Ignition System Troubleshooting

by Rich O’Hara

(From Healey Motor News, 5/80)


Those of us, who have owned a Healey, or any other British automobile for that matter, have learned to deal with the occasional and persistent electrical difficulties associated with these cars.


To be fair, these problems often are not strictly a function of LUCAS, but are problems common to almost every car at some time or another. It is my experience that the most frequent problems with electrics reside in various components of the ignition system.

For us, these kinds of problems are frustrating and quite serious because either our car fails to run at all or it runs poorly and sluggishly. After frequent close encounters with the ignition systems of my 100-4’s over recent years, I would like to share with you what I consider to be the most common difficulties and how to go about attacking them. It will be impossible, of course, to cover every foreseeable problem.


As with anything, before you can begin to solve a problem you must have some understanding of how the system works and in what sequence (preferably before you begin dismantling every thing in sight). Once this is understood, it is relatively easy to diagnose where your problem is located. For electrics, simply identifying current pathways and being able to determine whether certain units are responding or not is 90% of the battle. If you otherwise approach the problem with logic, patience, and a little common sense you will find the solution is often quire obvious.


Many, but not all problems in ignition systems become apparent when starting the car. It may become very difficult to start and the condition often becomes most acute in wet or cold weather. If you get no response from your starter at all, your problem is likely in the ignition-starter switches, battery cut-off switch, battery, starter solenoid, starter, or the wiring and connections between these. Most frequently the trouble will simply be a loose wire connection or a battery in a low state of charge. The battery should be kept topped-up with distilled water. Even “maintenance free” batteries (e.g. Sears Diehard) should be periodically checked when access caps are provided. If you store your car for long periods without driving it, it’s a good idea to keep batteries charged up with a battery charger. Frequent or lengthy periods of discharge can be damaging to a battery. If you suspect a weak battery, first check its state of charge. The battery hydrometer, well worth its cheap price, is handy here and can be had at virtually any local department store. If the charge is up, inspect the battery terminals. The fact that they may look okay is not enough. They must be absolutely clean, tight, and firmly connected to the battery for peak power. If either terminal is warm or hot immediately after trying to start your car, this is a good hint that the connection is bad.


In the same way, check to see that all connections are clean and tight between battery and starter. The negative cable first connects to the starter solenoid, a shorter cable connects the solenoid to the starter. The starter in turn must be properly grounded. In the 4’s this is accomplished by a short braided cable from the end of the starter to the frame. Next make sure the other wiring to the starter solenoid, the ignition coil, and the distributor is in good condition and secure to terminals. Look over your wiring diagram to get a clearer picture of what I’m talking about. Quite commonly, your problem will be in one of the above areas and is easily remedied. Spend the 2 to 5 minutes it takes to check these primary electrical connections and it may save you hours and even bucks later on.


The next step is to concern oneself with getting adequate spark from the ignition coil to the combustion chamber of each cylinder. Your engine may be turning over in good shape but will not start or it may start fine but cuts out, misses, or otherwise runs poorly. If so, your problem is likely in this section. Major components involved are the coil, the high tension spark wire from coil to distributor, distributor cap and terminals, the rotor, points and condensor, high tension wires to sparking plugs, and the spark plugs. This may sound hopelessly complex, but don’t panic! Think it through and any mechanically incompetent boom is capable of troubleshooting this system. If there is just one area of the workings of your Healey with which you should become familiar, this is it.


First of all, I am assuming you are getting sufficient fuel to your carburetors and that these are in good working order. The chronological order in which you begin to pick things apart is perhaps a debatable one. Personally, I prefer to start tracing at the source, the coil, and progress through to the spark endpoint, the plugs. If, on the other hand, you just finished working on one particular section, or had some part renewed, it would be wise to start there. There is no assurance a new part is free of fault or was installed properly.


For the backyard mechanic, there is little one can do to check coil performance short of looking to see if it is sending a spark to the distributor or by changing the coil itself to one that you know works properly. Check its terminals and the spark first. If the spark is strong (gives a good zap) and it sends out constant bursts, move on to the distributor. If everything else checks out, you may have to return to the coil and substitute it. Often they function intermittently. But considering the frequency of coil failure it is probably a good idea to have a spare on hand anyway. (All factory race Healeys ran with two coils, which may be some indication to you.) To check the spark, remove the coil wire from the distributor cap and prop it against a piece of metal (e.g. engine block) leaving a short gap of about ¼ inch. Turn over the engine and observe spark firing. (Or turn ignition on and quickly separate points by hand.) If not firing properly, the fault may lie either in the coil or in the wire itself. If it is in the wire, the only way to check it, if it is not visible cracked, is to replace it with a good one. Old wires or new ones that have been stressed in some way may have leaks in their insulation. I recommend replacement with copper core wires. They seem to provide a consistently stronger spark (although some radio interference will result unless you include a suppressor).


The same procedure can be used to check firing of wires from distributor to spark plugs.

It’s advisable to systematically check each wire and not just one. Again, the spark should be strong and fire at a constant rate with no missing. By checking there and the coil wire, you should be able to isolate your problem. If the coil wire fires but the distributor wires do not, you have a problem at the distributor. If both fire, a spark plug or plugs could be defective or fouled, distributor timing could be of, or fuel supply is the culprit.


If the distributor is suspect, do the following. Remove the cap. Inspect and clean distributor cap contacts, make sure the central carbon stem is not broken and that it moves freely, and closely look for hairline cracks in cap casing (inside and out). These are not always visible. If cracked, replace cap and condensor. Next, remove the rotor, check for cracks, and thoroughly clean its sparking surface. Examine the condition of the breaker points. Contacts should be free from pits, grit oil, and moisture and should be gapped at 0.015. Clean, renew, or adjust. NOTE: When replacing points, the order in which the fiber and plastic washers are installed is of the utmost importance. If out of sequence you car will not run. Try checking sparking at the contact breaker points by turning ignition on and separating points with a screwdriver. They should spark as points are opened but not when points close and come back together. From personal experience, I recommend carrying new points and condensor and ever a cap as spares in your tool kit. Providing all of the above is in good working order, install the rotor, lightly lubricate the cam, secure the cap, and make sure all plug wires are returned to their correct snug positions.


If spark is reaching the plugs, your fault may lie here. Assuming plugs are of proper size, remove each and inspect, clean, and check gaps. If fouled with oil or carbon or in otherwise worn condition, this could cause a miss, poor performance, and difficult starting. Remember, just because plugs are new does not mean that one may not be defective.


If you now have painstakingly checked out all of the above and you are convinced you problem is not timing ,carburetion, or bad fuel, go back into the house, kick back, and slowly consume the content of one beer. Reflect on what you have just done, look over your wiring diagram, then make one more patient and brief check of the complete ignition system.


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