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Automotive repair help is here! Get free information about automotive emissions and easy automotive diagnosis. And more free information on other topics can be found on the articles, printed books, e-books and home pages.

1. Smog Refresher Course (Exhaust Gas Analysis Theory, Examples and Test questions; Basic Needs of an Engine; Emission Control Devices)
2. Introduction to Lab Scopes (Introduction; Compared to a Scan Tool; Zero Point; Pattern Recognition; More about Pattern Recognition)
3. Advanced Lab Scopes (Relative Compression; Fuel Pumps; Primary Ignition Amperage or Current Ramping)
4. Lab Scopes: Introductory & Advanced (combination of the above two Lab Scopes books - please see the exerpts from the Introduction and Advanced books)

Quickly discover what you need to know so you too can perform successful auto repairs.

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Smog Refresher Course

On modern vehicles dealing with exhaust gas systems is important to help a vehicle run well. Let's take a quick look at a few things that you need to know.

1. Exhaust Gas Analysis Theory
2. Exhaust Gas Examples
3. Exhaust Gas Test
4. Exhaust Gas Test Answers and Explanations
5. Basic Needs of an Engine
6. Emission Control Devices

I also cover other topics like: emission control devices, scan tool diagnosis, feedback carburetors and touch on OBDII.

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Five Gas Exhaust Analysis Theory

| Good combustion | Bad combustion | Smog Machine Measurements |

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:

• Air/Fuel Ratio
• Combustion
• Ignition
• Emission Control Device

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 one pound of gasoline for the cleanest burning. (Stoichiometric ratio, a term used in chemistry where the right amount of ingredients are present so everybody has a dance partner and nobody is left out.)

Bad Combustion:

Now for Bad Combustion. This is where the wrong things happen, and the byproducts of combustion produce gases which contribute to air pollution or other problems. One example is raw gasoline (HC) which goes in, then comes out, and isn't burnt up in the process. Another example is carbon monoxide (CO). It doesn't create smog, but it's deadly, so you don't want it around. A third example is NOx. It helps create out brown smog. These are all a problem, and we are soon going to talk about them in more detail. But first, look at what it takes to create photochemical smog:

HC + NOx + Still air + Sunlight = Smog. Get the idea? The HC and NOx are what it takes to create smog, so if we prevent them from coming out of the tailpipe, we cut down on the smog.

Smog Machine Measurements:

Next we need to know what the Smog Machine measures. These are the gases that the 4 or 5-gas smog machine sees:

• HC: Unburned Gasoline
• CO: Partially Burned Gasoline
• CO2: Completely Burned Gasoline
• O2: Oxygen, the Good Stuff
• NOx: Oxides of Nitrogen (This is only seen by a 5-gas smog machine)

When the tailpipe emissions are bad, what kind of problem do we look for? Here is a summary of what we are going to talk about:

• HC: misfire or bad burn
• CO: too rich
• CO2: engine efficiency
• O2: too lean or just air
• NOx: too hot or too lean

Now, let's talk about these gases in more detail, and see what causes each of them to be out of normal range.

More free information on this topic can be found on the articles, books and e-book pages. The sections that are included are:

• HC, Hdrocarbons
• CO, Carbon Monoxide
• CO2, Carbon Dioxide
• O2, Oxygen
• NOx, Oxides of Nitrogen
• Review
• Five Gas Chart

Get the rest of this article now for only $2.49 by clicking here . This article is a chapter from the Smog Refresher Course book (includes 16 articles) available in the following versions: printed (direct from our printers, AES) or electronic or special introductory offer e-book

Now here is a sample of the Exhaust Gas Analysis Examples:

Exhaust Gas Analysis Examples

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.

			Normal clean emissions This is a '91 Mitsubishi Galant, 2.0 fuel injected, with no air injection. These are the clean emissions of a good system and great catalytic converter.
	Idle	Cruise
HC	1 ppm	5 ppm
CO	0.04 %	0.01 %
CO2	15.5 %	15.4 %
O2	0.1 %	0.1 %

			Clean emissions with air injection This '81 Plymouth Reliant 2.2L has air injection. Notice the high O2 (7.4 - 7.8 %) but the CO2 is lower (9.6 - 9.4 %) The added air (which has lots of O2) has diluted the CO2.
	Idle	Cruise
HC	28 ppm	30 ppm
CO	0.01 %	0.04 %
CO2	9.6 %	9.3 %
O2	7.4 %	7.8 %

			Lean Misfire This '78 Volvo with fuel injection has a massive intake air leak. In this lean misfire HC is at the max. The lean air/fuel ratio makes it hard to burn all the fuel. There is far more oxygen than could be used, and the CO2 is showing low efficiency.
	Idle
HC	2000 ppm
CO	0.63 %
CO2	9.5 %
O2	7.4 %

			Failed emissions - rich at idle This '85 Mazda is rich at idle - the CO is way high, the CO2 is lower, and HC came up a bit. The idle mixture screws had been richened to make up for rough idle from retarded timing. At cruise it's clean, just not as efficient. It has pulse air, but at idle all the O2 was used up to clean up the CO as much as it could.
	Idle	Cruise
HC	148 ppm	45 ppm
CO	5.67 %	0.07 %
CO2	11.3 %	13.4 %
O2	0.2 %	2.9 %

			Failed emissions - Bad O2 sensor This '88 Honda 119 CID with feedback carburetor system has a dead O2 sensor. So the ECM can't adjust the air/fuel ratio, it leaves the carburetor slightly rich. The CO is a bit high. Being a carburetor, it also brought up the HC. A new O2 sensor fixed it.
	Idle	Cruise
HC	337 ppm	158 ppm
CO	1.64 %	2.57 %
CO2	14.8 %	13.6 %
O2	0.3 %	0.4 %

The other four gas reading examples are:

• Failed emissions - timing too advanced
• Passed - timing reset to specs
• Runs rough, low power

Then there are examples of five gas analysis readings:

• Cool engine, cold CAT
• Warm engine, warm CAT
• EGR disconnected - high NOx
• EGR connected - lower NOx
• High Octane fuel lowers NOx

Get the rest of this article now for just $1.59 by clicking here . This article is a chapter from the Smog Refresher Course book (includes 16 articles) available in the following versions: printed (direct from our printers, AES) or electronic or special introductory offer e-book

Next, we will provide you with a few sample test questions that will help you prepare for taking your smog license examination.

Five Gas Test Questions

| 1 | 2 | 3 | 4 | 5 | 6 |

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.

A: NOx
B: CO2
C: CO
D: HC

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
B: HC
C: NOx
D: CO2

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
B: Too much carbon inside the combustion chamber
C: A bad thermostat that causes the engine to run hotter than normal
D: Both B and C

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?

A: Air-fuel ratio too lean
B: Air-fuel ratio too rich
C: Normal, nothing wrong
D: Too much air

5. Which exhaust gases are measured in percentage (%)?

A: HC, CO, CO2
B: CO, CO2, O2
C: CO, CO2, NOx, O2
D: HC, NOx

6. Let's say an engine puts out these tailpipe readings: HC 537 ppm, CO 0.05%, CO2 9.7%, and O2 4.5%. What do you guess is wrong with this engine, if anything? (Hint: there is no air injection.)

A: Air-fuel ratio too lean
B: Air-fuel ratio too rich
C: Normal, nothing wrong
D: Plugged exhaust

There are 15 test questions in total in this section. Get the rest of this artlicle now for just $1.59 by clicking here. (Test and answers come together.) This article is a chapter from the Smog Refresher Course book (includes 16 articles) available in the following versions: printed (direct from our printers, AES) or electronic or special introductory offer e-book

Now lets see a sample of the "Answers and Explanations" section.

Answers and Explanations
5-Gas test

| 1 | 2 | 3 | 4 | 5 | 6 |

1. D, HC or raw gas that went in will come out when it isn't ignited.

2. C, when EGR isn't flowing, the combustion chamber gets hotter and creates more NOx.

3. D. Extra carbon causes more pressure in the chamber, which causes more heat, which leads to more NOx formed. An engine that overheats will do the same thing. An ignition misfire will create much less heat, so much less NOx.

4. B. The high CO and high HC show a rich mixture. Notice the O2 is very low and the CO2 came down too. Without enough oxygen, not all the CO becomes CO2 and not all the HC can burn. The HC may only come from the rich condition. So first get the air-fuel ratio correct, and then retest to see if the HC are still too high. If it had been running too rich for too long, you may have to clean the carbon out of the combustion chamber with a top engine cleaner to get the HC to lower.

5. B. CO, CO2 and O2 are measured in percentage, HC and NOx are measured in parts per million.

6. A. This is a lean mixture when the HC and O2 are high, (but there is no air injection) and the CO is low and the CO2 is lower than our normal 13-14%. With too much oxygen, there is some left over and the fuel is thinned out so it can't all be burned. A plugged exhaust often makes the system richer. The CO being so low and the O2 being high is a clue that the HC comes from a lean condition, not an ignition misfire. With an ignition misfire you will see excess O2, but not as much and the CO won't be quite so low.

There are 15 test questions with answers in this Exhaust Gas Analysis section. Get the rest of this article now for just $1.59 by clicking here. (Test and answers come together.) This article is a chapter from the Smog Refresher Course book (includes 16 articles) available in the following versions: printed (direct from our printers, AES) or electronic or special introductory offer e-book

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Basic Needs of an Engine

Let's review the basic needs of an engine. We will be looking at the air/fuel ratio needs of an engine, depending on the condition when it's operating. We'll also throw in a few comments about ignition timing needs during these conditions.

1. Cold Start: When starting cold, the sprayed fuel tends to condense on cold engine metal, so we need a very rich air-fuel ratio to get enough vaporized fuel to run properly. When the engine is cranking there can't be a lot of timing advance or the burning will complete before the piston is at the top of the stroke and it will try to push the piston down backwards.
2. Warm Start: When starting with the engine not as cold, or maybe warmed up, we still need a slightly rich mixture to get started, but not as rich as a cold start. There will still be some condensing of the fuel on engine metal that isn't up to total operating temperature.
3. Cold Idle: We still need a richer mixture than normal running because of the vaporization problem, but not as rich as a cold start. We could also use more timing advance for a smoother idle.
4. Warm Idle: Once we are warmed up, the air fuel ratio can get closer to our middle stoichiometric ratio for clean emissions and we will still have a reasonably smooth running engine. Some manufacturers run at stoichiometry, some may run the engine slightly rich to give a smoother idle.
5. Warm Cruise: Now with higher engine speeds and moderate engine load (higher load means the engine is working harder-it has more air coming in) we can run right at the ideal stoichiometric air fuel ratio for clean emissions or even leaner to get good fuel economy. Our ignition timing needs to be very advanced now. Since the engine is spinning faster, we need to start the spark sooner so that the burn is complete when it's time for the expanding gas to push down on the piston. And leaner mixtures take longer to burn too, since the fuel is more diluted among the oxygen.
6. Heavy Load or Sudden Acceleration: Under these power conditions we need a slightly rich air fuel ratio. It helps to get more power out of the engine. And our timing can't be as advanced because the richer mixtures burn faster, and the heavier load also burns faster. So we don't need to start the spark as soon to have the burn complete by the time we want the expanding gas to push down on the piston.
7. Deceleration or Coasting: This is easy, when decelerating we don't need any fuel at all, so we can turn the injectors off.

Input Sensors:

Now the whole job of the computer is to analyze the inputs to figure out what condition the engine is running under. Then it uses the logic to figure out what fuel, timing etc. is needed for this condition. Then with the actuators, it outputs to the engine what it needs. A problem occurs when some part of this process goes bad.

Since the computer doesn't have eyes and ears like you and I, it has to have sensors to tell it what's going on with the engine. These are the usual types: Engine speed (and position) or RPM, Engine Load, Throttle angle or position, Coolant temperature, Air temperature, Exhaust gas air/fuel ratio, and a Knocking, pinging or detonation sensor. (There may be lots of others, but these tell the major story.)

Let's look at each of these in more detail, and what kind of information you will see on a scan tool. Pay attention to the initials used to symbolize each of the sensors, you will want to know that for later..."

Next I cover things like map sensors, throttle position sensors, oxygen sensors and egr valves.

The above info is from pages 24 and 25 of my "Smog Refresher Course" book - click here to get this now. Special offer here. Electronic information available worldwide, instantly!

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Emission Control Devices

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 developing, the more of these HC vapors get crammed into the crankcase. So, what to do?

If we have a crankcase that is totally sealed, this gas under pressure will eventually blow out the seals. So we have to find a way of relieving this pressure.

In the old days, when I was a child, we had road draft tubes and open oil filler cap covers. That way the pressure could get out, and as the car drove down the road, suction was created at the road draft tube and it helped pull out the gas vapors. Fresh air could come in through the oil cap and help keep the engine oil from being too contaminated by the gas. This helped the oil last longer.

But, then came pictures of L.A. smog, and the smart scientists realized that we could cut down on about 20% of the smog if we didn't let that gas out that we paid for anyway. So now we have what is called a closed crankcase.

The oil filler cap should not let out any fumes. And the oil dip stick should also be sealed, in some newer cars better than some older cars. And we have a fancy PCV valve or orifice that lets the intake manifold vacuum recycle and burn that gas we paid for.

Inside the PCV valve is an orifice regulated by a plug and a spring. When manifold vacuum is high, this plug is sucked in hard against the spring and we just have a small calibrated orifice for blowby to flow through. Then, as engine load increases, the vacuum drops and the plug is pushed back by the spring and we have a bigger opening for more crankcase flow.

But if we have no vacuum, the plug is pushed against the other end by the spring, and we have no flow. This is a flame arrester in case of a backfire. We wouldn't want the flame in the intake to spread to the crankcase. Also in this system, instead of a road draft tube, we have some sort of vent tube usually running between the crankcase or valve cover and the air intake or air filter area.

Here's how the PCV flow goes...

The above info is from page 45 of my "Smog Refresher Course" book - click here to get this now. Special offer here. Electronic information available worldwide, instantly!

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Introduction to Lab Scopes

Lab scopes are great for effective and efficient diagnosis. Never used one before? Don't worry - I can teach you how.

1. Lab Scopes – Introduction
2. Compared to a Scan Tool
3. Zero Point
4. Pattern Recognition
5. More about Pattern Recognition

Lab Scopes- Introduction

How good do you want to be at fixing cars? Just OK, so you can fix the easy ones? Or do you want to be able to figure out almost anything that comes your way? That’s the edge using a lab scope can give you. Let me put it another way. If you wanted to look at something pretty, would you want an old, faded black and white photograph, or would you rather look at it with a video camera on your widescreen TV? That’s what a lab scope can do for you that a scan tool can’t. Oh, you need a scan tool nowadays to fix cars. But if you aren’t using a lab scope, with amp probes, there’s a whole world you are missing.

This book is designed to get you into that world…  Some techs can’t use a lab scope at all, and others can get a couple of patterns up on the screen. But they don’t know how to make it really fly. They get nervous and confused trying to get a pattern on the screen. When it doesn’t work at first, what do they do? What does the pattern mean? How do you know if the signal is good or bad?		Without a lab scope and amp probes...there's a whole world you are missing.
That’s what this book is about. You could call this “Lab Scopes for Dummy’s”, except I’d probably get a call from the lawyer of the group that puts out all those books, and we don’t want that.
	We keep it simple. The purpose of this book is to get you measuring all kinds of things with your lab scope. And I firmly believe that if you can’t make something simple when you explain it to somebody else, you don’t really understand it. Later on, we’ll get into some more complex applications of lab scopes. But we’ll still make that simple, too. (You’d be surprised at all the testing you can do that will help you with your diagnosis.)
This book is designed for the technician who doesn’t really know how to use a lab scope, also called a DSO. (Digital Storage Oscilloscope) Or the tech who wants to take his diagnosis to the next level. We’re going to explain these things:
How does a lab scope work? (in very simple terms) When you look at a pattern on the scope, what are you seeing, and how do you know if it is bad? How do you get a pattern on the scope, how do you do the adjustments to make the pattern look right? What do you do when you can’t get a pattern on the screen at all? (A lot of guys have this problem, but don’t admit it to their friends…)
What are some of the different things you can do and see with the lab scope? (Most technicians don’t know how much diagnosis you can do with an inexpensive scope, and a few attachments.) Where and how do you hook up the scope to the circuit? Does it make much difference? The above info is from page 1 of my "Lab Scopes: Introductory & Advanced" book. Special offer here. Electronic information available worldwide, instantly!

Compared to a Scan Tool

Compared to a Scan Tool: Many of you are used to working with scan tools. You pull up the data on a screen, and you read something, let's say the throttle position sensor. Maybe it says 0.6v. How quickly can that number change when the throttle changes? On many scan tools it can take a second or more, right? So, what happened in between those numbers? Did things happen that you didn't know about? That can be a problem.
Scan tool data only shows what the PCM thinks it sees, and it doesn't update very fast.	Some scan tools let you graph data, so you get the info updated at much quicker internals. But it still isn't as fast as you can get from a good lab scope. You could be missing something. Let's think of an example.
You are driving along in a Ford, you decelerate for a stoplight, and you hit a chuck hole that causes the engine to shake. This causes the TPS voltage to go below your normal 0.6v at closed throttle, down to 0.4v, just for an instant. (The TPS has started to go bad, but hasn't set a code yet.)		A lab scope draws a picture of the voltage...
Now the computer thinks this is your closed throttle idle position. So when the TPS is back to 0.6v at the stoplight, the computer thinks you're cruising. So it keeps the idle speed high. (It's preparing to drop the idle speed slowly for you when do your next deceleration, to keep the emissions low.) You have just duplicated the high idle problem your customer was complaining about, but will the scan tool have recorded your glitch? Probably not, with a fast glitch. Remember, those numbers on the scan tool that just sit there and don't change, don't mean the... The above info is from page 9 of my "Lab Scopes: Introductory & Advanced" book. Special offer here. Electronic information available worldwide, instantly!

Zero Point

Zero point:  Another thing to look at is our zero point. (Sometimes called the ground point. This is where the zero amount of voltage would be.) This is also adjustable, and may be in different places on the screen, depending on what we are looking at. We might have the zero point near the bottom, because we’re looking at positive DC (direct current) voltage. And this will be all above the zero. Or we might have the zero point in the middle, because we’re looking at AC (alternating current) waveform of an ABS signal. And with AC, half the signal may be above the zero, and half the signal below the zero.

The rest of this chapter covers:

• Compared to a Scan Tool
• Compared to a Voltmeter
• What a Lab Scope Shows
• Analog or Digital
• Analog Lab Scopes
• Digital Lab Scopes
• Downside of Digital
• Advantages of Digital
• Introduction to a Basic Model
• Divisions or Graticules
• Voltage
• Time
• Zero Point
• Channels

From: Chapter 1, page 6 of "Introduction to Lab Scopes"

Pattern Recognition

Throttle Position Sensor

Here’s an example of a Throttle Position Sensor sweep. You see us open and close the throttle, and the voltage goes up and down. If there was a really bad spot on the potentiometer contact strip, you would see the trace go down suddenly where it shouldn’t. This causes all sorts of havoc in how the engine runs—everything from hesitation, stalling or even an intermittent fast idle.

But I must tell you here, testing a TPS with a lab scope is not the best way to catch intermittent TPS. Do a ohms sweep with a digital DVOM and watch the analog bar graph. That is really sensitive, and problems will show up there that won’t show up anywhere else.

Fuel Injector Let’s look at the different parts of the fuel injector pattern. This is just a basic port or sequential injector where battery voltage goes to the injector coil, and the computer grounds the coil to create the magnetism to open the injector.

A shows that beginning voltage level. This is usually close to system voltage. 

B shows the voltage dropping low as the computer grounds the coil. If this doesn’t get close to zero, there could be ground problems, or a weak computer transistor can’t pull the voltage low.

C shows the computer turning off the injector by no longer grounding it. The voltage goes up. From B to C is the “on-time” of the injector.

D When the coil is turned off, the magnetic field collapses, and this generates a spike, similar to an ignition coil generating a spark. If this coil doesn’t go up very high, it shows the magnetic field wasn’t very strong. Could be shorted coil windings in the injector, or low amperage to the injector for some reason.

The rest of this chapter covers:

• Magnetic Pickup RPM Sensor
• Hall Effect RPM Sensor
• Optical RPM Sensor
• Throttle Position Sensor
• Fuel Injector
• Duty Cycle
• Ignition Primary
• Alternator Ripple

From: Chapter 3, page 15 of "Introduction to Lab Scopes"

More about Pattern Recognition

Duty Cycle

This is an EGR valve vacuum regulator solenoid being turned on with a duty cycle signal. Battery voltage is being grounded about 30% of the time, at a fast cycling rate.  This gives a small vacuum signal to the EGR valve to turn on the EGR valve a small amount. When we want more EGR, the EGR is grounded at a higher duty cycle, like 50%, and this gives more vacuum to turn on the EGR valve more. 

Ignition Primary

The function of and ignition coil is in some ways  similar to the fuel injection coil. We ground the coil to create a magnetic field, then unground the coil to get the field to collapse. It’s this moving magnetism, as the field collapses, that generates a spark in the secondary coil windings.

B is when there is current limiting applied to the grounding circuit. It keeps too much current from running through the coil, so it doesn’t overheat.

The rest of the chapter covers:

• Magnetic Pickup RPM Sensor
• Hall Effect RPM Sensor
• Optical RPM Sensor
• Throttle Position Sensor
• Fuel Injector
• Duty Cycle
• Ignition Primary
• Alternator Ripple

From: Chapter 3, page 16 of "Introduction to Lab Scopes"

The graphics are larger and clearer in the books than they are on this website. More free information on this topic can be found on the book and e-book pages. "Introduction to Lab Scopes" is available in an electronic format for only $12.95 with instant delivery worldwide. A printed version is also available - it is the first half of the book "Lab Scopes: Introductory & Advanced" and can be ordered directly from our printers, AES, now. There is also a special introductory offer on this product.

Advanced Lab Scopes

For those of you who already know abit about lab scopes and want to increase your abilities, this information will help.

1. Relative Compression
2. Fuel Pumps
3. Primary Ignition Amperage, or Current Ramping

Relative Compression

Relative Compression

You need to qualify if the mechanical part of the engine is good, but it will take a lot of time and effort to get to the back spark plugs on a V-6 engine. The engine is missing on one cylinder, and you don’t know if the problem is compression related, or not. Good news—there is an easy way to test this! You can view the waveform of amperage going to the starter motor and tell if the engine has good relative compression. Here’s why.

There’s this thing called “counter electro-motive force”, and we need to talk about it for a bit so you see how it can help you. As electricity flows through a starter motor it’s not an even amount. The amount goes up and down, depending on the condition of the engine. When you first start to crank the engine, the starter isn’t turning. This makes the internal resistance of the starter low, so lots of amps can flow. You will notice, if you measure it, that when you first start to crank an engine over, the starter motor draws more amps. Then, as the motor is turning, the amp draw goes down. This is because the starter motor tries to act as a generator when it is turning. It tries to push some electricity back in the opposite direction. (This is the “counter electro-motive force”, or C.E.M.F.) It can’t, but it does increase the resistance of the starter, and slow down the current flow.

The rest of this chapter covers:

• Counter Electro-motive Force
• To Measure Starter Current
• High Amp Probe (or Current Clamp)
• Set Up Your Scope
• How Do You Know Which Cylinder is Low?
• Relative Compression Test

From: Chapter 1, page 1 of "Advanced Lab Scopes"

Fuel Pumps

This chapter covers:

• Low Amp Probes
• Where to Attach the Current Probe
• About Fuel Pumps
• Fuel Pump Commutator Segments
• Fuel Pump Brushes
• Good Fuel Pump Pattern
• Bad Fuel Pump Pattern
• After Replacing the Pump

From: Chapter 2, page 9 of "Advanced Lab Scopes"

Primary Ignition Amperage, or Current Ramping

Primary Ignition Amperage, or Current Ramping

Looking at voltage is only part of the picture of what’s happening with the ignition system. (No pun intended.) Another part is amperage. To really know what’s happening in a circuit, we need to be able to measure the amps too. And now we have some awesome tools to do just that.

The answer is counter electromotive force. (CEMF) As current flows into the coil, it builds up a moving magnetic field that tries to force current in the opposite direction.

This chapter covers:

• Counter Electromotive Force (CEMF)
• Primary Ignition Volts
• Primary Amperage
• Computer Controlled Dwell
• Low Current Probe
• What To Look For
• Normal Good Current Ramp
• Possible Problems to Diagnose

From: Chapter 4, page 18 of "Advanced Lab Scopes"

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