Verifying The TDC Offset With A Dual Pickup Distributor

Verifying The TDC Offset With A Dual Pickup Distributor

About

When installing a Dual Pickup Distributor and we do not have data on when in the engine cycle the Home (sync) pulse is occurring, it can found with a little testing.   Because the distributor is mechanically distributing the spark to each cylinder it is possible to have multiple TDC Offset values that line up the ignition timing.  In fact there are as many TDC Offset values that will do this as there are the number of cylinders.  So even with an incorrect TDC Offset angle the ignition timing can be correct and the engine will run, but what can be incorrect though is the injector phasing.

There is some testing we can do to find the correct TDC Offset.





Testing Process

To test for the correct TDC Offset Angle we need to follow this process:


1. Connect a Timing Light to the spark plug lead for Cylinder #1.

2. Go Online with your ECU so you can see live data including the "Ignition Angle" channel.

3. Go to the Main Setup / Engine / Ignition section and tick the box to enable Cylinder Correction and hit OK. You may be prompted to Power the ECU Off and back On again.



4. Start the engine and check the ignition timing. It should match the value you see on your software.

5. Go to the Ignition Angle tables and find the Cylinder 1 table.  Set all values in this table to a value of  "-15". This is done so that the ignition timing for just Cylinder 1 is different from all others.



6. Check your timing with the timing light again. If the timing has not moved then you need to adjust the TDC Offset by one firing interval angle.

Number of Cylinders
Firing Interval Angle
4
180
6
120
8
90

i.e. if you have a V8 and your TDC Offset was set to 50, you will increase this by 90 to a new value of 140.  Because we are shifting the timing by one cylinder interval the actual ignition timing is the same, only the cylinder that the ECU thinks is firing has changed.

7. Check the timing again, if it still has not moved keep repeating this process until you find the offset value where the timing has retarded by 15 degrees.

8. Once found, set the Ignition Cylinder 1 Correction table back to all Zero and the test is complete.  You can choose to disable the Cylinder trims if they are not needed.

You now have set the TDC Offset Angle so that the ECU can correctly identify Cylinder #1 and everything is in perfect sync!







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