For an engine to run, you need three things
Air (Vacuum, compression)
Fuel
Spark (Electrical)
Without any one of these things the engine will not run
Air
The air intake system is pretty simple to check. The first, and most obvious, thing to check is the air filter. Some air
intake systems are designed in a way that small animals like to move in and call it home.
I have pulled real rats nests
out of some air cleaners. I had one customer who wrapped window screen around the air intake to keep squirrels out. It only
takes a few minutes to check an air filter.
If you hold it up to the light and you can't see through it, throw it away
and put in a new one.
Another thing to check is the tube that connects the air filter housing to the intake manifold. It
is designed to flex and over time they dry up, get brittle and crack. Look for small cracks at the bottom of the bellow folds.
Cracks there will allow un-metered air (air the computer doesn't know about) into the engine, causing a lean condition.
Further
up the line is the throttle body. A lot of air gets worked and routed in here. It is also a great place for gum, dirt and
varnish to collect and clog up small air passages. Believe me, a lot of drivability problems are fixed just by cleaning the
throttle body.
Fuel
In the fuel system the fuel filter is the weak link in the chain. Fuel filters will cause all kinds of drivability problems
that you may not relate to at first thought. If you have a drivability problem such as loss of power or stalling, one of the
first things to do is replace the fuel filter. It's a simple thing to do and could very well fix the problem.
If the car doesn't start, check the battery. The battery has to be good and fully charged. More often the question is
"Does it crank?" but "Does the battery voltage stay above 9 to 9.5 volts while it is cranking?" Most fuel pumps will not run
on less than 9 or 10 volts. Check the fuel pump fuse. Is it blown?
If it is, that's an excellent reason for not starting.
Spark
There are a lot of silly little things here that can go wrong here. Most of the rough running and no start complaints
can be traced to an ignition system basic. The first is the distributor cap and distributor rotor if equipped.
It is surprising
how many people don't even think of the distributor cap and distributor rotor as a cause of a problem. Distributor caps have
to work under very severe conditions. Heat and high voltage take its toll on the distributor cap. They start to crack at the
towers or inside the distributor cap itself.
Distributor rotors burn out their tips or the center electrode burns out the center of the distributor rotor and the spark
grounds to the distributor shaft.
Spark plug wires are another place that can cause a variety of drivability problems. They work hard also. They have to
carry very high voltage in conditions that are less than ideal.
When they get old they can start to crack. If there is
a ground close enough, the spark will take the shortcut and ignore the spark plug. Remember, electricity is lazy and will
always take the short and easy path. And it's a lot of hard work to jump across that spark plug gap.
An easy and simple way to check spark plug wires for cracks is to use a spray bottle to spray the wires with water. If
there are cracks in the wires you will see and hear the sparks jumping to ground.
Doing this at night makes seeing the spark much easier.
Spark plugs can go bad internally as well. Inside most spark plug wires is a carbon core. After a while this core can
crack and small gaps develop in the core. This makes the resistance in the spark plug wire increase to the point where the
spark won't travel to the spark plug, or get to the spark plug greatly weakened.
Another thing is spark plug wire routing. Some cars, Chryslers especially, are sensitive to spark plug wire routing. If
they are too close to each other, they will develop cross fire and lead to all kinds of drivability problems. So when you
replace spark plug wires, make sure you route them in the same way and that any protective shields or wraps are put back on.
If it's been a while the best thing to do is replace the spark plug wires so there is no question of their quality.
Now we go to the spark plugs. Here we have to check for the proper spark plug type and gap.
Also "reading" the spark
plugs will tell a story of the general engine condition. The brand of spark plugs you use can make a big difference. I am
a great believer in using the OEM spark plugs in an engine.
I would use Motorcraft in Ford products, AC Delco in GM products
and so forth. Japanese cars do not,for some reason, like American spark plugs so I use only NGK brand spark plugs in them
and Bosch spark plugs in German cars. So if you have any doubts about the spark plugs, replace them.
Basic Engine
Check the ignition timing. It may be computer controlled and no provision for adjustment is made, but how do you know
the computer has it set right? It only takes a couple of minutes to check and if it's off, you found a problem. If the ignition
timing is off, and provision for adjustment is provided, then adjust the ignition timing to the correct specification.
Check the engine vacuum with a vacuum gauge. At idling speed, an engine at sea level should show a steady vacuum reading
between 14" and 22" HG. A quick opening and closing of the throttle should cause vacuum to drop below 5" then rebound to 23"
or more.
If you have a cylinder misfire, check the compression in that cylinder. If it's good then you know the engine itself is
sound and the problem lies elsewhere.
If you have adjustable valves, make sure they are adjusted properly before doing anything. A tight valve will cause a
misfire or backfire.
Electrical and Vacuum
The cardinal rule in any electrical shop is "Check the fuses first!" I don't know how much time has been wasted looking
for an electrical problem, which could have been solved by replacing a simple fuse. At the very least it will tell you which
circuit(s) the problem is in.
Look at the wiring and connectors to make sure they are in good condition. Make sure they
are clean and tight as well. Loose connections can cause a lot of weird, intermittent problems. That's why Ford developed
the "Wiggle Test".
Check the vacuum lines. Make sure they are connected properly and don't have any cracks or breaks.
Vacuum lines never
break or rub through where you can see them. They always get damaged behind or underneath something. So. If you have to, remove
the vacuum line and check it from end to end.
Sometimes a drivability problem is caused by a lot of little things not bad enough in itself to cause a problem. But when
combined with two or three other little problems, they make one big problem.
If you can't find something obvious, then
a good, through tune-up with a new distributor cap, distributor rotor, spark plug wires and filters should be the first thing
you do. This will insure that most of the basics are good and this in itself, most times, could solve your problem.
Studies show that millions of dollars are lost every year because of misdiagnosed car problems.
But you can keep this
from happening to you if you take an hour or less to check the basics.
