Board logo

Ignition Coil
thefreak - 22/8/08 at 02:14 PM

Hi Guys,

Wonder if anyone can help me out with a bit of advice.

I've aquired a Locost with a 1.6 xfow engine fitted. it's about 90% complete (bought it from Chris - flyingkiwi I think on here a couple of years ago) and I'm having issues with the ignition coil.

When the ignition is on, without the engine running, the coil gets very hot, as well as if its left running for any length of time.

I've bought a new coil as I though the old one may have been faulty (the plastic end cracked) but it still does it with the new one?!

Anyone got any suggestions?

Thanks

Stewart

David Jenkins - 22/8/08 at 02:44 PM

Assuming it's points ignition, and a matching coil - have you fitted a ballast resistor?

Normally these engines are set up with a 9 volt coil, with a big fat resistor to reduce the car's 12v to 9v. This resistor might be a length of what looks like ordinary thick wire. When you turn the ignition key to start, this resistor is bypassed - but as the battery volts will drop to 9 or 10 volts when the starter is turning the coil still gets the correct voltage.

If you don't have the ballast resistor the coil continually gets 33% more volts than it needs, which cooks it.

If you have electronic ignition, you might have fitted a 9v coil by mistake - you will need a 12v coil specifically designed for it.
HTH,
David

[Edited on 22/8/08 by David Jenkins]

02GF74 - 22/8/08 at 02:59 PM

what exactly do you mean by "very hot"?

can you quantify it by giving temperature in degrees C?

ohm's law and the laws of physics will mean the coil gets hot - do the sums and it is equivalnet of 60 W light bulb - can you hold one of those in your hand and not go OUCH!!!!

Two things you have to do.
1. verify that the coil is correct type. For points, the primary resistance will be 3 ohm. For electronic ignition, it will be 1.5 ohm.
2. Do not leave car with ignition on for any length of time; chances are if points are closed, then current is passing through the coil with the result t hat it is being heated up more than when engine is running (think dwell angle) - they can explode!

You do not want that to happen as you will get nasty oil stuff over your engine bay.

MikeRJ - 22/8/08 at 05:14 PM

Never leave the ignition turned on for any length of time if you ignition system uses points! I'm sure lots of (errm..older) people here have seen melted coils from this.

Modern electronic system turn the coil off if the engine stops running, points just keep the current flowing as engines rarely stop with the points open.

02GF74 - 23/8/08 at 07:31 AM

quote:
Originally posted by MikeRJ
as engines rarely stop with the points open.


Assuming that the igntion is cut off at random, then surley the chance of this happenning is related to dwell angle?

rusty nuts - 23/8/08 at 12:05 PM

quote:
Originally posted by 02GF74
quote:
Originally posted by MikeRJ
as engines rarely stop with the points open.


Assuming that the igntion is cut off at random, then surley the chance of this happenning is related to dwell angle?


A 4 cylinder engine is likely to stop in one of two positions, usually with the pistons half way down the bores. That would normally leave the points closed

MikeRJ - 23/8/08 at 12:11 PM

quote:
Originally posted by 02GF74
quote:
Originally posted by MikeRJ
as engines rarely stop with the points open.


Assuming that the igntion is cut off at random, then surley the chance of this happenning is related to dwell angle?


Only if there is an equal chance of the engine stopping at any crank angle. In practice the engine will nearly always stop with one piston partly up the bore on it's compression stroke (in fact always on a 4 or more cylinder engine). Since the dwell angle is fixed on a points system, and is typicaly 60 degrees or so (i.e. 120 crank degrees) this gives a very high chance of the engine stopping with the points closed.

David Jenkins - 23/8/08 at 12:56 PM

It's worth noting that Stewart originally said that the coil also gets very hot when the engine's running, so how the points sit when the engine's stopped is not entirely relevant!

It's a fair answer though - apart from checking whether a ballast resistor is fitted, and whether there's a 9v or 12v coil, NEVER leave a car with points ignition with the engine stopped and the ignition on (not for more than a minute, anyway).

thefreak - 26/8/08 at 03:32 PM

Thanks guys, I'll investigate the coil/ballast requirements.
It's got points, as the funds for the electronic ignition aren't available at the mo.

It does get OUCH hot if left for any length of time. Would I just check the resistance over the +/- terminals when it's disconnected (of the original coil) but then how would I know if this was the correct one in the first place, as this happened to that too. Or would I check the resistance across the +/- leads coming from the battery/going to the points?

rusty nuts - 26/8/08 at 06:13 PM

If you can find one a Fiesta with the Valencia engine will supply an electronic distributor . Make sure you get the matching coil and wiring with the multiplugs . Needs only one extra earth connection , should be cheap and worth while

David Jenkins - 26/8/08 at 06:15 PM

That's what I did originally...

Amazingly useful link

Once it's set, you'll never need to adjust it again. Not as good as a full-blown programmable ignition system like Megajolt, but loads better than points.


[Edited on 26/8/08 by David Jenkins]

02GF74 - 27/8/08 at 11:26 AM

quote:
Originally posted by thefreak

Would I just check the resistance over the +/- terminals when it's disconnected (of the original coil) but then how would I know if this was the correct one in the first place, as this happened to that too.


disconnect all wires to coil; then measure resistance between + and - tabs.

3.0 ohm indicates 12 V coil
1.5 ohm is 9 V coil which requires ballast resistor.

ok, your readings may differ from the above but it should be possible to figure it out.