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Automotive Repair ArticlesAutomotive repair instruction including information on oxygen sensors, map sensors, egr valves, pcv valves, catalytic converters, exhaust gases and other smog testing repair issues. Here is a quick summary of what each article contains. Articles are chapters from the Smog Refresher Course book. | Five Gas Exhaust Analysis Theory | Exhaust Gas Analysis Examples | Five Gas Test | Scan Tool Diagnosis Theory | Scan Tool Diagnosis Computer Examples | Scan Tool Diagnosis Test | Emission Control Devices Theory | Emission Control Device Examples | Emission Control Device Test | Feedback Carburetors Theory | Feedback Carburetor Examples | Feedback Carburetor Test | Rules and Regulations | Rules and Regulations Test | Dynamometer Testing Theory | Smog Refresher Course Book | E-Book - Smog Refresher Course | Prices | Quickly discover what you need to know so you too can perform successful auto repairs. Five Gas Exhaust Analysis TheoryExcerpt: Introduction: "When we do exhaust analysis, we are being a detective. We look at what came out of the exhaust and figure out what could have happened before to create those emissions. What happened in the combustion chamber, or before the combustion chamber, to create these results? We can use clues and patterns of exhaust readings to figure out if we have a problem in one of the following areas:
Then we know where to start our diagnosis with visual and functional tests. Good Combustion: Let's start by reviewing good combustion. The idea is to properly burn up all the gasoline and not have any "leftovers". Into the combustion chamber we put gasoline, symbolized by 'HC' for hydrocarbons. These are combinations of hydrogen and carbon atoms, organic matter from old dinosaurs maybe? We also add lots of air, which contains oxygen, symbolized by 'O2'. (Oxygen atoms feel more comfortable going around in pairs.) Normal air is about 20.7% oxygen, and if your shop smog machine doesn't show about this when reading the air inside your shop, you could have a bad oxygen sensor in your smog machine, or a serious problem with the air in your shop, or the planet has a problem... Back to combustion. The air we add to the combustion chamber is mainly nitrogen, about 78%. (No, that's not nitrous, but related.) This doesn't burn, it just goes along for the ride and expands with the heat, helping to push down the piston. Coming out of the combustion chamber we have carbon dioxide, water and nitrogen. The carbon dioxide is symbolized CO2. (One carbon atom combined with two oxygen atoms) It's good, in that plants like it and it doesn't hurt us, but too much is blamed for global warming. The water is symbolized by H2O, two hydrogen atoms combined with one oxygen atom. Did you realize that for every gallon of gas we burn, the tailpipe puts out about about a gallon of water? And then good combustion also puts out all the nitrogen that came in. Good combustion is simply put this way: HC + O2 + N2 = H2O + CO2 + N2. I leave out the numbers which show proportions. Most of you know we want an ideal mixture of 14.7 pounds of air to ..." This article contains these sections:
Get the rest of this article now by Exhaust Gas Analysis ExamplesExcerpt: "This first set of examples shows four gas readings (HC, CO, CO2 and O2) during the two speed idle test commonly run on the BAR 90 machine in a basic smog test area. Some tests were only run at the low speed idle to save the catalytic converter. These are real readings from real cars.
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Get the rest of this article now by Exhaust Gas Test and AnswersExcerpt: "Let's start out with some simple questions on 5-Gas Exhaust Analysis for review, then we'll get into the more complex questions. Let's assume the catalytic converters on the cars in the test are not real good, maybe only 50% efficient. If we had really good cats, no matter what the problem the cat could clean it up for a while, and we wouldn't see any emission problems coming out the tail pipe. And please keep in mind that in real life these emission readings would vary a lot depending on the exact vehicle being tested. You may have seen one in the shop yesterday that was different. Just think about the general concept or theory involved in the test question. 1. A simple problem like a spark plug wire that fell off will likely cause lots of which pollutant to come out the tailpipe? Let's assume the engine is a non-feedback engine, or it stays in open loop.
2. If an EGR valve functioned properly and came open, but the passage was clogged with carbon, which pollutant would likely be high in a loaded mode test on a dyno? A: CO 3. High numbers of NOx come out the tailpipe when Vehicle A had it's dyno smog test. Which of the following conditions could cause this? A: An ignition misfire from a shorting spark plug wire 4. Let's say an engine puts out these readings at the tailpipe: HC 459 ppm, CO 4.7%, CO2 10.3% and O2 0.1%. What do you think is going wrong with this engine?
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Get the rest of this article now by Scan Tool Diagnosis TheoryExcerpt: "Now for some theory on Computer Inputs and Outputs. This is really simple once you understand a few basic rules. Kinda like life, when you start to understand a few simple things, it starts to work for you, but we won’t go there... Computer Rule #1:Computers are dumb. They can only do what their programers have told them to do. (They had you bluffed to think they were smarter than they are?) And what they do is this simple: Input ... logic ... output. Computers get input from their sensors. They look up in their logic tables what they are supposed to do for this condition. They they actuate something, they do something, like turn on an injector for a set time or tell you what trouble code they have stored. All computer operation is this simple. And diagnosing a computer problem is finding out where they went wrong. Was it a bad input sensor that caused the whole chain of events to go haywire?. Was it a logic problem, like maybe the computer memory needs to be updated, or the whole insides of the computer is fried. (It's hard to put that smoke back in once it gets out!) Or is there a problem with an output, like a solenoid is stuck and can't move even when the computer tells it to. That's all there is to it. It only gets complicated when you don't understand all the pieces to the puzzle. Maybe there's a sensor you don't know how to measure, then how can you figure out the problem? Or maybe there are a chain of computers in a network talking to each other, and you don't know a problem with a sensor for the antilock brake module will cause the engine computer to not complete a drive cycle. If you don't know enough about it, it gets hard. But if you know, it's simple. Computer rule #2: Computers depend on the engine doing it's job, being in good shape. The rest of the engine must be good. (They are truly codependent; ask your wife if you don't know what that means...) The mechanical engine must have good compression and develop good vacuum. Ignition timing must be adjusted properly, the timing belt can't be installed one tooth off. Fuel pressure must be correct, the fuel filter must flow enough gas, the exhaust system must not be plugged up or leaking near an oxygen sensor (you'd be surprised the kind of problems a loose oxygen sensor can cause), the intake ..." The article contains these sections:
Get the rest of this article now by Scan Tool Diagnosis Computer ExamplesExcerpt: Introduction: Next, let's look at some Computer Examples, to see how the inputs would combine to tell the computer what the condition is, and we can see how they would affect the outputs. Let's make up a sample car to do this, I call it the Theory Car (it only comes in "on-line blue"). It has a normal sequential fuel injected four cylinder engine, similar to the ASE Composite Vehicle #1, if you have heard of that. Notice that there are two possible ways of measuring load. Most Theory Cars have a MAP sensor. But some have been ordered with the MAF sensor option. That way I can ask you questions related to a MAF sensor system. We have these kinds of input sensors with these kinds of values: RPM: a magnetic pickup but
the scan tool just shows the RPM The article contains these sections:
Get the rest of this article now by Scan Tool Diagnosis Test and AnswersExcerpt: "These are based on our Theory Car as described in the Scan Tool Diagnosis Examples section. You will notice the data is divided into frames as you would capture and record data on your scan tool during a road test. Frame '0' is where you pushed the button to record the data. And since the scan tool was in the record mode, it remembered data before you pushed the button that so you could review it later and see what was going on with the vehicle when it messed up. These are the '-1', '-2', '-3' etc... frames. Good luck! 1. Use the following scan tool data for this question. The engine
is idling in the shop. It has a regular engine miss and has failed
a smog inspection at idle with high CO. What is the likely problem
with this Theory Car engine?
2. This Theory Car engine runs very rich and gets very poor fuel
economy. Using the scan tool information below, what is the likely
problem?
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Get the rest of this article now by Emission Control Devices TheoryExcerpt: "Here we’re going to talk about PCV, Fuel Evaporative Systems, Thermostatic Air Cleaners, Air Injection, EGR, and Catalytic Converters. What theory do you need to know about how they work? How do they usually fail and cause problems? How do we test them? And we’ll have some sample test questions. PCV:(Positive Crankcase Ventilation):These were our first emission control devices. (Unless you want to call a gas cap a smog device, but the first gas caps were vented, right?) Inside the engine crankcase, where the oil lives and breathes we have gas vapors that got there by sneaking past the piston rings when the piston is compressing the air-fuel ratio or the fuel is burning up. And the more power the engine is ..." The article contains these sections:
Get the rest of this article now by Emission Control Device ExamplesExcerpt: PCV valve Problems: "Now this system is so simple, what could go wrong? Well, it turns out, lots of things that cause more problems than some people realize. What if you take your fancy European Luxury car to a quick lube place, and the new guy changes the oil but leaves the dip stick out some. And then the engine won't start because now there is an extra vacuum leak through the engine. And he panics because he thinks he just ruined this $40,000.00 car, and he cries to his boss that he didn't mean to... And the boss plugs in the dip stick, and all is right with the world again. Or what about the old Volvo owner that has had every seal and gasket on the engine replaced, but the engine still leaks oil. Until somebody cleans the flame arrester screen that is part of the PCV system. Now the blowby doesn't get trapped in the engine and blow out the seals to escape. Or what about the new Ford brought into the dealer for a tune-up, but the parts department can't be bothered keeping those little valves in stock, so they get an after-market valve and now the customer has a hesitation on acceleration. And there's lots of complaining about this $300.00 service. How can this be? Well that valve and spring in the PCV are both calibrated to give the right amount of vacuum leak for that engine--a small leak at idle and a bigger leak under light to medium load when more blowby is created. If you don't have the exact valve for that engine, the valve can open too much and be too big a vacuum leak on light acceleration. (Don't ask me how I know about this one.) One more. What about the top notch driveability technician that has a car in his stall that won't idle. He does every check in the book, but finally, after two hours, pulls the plastic PCV valve from the valve cover and sees that it came apart on the inside. There is no valve on the inside that shuttles back and forth against the spring to create the right amount of orifice. So there was a huge vacuum leak, but he couldn't hear it because it was inside the crankcase. Another problem: the engine ..." The article contains these sections:
Get the rest of this article now by Emission Control Device Test and AnswersExcerpt: "Starting from simple to more complex, have fun looking at these: The answers and explanations are below in another section. 1. The PCV system is designed to keep what emissions from getting out into the air? A: HC 2. The PCV system of late model vehicle built to be legal in the US:
3. What could Technician B say about the PCV system and get it right on a test question?
The article contains these sections:
Get the rest of this article now by Feedback Carburetors TheoryExcerpt: "There used to be lots of test questions on them, but I hear there aren’t many now. Information on them is hard to find, so maybe this will help you at work. And there are lots of cars still running around on feedback carburetors. So, here goes. What Is It?First, what is it? This is a carburetor that is controlled by the engine computer. The computer can make the carburetor richer or leaner for cleaner emissions or better fuel economy. And the computer can monitor, or get information back, on how well it is meeting that ideal ..." The article contains these sections:
Get the rest of this article now by Feedback Carburetor ExamplesExcerpt: "Now let's look at some examples of feedback carburetor problems, to help you see how this would work. All these examples have really existed in reality or at least as close to reality as I can remember. Example #1: This '85 Mazda failed a smog test, but had no other complaints from the customer. The readings from the emissions report showed about 4% CO at the 2500 RPM part of the two speed idle test. All other readings were normal. (Well, OK, the HC was also a bit high at 2500, but you could see it was just because of the CO.) So what are we to think? The first test was to see if the O2 sensor knew the system was running rich. Sure enough, the O2 sensor showed about 0.9 v. So we have a real condition that is rich, and the computer knows the condition is rich. Shouldn't the computer command be to lean out the condition? How would we test this? Yes, you knew. We measure the command at the mixture control solenoid. Since this is a normally rich carburetor, and the solenoid leans out the mixture when the computer grounds the circuit, we can just measure the voltage and see the average to tell what the command is. In this case, the voltage was real low, I think between 1and 2 volts. This tells us the computer is trying to ground the circuit a lot, to lean it out. So is this a computer problem? No. Do we need to ground the solenoid ourselves to see if the system can go lean? We could try that. But the computer is already doing that. We could unplug the solenoid to see if not grounding it makes any difference. (Ya, best to do this when the engine is off, to avoid voltage spikes say some people.) But this doesn't make any difference. So is the carburetor responding to the computer command? No. So what would you do? Yes again. There has got to be something in the computer preventing the command from working. And in this case the solenoid part that blocks off the fuel to make it lean just isn't working. It seems stuck. You can ground the solenoid and ..." The article contains these sections:
Get the rest of this article now by Feedback Carburetor Test and AnswersExcerpt: 1. A feedback carburetor will most likely run in closed loop under which driving condition?
2. To adjust the air-fuel ratio, the feedback carburetor has something controlled by the computer. What is often controlled on a feedback carburetor?
3. The feedback carburetor has something controlled by the computer to adjust the air-fuel ratio. Which of the following might be controlled on a feedback carburetor?
The article contains these sections:
Get the rest of this article now by Rules and RegulationsExcerpt: "You will need to know Rules and Regulations for the smog test. We will cover some of them here. Then you can take the quiz on it, and that will cover some more things I may not review here. But looking at the answers will help you. Remember, many of the rules you need to know are in the Inspection Manual put out by the Bureau of Automotive Repair. It is a book with a light blue cover. And you want the latest revision... For other rules and regs, you can check their web site (www.smogcheck.ca.gov) and find information there under Smog Check Advisories, Fast Blasts, and Fact Sheets. They even have all the laws you could ever want to read under the Laws and Regulations section. Of course, if you aren’t a lawyer, you may not understand them. That’s why the Inspection Manual is so good, it puts things in normal English. Keep in mind that regulations may be changing all the time, and so the Inspection Manual can get out of date. The Smog Check Advisories, Fast Blasts, and Fact Sheets will help keep you up to date. If you have a current smog license and have updated your address to them, you should get the Smog Check Advisories in the mail. The Fast Blasts are supposed to come automatically to the smog machine. Ask around, somebody in your shop may know where they have been tossed or stored. The Federal Clean Air Act of 1970 was the big deal which regulates a lot of what the state of California must do to keep pollution under control or loose money to build highways. Non-attainment areas are places that don't meet the air quality standards. Enhanced Areas: The state has been divided up into three areas, mainly by zip code. Enhanced areas are places with the worst air pollution. Like L.A. and Bakersfield. They require the dyno smog test, known now as ASM testing. The Basic areas are places that have better, but not ideal smog. Like the Bay Area. They don't need dyno smog testing yet, just the two speed idle test. But both these areas require a smog test every two years, besides initial registration when you buy a car or move into the state. The Change of Ownership areas only require the smog test when you move into the state or buy a vehicle, because they are the country areas where the air quality is pretty good. They are Attainment areas, they meet the air quality standards all the time. The Clean Air Act was amended in 1990 and revised to do more things. (Government rarely changes to get smaller and do less.) So California had to change their program to keep up. This made the change to measure NOx under a Loaded-mode test (dyno test, called ASM), to identify ..." The article contains these sections:
Get the rest of this article now by Rules and Regulations Test and AnswersExcerpt: "Welcome to this test on Smog Check Rules and Regulations. 1. The Clean Air Act says that areas that do not meet air quality standards will:
2. "Non-attainment areas" are places that:
3. The Smog Check program applies to ________ and newer vehicles.
4. The Smog Check program applies to vehicles powered by:
5. Technician A says "Hurray, no more paper smog certificates." Technician B says the vehicle inspection report can be used to show that a smog inspection was done. Who is correct?
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Get the rest of this article now by Dynamometer Testing TheoryExcerpt: Dyno Testing: What is an Enhanced Smog Check or ASM test anyway? "Remember how NOx emissions are created when the combustion temperature gets above 2500¾F? Well, if we do a smog inspection at idle speeds, there isn’t enough heat to create much NOx. Even at 2500 rpm, there isn’t enough load on the engine to create enough heat to make high NOx emissions. So our regular ..." The article contains these sections:
Get the rest of this article now by Smog Refresher Course Book
This book was written by Steven McAfee, an instructor who assisted in developing training materials for the Bureau of Automotive Repair. It is also helpful for those preparing for the ASE L1 test. 2/3rds of the information overlaps. For example the Exhaust Gas Analysis and Scan Tool (computer diagnosis) sections are similar to the L1. And the Emissions Devices section will also help. Get this book from our printers, Automotive Electronic Services,
now by E-Book - Smog Refresher Course
Includes all the above sections and OBDII Theory. 120 pages. Written for technicians preparing for the California Smog Check Technician License Exam and helpful for technicians dealing with emissions, driveability, and computer systems repairs. Through years of experience teaching smog preparation classes we have found it most helpful in diagnosis to cover the following four areas:
This book was written by Steven McAfee, an instructor who assisted in developing training materials for the Bureau of Automotive Repair. It is also helpful for those preparing for the ASE L1 test. 2/3rds of the information overlaps. For example the Exhaust Gas Analysis and Scan Tool (computer diagnosis) sections are similar to the L1. And the Emissions Devices section will also help. Get this book now by What are the prices?
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