What I learned from not one but TWO CDI failures
 

The definitive squeal is no guarantee the box will function. Quit while under load with a loud backfire.

The one from the parts car thats been getting a free ride in the smugglers box likely won't be functional. Mine wasn't.

The old blue Permatune and coil was a good thing to hang on to.

The wiring harness that goes out from CDI box to points and coil is NLA from Porsche.

The CDI+ guy has a point. These old Bosch boxes, even with a good ground, no overcharging or reverse polarity events, are not going to last forever.

I can't drive with confidence without a spare. Gotta get one rebuilt.

Ingo Schmitz does a good job rebuilding them. He's in Santa Barbara and a member of this list. He does it on an exchange basis. Offers a warranty as well as I recall.

Thanks. Might give it a go myself but I don't have much time to spare these days.

Lot's of old school NLA parts in them that are the cause for failure.....plus you need bench test equipment to run them and look for heat failures....but nothing says you can't try.

I swapped in an MSD for a world of difference.
I would like to get my CDI rebuilt but I'm leery about being able to find a reliable coil - I have two bad Bosch black now.

yes, the squeal is no guarantee it works.

the boxes are very old. the capacitor in there is old and good bad from age. I always say they dry up.

always test your spare.

MSD is a great alternative. there is also a guy here that makes or modifies the original and makes it better.

I have the MSD in my 930. I also carry a spare bosch unit. I can simply unplug the MSD and plug in the bosch but I also have another coil wired in to the original wiring. then I just swap the coil wire over to the other coil and off I go.

happened a few weeks ago. my coil went bad. swapped in the bosch and moved the coil wire and off I went.

I don't know of any good answer anymore other than to carry spares whether it be original ignition boxes and coils from Bosch, permatune or MSD or other. I know of CDI failures on all three makes that have stranded people. The only time I've had to get towed in 14 years was when my original CDI quit. Right now I run a circa 2015 permatune box have a spare permatune and coil in a little box ready to go if needed. I know the rep, but I've had good luck so far. If those go, I may try an msd box (and get a cheap spare). Even rebuilt Bosch seem to be same story. Watch pelican and eBay for your spares...

Go to ************ for the CDI and Bosch coil. Not to take away from Pelican here, this vendor in Arizona has been manufacturing a coil that I believe exceeds the original Bosch and at a great price. Add to that, they have taken the CDI unit and have replaced the guts with updated digitized components at a very fair price. Even better, they have a direct wiring harness replacement that goes from your three pin CDI unit to the distributor made for the original points or for the points replacement.

I have been very satisfied with the components thus far.

Bob
73.5T/CIS

interesting that Pelican BLANKED out a competitor parts replacement name!!!!!!!!!!!!!!! Really guys?

Parts Klassik

Rebuild CDI
 

X2 on Ingo for the CDI rebuild.

Ha, so it happened to you too! I tried to reply to a post about hose end fittings and had this site delete the same company name. As you found out if you separate their name it works. Behave or you will be banned.....

you can buy the capacitor on line.

it is kind of a pain to replace. you better have GOOD soldering skills. (girls like it when you have skills).

Our own Bob Ashlock (Mr Tach Adaptor) also rebuilds the 3 pin Bosch CDI units. I sent mine to him, before a long road trip, and was almost embarrassed to install it. Case was media blasted and a new decal applied. Looked beautiful! Made me clean-up my engine compartment. Bob uses all modern components. His turnaround was quick and price, reasonable.

Firstly, to the repair guys, you are doing a grand service to the community. I happened to meet Bob Ashlock at the Anaheim swap meet back in March and he's just another EE like me and a thoroughly nice chap. There are plenty of 911s out there for all of us to scratch a living with these CDI boxes!

Here's my $0.02

Bath tub
----------

Electronics adheres to the well proven 'bath tub curve' for reliability. Basically, it is more likely to fail early on in its life but once it gets through that it will probably soldier on into old age at which the likelihood of failure rises steeply.

We are without a doubt in the 'increasing failure rate' portion of the graph with the Bosch units.

https://upload.wikimedia.org/wikiped..._curve.svg.png

Rebuilt or repaired?
----------------------

The repair that simply gets the thing working again is unlikely to last, since all the parts are old. We all know this with our cars. A clonking suspension indicates worn bushes, Replacing the bushes shows up worn dampers etc and so it goes on. Same with the electronics. Unless you replace all the parts, something is gonna go pop again. Capacitors more so than resistors but electronic parts do suffer from wear. The main spark capacitor is only one of numerous components.

So are we talking about 'repair' or 'rebuild'? We have had (failed) boxes in that proudly state 'rebuilt' but they are clearly repaired as only a couple of parts have been changed. In my view rebuilt means ALL the parts are either tested or replaced. Just like an engine. You would not call an engine 'rebuilt', just because you got it running again!

New failure modes
---------------------

When the Bosch CDI was new, it was designed to work with the other parts of the ignition when those parts were also new. There was no requirement to protect the box against short circuited coils, failed voltage regulators or over zealous battery boosters (they didn't even exist!). These represent new failure modes that did not exist 'in period'.

If you are designing some electronics to be put in to a system (the car) that you know is old and not perhaps at its best, you have to take extra measures to protect and guard against those common scenarios. If you just copy the existing design, of course it will fail, just like the original design.

This is why when we set out our design goals for CDI+, high up on the requirements list was to protect for all common failure modes, that includes those caused by other components in the car. You can't claim a system is more 'reliable' unless you have something tangible behind that statement.

Interesting discussion.
Is there any disadvantage to using a MSD box? For example a lower end StreetFire unit?

Being out here in the Australian Colonies - a MSD replacement was quicker than sending my Bosch CDI to USA for repair & a lot cheaper too. Actually I like it a lot because I live in a hilly area & I sense that the Streetfire has given me more spark at low revs going uphill.

I have wired it to the original plug so that I can just put the Porsche CDI back in anytime after its refurbished - I might find someone in Australia who does it or I can take it to USA for repair on our next trip.

The street fire box is not pretty on the outside & looks out-of-place in the engine compartment, however I have painted mine so it now looks like it belongs.

The MSD is OK, but a huge improvement over the Bosch CDI....even the Streetfire is OK. For my money I like the Daytona-Sensors CD-1.....Have had one in my MFI 2.7 for 8 years or so. Around $600 with a matching coil. Look it up. Pelican can special order for you.

Has anyone checked into the Lakeland CDI unit for $299. Kind of interested for the price and 5 year warranty.

I have one.....works well.

It also bench tested very well.

Would like to sell it....PM me.

hey, we have had some conversations in the past. doubt you remember me.

anyway, electronics tech for about 30 years now. I work for the FAA.

could not agree more.
as a tech that has to fix electronics I see a lot of cap failures due to age. also into tube guitar amps. another big failure is the caps, they get old and noisy or just fail.
solder joints might be the biggest issue.

I have repaired a few bosch units, always been the big cap in there.

MSD and done.

I like driving. I dont like looking at a shiny car on the side of the road. I like reliable and predictable.

I have been advised that if and when the CDI (three pin) CDI unit get very hot, they will shut down so engine compartment temps play a roll. I have had several shut downs over the years with my 1973.5T/CIS. What was so amazing was that once the unit cooled down the car would run well again. Fact or fiction? I do not know what internal components in the CDI would fail in particular from heat and I would like to know. you have three components that work together; the coil, CDI unit and wire harness that connects the CDI to the distributor/coil.

Maybe someone can explain the heat issue better..............please.

Bob
73.5T

The temperature failure described above represents less than 5% of the Bosch CDI failures,
both for the 3 & 6 pins. That failure affects the anode voltage rise time of the SCR causing it
to conduct while the energy storage capacitor is being charged.

Poor analogy!

A naive statement! So you're suggesting that ANY component failure in ANY electronic circuit
board requires replacement of all the components, right? Please! Bosch now provides rebuilt
electronics for the pre-2000 Porsches, and they are NOT replacing all the components.


Another naive statement! Today the Bosch Porsche DME ECM, e.g. 2015, is NOT designed
to protect for all possible failures, e.g. the COP drivers for battery overvoltage or reverse polarity.
It's all a matter of cost and the probability of that failure. That's basically the same design strategy
used by Bosch when they designed their CDI units. Any system design is approached the same way.

Jonny, you should know by now that the old Bosch CDI is just fine!!!!


I personally want to get in my car and DRIVE..... MY Bosch CDI is just fine sitting in a drawer under my workbench. I have Pertronix hall effect system for points and a modern reliable CDI with an "E" coil to drive the plugs and it all runs fine and has never stranded me in 10 years.

AND if I had your system it would cosmetically look like a Bosch.

[and no red box for me]

So dumb question, how do you know when the CDI is not working correctly. My car ran fine when parked last fall but now refuses to run. It kind of fludders runs for 5 seconds backfires and will not rev up. The coil seems to spark when the ign wire is retracted.
Could this indicate a CDI failure, haven't had this touched in my 30 yrs of ownership.

1. Just because the engine backfires & fails to rev, it doesn't necessarily indicate a bad CDI.
2. First check that the ignition coil (hopefully not a Bosch silver) wire when placed
about 10mm from the engine sheet metal produces a strong blue spark.
3. If the distributor has points, check for their proper setting and clean with emery
cloth.
4. Make sure that a good 12 volts is powering the CDI.
5. Try and borrow another CDI form a friend/Pelicanite.
6. Next, use carb cleaner to determine if you have a very lean mixture (backfiring).
7. Bosch CDIs rarely if ever fail because of non-use.

We live dangerously. I had no idea these things are prone to failure. I'll carry a spare in frunk.

Here is a picture from a Forum post about 2 years ago that I saved;

http://forums.pelicanparts.com/uploa...1429702233.jpg

It seems that the 911 with this module ran well ( perhaps not as good as with proper CDI) but good enough to get you out of a spot.

I was going to make a mini loom of 4 wires connecting to the Engine/CDI plug (a 6 pin) following to a common Ignition module like this. That would have got me going & then I would just keep it as a spare in the tool roll.

In the end I just got a MSD StreetFire & all is now good.