If you go into your doctor s office,

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Georgia Potter
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1 Keeping Up by Steve Bodofsky Translating Engine Vacuum Measurements If you go into your doctor s office, complaining of whatever s making the rounds this month, one of the first things they do is take your temperature and blood pressure. They don t do that just to annoy you and run up the bill although there s little doubt that s part of the appeal for them. But mainly they do them because those simple measurements tell them a lot about your overall health, and warn them if there s something serious that needs their attention. That s not so different from auto repair. Think about how much information you can get from a mainline pressure test; information about the transmission pump, regulators, clutches, accumulators and more all from a simple pressure check. There s also a simple test you can perform to help analyze engine and performance problems. Measuring the engine s manifold vacuum is a great way to evaluate the condition of the engine, exhaust system, and many of the emission devices that can affect driveability. To understand how to use these vacuum readings, you must first understand what vacuum is, and be able to recognize the three different types of engine vacuum you re likely to run into. What is Engine Vacuum? Look around you; everywhere you look, there s atmosphere. That s a good thing: Without it, breathing would be fairly difficult. While we all know it s there, it s easy to forget that atmosphere has weight: 14.7 PSI at sea level. But since that s more or less where we live, Figure 1: There are three basic types of engine vacuum: manifold, ported and venturi. The difference depends on where they originate in relation to the throttle plate. we tend to think of atmospheric pressure as the zero point, on what might easily be considered a relative pressure scale. Anything less than 14.7 PSI we consider to be vacuum. We measure this vacuum level on a scale of inches of mercury (in/hg). Absolute vacuum, or zero PSI, is about in/hg on our relative pressure scale. When the pistons in an engine are moving and the valves opening and closing, the combination of these actions creates a low pressure zone in the intake manifold; manifold vacuum. It s from this manifold vacuum that all other engine vacuums are created. Three Types of Engine Vacuum There are three basic types of vacuum created in today s engines. All are created from the same basic source; the big difference is where they occur in relation to the throttle plate (figure 1). Manifold Vacuum This is the type of vacuum we think of for engine diagnostic purposes. Manifold vacuum originates below the throttle plate. It tends to be high at idle, and drops as the throttle opens. At full throttle or stall, manifold vacuum should drop back to almost 0 in/hg. Manifold vacuum also tends to reach its peak on deceleration, when the throttle plates are closed but the engine is running faster than at idle. Ported Vacuum Ported vacuum originates just before the throttle plates. It s usually about zero in/hg at idle, and increases with throttle opening until it equals manifold vacuum. At heavy throttle opening it varies with manifold vacuum. Ported vacuum is often used to control EGR valves and ignition vacuum advance in older cars. 46 GEARS January/February 2008

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3 Keeping Up Translating Engine Vacuum Measurements Because manifold vacuum varies with throttle position and engine RPM, it s a great way for the computer system to monitor engine load. Enter the Manifold Absolute Pressure (MAP) sensor. Ready to Shift to a Better Insurance Program? Get into Gear with Heffernan Insurance Brokers. We offer: Property/Casualty Garage Liability/Garage Keepers Property/Tool Coverage Auto Workers Compensation Property/Casualty Earl VanBuskirk earlv@heffgroup.com Paul Wills paulw@heffgroup.com Contact us today! License # ATRA program facilitated by Employee Benefits Medical/Dental Vision/Life Disability HR Assistance Employee Benefits Jani De La Rosa janid@heffgroup.com Shauna Gilbert shaunag@heffgroup.com Heffernan Insurance Brokers and Brant Watson. Venturi Vacuum Venturi vacuum is similar to ported vacuum, only lower. It originates much higher on the throttle housing, so it only gets to about 4 6 in/hg. But venturi vacuum is actually created by the movement of air through the venturi, so it won t really drop off with manifold vacuum. Venturi vacuum is usually used for a signal vacuum, to control other devices, such as an EGR vacuum amplifier. It s not particularly common on any vehicles these days. When discussing engine vacuum for diagnostic purposes, always assume you re looking for manifold vacuum, unless otherwise specified. MAP Sensor Monitors Manifold Vacuum Because manifold vacuum varies with throttle position and engine RPM, it s a great way for the computer system to monitor engine load. Enter the Manifold Absolute Pressure (MAP) sensor. The MAP sensor monitors manifold vacuum, providing the computer with two important measurements: 1. When the engine s running, the computer uses the MAP sensor signal to monitor engine load. 2. When the engine s off or at wide-open throttle, the computer uses the MAP sensor signal to check barometric pressure. From this, it gets a useable indication of altitude, and can modify fuel delivery to compensate for changes in atmospheric pressure. Analyzing Manifold Vacuum Your first step in checking manifold vacuum is to connect a vacuum gauge. Unless the engine you re working on has an unused, plugged manifold vacuum port available, you ll probably want to tee the gauge into an existing line; that way, you won t disable a vacuum device that s important to engine operation. Normal Operation An engine that s operating normally should provide between in/hg at idle. Vacuum levels should drop off instantly with throttle opening, to almost zero in/hg at wide-open throttle. Vacuum will increase above 18 in/hg on deceleration, and it should hold fairly steady at all throttle openings. 48 GEARS January/February 2008

Condition 1 Vacuum is low at idle; maybe as low as 12 in/hg or less. It may still rise above 18 in/hg on deceleration, and it holds fairly steady at all throttle openings.

The PCV is a calibrated vacuum leak; the wrong one can show up as a vacuum leak, and cause all sorts of performance problems.

Condition 2 Vacuum fluctuates slowly between 14 17 in/hg, varying with engine speed. All other conditions appear normal.

Look for an engine problem, such as a burnt valve, worn valve guides, or a worn camshaft. Checking for a Plugged Exhaust The complaint is a lack of power, maybe poor gas mileage, too.

4 Condition 1 Vacuum is low at idle; maybe as low as 12 in/hg or less. It may still rise above 18 in/hg on deceleration, and it holds fairly steady at all throttle openings. You could be looking at a vacuum leak, retarded valve timing, or general engine wear. Diagnostic Tip If you run into this condition, check the PCV valve. The PCV is a calibrated vacuum leak; the wrong one can show up as a vacuum leak, and cause all sorts of performance problems. If you re looking at a vacuum leak, and the PCV was replaced recently particularly if it was replaced with an aftermarket valve always suspect it as the cause of your vacuum leak. Condition 2 Vacuum fluctuates slowly between in/hg, varying with engine speed. All other conditions appear normal. This could indicate an air/fuel problem, ignition timing problem, or a problem with the EGR valve. Condition 3 Vacuum pluses rapidly between in/hg; engine seems to run rough. Look for an engine problem, such as a burnt valve, worn valve guides, or a worn camshaft. Checking for a Plugged Exhaust The complaint is a lack of power, maybe poor gas mileage, too. If the exhaust is really plugged, you ll hear a whistling noise during a hard acceleration. One way to test for a plugged exhaust is with a vacuum gauge. 1. Disable the EGR valve The EGR will normally cause vacuum to drop by at least 2 in/hg at 2000 RPM, so a working EGR will affect your results. Keep in mind that disabling the EGR may set a code in the computer s memory. 2. Connect your vacuum gauge to manifold vacuum. 3. Start the engine, and let it warm to normal operating temperature. 4. Record the vacuum level at idle. 5. Raise engine RPM slowly to 2000 and watch the vacuum gauge. If the exhaust is okay, the vacuum will drop no more than about 1 in/hg or so as you raise the throttle, and then recover. If the exhaust is plugged, the vacuum will drop off more than 2 in/hg. Figure 2: The best way to check for a leaking EGR valve is to make up a test gasket that seals one of the passages. Install the gasket and start the engine. If the engine smoothes out and idles better with the gasket in place, the EGR is leaking. Learn how the most successful shop owners of our industry are dealing with Remans vs Custom Rebuilds Employee Compensation Pricing Profitably Advertising and Marketing Strategies Reaching New Customers Dealing with Extended Warranty Companies And much more.. Be a part of the all new What s Working Forum! The What s Working program is all about improving your business based on what the most successful shop owners are doing! By joining the What s Working forum you ll have access to great discussions on a wide range of management topics pertaining to running a successful shop from some of the greatest minds in our industry. The forum is currently open to the entire industry! Sign up today - Join the What s Working Forum it s FREE! *Offer to non-members ends January 31 st 2008* GEARS January/February

5 Keeping Up Translating Engine Vacuum Measurements In severe cases, the vacuum could drop below 5 in/hg, and won t recover until you release the throttle. While there are a number of areas that can cause an exhaust restriction, the most common cause today is a plugged catalytic converter. Checking EGR Operation The Exhaust Gas Recirculation or EGR valve is another type of calibrated vacuum leak; this time it s between the intake manifold and the exhaust. It s designed to allow a metered amount of inert exhaust gas to mix with the intake, reducing the combustibility of the mixture, which, in turn, lowers combustion temperatures. On a normal gasoline engine, the EGR should be closed at idle, and will open at part throttle. A clear, working EGR valve will cause manifold vacuum to drop about 2-3 in/hg when it s open all the way. This is important for a number of reasons: 1. If the EGR isn t opening, it increases manifold vacuum. This affects all components that operate on manifold vacuum, including vacuum modulators. 2. If the EGR isn t opening, it can fool the computer into assuming a lower engine load. This can keep the computer from disabling the converter clutch, causing a shudder or chuggle on light throttle. In some cases, the EGR can remain stuck slightly open. This can cause rough idling or poor light-throttle performance. It can also affect fuel efficiency and emissions, because the computer can overcompensate by richening the mixture. The only real way to check for a leak in the EGR is to create a special, temporary gasket, with one set of holes blocked off (figure 2, page 49). Install the test gasket and recheck engine operation. If the engine idles better and fuel delivery is altered with the test gasket in place, assume the EGR is faulty. Caution Only use this modified gasket to test the EGR for leaks; always remove it after testing. Never leave a test gasket in place: It ll disable the EGR, causing combustion temperatures to rise, and increasing NOx levels. Diagnostic Tip Many aftermarket companies make EGRs to fit a wide range of engines; they include selective orifices to calibrate the EGR for each engine. Using the wrong orifice or none at all can cause a severe hesitation and allow manifold vacuum to drop too much on throttle opening. If you run into these conditions, check the EGR: If it was replaced recently, suspect an improper calibration as the culprit. A Word of Caution One of the biggest problems with using manifold vacuum for diagnosis is there are no hard and fast rules about the results. On one car, 18 in/hg is normal at idle; in another vacuum might be only 14 or 15 in/hg. A regular fluctuation in the needle may indicate a burnt valve, or just a bad spark plug. In fact, some 4-cylinder engines will get the needle vibrating like crazy, without anything being wrong. That s why you should never condemn a component or system based solely on the vacuum reading. Use it only as an indicator; a pointer, to show you where to look further for a problem. From there, you ll be able to focus your diagnosis, to help you find the problem quickly and efficiently. QUIZ QUESTIONS 1. Which of these isn t a type of engine vacuum? A. Manifold Vacuum B. Ported Vacuum C. Vortex Vacuum D. Venturi Vacuum 2. Tech A says a MAP sensor provides the computer with an engine load signal. Tech B says a MAP sensor provides the computer with an indication of altitude. Who s right? A. A only B. B only C. Both A and B D. Neither A nor B 3. If the EGR is plugged or stuck closed: A. Combustion temperatures will rise. B. NOx emissions will increase. C. The converter clutch may hang on too long, causing a shudder or chuggle. D. All of the above. 4. Tech A says the EGR must be working to use manifold vacuum to check for a plugged exhaust. Tech B says, if the exhaust is plugged, manifold vacuum will drop at higher throttle openings. Who s right? A. A only B. B only C. Both A and B D. Neither A nor B 5. Which of these conditions could cause manifold vacuum to fluctuate slowly between in/hg? A. Improper air/fuel mixture B. Faulty oxygen sensor C. Worn spark plugs D. Nothing; this is a normal condition. Answers: 1. C; 2. C; 3. D; 4. B; 5. A 50 GEARS January/February 2008

6 Would You Rather Have 60% Gross Profit or a 20% Net Profit? Many of our clients aren't happy with either of these choices...find out why. The Expo in October has rekindled the passion of many shop owners. The "What s Working" Forum has been very educational with many great discussions. Attention has turned from technical to business management. This has fueled emotions, and this is a good thing. We ve started asking good questions about how best to operate a profitable business, how to sell better, how to hire and pay, and where to advertise. Rewards are the result of putting ideas into action, which requires effort. Not all ideas are good...not all results are what you really want. To know if the effort is worth the reward, you need to be clear on your objective. Gather good statistics prior to making any change, and then continue to gather statistics to monitor and measure the results. Change without a system to monitor and measure results leads to management by feelings. This is dangerous because you may even be working hard on the wrong project and wasting valuable resources. Dean Kuhn, owner of Oceanside Transmission, has been monitoring and measuring key areas of his business differently than in the past. With ProfitBoost Software, Dean tracks parts costs, markups, productivity, and sales, and he has fine tuned his business. Dean now has access to statistical reports 24/7, and he can see in real time the effects of any change. Each business has different overhead expenses rents, insurance, utilities, etc. technicians and service writers have varied skill levels. Parts markup, labor rates and regional pricing factors vary greatly, as well; so what works for one business may not work for another. In fact, this makes sharing sales and pricing information between businesses risky. Since installing ProfitBoost Software, Mark Schwartzman, General Manager of Glen Burnie Transmissions, has more decision making information at his fingertips than ever before. Mark is able to offer choices to his customers that are all profitable for the shop, but provide greater levels of customer confidence and satisfaction. With the use of ProfitBoost Software, Mark identifies job profitability instantly...managing for profit has become easy. ProfitBoost Software offers an easytouse Repair Order Writing solution while providing Reports and Data for making factbased decisions that will boost the bottom line and your checking account balance. Isn t it about time that you stopped running your business by the seat of your pants? It s worked for Dean Kuhn and Mark Schwartzman. Take the next step; call and join the hundreds of others who are enjoying more time, money and freedom.. you ll be glad you did. Call ProfitBoost Software for a personal online demonstration at ext 820 or watch our videos at ProfitBoost Software can make a difference in your business. Get the ProfitBoost Team involved. We are available 8 to 5 MF to help you become more profitable and secure in your business. Mark Schwartzman & Dean Kuhn with the What s Working Panel / Expo Business Owners & ProfitBoost Software Working together for success! ProfitBoost Software LLC Advertorial

It s Not Your Everyday Bind

The Honda with a Bind in Reverse Fun with Transmissions It s Not Your Everyday Bind by SPEAKER Bill Brayton Unwanted oil pressure causes a Honda BAXA/MAXA to bind in reverse. Iwrote an article introducing