Misfiring - CDI connections

I'm getting well sick of my car at the moment - the troubles seem endless!

Here's the latest:

Over the past couple of months I'd noticed that the engine seemed to cut out for a fraction of second and then continue as normal... This was infrequent to say the least - about 6 or 7 times only.

Symptoms:

1) Very brief time period - less than 1 sec.

2) Rev-counter dips and then returns to normal.

3) Doesn't seem related to acceleration, decelleration, cornering, steady crusing etc.

4) Car is difficult to start - or rather, keep running. It starts fine then seems to cut out. If you keep your foot on the gas for a few seconds then gradually lower the hand throttle it seems okay. Also the idle speed is very low - at about 550 rpm - pretty much the lower limit for the car.

I asked my local dealer to check it out - they narrowed down the problem to the CDI unit. They checked out the connections to the unit and sprayed the connections with cleaning agent.

The car ran a lot better but this week-end I noticed the problem reoccuring - only this time the rev counter dipped and then came back to normal - the cut-out or whatever was so short it was actually un-noticable at crusing speeds.

Questions:

1) Should I attempt to replace the connections to the CDI unit? This looks tricky, as there are multiple wires feeding into the square connectors - it reminds me of computer cables!

2) Should I fork out over $1000 for a new CDI unit and connectors?

3) Should I spend about $400 on an aftermarket CDI unit and blue coil - this will presumably come with a set of new wires and connectors?

4) Maybe the problem is nothing to do with the CDI unit and connectors at all - particularly the starting/idle problem?

Right now I'm tilting towards solution 3, as it stands a good chance of success. But if anyone has a good case for another solution please say.

Thanks very much in advance,

- roGER

Roger,

First, of all, I don't think it is you CDI-unit, for the simple reason that your tach. is misbehaving when the speed drops AND at times when it alone is having a problem! Sounds most definitely like a distributor problem!

But, before going after the distributor, I suggest reading an article aout the CDI-unit installation, wiring, and some troubleshooting hints at:
http://www.perma-tune.com/tech/911.htm

All of the diagrams pertain to the factory CDI-unit as well as the Perma-Tune box! So, familiarize yourself with the 'not-so-mysterious world' of point-triggered CDI ...

Check the single 1/4" 'quick-disconnect' lead on the outside of the distributor for 'looseness' and corrosion: both the female connector to the wiring harness, and the male connector at the disfributor! Needle-nose or regular pliers can be used to slightly crimp the female connector on both sides for more tension. An ink eraser can be used to clean the male connector ... after all cleaning a bit of Vaseline or Dow Corning 111 can be put on both connectors to retard corrosion in the future.


Just to ward off future problems, the CDI-unit can be removed from the relay-panel, so the ground connection and three wiring-harness connectors can be cleaned the same as the dist. just done! The ground connection needs to be bright, shiny clean before Vaseline or Dow Corning 111 is applied. A stainless-steel 'toothbrush' is very good for cleaning corrosion on wiring connectors!

For further investigation inside the distributor, I suggest this thread:
http://www.pelicanparts.com/ultimate/Forum3/HTML/001522.html


Good luck!


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Warren Hall
1973 911S Targa

I don't think that it is your CDI unit either.

Let me ask you to do one thing (as I pull out my belt-fed, water-cooled "trouble shooting" shot gun to take a wild shot in the dark) disconnect the tach lead from the coil and tape it up for a few days and see if your intermitent problem goes away. I think (Guess) that it is possible that you have an intermit. short that is momentarily grounding the coil out (stopping the coil/dipping the tach). Also make sure that there is no other wire connected to the post that could be grounding it.

Try it, it might be an easy fix for you and you might be able to isolate the problem better. Good Luck.

s

Thanks to both of you (again!) for quick and thoughtful replies...

I'm going to do all the checks you suggest, but I'm going to do the CDI box/connectors first.

Why? Because the problem got dramatically worse, then as soon as the garage mechanic sprayed some cleaning agent on the 14 pin connector to the CDI/relay unit the problem seemed fixed, if only for a day or two.

That damn 14 pin connector is my prime suspect for the moment, along with its accomplices - the ground wires. If that's no good, then I'll try the coil and the distributor.

- roGER

PS: Please get in touch if you are ever in the Boston/New England area - at the very least I owe you a drink or three.

A couple more thoughts:

I had forgotten about the 14-pin connector ... it sounds like the 'genius' who sprayed something there really didn't do you a favor at all! My suggestion for cleaning it ... and hopefully any 'residue' left behind is:

Use NOTHING but Isopropyl alcohol, 70% or 90& should work ... use pipe cleaners on the female connector, and an old (or new) soft toothbrush on the male connector. Those pins and receptacles are silver-plated copper, and need to be cleaned VERY carefully! Use plenty of alcohol to drench the connectors and rinse away any particles that come loose, and use compressed air to dry-off, if available.

I don't recall if you ever said whether your 'T' is MFI or a CIS-model, but the tach doesn't get a signal from the coil on either version. On an MFI, the tach. gets it's signal from the Speed Relay that cuts off the injection pump on over-run above 1800 rpm. On a CIS, the tach. gets its signal directly from the distributor, and I believe there is only one crimped connector, so I don't think it is easy to separate the tach. signal. If you have MFI, try pulling the speed relay out of its' socket and cleaning it.


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Warren Hall
1973 911S Targa

oops sorry, I was going by an old security kill switch that I have heard of (By grounding the coil with a switch the car can't be started).

s

Thanks again for giving me all this useful advice.

The car is a CIS version, believed to be one of the first CIS 911s ever made (big deal huh!?!).

I'm definately going to try cleaning that connector - ruined or not, cleaning it made
an immediate and very noticable difference.

Warren - you should write a book (or a series of magazine articles) on the early 911 - you really seem to know every component of these cars.

Thanks again,

- roGER

I had a 73.5 911 T (CIS) this was a FUN FUN FUN! car. My CD unit did this exact same thing. I would be driving in third gear going to school and then the engine went dead. I shut down the ignition turned it back on heard the fuel pump and the CDI whining. So I thought, OK. Started it, it started right up.

I checked the CDI connections, checked the battery, checked wiring on the battery, replaced, replaced coil connections, replaced coil with my dad's '80 SC (this didn't work at all), looked at the ignition, unable to duplicate the problem via ignition switch.

I finally replaced the three wire OEM Bosch CDI with a Permatune unit. Problem went away.

Good luck with yours!

I want my 73.5 back... :-(
Nick
'85 Carrera

These kinds of problems are the reason I have a 'spare' Perma-Tune box and distributor in my spare-parts cabinet!

Thanks, Roger, for the compliment and suggestion ... I am thinking about such a project for 'the practical 911 owner/mechanic' ... maybe that's the title for it!

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Warren Hall
1973 911S Targa

Just a quick update - yesterday I spent a nice couple of hours in the sunshine taking everything out and cleaning the connections.

As Warren suggested, I used plenty of alcohol and scrubbing with an old toothbrush on the 14 pin connector - I also removed the CDI box and did the diagnostics as listed at the Permatune web-site.

The car is now running quite well, although it still hesitates a little when accelerating from low revs - I suspect the distributer (27 years old) may be getting worn-out and I may try cleaning up the coil connectors as well.

Many thanks to everyone who answered!

- roGER

Unless attacked by major rust damage, your distributor can be resurrected. Remove the distributor after the crank has been turned to Z1 on no. 1 cylinder. Thoroughly degrease with brake parts cleaner from a spray can. If play in the central shaft can be felt at either the bottom by the drive gear, or up at the top where the rotor snaps on, bushing replacement is indicated.

Disassembly is straightforward. A large compartmented plastic box (or multiple egg cartons in a pinch) is recommended for temporary storage of small components: screws, clips, springs, etc. If bushing replacement is needed, an entire day, or maybe even an overnight period will be needed, so a 'resting' place will be needed for all of those small parts other than a newspaper on the dining-room table! Removal of worn bushings can be accomplished by heating the distributor body in an oven at 350 degrees F for 45 minutes or so, then driving out the worn bushings with suitable drift or punch. A local bearing supply house should have suitable replacement oilite bushings in stock. You will need to take distributor body, shaft, and removed bushing with you to bearing supply to ensure a correct replacement part. Heat the dist. body, freeze the new bushing, and lubricate outide of new bushing with moly grease before attempting installation. Quick work is needed to get the new bushing in place and fully seated without burning yourself, or getting a bushing stuck half way in!

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Warren Hall
1973 911S Targa

Wow!

I'm not sure what to think about that, especially as my "workshop" is the condo car park and "the bench" is my front room...

Still, I may well attempt to remove the distributer and check for free play at the rotor and the cog at the bottom - I assume there should be none here.

I'll have to think about this - it sounds a potential nightmare but with a potential saving of at least $300+

Thanks,

- roGER

You might check with a local shop to see if there is anyone locally that does or specializes in distributor work ... shouldn't be more than $100-$150 to recondition, including the new bushings.

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Warren Hall
1973 911S Targa

Roger, I know EXACTLY how you feel, my work shop is a parking lot and my bench is my dorm room floor.
All I want out of life is a garage and a dog....

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Leland Pate

___79 SC Targa

Go Warren, go! We expect AUTOGRAPHED copies. I hope you do write something.

I've never replaced distributor bushings on a Porsche, but it's pretty easy on other cars. Naturally, the procedure (including tips and cautions) outlined by Warren are exactly how it's done. I'm a little surprized though, that Warren thinks this is 1 day plus, but upgrading to a much newer motor was a 1 day job in an earlier thread. Not doubting you, Master.

I suspect the distributor bushing change is a three hour job if the bushings are in hand. Point is; change 'em.

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'83 SC