3 replies to this topic

[pierres]

Can you test a coil to see if the HT and LT are woking as they should and what voltage should i get on a standard 998cc mayfair

 

Thanks

[dklawson]

Never, ever try to measure the high-voltage coming out of a coil.  It will damage most common DIY test equipment and can be quite painful for the person doing the test.  The output voltage can be anywhere from 20kV on up.

 

You can bench test a coil using an improvised ignition system.  Connect a high tension wire between the coil's tower and a spark plug gapped to around 0.025".  Rest the spark plug on a sheet of metal.  Connect an ignition condenser between coil (-) and the plate (clamp the mounting foot of the condenser to the plate the spark plug is resting on).  Connect a 12V power supply with its (-) cable connected to the plate.  Also connect a jumper wire between coil (-) terminal and the metal plate.

 

This gives you an earth/ground connection for the plug, coil (-), and the condenser.

 

Now turn on your power supply and TAP (do not hold, TAP) the power supply (+) cable to coil (+).  Each time you lift the cable off coil (+) there should be a spark across the spark plug gap.  There will also be a spark on the power supply cable each time you touch and remove it from the coil (+) terminal.  Don't let this startle you.  Do not expect the spark across the plug gap to be huge, or super bright.  Try and conduct your test in shade or an area without a lot of bright sunlight.  A blue spark means the coil is OK, an orange spark means you should try a different condenser and repeat your test.  No spark means EITHER that the coil is bad or the condenser is bad.  Do NOT assume your coil is bad until you have tried a new condenser during these tests.

 

EDIT:  I should have mentioned if you disconnect the low-tension wires from the coil you can measure across those terminals for resistance (the wires must be disconnected).  The low-tension windings for a "standard" ignition coil will measure about 3 Ohms.  For a "ballast" ignition coil the windings should measure somewhere between 1 Ohm and 2 Ohms.  If you measure from either low-tension terminal to the high-tension (tower) terminal you should find several thousand Ohms.  This high-tension to low-tension resistance value varies a lot from coil to coil so there is no set "right" answer. 

Edited by dklawson, 21 January 2014 - 06:34 PM.

[KernowCooper]

This may help you http://www.theminifo...-testing-coils/

Testing coils

[pierres]

Thanks for the replies this will all be checked at the weekend, thanks agian