Need Help With Permatune CDI in a 71T - Change to Stock Bosch.

[t6dpilot]

My 71T has a Permatune CDI part number ZVP 125 101 A installed by a PO sometime in the past. I have a couple of questions regarding this installation. The car runs just great with it, so there is no real reason to change it out, but... My tacho does not read correctly especially above about 3,000 revs and I am sure it is due to this installation - I think. It bascially slows around 3k and tops out at 4k. I would really like to fix that. I have a Bosch CDI that I purchased used that I could install, but don't know if that is the best thing to do at this point. I need some help from the experts on this board.

The Permatune has 6 colored wires coming out (purple, black, green, white, yellow, and brown) and is wired as following:

1. Purple wire is connected to 2 red wires coming from a part of the factory harness. These two red wires are terminated at one spade connector.
2. The black and green wires connect to either side of the coil.
3. The white wire does not terminate anywhere and is pulled aside.
4. The yellow wire terminates to a spade connector on the base of the distributor.
5. The brown wire is of course ground and terminated at the engine block.
6. As a note, the factory coil wire (blue with yellow stripe) is tied back and not used.

Also, I cannot find any tied off wires that should go the the Bosch CDI and would really not know which ones they would be anyway. Does anyone know what colors they should be and what I should look for?

Anywhoo, I have two questions... Can anyone help me fix the tacho reading problem as it relates to the Permatune? I really think it is something electronic, right? And how would I go back to the Bosch CDI if I wanted to and does this make sense?

Thanks a bunch.

[304065]

Scott,

Here are a couple threads to check, they will answer all your questions.

Before there was BHKZ: SWB engine electrics

Retrofitting a 69-73 MFI engine to a 1966 carb'd 911?

[t6dpilot]

Thank you John! I knew you would chime in and set me straight.

[carsngolf]

Hi Scott,
If the threads don't help, I think Hollywood Speedometer could probably get it working correctly. They aren't cheap but they do good work and stand behind it.
Good luck,
Jerry Weiland

[t6dpilot]

Thanks Jerry. They did all my gauges in my silver lightweight and they are awesome. I am not convinced that this is a rebuild issue yet. I think it is electrical - but I could be wrong. It certainly would not be the first time.

John, I looked through your threads and the only thing that I could apply to my issue is the color of the wires going into the Bosch CDI. The rest does not seem to apply to my Permatune - either that or I am too dense to figure it out. So, the two red wires connected to the green Permatune wire are probably from the ignition. Easy enough to check with a VOM. Now I need to find the CDI termination of the blue/yellow wire. I did not see that tied off back there. The more perplexing question is where the black wire is for the pionts? Gotta do some more looking for that one. That and the black/purple wire from the distributor to the tacho.

The yellow wire that terminates at the base of the distributor - could that be for the tacho? I have got to say no since it is a long way to the points from that termination, but again, I could be wrong. I need to take a photo and post for better reference. Might be able to do that tonight, which could help the diagnosis.

[304065]

Scott,

The permatune wires have been hooked into the factory harness.

Purple wire is connected to 2 red wires coming from a part of the factory harness. These two red wires are terminated at one spade connector. -- this is the factory power for CDI

The black and green wires connect to either side of the coil. - coil pos and neg

The white wire does not terminate anywhere and is pulled aside. - this is the tach signal wire to drive old-school tachs

The yellow wire terminates to a spade connector on the base of the distributor. - this is the points trigger

The brown wire is of course ground and terminated at the engine block.

Here is a link to Permatune's web site- to the support info for this box. It sounds like someone is using a tach adapter instead of the tach driver circuit. Photos would be a big help to see what you have.
http://www.permatune.com/T-ignition-Porsche-911E-os.html

[t6dpilot]

John, thanks again for the info. I sort of summized that those were the connections. I will get some photos later today. The damned snow last night kept me away from the car. The last thing I wanted to do after a 2 hour commute was get back in the car to head out to the airport.

[304065]

I know what you mean, I kept my cars in a hangar for four years (under the wings of an airplane)-- cold, creaky and isolated. I used to listen to music like Louis Armstrong and Edith Piaf, made me feel like I was in WWI.

Where was I? Anyway, as Warren used to tell us the Permatunes have a nasty habit of failing, so ripping it out in favor of a Bosch would be an OK move. I am using an MSD right now, and it does a great job keeping the plugs clear for the rich-running MFI. MSD has a separate tach output that can be run to a converted tach, Palo Alto or North Hollywood can convert to make it work with the MSD tach output. Inexpensive, reliable solution.

[t6dpilot]

OK John, it has taken me awhile to get these posted. Here are some photos of my Permatune setup.





Next question... The tacho electrically generates the impulses to show revs mechanically (on the gauge), correct? The gauge acts like it is binding between 3 and 4k revs and just hesitates so it won't go above 4k much. Is there a way to check the electrical voltage/amperage at the wiring going into the tach to see if I am getting the correct values? And what would those values be? Or... is the actual unit being bound up inside and is that something a DIY guy can pop the tach case and check out/fix?

Thanks for the help.