captnathan

Ok Gentlemen, I've gone through every mechanic in the area in the last 6 years and none have relieved me of this curse. My 77 911S just loses ignition and won't start--sometimes for a short while and other times a long while; often if I just keep turning the key on and off it starts up. Everything else works in the car and the headlights don't dim or anything noticeable. I've tried proving that it was the stereo, the wipers the... but no corelation found. If the car sits for a long time it usually drives for awhile before it acts up and sometimes it even tempts me onto the freeway where I've been towed off 3 times now. When I got the car the Bosch CDI box was fried and I replaced it with a Permatune which lasted for a few years. Then I replaced that Permatune and it lasted about a year, and then the next one lasted two weeks, now I just don't drive the car. Before the complete failure of the ignition system happens the Tach usually bounces and then drops and bounces. Then the car cuts out almost imperceptably foe awhile and then it cuts out long enough to backfire and then it eventually dies (usually). After awhile whatever the problem is causes the CDI box to burn out (1 Bosch, 3 Permatunes - so far). Now before we get busy with this you should know that every cocksure mechanic has been through it already: Coil replaced (3 times now) currently with Permatune coil, Newest version of Permatune CDI box installed, grounds checked, plug wires replaced, tachometer removed (problem still existed without tach), alarm disconected, alternator checked, regulator checked, pins cleaned and probably some other things I've forgotten. But that's not to say that I'm closed to suggestions. I've been considering yanking the wiring harness and I suspect that there may be a short in the distributor but I'm fried on the shooting in the dark and emptying my wallet to another parts replacer--I want to fix it. So, if you know what you're doing will ya help me out? Please and Thanks!

Steve Weiner-Rennsport Systems

Hi:

You didn't post where you live so its impossible to recommend some qualified people to help you but it sounds like there are several issues thats simply require some very detailed, systematic troubleshooting to fix this. Just a guess here, but it looks like some wiring, connector, and/or ground problems.

These are really very reliable cars and just suffer the effects of age and less-than-skilled maintenance personnel,.....

Daniel Dudley

If you live close to an automotive wiring or electrical specialist, that might be a resource to consider.

butzip

I feel your pain. I had similar behavior on a(n) 83'SC. 80mph on the hwy and then .... dead nothing hope there was a shoulder to pull off on and pray there was no 18 wheeler behind you. Wait 5-10 minutes and she'd fire back up. This became more frequent over time. I diagnosed as the Perma-crap box and replaced with a good used Bosch box and matching coil. Never had another issue. I would stop beating yourself over the head with the permatune and replace with oem equip. I found mine on e-bay for $175 for the box and coil. Good ole ebay :-)

Good luck and brgds, Peter

Peter Zimmermann

Cap'n: There's a guy named Loren that posts on this forum; he owns Systems Consulting. Attempt to reach him here, or through his web site, he might be able to get you switched over to Bosch parts - Permatune is crap and the company is even worse. I have a hunch Steve W. is correct, a wire harness for the CD should be built before any more new parts are installed. That said, has anyone replaced the trouble-plagued Bosch ignition points? This may seem ridiculous, but I've seen points cause your problem if (1) plain and simple, the points are bad even though they "look" perfect, or (2) too much distributor cam grease was used. A little grease flies off and gets on the point contact surface, and whammo, backfire and die. Also, has anyone confirmed that the wire connection at the distributor body is not shorting to the distributor? Removal is necessary to check this, and the insulator around the wire connector must be perfect.
Pete

wwest

Would you believe that a failing alternator can cause this problem..??

Intermittent shorting of the stator wiring inside the alternator will inductively couple to the nearby inductive pickup/sensor in the distributor and cause tach bounch, often tripping the rev limiter which wil latch up if the battery is being overcharged, common occurance in older 911's.

Regulator or RFI/EMI filter fails, overcharging the battery, boiling off the electrolyte, the alternator is "asked" to put out full power continuously, the stator leads to the rectifying diodes overheta, melt their insulation....

Sparks/Arcing.

butzip

Somebody's and electrical engineer..... who's the engineer.... come on....come on....

wwest

Nope, 10th grade drop-out, life's experience.

pjc

Hi - no elecrical guru but I have suffered similar symptoms, cutting out after a short while, rev counter dropping to zero.

Does sound like you have more than one problem but......the solution to my problem was very simple, speck of dirt on the points. The points on these cars only pass low voltage and even a small speck will cause this problem. I didn't even change the points, just gave them a wipe.

PJC

wwest

Only suspecions...

The factory "add-on" after-thought, emi/rfi filter in my '78 Targa failed, began failing, at ~90,000 miles.

This is a small metal box/container mounted just under the external voltage regulator, the original wiring going to the regulator plugs into this box instead and then an extension from the box to the regulator carries the OEM circuit function.

2006-7, the engine would die, wouldn't bump/push restart, and the ignition key had to be switched off for a count of 5 and then could be restarted via the starter.

Put in a brand new heavy duty NAPA battery and the problem went away, car mostly garaged, for about a year or more.

Last November on a drive to McCall Id from Seattle the engine starting acting up in riggins Id in the same way.

I immediately suspected battery overcharged again, the rev-limiter latching up due to the over voltage.

Installed yet another new battery, disconnected the external voltage regulator and the car was driven on to McCall. A new regulator and fuel pump relay was then installed.

The car was driven off and on throughout the winter and then on the first warm, 80F day, the day I arrived in McCall(???) it started exhibiting the very same symptoms. Found the battery to be only half full of electrolyte.

Interim conclusion was that the battery was still being overcharged but this time disconnecting the regulator didn't seem to help. Note: car seemed to run fine in the cool of the evening but not in the daytime even with a newly bench trickle charged, 12.25 volts (partial charge), battery installed.

Discovered on the INTERNET that the emi-rfi filter "add-on" often failed and might be the cause of over-charging the battery. removed same and now the symptoms changed. Car ran more reliably overall but still quit, especially on a bumpy road.

Hmmm..

Very early on, Riggins incident, Squire (Bellevue Porsche shop) had advised changing out the regulator AND the alternator. During our trials last week in McCall I called Squire yet again and he was quite sharp (justifiably, experience trumps theory yet again) in telling me to swap in a new alternator with a built in regulator.

I ignored his advice for a day or so to my detriment. To my credit I wasn't exactly relishing diving into an alternator DIY (McCall Id) change out. But a failure, slow leak, of the right rear BBS 3-piece wheel on our own 911 sorta forced my hand. If I had to wait for a new inner wheel rim to arrive from Ga I might as well spend my idle time on the '78 alternator.

Long story short the installation of the new alternator went fine and the '78 seems to be operating as factory original.

Disassembly and analysis of the removed alternator indicated severely burned wiring and wiring insulation from the stator (varnished) windings to the rectifying diodes. All 9 diodes measure correctly.

It appears that the long period of overcharging the battery, probably using FULL alternator output constantly, took its toll on the wiring/insulation and the resulting intermittently shorting/sparking/arcing internal to the alternator would couple to the nearby ignition timing inductive pickup in the distributor.

That results in TOO many sparks, or sparks TOO close together, from the CDI and the (separate) rev-limiter would see that as an engine over-rev and open the fuel pump relay circuit.

The rev-limiter itself has some strange aspects. I know that if I "nuzzle" gently up to the rev limit the limiter response will be fair gentle. On the other hand if the engine hits the rev-limit "hard", rapidly, it feels (BLAM..!) as if something in the driveline suddenly parted company with the car.

In the beginning I thought the fact that the rev-limiter latching up, requiring an ignition switch off period before restarting, with an overcharged battery was a design flaw but now I suspect that it might be an intentional design aspect.

Dr. 914

so I really need some help with a three pin CD box on a 1970 914-6

Car runs perfectly with a factory box from a 71 914-6. (this is a 30 ohm box)

Car will not start with a rebuilt box from Lauren (this is a 100 ohm box)

Lauren's box runs two other 914-6 just fine

Permatune causes the car to break up at higher rpm, have tried three of them

Disconnecting the tachometer and ballest makes no difference

permatune boxes run other two cars just fine

have replaced the points and set the dwell, just the same before or after

have switched the coil, no change

What in the world could be wrong?

Spyerx

Verified grounds?
Verified wire continuity and no weak wires?
Opened CDI and checked the pin solders to the board, all OK??

Not that this will help you but... I had a silver Bosch coil on my /6 and it was intermittent and died. Swapped that with a partsklassik coil started right up and seemed like it ran stronger. Replaced CDI with a partsklassik CDI and it runs fine. I also ran it fine on the CDI from a 77.So the 70, 77, and partsklassic CDI (in the Bosch box) all ran fine on the car. No idea the Ohms on any of the 3, but they all ran the car fine and the tach ran fine.

Lorenfb

The conditions for the 3 pin Bosch CDI (distributor points input) to develop a spark signal output to the ignition coil are:
1. Distributor points closed; the voltage between pin C & the CDI case should be about zero volts.
2. Distributor points open; the voltage between pin C & pin B (12V power input) of the CDI should be about zero volts.
If the voltage between pin C & pin B (points open) is never less than approximately 1.0 volts, the CDI will not output a signal to the coil.
Also affecting the triggering of the CDI is the rate at which the points input signal changes voltage levels, e.g. using a points condenser in the distributor can be problematic.

The Bosch 3 pin CDI with an internal resistor between pins C & B of 30 ohms is less critical in its operation to the voltages noted above than CDIs with 100 ohms between pin C & B.
Always begin testing for a no-spark at the coil by measuring the voltage at pin C with the points open. If it's less than the battery voltage at pin B, that's a potential problem!

Read here under No-Start for info about a Bosch CDI system; https://www.systemsc.com/diagnostic.htm

Lorenfb

In summary for 3-pin CDIs with 100 ohm resistors between pins C & B, the voltage measured with the points open between pin C and
ground must be greater than 9 volts to develop a spark at the coil, with 12 volts at pin B.