How to Diagnose a No-Start Problem
by Douglas Samuelson - email:  dsamuelson@frii.com

1. Engine will not "crank" when the ignition switch is turned to the start position. 
2. Engine will "crank" but will not start.

Let us first will address condition #1.  If the starter does not attempt to engage, and if no "clicking" noise is heard, the first step would be to check the condition of the battery and battery cables.  If a volt meter is available, check the battery voltage at the battery.  If you do not have access to a volt meter, a simple (not fool-proof) method would be to turn on the headlights and check the brightness, operate the heater blower or other accessories to determine if they are functioning normally.  It is always a good idea to check the battery terminal connections at the battery.  Even though they may not appear to be corroded it is possible that corrosion has formed between the battery cable terminal and the battery post (referred to as a "frost line" by many mechanics).  Clean the circumference of the battery cable terminal and the battery post (on top post batteries) with a terminal cleaner or suitable tool, and the mating surfaces of the cable terminal and battery on side terminal batteries.  Re- attach the cables, making sure that they are tight.  Some side terminal connections may appear to be tight, but the insulating material around the cable terminal may be tight against the battery but the mating surfaces may not be in contact.  Trimming away excess insulating material from the cable terminal is a temporary way to correct this condition, but cable replacement would be recommended.

If the battery and cables check out O.K., proceed to the starter.  If the starter is accessible, and if it is the type with a integral solenoid, check to see if the small gauge wire attached to the solenoid is "hot" when the ignition switch is in the start position.  This can be accomplished with a test light.  Some solenoids may have 2 small gauge wires attached, in which case one of them should be "hot" during this test.  If the solenoid is in another location such as on a fender well, the same test will apply.  If the test light does not light, the problem could be in the ignition switch, the transmission neutral safety switch, the clutch safety switch, or the theft deterrent system if so equipped.  If the test light lights up, the problem is in the solenoid or the starter, and replacement or rebuild will be necessary.  If the solenoid "clicks and the starter does not crank, replace the starter. 

Testing the ignition switch, transmission neutral safety switch, clutch safety switch, and theft deterrent system is not something that should be attempted by an inexperienced mechanic unless you have access to wiring diagrams and the necessary test equipment.  Due to the remote location of these components, they are difficult to access.  A service manual should be used to perform test procedures.  A word of caution: do not attempt to probe wiring that you are not sure of.  You could wind up with a deployed air-bag.

Now we will address condition #2: engine will "crank" but will not start.  In order for an engine to start and run it must have the following:

1. Fuel
2. Ignition (spark)
3. Compression
4. Correct valve timing

Most fuel injected engines have a test port where a fuel pressure gauge can be attached.  On carbureted engines, a fuel pressure gauge can be attached where the fuel line attaches to the carburetor.  If fuel pressure is low or non-existent proceed to testing of the fuel delivery system (fuel-pump and relay, fuel filter, and fuel lines).  If a fuel pressure gauge is not available, a shot of starting fluid or carb cleaner in the carburetor air-horn or air plenum will enable the engine to start and run for a few seconds if the problem is in the fuel system.  Take extreme caution when using this method because an engine "back-fire" could cause a fire or personal injury.  If the engine starts, do not condemn the fuel-pump before checking the fuel filter, pump relay, and fuel lines.

If the engine is getting fuel, check to see that it is getting spark.  A simple test is to disconnect a spark plug wire at the plug and hold it 1/4" away from a ground while having an assistant crank the engine.  Use an insulated pliers to hold the wire or you could get an unpleasant surprise.  If spark is present, pull that spark plug and maybe a couple of others to make sure that they are not fouled or wet with fuel or coolant.  If there is no spark, and if the engine utilizes a distributor, remove the distributor cap and inspect the dist.  cap and rotor.  If the rotor has a crack or carbon track, the spark could be traveling from the rotor to the dist.  shaft rather than to the plug wire.  With the dist.  cap removed, make sure that the shaft is turning when the engine is being cranked.  On older model vehicles with conventional ign.  systems, ascertain that there is voltage present at the positive terminal of the ign.  coil when the ign.  switch is in the run position.  If no voltage is present, check the ign.  switch, ballast resistor (if equipped), and wiring.  If the distributor has and internal ign.  module, most auto parts stores have test equipment to test them if you do not have the necessary equipment.  Most later model vehicles do not have a distributor.  The ignition systems on these vehicles consists of an ignition coil (or multiple coils), ECM, and crankshaft angle sensor in addition to the spark plugs and plug wires (except applications that have a coil for each cylinder plugged directly to the spark plug).  Testing of these components requires a service manual and specialized equipment. 

If the engine has spark and fuel, the next step is to test compression.  Remove the spark plugs, and perform a compression test with a suitable compression gauge or cyl.  leak tester.  If the compression is extremely low, repeat the test after injecting a small amount of engine oil into each cyl.  through the spark plug holes.  I have experienced a few vehicles that were so "flooded" with raw fuel, that the piston rings would not seal the combustion chambers and and after this procedure, the compression was restored.  These were extreme cases.  If there is no compression, the engine has probably experienced severe damage from overheating (severely scored pistons or bent valves).  Removal of the cylinder head will confirm the damage.

If the engine has fuel, spark and compression (sometimes low compression or varying compression from one cylinder to another) the next step is to verify correct valve timing.  This is determined by removing the timing covers and aligning the timing marks on the crankshaft sprocket, camshaft sprockets, balance shaft sprockets, and oil pump sprocket (some engines do not have balance shafts and oil pumps driven by the timing belt).  If the belt has stretched and "jumped" the marks will not line up.  Most engines will not run if the belt has jumped more than a couple if notches.  The same is true for engines using a timing chain.  If your engine is an "interference engine", the pistons have probably contacted the valves, and cylinder head removal will be necessary to replace the bent valves.  An interference engine is one that does not have provisions for piston to valve clearance in the event of timing belt or chain failure.  An interesting note: many Subaru engines can actually break a timing belt, and no damage will occur.  There are manuals available that show valve timing specifications and identify interference engines. 

Before resorting to trial and error, follow these procedures.  Good luck and happy motoring.