5 replies to this topic

[stevelane]

Is there any way of testing that my coil works when it's not on the car? Maybe using a multimeter

I have a couple lying around and not sure which one works but am not in a positsion to put them on the car at the moment.

[dklawson]

Coils are often blamed for problems that lie elsewhere so it would not be uncommon to have one or two available that you are unsure of but probably work.

All you can check on the bench are a few resistance measurements. Unfortunately, short of a complete failure (open circuit) the multimeter will not fully identify a problem coil.

Start by measuring resistance between the two low-tension terminals. For a standard coil you should measure about 3 Ohms. For a ballast coil you should measure between 1-2 Ohms. For a FACTORY electronic ignition you should measure somewhere around (and possibly below) 1 Ohm. (Others will have to tell you what the exact resistance for the factory electronic ignition coil is). All measurements must be made with no wires on the coil.

The second measurement you can make is from the output high-tension terminal and the low-tension terminals. You should find several thousand Ohms. The exact figure will vary from coil to coil so I do not feel comfortable telling you specific numbers.

An obvious sign of coil failure is any evidence that oil has leaked from the coil.

The problem is that a coil may pass all these resistance tests and work fine at idle. Typical coil failure symptoms such as misfiring do not show up until the engine is running at high revs and/or is hot.

[stevelane]

So this would at least tell me that i can use it to get the car started? And then check more once its on?

[dklawson]

Absolutely. If you make any of the measurements above and detect "infinite resistance" (open) then the coil is definitely no good. If you get resistance readings that are compatible with what type of coil your car needs then you can install the coil and use it. If you don't experience any misfires at speed or at temp it will be fine to continue using the coil.

[carbon]

As well as the multimeter checks as outlined by Doug the old style (non-electronic) coils can be checked by 'flashing' 12 volts from a battery across the two low tension contacts, with a length of HT coil going to a spark plug with body resting on the coil.

If you see a half decent spark at the plug gap then chances are it will work on the car, at least get it started.

[stevelane]

^{Thanks for all your help guys - Looks like they both have resistance so at least I can rule out chucking them at this stage and hopefully use them to get the car going at least}