3 pin cdi in a 82 targa sc

Superdave1 · 12-05-2007, 06:51 PM

Hi: I purchased my first porsche a week ago. A 1982 911 targa. It is all original even the paint. I am new to Porsche but not new to wrenching on cars. It has two issues that I am trying to fix. It runs a little rough untill it warms up, after a minute or two it runs great. (I think it is the cis) The other issue is the tach is dead. I found some creative wiring in the engine compartment around the cdi/coil/distributor. When I had a closer look I found the car has a 3 pin cdi box. The guy I bought the car from races a 77 2.7. I am guessing the original 6 pin died and he replaced it with one of his spare 3 pins from his race parts. I am happy the way the car runs except for the two issues. The questions I have are, can I make the tach work with the 3 pin CDI box? Black purple wire from the 6 pin harness plug to the - on the coil? Get a used 6 pin cdi? Buy a Crane, MSD, permatune CDI??? Would the 3 pin have anything to do with my cold start??? Any thoughts on how to proceed would be greatly appreciated. Here is a pic of the car. Thanks dave...

group911@aol.co · 12-05-2007, 06:59 PM

Nice car. Are you sure it has a 3.0 in it?

Superdave1 · 12-05-2007, 07:16 PM

Yes It has a 3.0 for sure. The 3.0 harness is there. I can show you a photo of the engine bay if you like. He has the power to the (center) three pin cdi coming from the 6 pin harness. From the cdi box the right pin goes to the distributor, the left pin goes to the coil. There are no points. I know it should not work but like I said the car runs great. Just a little rough when cold. Lot of power, quick starts when warm. No miss, very smooth. Here is a pic of the engine bay. Take note of the wiring. Thanks dave...

Superdave1 · 12-05-2007, 08:29 PM

What do you think 911 groupe? Bit of a puzzle????? Can I trigger my tach from the - side of the coil? Does a 2.7 and 3.0 tach get triggered with the same voltage??? I would be happy keeping the 3 pin cdi if my tach worked.

Thanks dave...

Superdave1 · 12-05-2007, 09:20 PM

It's a Lambda car. Anyone have any ideas about the tach???? Thanks dave...

group911@aol.co · 12-06-2007, 06:05 AM

Dave, here is the link to the wiring diagram for an 82 and link to the diagram home page. You should be able to trace and compare the 2 years to figure it out.
It might be easier to go the the correct Cd unit.
http://www.pelicanparts.com/911/911_Parts/Electrical/911_electrical_82SC_Part1-2.jpg
http://www.pelicanparts.com/911/911_Parts/911_electrical_diagrams.htm

Superdave1 · 12-06-2007, 11:58 AM

Thanks for the Info 911groupe. I will look it over. I had another look under the hood today. Here is the engine # 6451198 and 911 43. I think the #'s confirm it is a 3.0. I made a mistake on the points. It does have points. I think what has happened is the previous owner has converted the 6 pin cdi ignition to the older 2.7 set up (cdi, distributor). Like I said he races a 77 2.7 so not much of a leap to assume so. My only goal here is to get the tach working. Can I run a wire from the 6 pin harness (black violet) to the negative side of the coil? Would that not trigger the tach? I looked at a Crane X700 as an option to get rid of the points and the wiring diagram shows the tach pulse conected to the - coil. The car runs great with this setup(except for the cold start) I just want the tach to work. I can't be the first guy this has happened too???? What are my options? Is that Crane ignition a quality unit? Might solve all my issues at once. More reasonable money wise than getting an oem 6 pin cdi and distributor. Thanks dave...

ischmitz · ischmitz's Garage

Why not try your tach and check if it works with the 3-pin. The 3-pin setup takes the tach signal right from the trigger signal (points). Try if it works that way. It's pin C at the 3-pin box connecting to the distributor points. If that does not work get a tachometer from a 74. They float around on Ebay frequently.

Do not hook the tach to the coil. The 400 volts and the spikes during spark events will detroy it for sure.

Ingo

Superdave1 · 12-06-2007, 02:55 PM

Hi Ingo: Thanks for the reply. That was my next step after looking at the wiring diagrams. I was afraid of hooking it up to the coil. I was thinking that I would put a .5 amp inline fuse on the wire to the distibutor, just for safety sake. I thought the tach would be able to take .5 without any damage. If the tach worked I would eliminate the fuse. I thought of the older model tach but the connections on the back of the tach are different. I didn't want to hack the connector off at the tach. I don't like to cut into the factory harness. The ignition connections are messed up a little already but I can work with the factory harness around the engine without cutting anything. Just in case I come across a 6 pin cdi in the future I can put it all back the way it is suppose to be. I think your suggestion is a winner. I will give it a try tomorrow. What do you think about the cold start issue. Do you think it might be related to the old ignition setup or is the cis off a little off? Thanks dave...

ischmitz · ischmitz's Garage

Superdave1,

a fuse only limits the current that flows into the tach. And 0.5 Ampere is huge for electronics!!! It takes a lot less to inflict permanent damage to transistors. Furthermore, a regular glass fuse is not fast enough for the voltage transients seen at the coil. So bottom line: Do not hook it to the high-tension side of the coil even with a fuse. It will kill the tach.

For the connector you can fabricate a little splitter at the distributor. There should be a spade connector where the trigger signal wire going to the 3-pin is hooked up to. Connect it to the tach signal wire. No need to hack into the harness at all. The tach lead should be present on the 6-pin connector (if that is still present in the engine bay). It is the violet wire. On the 6-pin connector it is the center pin on the row closer to the cooling fins.

Your cold-start is not related to 3-pin vs. 6-pin as long as your timing is set properly. Do a search here. There are numerous posts regarding cold-start and CIS and potential causes.

Cheers,
Ingo

Superdave1 · 12-06-2007, 03:37 PM

Thank ingo. I read you loud and clear about the coil. Coil bad, dis good LOL! I was thinking I would still use the fuse on the distributor. I guess not realy needed. Just trying to be safe ( read paranoid) . I have a VW spade connector that can go on the distributor spade that gives me two spades. That shoud work quite nice. I already have a length of wire made up with a spade on one end and a female on the other for the distributor. I found the black violet in the harness. I am good to go. I have asked a few guys about the Crane X700. No response???? Is that setup something to avoid??? Pelican sells them....can't be all bad? dave...

Eagledriver · 12-06-2007, 03:45 PM

You will not be able to convert to the stock SC set-up. The gear on the crankshaft has been changed...the SC dizzy spins the other way. I would try the tach on the points thing. If that doesn't work you could use an aftermarket ignition box like an MSD or Mallory 6AL. With the aftermarket box there is an out put that works on most 911 tachs. (Mine is a 72).

-Andy

ischmitz · ischmitz's Garage

There are lots of mixed opinions floating around here on the aftermarket ignition systems. Performance gains are questionable and some units are notorious for poor reliability. Why spend big bucks when your 3-pin Bosch works fine.

If the current tach does not work it'll be a lot cheaper to buy a tachometer to match your existing setup from a 74 - 77 car rather than source a 6-pin and mess with the dizzy. Ebay or Parts Heaven for around 100$. Any aftermarket ignition will set you back a lot more....

ingo

Superdave1 · 12-06-2007, 04:24 PM

Hi Andy: Not quite clear what you mean about the dizzy. Should my car's proper dizzy have points? I thought they went electronic after 77??? 77 dizzy different rotation than later SC's??? Is the only thing not correct on the car the 6 pin cdi box??? Will a 74-77 tach plug right into the harness at the tach? You guys are great! Thanks for your time!
dave...

Superdave1 · 12-07-2007, 02:46 PM

Hello again everyone! Connected the black/violet wire to the distributor today. Fired her up and the tach worked!........for a few seconds then started to bounce. %^$&** So close! From what I have read the tach is not getting the proper "square sign wave of voltage". Not sure if I am saying that correctly. I talked to the previous owner of the car and he has a tach from a 2.7 he is going to send me. Looks like that is the way to go. Is there another option with my tach, inline resistor or something???? On another note, I put a can of gas treatment and put a few gallons of super in the tank and took it for a spin. After letting it cool for severl hours outside in the cold it started right up. The old girl just might need a good run to solve the cold start. Just needs a bit of loving! LOL Thanks dave...

group911@aol.co · 12-07-2007, 02:53 PM

Dave, I think he is saying the 3.0 and 2.7 distributors aren't interchangeable because they rotate different ways.
Didn't look up the first number but the 911 43 doesn't sound like a 3.0 type.
Visually, the top end stuff looks later 3.0 correct - steel fuel lines etc.

Superdave1 · 12-07-2007, 03:50 PM

I just crunched the #'s......looks like the block is a 1975-911s carrera USA. Maybe this car wasn't such a steal after all? Are the s model motors as bad as everyone makes them out to be? Who ever did the swap did a good job. The nuts and bolts holding things together look undisturbed. The guy I got the car from said if you ever want to sell this car, I want the first chance to buy it back. I guess this explains the 3pin cdi and tach. This is the cleanest 911 I could find, ( looking for 2 years) Not sure I want to give it up for a rough car with matching #'s. Any thoughts?

ischmitz · ischmitz's Garage

Superdave,

the 3-pin box get triggered by shorting the trigger input (pin C) to GND. In a stock setup the points in the distributor close and that's was triggers the spark. The same signal drives the tachometer. It is close to being a square wave. The dwell (time the points are closed) is not important for the spark duration in a CDI setup but could make a difference for the tachometer. Maybe a slight tweeking is all that's needed.

A 6-pin box gets triggered by the falling slope of a transient (signal that has a zero-transition). It is generated when the magnetic field through a little coil is changing rapidly as it passes by a permanent magnet inside the distributor. A 6-pin will not trigger when driven by a distributor with points. Consequently, the 3-pin box will not trigger from the signal produced by a later distributor.

First you need to find out what has been done to make the 3-pin work in your car. I assume there was never a 6-pin in the car with that engine. If your block is a 75-76 I bet you have an early distributor with points. That was the reason for the PO to put the 3-pin in.

Try the dwell adjustment first or get another tachometer for a 3-pin (from you neighbor). Just the other day I saw several on Ebay for 60$ or best offer.....

Ingo

group911@aol.co · 12-07-2007, 04:35 PM

Quote:

Originally Posted by Superdave1

I just crunched the #'s......looks like the block is a 1975-911s carrera USA. Maybe this car wasn't such a steal after all? Are the s model motors as bad as everyone makes them out to be? Who ever did the swap did a good job. The nuts and bolts holding things together look undisturbed. The guy I got the car from said if you ever want to sell this car, I want the first chance to buy it back. I guess this explains the 3pin cdi and tach. This is the cleanest 911 I could find, ( looking for 2 years) Not sure I want to give it up for a rough car with matching #'s. Any thoughts?

Dave, other than the fact the car was misrepresented to you, there is nothing wrong with a properly built 2.7!
The good news is that if the 2.7 is from a 74.75 Carrera, they are starting to gain in value and someone will want that engine to make their car "correct".
In fact, if you do a search, there was a guy looking for one recently.
You may be able to sell the 2.7 for enough to buy your 3.0.
But, if you are happy with it, drive it and forget about all the correctness.
The 2.7 is a great running engine.
The other good news is that the problems will be a lot easier to deal with now that you know where you are starting from.

Superdave1 · 12-07-2007, 04:56 PM

Like I said the car is soooooo clean. I am a bodyman and hate rusty cars. I thought I was buying an sc. I was more concered with the body than the motor. Steel fuel lines on the motor had me fooled. The car has a front(under bumper) oil cooler, timing chain tensioners, 11 blade fan and the car doesn't leak a drop of oil. Someone has gone to a lot of bother to make this motor right. It's those dam curvy fenders. Like my wifes butt. She tricked me too!LOL I am not ready to give up on this car yet. I didn't want a trailer queen, I wanted something fun to tinker with and drive in the summer. I think the 2.7's get a bad rap. I am sure I will quite happy with the car when I get all the bugs worked out. This whole tach/ignition thing is making sence now. I will keep plugging away. Thanks dave...