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Engines need a few things to run; air, fuel, and spark. But to run properly engines also need to have a good amount of control over these; timing, throttle position, crank position, emission, and pressure. Throw all those into a basket and you get your ECU reading all the sensors on the engine. There's more to just the basic three than just getting the engine to turn over and run.

Starting out though, the basic three will do for a preliminary diagnostic on why the engine isn't staying running, won't turn over, or runs poorly.


Air will always go into the engine, there is a rare occurrence where the engine will not get air, but a clogged filter, bad gaskets, closed throttle plate(s) will of course affect the amount of air which reaches the combustion chamber.
Doing the minimal checks before assuming that the intake valves are stuck closed should be the first thing you complete. Make sure the air filter and intake pipe are not clogged. Check to see that the intake itself is attached properly. Remove the filter plenum/top hat at the throttle body to make sure that the throttle body butterfly is not sticking and there is a visible slit to the intake manifold.
Check to see if all vacuum hoses are hooked up, not cracked, and in the correct order as per your vacuum diagram. Replacing vacuum hoses for peace of mind is a good idea as well. Parts stores sell them by the foot in many different lengths. You also can purchase vacuum caps to remove hoses if necessary. The more hose you eliminate the less problems you will have in the future chasing down a leak.

If all is well, chances are air is not your problem.


Fuel can be a little more difficult to diagnose. First thing to check quickly would be the fuel pump; simply turn the key to "On" and see if you can hear a whir from the tank. If you've got noise, good chance the fuel pump is working. Next would be to check fuel pressure at the carburetor/throttle body (14.5 PSi)/fuel rail (35-45 PSi). Fuel pressure below, but with a constant pressure, is indicative of a clogged/clogging fuel filter.
Failing pumps, though they still may turn on, tend to have an immediate blast of pressure and then drop off dramatically.
Hesitation when applying the accelerator pedal, ticking from injectors, lean/rich burn in one or more cylinders (you can tell by pulling the spark plug) usually turns out to be a bad injector(s). If the injector has failed completely; full open or full closed, you still might be able to get away with cleaning the injector, but chances are purchasing a new injector is the route to go. Failing injectors tend to tick, not too loud, but the ticking is apparent when listening to the injectors while the engine is running from a few feet away. (On the plus side Mopar injectors are well made).


No spark conditions can usually be traced to the ignition coil to start. With older vehicles you still have the option of pulling the lead wire from the distributor and grounding it to the engine while cranking. Good spark is blue in color. This simple check will let you know if the coil is in good working order. Make sure you use the appropriate pair of pliers to remove and hold the wire.
Next is to pull the distributor cap and the distributor rotor. Brass is the best, cheapest connection for electrical current on both the cap and the rotor, however, it does foul up rather quickly. If you notice heavy carbon deposits, get those cleaned off with some fine grit; 200+ sandpaper. Make sure not to clean them so heavily that the spark will have to make a long jump from pole to pole.
Cracked distributor caps have a tendency to 'leak' the spark to the closest ground point outside or inside of the cap. This causes a noticeable misfire on one or more cylinders. The caps, if on the engine for a long time, can become brittle and crack rather easily due to the amount of temperature changes. Easy way to check for arcing is to put water in a spray bottle and spray it on the cap itself while the engine is running.
Much like the lead wire from the ignition coil, you can do the same test with the spark plug wires. Before removing and checking spark, make sure that there are no areas on the spark plug wire that are worn. Getting a good amount of voltage and current going through you is never a good feeling.
If you've got great spark to all wires, now is the time to pull spark plugs. Healthy spark plugs are tan in color on the electrode and the ground with a gap close, or at, the specifications required for the engine. Larger gaps have worse spark which leads to a darker, if not sooty-black, color on the spark plugs. Smaller gaps tend to have a lighter color, near white, on the tips, which can mean that the fuel mixture is quite lean ; you'll have pinging and detonation in one or more cylinders.
Cleaning off the spark plugs is possible, much like the cap and rotor, to see if the problem persists, but if the color and gap is not in good condition, might as well replace the affected spark plugs as they are ~$1.99 a piece for OEM style copper core.

In summary, these are just quick ways to check and diagnose symptoms of a no start on most vehicles. Each vehicle is different and can have different quirks and procedures for testing. A new turbocharged vehicle may have a coil pack, two coil packs, or Coil On Plug setup along with one or more injectors per cylinder with more electronics; which will be easier to diagnose with all the sensors.
Diagnosing an engine problem, transmission problem, or any other failure requires that all necessary information be accounted for and run through simple 'if/then' tests. Just remember, you may have more than one problem at a time compounding to the same outcome. Fixing one problem may not solve the total issue at hand: No start because of bad ignition coil, fix coil, still no start. Check Crankshaft Position Sensor, no voltage, replace, engine starts, although runs poorly. Check Cap and Rotor; faulty. Replace, engine runs smooth. Etc.
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