I am sure the 1984 911 did not need CDI

I installed Pertronix and Nology wires and coil in my '73 911 12 years ago and it made a difference. The CDI with that same confuguration minus the coil and CD-1 coil instead made a BIG difference,

I have no experience with anything but my 1973 2.7 MFI engine with this CDI. I am not surprised that the '84 did not need it. In my mind the 1973 needs it.

wwest....do they make a trinaural switch for CDI?

"I think what we conclude here is that the older points CDI could be improved. And we have 2 choices: electronic triggered CDI or inductive and either would be an improvement."

The 911SC CDI (6 pin) has this feature, i.e. a magnetic pickup.

Seems like the 73-83 cars could use some ignition help and CDI is readily cheap available option to replace the expensive stock system. It's just to bad I have not seen any decent drop in units with electronic pickup and small ECU to just run a inductive coil. Back in the 80s I had a 75 911 2.7L and I did buy such a electronic triggered unit with simple coil. I can't recall who sold it but it worked very well and replaced the points, the cdi box and the coil. It came with simple hardware that replaced the points with a plastic trigger wheel and a simple LED with a optical pickup on the opposite side of the trigger wheel. But you don't see these simple systems any more.

The Bosch CDI in my '78 Targa has only failed me once(***), and in that instance it was the over-voltage battery charging that caused the failure. That module now has a voltage input limiting circuit, a high wattage resistor in series with the input and an "amplified" zener diode in parallel with the CDI internal circuitry.

***About three years ago and with over 100,000 miles.

The question becomes: are the old CDI systems that used the points compatible with a magnetic sensor, etc, without some sort of signal pre-processing. Were I having to address this issue I would be searching for a used or refurbished Bosch CDI module that was shipped with the magnetic sensor.

The later inductive system would be best but that requires a flywheel gear tooth timing sensor, 2 actually.

This is what I often see as response when there is no intelligent, substantive, rebuttal possible.

NO its what your get when you state: "Now that's showing a bit of unjust ARROGANCE! One person's opinion vs teams of highly educated, skilled engineers over the decades."

You had me at ARROGANCE. For me that ended the intelligent debate I thought we had going on.

"Seems like the 73-83 cars could use some ignition help and CDI is readily cheap available option to replace the expensive stock system."

The 911 ignition systems are being confused. From 1966 thru 1977 the 3 - pin CDI with points
was used. From 1978 thru 1983 the 6 - pin CDI with a magnetic pickup was used.

Dave,
So the 78-83 system would most likely resolve a lot of these issues?
Also is it possible to replace the points in 73-77 with some sort of electronic trigger? Like maybe a Pertronix aftermarket trigger that then triggers the CDI? Something like this:
Ignitor
They actually list these for the 73-77 911 cars as part #1867A.
Has anyone ever tried something like this?
Thanks for pointing out the differences.

If the shoe (glove) fits.....

This might well be a most excellent product, certainly could be...

But.....

Features...

A.) "delivers twice the voltage to the spark plugs...."

Very, even extremely, remote possibility...

They're referring, of course, to the continued use of the Kettering inductive ignition system in which the condenser is removed. In standard use that condenser primarily serves to slow the voltage rise time such that the points can reach fully open without an arc across the points themselves.

So, no doubt, the risetime would now be limited only by a snubber circuit/network in place of the condenser to protect the new solid state switching device.

Not limiting the coil primary's voltage rise time will not substantively increase the peak secondary voltage, most certainly not by a factor of two.

B.) "2:1 improvement over points in current fall time for increased coil output."

May I say....Huh?

Why, how, would the spark plug arc sustainment time/period be increased? If the now removed condenser was serving any purpose at all in the sense of spark sustainment it was providing a circuit "resonance" effect thereby extending the spark sustainment period.

Remove it, and.....

C.) "Stable timing ...no need for any adjustments."

Agreed ....in the long term sense.

Short term...the hall effect signal output waveform will change with RPM. Does the new switch trigger at the same engine rotational point as the sensor output waveform changes due to RPM...?

And lastly....

D.) "Use with Flame-Thrower 40,000 volt coil for optimal performance"

This "Ignitor" is, no doubt, a break-through product, addressing the exact problem faced by the Porsche design engineers back when the CDI was first introduced.

Then, "Optimal", OPTIMAL, performance ONLY with the Flame-thrower coil....

The way I see it the use of the base product, the IGNITOR alone, results in substantially improved Kettering design ignition system PERFORMANCE!

And just what system needs 80,000 volts, assuming we can believe the vendor statements...

Well, maybe this is the problem
 

Another chapter in the saga.

I had put in the new cap and distributor the other night and got things fired up. I did have to push to tighten the coil wire before it started... that should have been a clue.

After work yesterday I headed across town. I was driving toward a major intersection where I wanted to turn left. I had a few backfires as I approached the red light and at the light it stalled. I tried a few times and did not get it to start. Crank no start. Then the decision was to push into or across five lanes of traffic, call my wife or call AAA. Or, hop out and fix this thing.

I jumped out and went to the coil wire pushed it into the coil and into the distributor. I went back to try and got some life, not enough. I went and pushed the wire again, tried to start and got it to fire. There were backfires, but got it through a u-turn and down the road. I got it through the next intersection without incident and it seemed to be "normal" the rest of the way home.

At this point, my suspicion is the coil wire. I thought I needed to make a run to the local auto parts store to see if I could find a replacement. I was hopeful to get it right away, or else I would have ordered from our host.

I went to pull the wire out of the car, and got a bit of a surprise. The engine was hot and it took a little tugging. I got the coil end out with not much issue, then wiggled the distributor side and gave it a pull. That's when I was left with the wire in my hand and the plug was still in the distributor. I pulled the rest of the cap off, shook my head and thought that this crappy wire could have been the issue from the beginning.

I was successful in finding a part, it will arrive at the parts store early this afternoon.

I'll let the group know what the performance is after I connect the new one.

Here are photos:

http://forums.pelicanparts.com/uploa...1397230157.jpg

http://forums.pelicanparts.com/uploa...1397230227.jpg

"So the 78-83 system would most likely resolve a lot of these issues?
Also is it possible to replace the points in 73-77 with some sort of electronic trigger? Like maybe a Pertronix aftermarket trigger that then triggers the CDI? Something like this:"

That will work just fine. Many on Pelican have done just that. Some, though, don't
like it became they claim the magnets aren't perfectly aligned on the shaft resulting
in uneven timing. Others use an optical system as has been recently posted on Pelican.

Here's the link for the optical trigger;
http://forums.pelicanparts.com/porsche-911-technical-forum/805185-how-i-use-crane-optical-trig-bosch-cdi-3-pin.html

IGNITOR, good, possibly EXCELLENT, product gone bad, REALLY BAD!!!

But not nearly as over-hyped as:

Ignitor III

Wholly unsupportable claims by Marketing...

I'm not proposing using this product as intended, I'm wondering if it could be used just to trigger the 73-77 CDI box. Simply replacing the points with it but keeping the CDI stock.

I like this optical solution even better.

The one wwest mentions is the later version which does some 'trick' things.
The one you referenced works great as a points replacement or as an actual
coil driver for an inductive discharge system.

Given my history of using, mostly unsuccessfully so, optical position sensors in industrial environments, pulp mills, saw mills, etc, I would ALWAYS choose a magnetic sensor over an optical one.

Great! It looks like you had an intermittent connection due to breaks in the wire, hope that is it and you can get back to enjoying you car. I'm not really sure if anyone else is paying attention still.

No, my derogatory statements were regarding the ignitor for use as switching source for a Kettering system, not the II or the III.

I suspect the Ignitor will work fine as a trigger for a CDI system that is designed to use the points.

I give it about a 0.01% probability of being the problem.

You are discounting a faulty coil wire as the source of the symptoms he is describing?

Absolutely!

One of the symptoms is backfiring, most common cause would be A/F mixture "ignition" while the intake valve is still open. Hard to have backfire if the HV never reaches the distributor.

Over the years I have all to often used to much force and separated the HV wire end connector. Pushed the wire back into distributor/coil tower, DRIVE until purchase new wire. If the wire center core is within <0.10" of the distributor/coil contact it will "jump" just fine.

Oh well, thanks for politely giving him a 0.01% chance.

If an engine backfires, stumbles etc. could it be a result of unburnt fuel from the previous revolution?

OK, the wire turned out to be a false fix. I got it in, it started up and ran a little rough, but I figured that was due to poor timing. I drove about 10 miles on back roads and it was OK.
After helping my son carry his new fridge up the stairs into his condo I decided to run to an auto parts store and pick up a timing light and dwell meter. Well a timing light is easier to find than a dwell meter.
Pulling into the third auto parts store the car started backfiring like crazy. After I came out I decided to try to get it home on back roads. This only made it about half a mile. I was backfiring so bad people were running for cover thinking it was a gang shoot out.
I got help pushing it into the lot of a 7-11 and popped the hood. I checked the connections again, but did not have any success. A friendly guy stopped to help and we checked for spark. We were getting no spark to the distributor. After figuring that the connections were all good we isolated the problem to the coil.
I called my wife and had her bring over the old Bosch coil that I had taken out with the MSD upgrade. I got the old one installed and it fired right up and ran like a champ all the way home. What I thought were misses before were likely shorts in the coil. I have read of guys getting bad coils before and I guess it was my turn.
The MSD was an 8222 High Vibration Blaster Coil. I just printed out the label for the RMA. I am hoping MSD will supply a replacement.

I have read that the old Bosch is not the way to go with the MSD ignition so I will be replacing it with a new MSD soon.

"Back"-firing into the EXHAUST?

Mixture ignites as the exhaust valve opens?

Possible.....

But I'm still not buying into the inability for the spark to jump that "broken" HV connection.

Ah, vindication....

The distributor cam, points, are designed such that the rotor "contact" will be positionally correct for firing the "selected" plug. So DWELL must be correctly set, 65-70%

I don't understand, completely, why anyone could design, or recommend (Wayne?) that a CDI system use an "I" core ignition coil. An "I" core coil is completely appropriate for a Kettering ignition system wherein the spark energy is stored within the coil's magnetic field PRIOR to plug firing, No high efficiency or QUICK energy "transformation" from the coil primary to secondary required.

Not so with CDI, the need to transfer spark energy from the primary winding to the secondary winding is co-incident with plug firing. That, in turn, results in the need for the coil to act as a transformer, QUICKLY accepting energy flow into the primary. The CDI's high voltage output, 300-500 volts, over comes primary winding inductance, while the E&I core laminations provide a highly efficient "closed" magnetic field, coupling the energy into the secondary more efficiently (~30%) than would a simple "I" coil open magnetic field "path".

Use one of these...

http://forums.pelicanparts.com/uploa...1397315605.jpg

Heads up!

Ford, for the past 2-3 years, have been replacing, under warranty, spark plugs, coils (COP), catalytic converters, even engines, as a result of plug gap no-fires. CAC condensate (water) ingestion results in compression pressures well above design specifications.

http://forums.pelicanparts.com/uploa...1397316058.jpg

Other than manufacturing defects the most likely cause for ignition coil failures is internal "flashovers", the insulative resistance for spark jumping from secondary to primary is lower than the design path, coil/distributor/rotor/HV wires/spark plug.

An out-of-position rotor due to improper dwell might well result in coil internal FLASHOVERS.

"...This was brought on by a no-start issue....."

Ignition points rubbing block worn down enough to increase the dwell to >90% and the 3 wire CDI system's input signal "anti-bounce" filter capacitor/network filled in the <10% "gap" = NO FIRE.

New MSD has less filtering so it "fires" but rotor mis-positioning (>90% dwell) results in enough plug no-fires that coil finally fails due to internal carbon path formed by multiple internal flashovers.

Pull the HV wire out of the MSD coil and watch the spark jump THROUGH the coil tower sidewall to the coil ground terminal as you crank the engine.

or these:

http://forums.pelicanparts.com/uploa...1397318024.jpg

http://forums.pelicanparts.com/uploa...1397318060.jpg

http://forums.pelicanparts.com/uploa...1397318120.jpg

http://forums.pelicanparts.com/uploa...1397318145.jpg

I tend to have preference for a HV connection DEEP inside the HV insulating tower.

OP:

Please check the point dwell and set it correctly, 65-70%, if needed, then check/set the timing by rotating the distributor.

And please post the results...SmileWavy

....says it ALL...!

http://www.msdignition.com/Products/Coils/Race/8222_-_High_Vibration_Blaster_Coil.aspx

100:1 turns ratio, maximum voltage, 45,000 volts.

MSD 6425, 530 volts output, 100:1 ratio 53,000 volts!

8222 MSD coil was designed, obviously, for use in a Kettering ignition system.

With a Kettering system the possibility for internal flashovers and the resulting carbon tracking is minimized via the condenser limiting the rise time of the ignition voltage. The spark plug wil often, or mostly, fire before the maximum voltage, in this case 45,000 volts, is reached.

With CDI the maximum spark voltage is reached virtually INSTANTLY in comparison. The second high voltage, in this case 53,000 volts, risetime is limited ONLY by the coil's inductance.

Another strong reason for NEVER using an ignition coil designed for a Kettering system with a CDI system.

I would have though the MSD engineers would know better.

The episode Friday night was due to me searching for a dwell meter.
It arrives tomorrow from Amazon so my son and I will work on the points gap, dwell and timing tomorrow night.
I did drive the car Saturday and had some misses at high RPMs at the end of an eight mile drive. Then on the way home I got my backfires again after a brief run on the freeway. I figured that I would just stop driving until the points and timing was done.
I thought about dropping in an electronic replacement for the points like the Pertonix Ignitor II, but I am tired of throwing parts at this problem.

set the dwell and points first. See if that makes it work.

Then think about the Pertronix. I have found it to be a great upgrade for a car with points.

or just trash can the MSD..........

Last night we made progress on the dwell and timing. The max we could get the dwell to was 29, the timing at idle is fine and we are 34 at 6000.

Setting the dwell is a pain and I will be looking up a Pertronix very soon.
In the trip to the gym and back it ran OK, but I didn't push it and on the way back at over 3200 RPMs I sensed it missing a little.

Could this be arcing in the old spark plug cables? so it that I need to replace the plugs and go to a wider gap? I was not having these issues before the new MSD and coil so I am trying to work my way through the system.

I am running the old coil since the MSD fried and I have not received the replacement yet.

Any thoughts?