Diagnosing and correcting a misfire that develops on the track can be far more frustrating than trying to figure out why a car will not start. There are, however, some similarities between trying to determine the cause of a miss and why a car will not start.
Troubleshooting and Fix misfires can be nerve wracking. Is it really ignition related or is it a fuel problem causing the misfire?It may be caused by a mechanical problem within the engine or even a cooling system problem. Other than mentioning the need to check for a blown or leaking head gasket and a bad or low-pressure radiator cap, we will not dwell on the engine internals. However, cooling system problems are responsible for over 20 percent of “ignition problems.”
Fuel system problems are more often than not attributed to ignition problems. Before delving too deeply into the ignition, rule out any basic fuel system maladies: A fuel pressure gauge will identify a weak fuel pump, clogged fuel filter, or collapsed fuel line. A warped carburetor base, worn throttle shaft, or other vacuum leaks will show up as a lean condition. A clogged main jet may pass a visual inspection if it is blocked by a piece of sand or clear plastic. If in doubt, use a piece of thin wire to make sure that the jet is not clogged. A blown power valve should be obvious from an overly rich exhaust.
A short checklist will help in determining the source of the problem:
· Using solid-core spark plug wires, including the coil wire, can induce an unwanted signal into the ignition amplifier, causing the amplifier to trigger at the wrong time.
· Poor connections on either end of coil and / or spark plug wires may cause a misfire.
· Bad crimps or connectors not seating on the plug or in the coil can both cause problems.
· Sometimes, a little moisture inside the plug wire boot turns to steam and blows the wire off. A thin film of oil will reduce corona and will help the moisture to escape.
· Spark plug wires must be separated. If possible, do not run them parallel to each other.
· In rare instances, having the coil mounted too close to the amplifier can cause problems.
· Do not run the coil secondary wire through the firewall with the distributor leads or the alternator lead as this can cause erratic operation due to “noise bleed over.”
· A weak ignition can cause a misfire, reduced power, or poor performance. This may be the result of a low battery or a malfunctioning alternator.
· Poor power connections, or wires and connectors that are too small can reduce ignition output.
· A master switch not rated for the application can restrict current flow enough to cause poor operation.
· Weak or damaged ignition components may work satisfactorily with a well-charged battery and cool conditions, but when the battery loses its surface charge or the box heats up, misfiring will occur. Low voltage and higher temperatures both require the ignition to work harder.
· Parts store switches might work well for a 10-amp blower or a 100-watt light but the ignition switch on current racecars may need less than 100 milliamps. This small amount of current may not burn through a thin film of moisture or across an oxidized set of contacts. Quality switches are a better and more reliable choice. A Mil-Spec number on a switch gives you, or the supplier, a reference where you can check and compare the qualities and capabilities of a given switch. Make sure that the switch you have chosen or are using will work well in your application. A $5 parts store switch may work most of the time, but do you use supermarket motor oil in your race engine?
Misfire or Stumble
A voltmeter in the dash of the car helps you or the driver diagnose a problem. It can alert the driver to a malfunction before it develops into a misfire. If the alternator quits, proper power management may allow you to finish the race with all electrical power coming from the battery. To accomplish this, all non-essential electrical consumption needs to be curtailed as soon as possible after the alternator quits. If the tach starts jumping, or the car starts missing, it probably too late to start a meaningful conservation of power. How the engine acts, combined with when and where on the track the engine skips, misses, or flattens out are all factors that may be used to diagnose proble