QuestionQUESTION: Hi,
had my 76 Spitfire 1500 for two years now,when i first got it i took it to a young guy that has a Brit car shop and got some of the basics done plugs,plug leads he also suggested a new coil which we did also.I've always had a rattling noise once the car is hot at around 3000 RPM under strong acceleration and cannot get the car timed or running just quite right,recently delving deep into part #s i find that i have a Lucas DLB 105 sports coil which says it's 12 volt but after researching engine #s and year of production i find the car is supposed to have a 15C6 lucas which is 6 volt with internal ballast resistor as it is the early electronic ignition,recently my son and i were trying to figure out why we seem to have an orange spark at the plug leads that doesn't look too strong and the rear plug gets wet with gas,a fellow car fan tells me that the spark should be almost white if the right power is getting through,what do you think,is the coil an issue?
Thanks,Barry
ANSWER: Hi Barry,
The coil must first match the ignition system and most have been changed by the time the car was out of warranty. Another factor is that your car came with a bypass system that used a low volt coil (usually called a 6v coil). The way it operated was that when the key was in the "Start" position the starter solenoid was activated and that connected a bypass wire directly (12v) to the 6v coil. However when the starter was operating there was not 12v available to the coil so only about 9v to 10v actually was going to the coil. Thus the coil operated without overheating it. As soon as the key was released back to the "Run" position the solenoid no longer supplied power to the coil and a power supply from the ignition switch now powered the coil through a resistor wire which dropped the voltage from 12v down to a voltage that the coil could operate on without overheating. The electronic ignition system needs to have a coil that matches it. Most electronic ignition systems do require the low voltage coils called 6v coils.
Many of the ignition systems have been changed over the years on these cars by owners so you need to try to ID what you have and what it needs in the way of a coil. Your Brit car shop should be able to do that. Engine numbers and coil numbers will do no good unless your ignition system is original and that is unlikely as most of them failed before the car got out of warranty many years ago. I replace some twice before they got out of warranty.
Howard
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QUESTION: Thanks Howard,
the way i read it in the parts catalogues is that the DLB 105 should be for systems with points and i do still have electronic the distributor is the original #45DE4 as you said i don't know if the electronic system is stock but most of the catalogues reccommend DLB 102 or sports DLB 110 for the later models,would the wrong coil cause poor spark and maybe cause what sounds like pinging at 3000 rpm or even a wet plug?
AnswerThe wrong coil can cause a weak spark or over heat a coil. But not pinging at 3000 RPM.
Pinging from an engine is detonation and that is destroying the engine. Detonation can be caused by several things. Low octane fuel, too far advanced ignition timing, over heating, Mixture too lean, Excess carbon in the combustion chamber, Spark plug heat range too hot, corner of a head gasket sticking into the combustion chamber and oil burning. Any one or combination of these will cause pinging especially noted under load.
Low RPM detonation (up to 3500 RPM) is heard as pinging but there is a high RPM detonation that is not heard that also will destroy an engine in a very short time.
If the coil is not over heating and the engine starts ok you should find a local shop that has a scope and have it put on the scope to look at the primary and secondary of the ignition system to see if that coil is a match for the system. Most shops don't charge much to just put one on the scope.
But you MUST correct the detonation or you will not need an ignition system soon.
Howard
