It doesn't take much for an engine to run, air, fuel, and spark, that's it. Sort of. First thing is to narrow down the possibilities as much as possible. Are we dealing with a starting/charging system problem, or an ignition problem. Maybe it's a fuel problem, or a mechanical problem that is giving symptoms of one of the others... If I haven't been able to get any preliminary information from the owner, I try to narrow in on the problem as quickly as possible. It's just a decision tree type of process that I've developed over the years that I find works well for me. I'll attempt to duplicate it here with links when it's necessary to skip over parts of the process. Bear with me as it either takes shape or collapses under its own sheer mass...Some of the links may change, disappear or act weird occasionally.
Try to start it: If the starter engages and spins the engine over and sounds like the first file, then the engine is "cranking" just fine, but it just doesn't sound like it's even trying to start. This means that the battery, starter, and neutral safety switch or clutch safety swith are all working fine.
We can now skip half of the trouble shooting process and goto "check
Check for spark- pull a spark plug
wire loose from a spark plug and get an assistant to hold it while you
crank the engine. If he yells and jumps back, a good spark is present.
(Just kidding, this is probably not a good way to check for spark, a better
way is to pull the wire off of the plug, stick a screwdriver into the
end and, while holding the plastic handle, move the screwdriver so that
the metal part is close to a piece of bare metal on the engine. Then get
someone to crank the engine. If there is good spark you should see a spark
jump from the driver to the metal. If not, try nospark.
It should be able to jump a gap of almost 1/4 inch.) If it makes a good
spark and you can hear a "snapping" sound, the ignition system
is probably OK, replace the wire and Check for fuel
TO the engine.
Whatcha got? If what you've tried up to now hasn't gotten you back on the road, we're in trouble. What we look at next depends on what we are dealing with. Open the hood. Prop it open. Look around. Is your car fairly new? look for the emissions decal. It's almost always on the underside of the hood. It is a treasure trove of information. It will tell you the engine size, the fuel type, and often something about the engine control systems. There is even a little schematic diagram of where the little vacuum hoses go, and what the acronyms are for all those little gadgets that the vacuum hoses connect. Can't find it? Step back and take a good look at the engine. It's usually not too tough to figure out the path that the air takes to get into the engine, there will be an air cleaner assembly somewhere in it, probably near the inlet. There needs to be a large enough diameter path for the air to flow reasonably unrestricted to the engine. After the air leaves the air filter, but before it passes into the engine proper, it will pass through one of three things; a carburetor, a flow measuring device, or a throttle body. There may be a combination of two or more. There may be fuel injectors in the throttle body, air inlet, intake manifold, or right into the combustion chamber. You may have to remove part of the air filter to see some models. If you see a bizarre collection of strange links and levers and tiny hoses and adjusting screws all collected in the same place, chances are you have a carburetor. If the linkage is fairly simple, and the throttle plates are mounted in a housing that also contains a fuel injector or two then you are probably dealing with a TBI (throttle body injected) engine. If the engine seems to be covered with fuel injectors then you probably have some version of a Multi Point system.
No spark: OK, nobody said this was going to be easy... First thing we have to do is find the distributor. It should be pretty easy to find because it will be on the other end of the spark plug wires you disconnected to check for spark. Examine the plastic cap that the wires plug into. Locate the hold down screws or clips and figure out how to remove it, it should be 2 or 3 or 4 screws or clips. Remove the cap, look at the inside, look for moisture, gray powder, and carbon tracks. Examine the center contact. Look at the rotor, wiggle it a bit, is it loose? it should be a snug fit on the shaft. Reach down and turn the engine over slightly by hand, watch the rotor, does it turn when the engine does? It better. If not, go to no rotation.
The distributor rotor doesn't turn:
Uh oh, this might be serious. Actually, it IS serious. The distributor
needs to be indexed to the opening and closing of the valves and the up
and down motion of the pistons. This is done by driving all three parts
from a single chain or belt. Either the distributor is driven by a gear
cast into the camshaft or by its own driveshaft driven by the timing belt.
If your car has a timing belt, (most do these days, sigh...) you need
to remove part of the cover to examine the belt to verify that it is in
fact broken. NOTE: It is usually fairly easy to remove the first piece
of the timing belt cover, but it is always a b*tch to remove the last
piece. Don't try to cut corners, once you have the first piece off, watch
the belt and sprocket while someone cranks the engine. If the sprocket
doesn't turn, you've got a "blown timing belt".
Gotta Carburetor, now what? If there is a single
universally recognizable component of an automobile, it would have to
be the carburetor. No other part approaches the complexity of the dozens
of mechanical links, flaps, bellcranks and jets that all carburetors have.
They look incredibly complicated. They look like they were designed by
Rube Goldberg. They have all kinds of little hoses and cables going to
them. There are several adjustment screws visible. DON'T TOUCH ANYTHING!
The two most common reasons they deliver too much gas are; the choke
sticks closed, and the needle valve sticks open. The two most common reasons
they deliver too little fuel are; the choke sticks open, and the fuel
level in the carb is too low. A stuck choke is pretty easy to spot, as
is gasoline overflowing out the top of the carburetor, but a low level
of gas in the bowl is a bit harder.
Omigod, It has fuel injection! Now what? Beats me, I'll think of something... This is a schematic of the Throttle body injection system found in many Chrysler Corporation cars. As you can see, it uses a number of input signals to determine the fuel needs of the engine and then uses the single throttle body mounted fuel injector to deliver it. It also uses some of those input signals to adjust the ignition timing and alternator charge rate. All electronic fuel injection systems work basically the same way. Once you understand which signals are used during which operating conditions you are well on the way to identifying the problem.
Cold engines need a richer fuel/air mixture to run smoothly. Once
the engine warms up, the mixture should get more lean. A carburetor has
a choke, which closes off the air passage into the engine, which causes
a rich mixture for cold operation. A FI system has a sensor that checks
the engine temperature, and changes the programming of the fuel injector
to richen the mixture that way. An engine with this cold engine option
disabled will idle poorly, and stall at intersections, but will run fine
once it warms up.
Fuel system, step one: Is there gas in the tank? Are you sure? Is it getting to the engine compartment? Are you sure? Most engines these days are fuel injected, with a fuel pump either inside the fuel tank, or between the tank and the engine. The power for this pump comes through a relay, and is supplied through a fuse. If you don't have fuel pressure in the engine compartment, check those first. Many engines have a "fuel rail" with a connection point for a fuel pressure gauge. If someone was to remove the safety cap, and press down slightly on the bicycle tube style valve pin inside, gasoline would spurt out with some considerable force if the fuel line was properly pressurized. This would of course be extremely dangerous if the gasoline was to ignite, and of course it could spray into someone's eyes and blind them. Don't ever encourage anyone to use this quick method for testing whether fuel is getting to the engine compartment.
OK, you've determined that your carburetor equipped car is flooded, now what? well, you need to open the choke,( just hold it open with your fingers) then you need to hold the throttle linkeage all the way open. What these two things do is to open up the air passage as completely as possible, allowing the maximum amount of air to get to the engine. You need this air to dry up the raw gasoline that is laying all over the inside of the manifold and cylinders. Now get someone to crank the engine. It should start after a few seconds and you'll need to fart around with the throttle a bit to keep it from dying until the idle smooths out. Put the air cleaner back on and get on with your life. 90% of all flooded carburetor engines will respond to this technique. ASSUMing of course that you haven't run the battery dead in your vain attempts to start it...
Here is a diagram of a F*rd Multi-Point system, not a lot different from
the simple system shown above. Still a logic unit getting a lot of input
from sensors and then controlling some fuel injectors to deliver the correct
amount of fuel to the engine. You probably won't be able to read much
of the printing, but some of the components are the fuel pump relay, the
fuel injectors, throttle position sensor, oxygen sensor, atmospheric pressure
sensor, knock sensor, EGR position sensor, etc.
Timing Belt? If your engine spins unusually
fast when you try to start it, but it doesn't even cough or sputter, you've
probably blown your timing belt. This is not a thing that you wanted to
discover today. The timing belt is there to drive the camshaft, which
opens and closes the valves. It also has the function of keeping the camshaft
and crankshaft properly aligned with each other to establish the "valve
timing" (the relationship between the opening and closing of the
valves with the piston's up and down motion.) Valve timing is essential
for the engine to run at all, as you have just discovered. When the camshaft
stops turning, the valves freeze in whatever position they are in at the
time, but the pistons keep going up and down as usual. The distributor
stops turning, so the spark plugs stop firing.
Check for fuel- If the engine has a carburetor, the simplest way to check for fuel is to remove the air cleaner and look down the carburetor throat while moving the linkage. If you see (and smell) a small stream of gas squirting there is fuel getting to the carb. WARNING: Make sure that the key is OFF when you do this, as the fuel can ignite and cause a backfire to send a ball of flame straight up into your face. This can be disconcerting, and can cost you your eyebrows or your eyesight. Wear safety glasses.
Most cars these days are fuel injected, which makes it a lot tougher to test. Fuel injected engines come in at least three varieties, direct injected(rare, except for diesels, which we won't be dealing with much on this site), throttle-body injected, and multi-port injected.
Direct injection engines have a mechanical fuel injection pump that is connected directly to the engine and has steel fuel lines going to fuel injectors at each cylinder. Most diesel engines are direct injected, but we won't be dealing with them here for a while.
Throttle-body fuel injection: just uses a fuel injector that is mounted where the carburetor would be. It is the easiest to check, just remove the air cleaner and look at the injector(s) while cranking the engine. They spray a cone-shaped fine spray of fuel which is easy to see.
Multi-port fuel injection: uses fuel injectors at each cylinder, activated by wires which go to each injector. The car's computer determines when to fire each injector and for how long. This one is a bit tougher to test, has more parts to act up, and much more wiring to get screwed up. As you might guess, this one is also the most likely to act up.
Check the battery: Maybe she just left the lights on overnight and ran it down. Check the water, if it's low top it up, especially if any of the plates are exposed. Put it on the charger for a while if you can. Check the connections. Check them again, absolutely the most common place to find a problem is the connection between the battery post and the cables that go to the electrical system of the rest of the car. Corrosion happens between the metal end of the cable and the metal post of the battery, where the two metals touch, where you can't see without removing them. Brushing off the green crud growing around the connection isn't enough, you have to remove the cable, scrape the surfaces clean and smooth, and then reconnect and seal them to slow down the corrosion.
Check for fouled or flooded spark plugs: Remove a spark plug and examine the end that is normally in the engine. If it is at all wet, covered with black, gooey stuff, or caked with deposits, clean or replace it. (Spark plugs only cost a couple of bucks, so they are hardly worth cleaning, replace them.) Make sure that you don't damage the plug wires when you pull them off the plugs,(pull the boot part of the wire, closest to the plug, not the wire itself, and twist the boot to break the bond between it and the plug.) and change one plug at a time, because the wires must go to the proper plug. And don't cross the threads when you re-install them, if you do, you are in trouble, 'cus I haven't covered what to do then yet...