Check Distributor Phasing

Having a little trouble with the Plymouth Roadrunner of later and decided to check over the entire ignition system. This vehicle is equipped with a Mopar electronic ignition. We wend over all the obvious things, checked the timing, replaced cap, rotor, plugs and leads etc. checked ober the earths and wiring connections and finally, decided to check distributor phasing.

What do you mean by check distributor phasing you say?

Well phasing refers to the point at which the rotor sparks in relation to the reluctor, when the point on the reluctor sent the signal to the coil to spark, the rotor should be just passing the point on cap.

Have a look below as we try to walk you through the process.

Old Cap and Rotor

First you will want an old cap and rotor if you have one.


Drill and Cap

Get the drill out, we used a 13mm drill bit and done a bit of extra filing


Cap with hole

You need to drill a hole directly in front of one of the plug lead towers, so that you can see down at the rotor with the engine running.


Cap and Rotor

you can get an idea of where the rotor will pass by sitting in on the king lead tower.


Inside of Cap

We’ve marked the center of the tower with some white tip-ex. to make it easier to spot with the timing light.


Cap Marking from above

Here is a view of the marking from above.



Rotor Marking

We also marked the center of the rotor with some tip-ex too.


Cap back on Vehicle

Here you can see the cap with back on the car, its difficult to see the through the hole with the plug booths, thats why it helps to mark the tower with tip-ex.


Timing light

Get your timing light ready, we recommend a trusty snap on gun. We also have an Innova gun that with advance setting which performs equally as well, and doesn’t cost an absolute fortune.


Timing light on the Distributor

Connect the timing light to the plug lead where you drilled the hole and point it into the hole with the engine running. you might have to zoom in a little, but you can see the marking on the rotor lines up nicely with the marking on the plug lead tower.


pahing with vacuum advance.

Its hard to see here as the white part of the rotor has lined with with the mark. This phasing happened when we reconnected the vacuum advance, this rotor turns anticlockwise, so its sparking a little earlier.


We hope this gives you a little insight into how to check distributor phasing, its not something that is often checked and becomes a lot more imported and running nitrous or forces induction. The idea here is to check the the rotor is lined up and sparking as close as possible to the plug point. The further away the rotor is, the weaker the spark, you also run the risk of it sparking to the wrong plug causing misfires etc.