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CDI+ Quick Start Guide. READ THIS FIRST!

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This is the most up to date guide for installing and running a CDI+ unit:

CDI+ All units

CDI+ units are designed to work with standard Porsche equipment - e.g wiring harness, cap, rotor, coil, leads and spark plugs.  Please make sure that what you have are as per standard.  This is a high performance ignition unit so it is vital that all the ignition parts are per factory specification and in good order. 

Pre-check of existing components:

1) Check condition of spark plugs and leads.  Standard plugs are fine.

2) Check rotor arm and cap.  Older caps can have tiny cracks which can cause the spark to 'track' to the engine case instead of the plug.  Also, the dust cap inside the distributor prevents interference between rotor and pickup so is a vital component of the ignition system.

3) Check the condition of the wiring to the pickup/points.  On 6 pin cars, the green wire is notorious for causing ignition troubles.  Inspect wires of cracked insulation.

4) The coil MUST be a standard Bosch coil 0221 121 00X or equivalent.  The current silver version will work ok although there have been some manufacturing issues with these.  Also, the Parts Klassik CDI coil is compatible.  MSD, Permatune, Beru and other coils will not work with our rapid multi sparks since these coils are slow to charge.   A workaround is to increase our standard spark interval from 400us to 800us by using the PC software.

5) The early cars use the 3 Pin unit and use contact breaker 'points'.  It is vital that these are in good condition and that the gap is set correctly.  Note that if the gap is changed, the timing must be checked and adjusted after.  It is VERY common for points to close after the adjustment screw is tightened so please check AGAIN.

Swapping over:

If you are starting with a running engine, then get the engine up to temperature.  Otherwise, only perform the timing check when the engine is warm.

As shipped, the CDI+ units are plug and play and the timing should be the same as the original Bosch unit.   Install the unit on the relay plate making sure the bolts are in good order so that the case is grounded.  With the 3 or 6 pin connector taken out, check the resistance between the CDI+ case and the engine fan housing.  It should be 0.5 ohms or less.  

Start the engine.   We strongly recommend that the timing is checked after installation as per the standard workshop procedure.

Standard  settings:  

As shipped, the electronic rev limiter is set to 7000 soft, 7250 hard (with cyclic cut).  This can be changed with the PC software.

Ignition mapping:

Refer to full manual  on this page: https://www.classicretrofit.com/pages/manuals-and-software

Video of setup on an SC:








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How to test a 6 Pin CDI unit:

CDI 6 pin connections are as follows looking at the PLUG** on the harness with it's two keyway 'ears' at the top

A  top left:  COIL 'A'

15 top middle: 12V

7 top right: Distributor Signal +

31/1 bottom left: COIL '1'  (-)

TD bottom middle: Tacho Drive

31d bottom right: Distributor Signal -

**Note:  The sticker on the side of the CDI case shows the CDI SOCKET connections on the unit as you look into the connector.

Basic checks

CDI box disconnected.  At CDI plug on loom with ignition OFF:

Check resistance between pins 7 and 31d.  Should be around 600 Ohms.  This is the resistance of the pickup winding in the distributor (must be plugged in to distributor of course!).    If you can plug the meter in whilst wiggling the green wire, it should stay locked at this reading.  If it goes open or short circuit, then the green wire is bad.

Check that TD is not shorted to GND.


CDI box disconnected.  At CDI plug on loom with ignition ON:

Check for 12V between pins 15 and 31/1.


Checking for spark

This check proves the CDI box output without involving the plug and cap.

1)  Unplug the 'king' lead from the coil.  Plug in a spare lead and spark plug into the coil.

2) Connect the threaded body of the spark plug to the engine case using a jump lead.

3) Crank the car over and check plug for spark.

If the spark is ok but the car doesn't run correctly, investigate cap, rotor and ignition leads.

NEVER CRANK THE ENGINE WITHOUT THE KING LEAD CONNECTED TO THE COIL.   If the spark has nowhere to go, there is a high possibility that the CDI unit and/or the coil will be damaged.


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