Emissions and Fuel-Related Problems
Diagnosing emissions and fuel-related problems is one of the most challenging tasks facing the automotive technician. Such problems can be the result of many different conditions and can exhibit a wide range of symptoms. While it would be very difficult to cover the diagnosis of all such problems in one short article, we can provide some basic guidelines to get you headed in the right direction. Plus, we’ll also examine a specific emissions-related situation; namely, Diagnostic Trouble Codes (DTCs) for the evaporative emissions system.
BASIC TROUBLESHOOTING PROCEDURE
Troubleshooting a complex fuel/emissions problem can be easier if you have a basic plan to verify, analyze and correct it. The underlying source of the symptoms reported by your customers can often lie in areas that seem unrelated to the complaint. This is especially true with emission and fuel systems. For this reason, it is critical to use a methodical diagnostic approach to uncover the root cause of the problem. This will help you make the right repair in the most efficient manner possible. The Six-Step Troubleshooting Procedure is the recommended diagnostic method to use for solving these very complex problems. It is detailed in Chrysler’s May 2003 MasterTech Reference Book, Fuel Systems Diagnosis Update. The six steps are listed below:
1. Verify the complaint
2. Verify the related symptoms
3. Analyze the symptoms
4. Isolate the problem
5. Repair the problem
6. Verify the repair
Many technicians follow this diagnostic troubleshooting procedure and have had great success in using it. This approach will help you cover all the bases and not overlook important information that can be used to solve the problem at hand. Not having a solid plan of attack could mean the difference between a satisfied customer and a comeback visit.
ON-BOARD DIAGNOSTICS
The on-board diagnostic system is a very useful tool that can be used in conjunction with the six-step procedure, particularly for analyzing and isolating the problem. Here’s a review of how it works. The Powertrain Control Module (PCM) monitors many different circuits in several systems, including those for fuel injection and emissions. If the PCM senses a problem with a monitored circuit often enough to indicate a problem, it stores a Diagnostic Trouble Code (DTC) in its memory. If the code applies to an emissions-related component, the Malfunction Indicator Lamp (MIL) will be illuminated (this light is located on the instrument panel). Monitored circuits include the catalyst, Exhaust Gas Recirculation (EGR – if equipped), fuel control and oxygen sensor.
So how can you access one of the DTCs? Well, it’s pretty simple. A data link connector, as shown in Figure 1, is located under the dashboard near the steering column (the location is the same on all vehicles, as required by Federal law). Plug the connector from the DRBIII® (or equivalent) scan tool into the data link to access any codes. As you probably know, a DTC is not a surefire answer to an unsolved problem, but many times it can lead you in the right direction. And, if you have access to Chrysler Service Manuals, that can be a great help to you too. The fuel system is found in section 14; the emissions system in section 25.
EVAPORATIVE EMISSIONS SYSTEM DTCs
Let’s look at a specific emissions system problem. This one will focus on the evaporative emissions system. This is a closed system that captures the gasoline vapors from the fuel tank and fuel system, preventing the release of these vapors to the atmosphere. In the pre-emission days, fuel tanks were not sealed. The fuel tank cap was vented, allowing mechanical pumps to draw gasoline from the tank to the carburetor. As a result, fuel vapors were vented to the atmosphere.
Today, the fuel tank has a sealed cap that prevents such venting. Vapors lines, connected to a purge canister, control the flow of air in and out of the fuel tank. Any vapors are drawn off the canister into the intake system to be burned with the air/fuel mixture.
The major concern with this system is leaks. These leaks can occur in the components and lines and at the seals and connections. There are other problems, as well, which include general failure of the system and electrical circuit faults. DTCs will be stored for all of these problems.
Since leaks are the most common problem with the evaporative emissions system, that will be the focus of this example problem. Leak DTCs result from failing the evaporative emissions system monitor (remember, emissions systems are monitored circuits). Separate codes exist for small leaks, medium leaks and large leaks. There is also a code for a general evap system failure.
The first step of the Six-Step Troubleshooting Procedure is verifying the symptom. This is of particular importance when dealing with evap system DTCs. In some cases, the customer might not complain of any driveability problem, but the MIL is illuminated. Something as simple as a loose fuel cap can cause a leak code and the MIL illuminated. To find a medium or large-size leak, you can use the DRBIII evaporative emissions system test to run the system monitor to quickly verify such a leak.
EVAPORATIVE EMISSIONS LEAK DETECTOR
When the MIL is illuminated as the result of an evap system leak DTC, the leak can be verified and found using the Evaporative Emissions Leak Detector (EELD / Essential Special Tool #8404). Using this tool is usually recommended in the diagnostic procedures for leak codes. Be sure that the EELD you’re using has been updated to include the .010-inch orifice.
The EELD uses a shop air connection for airflow and to introduce smoke into the evap system. The smoke is a visual aid for detecting leaks. It also contains a dye that is visible under ultraviolet light. The tool has two (2) lights that help locate the leaks: a white light is used to look for smoke and a UV light is used with special yellow glasses to check for visible traces of the dye left by the smoke.
The EELD is rather easy to use. First, check the fuel level. The tank should be, ideally, 85-percent full. Next, be sure the system is cool before doing any testing. Then, calibrate the EELD for the leak size being detected. This is done by placing the air hose in the appropriate orifice (let’s say .010") and flowing air through that orifice. Finally, seal the evap system using the appropriate adapter (Figure 2). Install the adapter on the Leak Detection Pump or the Natural Vacuum Leak Detection (NVLD) assembly vent.
Then, flow air into the evap system so that the EELD can verify that a leak exists. Remember, large volume fuel tanks and those tanks with a low fuel level might take as long as five minutes to fill with air. If the airflow is above the calibration marker, a leak is present somewhere in the system.
Next, use the smoke setting to fill the system with smoke. Use the white light to locate the source of the leak. Look for smoke coming from the components of the evap system. Pay close attention to hoses and connections, such as those shown in Figure 3. Don’t forget to look for splits, cracks and other signs of damage.
If the leak is obscured or you’re unable to pinpoint the exact location of the leak, use the UV light and the appropriate special yellow glasses to find traces of the dye left behind as the smoke passes through the leak (this is the same way dye is used to find leaks in A/C systems). Once you find the source of the leak, make the necessary repair. The final step is retesting the system to verify that the repair has been made correctly.
