point me good reference on debugging the CDI? Is an oscilloscope required?

Thanks

Gary

[Scott at Pelican Parts]

If you need your CD Box rebuilt, please consider doing business with your host:

Porsche 911 & Carrera Ignition - Rebuilt CD Boxes

- Scott

[Porboynz]

Originally Posted by Scott at Pelican Parts

If you need your CD Box rebuilt, please consider doing business with your host:

Porsche 911 & Carrera Ignition - Rebuilt CD Boxes

- Scott

Well I have an oscilloscope and other nurdy paraphernalia but I thankfully also have a working CDI. What I know is all theory and what I have read on this board therefore, and what I read is that if the SCR fails (eg due to a short on the wire to the coil, or just silicon fatigue) then sourcing the correct replacement SCR can be a challenge. There are plenty of posts that show the internal logical schematic and circuit board layout. I guess I might be tempted to open it up and check for an obvious dry solder joint, but otherwise follow Scott's advice, there is benefit in getting it done by someone who has knowledge of all the various permutations of 3 and 6 pin Bosch CDI units the factory used and has the correct spares on hand. Its the old story, its only a $2 part that's failed, but which one?

[savoyjfas]

I think it's the one I referred to above, that discusses the testing