The 'E' Type Forum

Hi all,
I have a curious issue where the car starts and runs perfectly for 40 mins or so before developing a misfire that brings it to a halt, almost. I've so far managed to limp home! Idles perfectly but won't rev. Coil is very hot. Runs fine up to this point so no reason to suspect timing of fuel. Switch off for a while and switching back causes it to run well for a mile or two before the misfire returns.
I have an electronic dizzy and a 'dry' electronic coil that was an expensive option after I suspected the last coil of failure for the same reason. Dizzy wired to coil. Newish rotor and plugs which I've examined and seem normal. Running high octane UL.
I recently replaced the battery as the 3 year old one seemed to weep all the time. I have replaced the alternator and voltage regulator with known good items.. no change to problem.
New problem is fuel, oil, water gauge, fan motor fuse going pop regularly after working sporadically for half an hour.. connected? Who knows..
All ideas welcome!

Try a new coil.

The overheating coil may be because your charging voltage is too high, and that would also explain your weeping battery, and your popping fuses.

Check your alternator output at higher RPMs.

Agree with the other posts....Check the running voltage . Try a new coil. Incidentally you mention a dry coil....I presume some modern type as traditional ones are oil filled for cooling and insulation purposes.

Just one other thought....is your new coil purpose built for your system or just an off the shelf replacement coil? If the latter make sure it is not a coil for use in a ballast resistor system. These coils are run with a resistor in series with them so they see about 6 volts when the car is running. Fit one in an unballasted system at 12 volts and they will rapidly over heat and expire.

What is an 'electronic' coil? Not sure I like the sound of that. Coils don't like getting hot, neither do condensers. If the points gap is too small the coil will overheat, but if you've got modern electrickery on there that rules that out I guess. Worth checking the fuel cap vent, just to rule it out. I would put my money on condenser - does it even have one though?
And I agree, the charge rate sounds suspect - don't believe what the voltmeter tells you - check it with a proper meter - should be around 14 volts at normal running speed.
I had an Aston that had a similar problem - they had put the coil right next to the exhaust manifold. I moved it inside the car - hidden under the dash somewhere, which also turned out to be a pretty effective anti-theft immobiliser - hot-wire that!

Hi - thanks for all your suggestions. I will order another coil (this will be the third i've tried to solve the same problem, but worth a go). The current one works a treat until it gets hot. The previous 2 i tried were standard 'wet' coils. Could the electronic sensor in the dizzy cause this?
I had thought there might be a charging issue, which is why changed the alternator, battery and the voltage regulator from a car that was working fine. The 'new' alternator was on a S2 so i changed the pulley for the smaller s1 type - would this account for overcharging? I've used it since i rebuilt the car and no probelems until recently. I dont really understand how there could be overcharging as I thought the voltage reg took care of that (i have tried 3 of those and all the same results) the ammeter reads just fine.. no overcharging reading there.
its very frustrating as the problem seems to have arrived out of the blue. Everything worked fine and then this problem started, hence i suspected a dodgy coil. Car has done 1100 miles since total rebuild and a good 1000 of those were trouble free.

If it's any consolation I had an almost identical problem on an Aston and it proved the very devil to sort out. I never did get a definitive answer - believe it or not, new plugs seemed to be an effective cure but I sold it before I really got to the bottom of it. It might pay you to get some long leads and bring the coil inside the car so you can feel how hot it's getting - or get one of those laser thermometers and see if you find a critical temperature at which it starts playing silly buggers.
All you have to do then is find out WHY it's getting hot!
That's assuming it is in fact the coil.
The smaller pulley will increase alternator output at idle but shouldn't make much difference beyond that.
That gives me an idea - how about pulling the wires off the back of the alternator and run on battery voltage alone. If it still faffs about, you have at least eliminated over-charging.

You need the correct coil to match your electronic distributor and the dwell angle it's working to and I suspect you've got the wrong one. 12 volt coils broadly have a resistance of either less than 1 ohm or around 2 to 3 ohms. The standard E type coil has a resistance of 2.5 ohms and I believe your distributor is expecting to work with a standard type coil.
If you buy another dry coil you need to ensure it has the correct resistance as I suspect most dry coils are designed for modern electronic systems and will be less than 1 ohm.

You are correct that the size of the alternator pulley will not affect the charging voltage as the regulator controls that but it would still be a good idea to check with a voltmeter that your voltage is around 14 volts when the engine is running.

John

To answer Hugo and why coils get hot......

Coils are energy transfer devices and the transformation mechanism is magnetism which doesn't involve heat so there's no intrinsic reason for a coil to get hot except.....

When the points close or the equivalent inside an electronic module the coil has 12 volts or so across it and current flows limited by the coil's resistance (well, technically, it's impedance) and the electrical energy is converted into magnetic energy stored in the soft iron core of the coil. At some point in time, the coil's core will be "full" of magnetism, ie saturated and any further current flow is just turned into heat until the points open, the current flow stops, the magnetic energy field collapses and the only place for it to go is via the high voltage generated by the coils secondary winding and off to the spark plug.

How long the points stay closed for is called the dwell angle and as in all design compromises the combination of how long the points stay closed, the number of cylinders to fire per revolution, the maximum RPM, the coil resistance and the mechanical constraints of a distributor all constrain the need to fully charge the coil and saturate it but minimise current flow that is just generating heat.

The most extreme situation is a stationary engine with the ignition on and in a position with the points closed (which is most likely) where the coil will just sit there sinking several amps and getting hot.

In a distributor with conventional points you are limited by how long the points can remain closed (and charging up the coil) by the fact that due to mechanical limitations it also takes time to open the points and you have to manage one open and one close cycle before the time comes to do it all again for the next cylinder which is not long in a 6 cylinder engine at 6000 RPM! If you have electronic points your open time is negligible and you can sink greater currents into the coil so there is more freedom to alter the dwell time to get a full spark at all RPM but to match that the designer may choose a coil with a lower resistance hence the rise of coils made specifically to get the most out of electronic ignition. That said, many electronic points modules or distributor replacements are designed to work with a standard "points" coil (2 to 3 ohms) for compatibility and originality and will do so very well and much better than mechanical points.

John

That is very useful information - thank you. I had a friend who left her Citroen 2CV with the ign on. After several hours the coil exploded, spattering bitumen all over the engine compartment. She got a surprise when she went to start the car!

It would be rather useful if we knew what Series car you have (suggest you put it in your signature which can be changed from your User Control Panel) as the S2 cars had a ballasted coil C35812 which means the impedance of the coil is less than 1 ohm but there is a ballast resistor in series with it - 5 in the diagram.


As John says you need to check the impedance of the coil and add a ballast resistor if one is required or buy a non ballast coil part number C30120.

Not all S2 cars had the Ballast resistor coil. Only Chassis Nos. from
1R.1393 1R.11052 OTS
1R.20486 1R.27051 FHC
1R.35643 1R.42850 2+2 (1970) onwards
[source xkebooks.com]

As Mark suggests only the later S2 cars had a ballasted resistor coil but no car that's subsequently been fitted with any form of electronic ignition/distributor should be run with a ballast resistor left in place and the coil used should match the particular type of electronic ignition fitted - which is NOT the same as an "electronic ignition coil"!

If in doubt the safest bet is to use a standard 12 volt coil, the part number for which David listed above.

John

Or, if you want to go faster, the Lucas DLB105 Sports coil:

OK, I'll bite. Just how much faster, David?
Or should I say how much slower would I have been if I didn't already have one of those?

Geoff

Its painted gold so it must be faster!

Heuer wrote:Its painted gold so it must be faster!

Naa, only billet CNC stuff makes them go faster.

(and it's not paint)

Heuer wrote:Or, if you want to go faster, the Lucas DLB105 Sports coil:

Well the increase in speed from the gold is somewhat offset by the Lucas sticker...

I have a feeling there is cheap Chinese cr@p being produced today with the Lucas label - have they bought the name or something?