Children have been known to make some very perceptive observations. A grade-schooler came up with this answer on a recent science test: When planets run around and around in circles, we say they are orbiting, but when people do it, we say they are crazy. Unfortunately, technicians chasing down a computer's diagnostic troubleshooting codes sometimes feel like they are running around like crazy. Electronic fuel injection (EFI) systems can be especially perplexing, but taking the right approach can lead technicians to an accurate diagnosis and timely repair.

In this brave new world of computerized systems, the key to success for technicians is as simple as ABC: Remember the basics no matter how complex the system or problem. With computers providing more data about increasingly complex systems, it's critical for technicians not to become so focused on the computer that they stop thinking about the overall operating dynamics and tendencies of the system: How it works, which components are involved, why it fails, etc.

Computerized test equipment effectively identifies a wide range of problems and saves technicians vast amounts of time. Something the systems don't do is pinpoint problems exactly. It's up to technicians to evaluate computerized information about the problem in light of what they know about the system and additional information from the car's owner, observation and results from diagnostic tests. Like all tools, diagnostic equipment must be used properly. In this case that means looking beyond the fault codes to test all possibilities and isolating the real problem.

In many cases, the source of technician frustration is simple: Diagnostic computers do not have all the answers, but it's all too easy to treat them as though they do. A diagnostic system's only input is from a limited number of sensors, so the fault codes computers display may only be symptoms of the real problem. Codes provide invaluable clues, but only trained technicians can make the final diagnosis.

For example, the fault code may indicate that the manifold absolute pressure (MAP) sensor is out of range. Reacting to the fault code alone, a technician may replace the sensor unnecessarily. The electronic powertrain control module (PCM) knows it is receiving an out-of-range reading, but it does not know why. Is there a sensor failure, or another cause? Only testing and analysis by the technician can uncover the root of the problem and prevent a frustrated customer from returning with the vehicle.

Oxygen sensor failures can also result in code chasing, where technicians replace component after component based on fault code readings. Oxygen sensors rarely wear out, so when one fails it is usually a symptom of another problem. The dead sensor could result from improper bias voltage, a blown plug or other causes.

A fairly common scenario involving oxygen sensors occurs when the customer comes in with a "check engine" lamp on and the fault code indicates a lean condition. Without much additional investigation, the oxygen sensor is sometimes replaced. In this case, the real culprit could be a vacuum leak, a plugged fuel filter or a fuel pump not performing to specification.

Another basic step to remember is to follow established troubleshooting procedures in order to verify the fault codes and identify the true problem. The basic troubleshooting steps for EFI systems start with the battery charging system. It is the simplest and most accessible system to check when isolating EFI problems. The battery charging system must provide the injectors with a specific and consistent power flow. When troubleshooting, be sure that the battery system is delivering a full charge. If not, check to see if the battery cables are clean and if the battery has adequate capacity. Also check the alternator charging system and be sure the fan belt is in good condition and at the right tension.

Some EFI symptoms point to a possible problem with the fuel pump. The pump is the heart of the EFI system, delivering a specified volume of fuel to the injectors at constant operating pressures. It is critical to know the suspect pump's current operating characteristics as well as how the rest of the system is functioning. However, telephone logs from toll-free help lines show that technicians often react to fault codes or their own intuition about the cause of a problem and begin making repairs without verifying the pump's output. In addition to a reliable repair manual, trouble-shooting should always in- clude using a pressure gauge and a flow meter. Diagnostic tool manufacturers often incorporate flow meters into their pressure gauges.

Consider the following when analyzing fault codes and determining the status of the system:

• Low fuel pressure- Vehicles may surge, stall, hesitate, lack power or misfire (imitating an ignition problem).
• High fuel pressure- Symptoms can include high CO emission, inability to start and low mileage.
• Low fuel volume- Interference with the amount of fuel reaching the injectors can lead to surging, hesitation, power loss or engine shutdown.
• No fuel- Loss of fuel pressure after engine shutdown results in fuel not being immediately available when the driver goes to start the engine. The car will come in with a hard-start or no-start complaint. The loss of rest pressure can be due to a leaking fuel pump, check valve, fuel injector, fuel line or pressure regulator.

Vapor lock and fuel contamination cause other fuel delivery performance problems. Remembering how the system works and what's causing the problem will help in making fast, effective repairs. Though rare, vapor lock can occur with today's complex gasoline mixtures. The result is usually hot restart problems or an engine that dies after warming up. The situation is caused when chemicals or additives within the fuel mixture boil and turn to vapor in the fuel line, effectively blocking it.

Even if the fuel pump is still working, always pressure test it when vapor lock is suspected. Air cavitation and scoring damage can occur inside the pump, causing it not to make pressure. Failure to check the pump may lead to the customer returning with complaints of sluggish performance or, worse, with a fuel pump that failed prematurely.

Unlike vapor lock, fuel contamination is a more common cause of fuel pump problems and EFI system diagnostic challenges. Additives, either in gasoline mixtures or bought off-the-shelf, are being used more to help maintain fuel systems, especially injectors. Most of these products do their jobs, but almost all too well in some cases. They break down deposits throughout the entire system, including the fuel tank where deposits can form even on plastic tanks. The result is that very fine dust-like particles enter the fuel. For newer cars that haven't seen years of use, this usually is not an issue, but with older cars, the introduction of the grit-like residue into the fuel can clog or restrict the flow through fuel pump strainers and fuel filters. These clogs can cause fuel starvation that results in low running pressure, poor performance or engine shutdown.

Car owners in these situations are sometimes frustrated because a strainer or fuel filter must be replaced sooner than expected. In reality, they should be grateful that they were spared the cost of additional repairs, such as replacing a failed fuel pump, because these filtration components did their job by removing contaminants from the system.

When fuel pump replacement is necessary, several basics need to be kept in mind to avoid opening the door to additional problems. For example, always put on a new fuel strainer when a new pump is installed, and be sure the strainer forms an effective seal around the fuel inlet port. Otherwise, unstrained fuel can reach the pump where even the smallest contaminants can quickly cause major damage. This is the primary cause of fuel pump failures.

Other keys to proper service revolve around taking precautions to keep the fuel delivery system clean and removing contaminants whenever possible. This includes thoroughly cleaning the fuel tank and installing a new fuel filter whenever the pump and strainer are replaced. Also, never add the old fuel back into the tank; instead, replace it with fresh fuel.

Though our business is sometimes a crazy one, technicians can effectively maintain their sanity, as well as their customers' cars, by sticking to the basics. Keep in mind how the system in question operates, and follow normal troubleshooting procedures to verify the fault code clues and isolate the real problem.

Craig Gottfried is a technical service representative for Airtex Automotive, the largest independent manufacturer of fuel pumps and water pumps

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