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“So, You Want to Become an Auto Technician — What to Expect Your First Day on the Job”

The following is the first chapter of Paul Grech’s book for entry-level technicians, first published in 1997 and available today to prepare them for working in today’s shops

Paul E. Grech owned the former San Franciso shop, Allied Engine & Auto Repair, before retiring. Grech’s book is available for purchase for $65 (includes tax; shipping is not included), of which $20 of each sale will be contributed to the Automotive Service Councils of California (ASCCA) scholarship fund. Contact Grech at p_grech@comcast.net for purchase and details.

Section 1 — THE BASICS

Your training should start out like basic training in the military. All cars are held together with nuts, bolts, clips, pins, washers, clamps, sheet metal screws, lock plates, lock tabs and rivets.

A good school should start the course with a week or so of identifying and helping you to become familiar with all of these and teaching you the difference in threads, according to pitch, length, whether they are metric or U.S.S., and what is the grade of bolt.

You should be taught how the bolts feel going in and coming out, so that you don’t break them off or jam them in their hole. If you break a bolt or jam it in a hole, someone more experienced than you must straighten the problem out, and this means two jobs are stopped: yours and the person who is straightening out yours, thus lowering shop productivity drastically.

You should be instructed to be aware that you must form good work habits. These habits will be a tremendous asset throughout your career, not to mention the fact that they will make you a productive employee much more quickly.

You will find that these habits started with what your mother tried to instill in you. You know, like “pick up your clothes, clean up your room, close the drawers,” and most important of all, “put it back where you found it please, Johnny or Jill.”


A garage must be an orderly place or work gets delayed and accidents can happen. In this profession you must remember what you were taught. The definition of remember is to listen to instructions, commit them to memory and put them into use when needed.

In other words the instructions enter your ears, pass through your ear drums and roll around your brain for a while. These instructions then must leave your brain and find their way to your arms and hands in order to repair the car you are assigned to repair.

If this process is not adhered to, your progress in this field can be greatly impaired. It is a very important habit you must develop. We all know what a habit is. Like breathing, a habit is something you automatically do the same way every time, without giving it a conscious thought.

You will start at what is called the D level entry level technician. The definition of a D level technician is one who listens to, understands and carries out verbal and written instructions.

As time passes by and you gain experience and confidence in yourself, you will advance to the C level. At the C level you will do some light diagnoses, change oil, fan belts, thermostats, water hoses, alternators and starters.


As more time passes, you will find yourself at the B level. This stage will bring you into diagnosis, meaning you will be given the responsibility to determine what is wrong, and these days that is a big responsibility. Hopefully you will then become an A level technician.

An A level technician is one who can diagnose and repair most systems on most cars. After you start to develop solid work habits, you should start to learn automotive concepts.

An example of an automotive concept would be to paint in your mind the idea that all internal combustion engines are air pumps. It doesn’t matter if the engine is from a 1914 Model Tor 1992 Ferrari. They both take in air and have fuel added to the air, where it is then compressed and ignited, and the exhaust leaves via the tail pipe.

Driveability problems start to occur when the air and fuel proportions are disturbed: there can be too much fuel or not enough fuel, rich or lean. The mixture can also be upset from the air side, i.e., carbon build-up behind the throttle blade that restricts the amount of air entering at idle, which can cause a stall at idle.

When the events occur at the wrong time, for instance if the timing is late, the spark occurs at the wrong time which causes some of the fuel to burn in the exhaust manifold. If you have a cracked exhaust manifold, wrong timing is one possible cause. The engine can also be set too far in advance or ahead of time, causing it to ping under a load.


So far we must have fuel and air in the right quantities and spark at the right time. With these ingredients in a container where all the events take place, we must have compression and ignition.

The valves, cam, timing chain and gears, rings and pistons, keep everything in the right place at the right time. We have intake, compression, power and exhaust taking place in one cycle of an internal combustion engine.

Exhaust is the last part of the cycle. The burned fuel and air must leave the cylinder to make way for the next fuel charge coming in. The exhaust valve must open at the right time and stay open long enough for the engine to breath properly.

The basics for an automotive engine start with vacuum. Good vacuum starts with the engine’s ability to breathe properly. That’s right, just like your body does, only an engine doesn’t have pink lungs like you do. An engine’s lungs are nice and black. Just as you can experience difficulty breathing when you have a cold or flu, so can an engine, if any of above conditions don’t exist.

The best way to demonstrate this breathing process is to get hold of a car to work on, preferably one that has easy access to the oxygen sensor. Remove the oxygen sensor and install a gauge that measures exhaust system back pressure (it screws into the 02 sensor hole). Next install a vacuum gauge on the intake manifold in order to monitor engine vacuum.


Find a propane bottle that has a dispensing valve which will enable you to add fuel to the engine at a controlled rate. Obtain a regular bath towel and soak it in plain old water until it’s good and wet.

You should also be wearing safety goggles, and you should also make sure that you remove all jewelry and secure any long or loose hair and/or clothing. You will be working under the hood while the engine is running, which means there will be rotating parts that your loose clothing, hair or jewelry can get caught in.

Now warm up the motor and remove the air cleaner. With the engine running, place the palm of your hand over the air intake and feel the air being drawn in. Now place your palm tightly over the air intake and cause the engine to stall.

This demonstrates that the engine needs air in order to run. Watch the vacuum gauge and you should see a rise in vacuum at the same time. Restart the engine and pull a vacuum hose off of one of the ports on the intake manifold.

Watch the vacuum meter and you will see a drop in vacuum, which is air that is going into the engine and is also bypassing the throttle blade. You can call this false air. On a computer-controlled car, this will upset the fuel mixture because false air is entering the engine, making the fuel mixture lean.


A mixture that is too lean cannot burn completely and contributes to pollution and poor driveability. Rev the engine up and watch the engine vacuum meter: it will drop dramatically as the throttle is snapped sharply, and recover if the throttle is held steady at around 2000 RPMs. This is the normal response on a healthy engine with a clear, unrestricted exhaust system. The exhaust gas pressure gauge should read O” of pressure at idle. If it reads 1″ or 2″ of pressure at 2000 RPMs, it indicates that the exhaust system is slightly restricted, but not necessarily plugged up solid.

When you get a reading of 4″ or 5″ of backpressure at 2500 RPMs, that is a sign of a restricted exhaust system. You must remember that this backpressure not only causes the engine to breath improperly, but also lowers the engine vacuum, causing the device that monitors the engine vacuum for the computer to read an incorrect signal. The computer will then make an incorrect calculation for that moment in time. In other words, “garbage in, garbage out.”

Return the motor to idle and get the propane bottle. Replace any vacuum hose you had removed earlier. With the engine idling, open the propane bottle a very small amount.

Allow the propane to enter the air intake of the engine. If everything is set correctly, the engine idle will rise slightly and then begin to stumble and maybe even stall. This shows that the fuel mixture at idle is correct. If the idle speed rises dramatically and stays there at a smooth pace, the mixture is too lean.

If the idle drops rapidly without a slight increase in RPMs, the mixture is too rich. Now do the same test at a steady 2000 RPMs and add some propane. If the RPMs rise dramatically, say 300 RPMs or more, the mixture is too lean at cruise speed. If the RPMs decrease by 300 or more, the mixture is correct.

The exhaust pressure meter should also stay under 3 lbs of pressure. 0 lbs pressure is the desired reading but 3 lbs is acceptable. To test for excessive backpressure, place wooden blocks under one front and one rear wheel. Place the car in drive and step on the brake pedal firmly with your left foot.

At the same time apply the gas momentarily, three to four seconds, to put the engine under a load. This is called lugging the engine down. Commit this term to memory, for you will use it quite often in solving driveability problems. Observe the backpressure meter to see if the pressure rises above 3 lbs.

Under these conditions, if the exhaust is restricted, the pressure reading will rise over 3 lbs.


The real test is to drive the vehicle and have an assistant observe the gauge to see if the reading exceeds 3 lbs. of back pressure. A severely restricted exhaust system will bury the gauge needle immediately.

If the car exhibits normal pressure readings, let’s induce a simulated restricted exhaust system. Get your wet towel and place it over the exhaust outlet at the rear of the car. Observe both the vacuum and exhaust pressure gauge. The vacuum gauge should drop a few inches and the pressure gauge should rise. Proceed with caution for the next test.

Make sure that your towel is good and wet because there is a lot of heat at the tail pipe tip. Again block the wheels and lug the engine down. The exhaust pressure gauge should rise over 6 lbs, and the vacuum meter should go down to 5″ of vacuum or less.

This clearly demonstrates that an internal combustion engine needs to breathe unrestricted at inlet or outlet. The fuel must be present in the right proportions under all engine load conditions.

If the exhaust is restricted, it will cause a low vacuum reading. The computer falsely sees this as a command for more fuel and allows more fuel to be injected into the engine, leading to poor overall fuel economy, increased pollution, fouled spark plugs etc.

Also, when you try to accelerate it will force the exhaust recirculation valve to open up too fast too soon. The EGR valve is actually a controlled internal engine vacuum leak, so it will lean the engine fuel mixture out at low speed, causing the engine to surge, stumble, or even die.


The simplest, quickest way to see if the EGR is the cause of the above complaint is to disconnect the vacuum hose to the EGR and road test the car. If the problem goes away, you need to do the above tests to see if something other than the EGR is causing the problem. In other words, the stumble or stall is the symptom. It will be your job to determine the cause.

The above paragraphs are pretty technical for a beginner to digest easily. On the other hand, driveability is the hottest area of the auto repair industry at this time, and this information is just basic knowledge you will need to master and understand if you want to diagnose driveabilty problems.

You need to familiarize yourself with the internal combustion engine from the very beginning, because it will help you to understand how the computer system works.

Even a complicated computer system starts with the basics. You must fully understand that all the air must enter the engine through a metered opening called the throttle plate or throttle opening.

The engine is designed to allow a precise amount of air to mix in the correct proportions with the fuel, and the manifold is the chamber under the carburetor or throttle body where the fuel mixture is distributed to the individual cylinders.

The ideal fuel ratio in a modem automobile is 14. 7 parts of air to one part of gas, or 14. 7 to I. If air is allowed to enter the engine without going through this opening, the fuel mixture will be too lean.


If it gets leaned out, then the fuel charge will not bum completely, resulting in a reduction in power, and more importantly, an increase in emissions out the tail pipe. Familiarize yourself with the term false air or unmetered air, for it is the cause of one half of fuel mixture problems.

The air that gets in the engine without going through the throttle plate is called false air or a vacuum leak. It can get in through a hard or cracked vacuum hose.

An excessively loose throttle shaft will allow false air to enter the engine. A device that is operated by vacuum can pass false air if the diaphragm inside is leaking. An example would be a vacuum advance that leaks, or a choke pull-off that leaks. A leaking power brake vacuum booster can develop a leak which will cause the motor to idle noticeably rougher when you step on the brake pedal, and there may also be a loud hiss inside the car when you step on the brake.

A hard, broken or loose base gasket under the carburetor or throttle body will also pass false air. If the vacuum hose that is routed to the map sensor is leaking, the computer will receive a false signal to enrich the fuel mixture. There are different ways to find these vacuum leaks.

The simplest way is to pinch off, with a pair of needle nose pliers, the vacuum hose to the device that is vacuum operated. If there is a vacuum leak the motor usually idles rough, but when you pinch the vacuum hose off, the idle will smooth out, except if the hose goes to the map sensor.

The reason for this is that when a low vacuum signal is present at the map sensor at idle, the computer will enrich the mixture. The engine will be receiving more fuel than it can bum at idle.

I highlighted the words at idle because they describe a condition or qualify an event. If you are not aware under what condition to check a component, then you will come to the wrong conclusion or make the wrong diagnosis.


You must learn to think this way if you want to be a successful technician. You need to develop the habit of thinking of ideas and thoughts in qualifying terms. For example, the timing is set at a specified idle, some wire disconnected, or some wires connected or a vacuum hose unplugged etc.

Get a new piece of vacuum hose and see how it feels. The hose should be pliable and have body to it. Push it on the vacuum nipple where it attaches and feel how it goes on. Pull on it and see how it grips the nipple. Now look at some hoses that have been in service for a while.

Check them for obvious cracks, then pull on the hoses a little and see if they just slip off their fittings. Sometimes vacuum hoses get either hard as a rock, or too soft, and sometimes they get gasoline-soaked from the fuel vapors in the manifold. If they are too soft, they will fall off or even collapse shut. Some people advise using carburetor cleaner to find vacuum leaks.

The problem with this is that you can’t control how much carb cleaner is dispensed when you push the nozzle. The spray pattern is not adjustable, and it is too wide to help you pinpoint the vacuum leak. When the carb cleaner is pulled in and burned in the engine, the fumes coming out of the exhaust are extremely toxic, and they can cause a shortness of breath and other health problems. The carb cleaner also will melt the paint on the engine and make it look quite messy.

The best way to find vacuum leaks involves the use of a propane bottle. You need to buy a propane dispensing kit which allows you to dispense propane in a controlled rate at a suspected vacuum leak. Great caution must be used when using propane.

It can flare up and burn under the wrong conditions. If too much propane is introduced in the engine compartment, it can be ignited by the sparks inside a distributor cap or even an alternator. You must not allow a large amount of propane to linger in the engine compartment, and keep it away from the distributor.

I advise you to always have a fire extinguisher with you at the car in case of fire while using propane. Be careful around the positive post of the battery or any live electrical source such as the alternator or the ignition coil. In back of the alternator is a wire that goes directly to the battery.

This wire is hot even when the ignition key is off. It had a protective cap over it when it left the factory, but it may be gone for whatever reason. If you should touch it with the tip of the dispensing nozzle you could cause a spark which will ignite the propane. It will flare up and scare the dickens out of you, but it should go out right away.

The fire extinguisher you have with you will put out any fire that doesn’t go out by itself. When the vacuum leak pulls in the propane, you will notice an increase and smoothing out of the idle. If the leak is large enough, it may pull in enough propane to make the mixture too rich.

If this is the case, the idle will momentarily smooth out and then get rough again due to the extra fuel being pulled in to the engine. Once you locate the vacuum leak, you can adjust the nozzle opening so that the engine will idle smoothly.


You can make a misdiagnosis if you allow too much propane to leave the nozzle, because the air inlet will pull the excess propane into the engine. The thin nozzle on the kit enables you to put the propane around the fuel injector o-rings, which tend to get hard from old age and create a vacuum leak.

Problems are also created when there is too much fuel or not enough fuel in the mix.

There are many ways too much fuel can get in the mix, among them are a sticking needle and seat, or a heavy float in the carburetor. The easiest way to observe this is to go the toilet in your bathroom and lift up the top of the toilet tank. Flush the toilet and watch what happens as the tank fills up.

When the float stops at the top and the water stops flowing into the tank, the water level will be at the level the float is set for. Now push the float down until the water starts to flow into the tank again, but don’t let the tank overflow.

This simulates what happens if the float gets heavy in the carburetor, if the needle and seat get worn, or if a piece of dirt gets inside.

The principal that makes a toilet tank work is the same principal used in carburetor operation. When the engine is running on a carbureted car you should not be able to see liquid fuel dribbling down the throat of the carb. If you do, the float setting is probably wrong or something else is causing too much fuel to leave the carburetor.

This is what is commonly called a rich condition, which could be caused by a faulty sensor sending an incorrect signal to the computer for more fuel.

Another source of too much fuel could come from the fuel evaporation system. If the car owner overfills the gas tank, some liquid gas could find it’s way into the evaporation canister, pump could be ruptured and allow fuel to enter the crankcase, and then fumes are pulled into the engine through the positive crankcase ventilation system or smog valve as it is commonly called.


Carburetors are ancient technology at the time of this writing, but you still need to know about them. Just yesterday I was working on a beautiful 1957 pink Lincoln convertible that had recently been restored at a cost of over $120,000 but it still didn’t idle smoothly.

One side of the carburetor was restricted. I was able to fix it because I remembered how a carburetor works. A carburetor is still a fuel dispensing device just as a fuel injection system is.

Rich running conditions in fuel injection systems are caused by different things, one of which is a leaking fuel injector. Think of it as a leaking faucet in your sink. The fuel pressure could be too high or too low and one of the sensors could be sending an incorrect signal to the computer.

The computer in tum will command too much fuel to be dispensed, and the exhaust system could be restricted. Some of the possible causes of rich running conditions could be a regulator stuck in the high pressure position, a blocked off or pinched return hose, or a leaking pressure regulator.

When the pressure regulator is leaking, the diaphragm leaks raw gas. The vacuum hose that regulates the diaphragm will pull the raw gas into the intake manifold and create a rich fuel mixture. If you want to verify this, simply start the engine and pull off the vacuum hose that attaches to the regulator.

Check to see if there is liquid fuel in the vacuum hose or coming out of the vacuum nipple on the regulator.


There is a qualifying statement in the preceding paragraph. You need to check for a possible leaking fuel regulator with the engine running. Again, caution should exercised, because raw gas could spill out of the nipple if the leak is bad enough. As always, have a fire extinguisher with you and perform this test on a cool engine, especially if it is a very hot day.

One more tip: if it is a real hot day and you don’t have a lot of time to let the engine cool off, get a large fan, lay the fan on top of the engine and let it run for a while. The air that it blows across the motor will cool the engine off very quickly.

I purposely put this rather seemingly complicated material in the beginning of this book in order to get you into the habit of thinking like a technician/mechanic. It seems overwhelming at first because you are a beginner, but it will fall into place with the passage of time. After a while it will all be second nature to you. Remember when you first learned how to ride a bike?

It doesn’t seem so scary now does it? Remember your first dance? Same thing. Now you can probably dance up a storm and think nothing of it. So it will be with repairing an automobile.

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