Engine turns over but wont start

Check for spark.
Remove one spark plug lead from plug. Place a new spark plug into the boot. Ground the tip to chassis. Have a 2nd person turn over car. You should see a bright blue spark with an audible snap. No spark? Orange, weak spark? Check cable integrity, check primary and secondary coil resistance, check ground leads. Check for +12V from primary coil (+) to chassis with key to 'on'. Check condition of rotor cap and rotor button if installed. Cracked rotor caps allow moisture in and spark short-circuits before going to plug.

Check fuel delivery.
Clogged fuel filters, failed fuel pumps or pressure regulators cause a no-start condition. Spray starting fluid into intake. Make sure you use the kind that contains cylinder lubricant. If vehicle starts and runs while you spray, and quits when you stop, then your fuel delivery system is not doing it's job. Isolate problem by checking for pressure at the fuel rail, and then on the incoming side of the filter. If fuel pump does not put out pressure, check to see if it runs at all. Modern electric fuel pumps are often located in the fuel tank and access is sometimes available via a panel under the rear seat (of cars)

Check timing.
Intake and exhaust valves are mechanically actuated on most vehicles by means of a camshaft gear/sprocket (or two) , a belt or chain, and a crankshaft gear/sprocket. The distributors are linked with the camshaft via worm gear or a simple direct drive spline. Mechanical timing is checked via marks (dots) on the faces of the camshaft and crankshaft sprocket. Electrical timing is set with #1 piston at top-dead center of the compression stroke. Set in the distributor so that the rotor button aligns with the #1 of the metal post set in the cap.

Vacuum lines
Often after a top end job has been done such as a head gasket job, vacuum lines were not marked, or markings became unreadable. The vacuum line for the EGR is especially important as improper hook up will cause the egr to stick open during cranking, making it impossible to start. Under most hoods is a diagram showing the vacuum line routing.


Valve clearance.
Intake and exhaust valves must be adjusted with the specified gaps. If an intake valve has no clearance at top dead center of that cylinder, then compression is not made.