| Auto Fuel Delivery System -- Diagnosing the Problem |
From "Weekend Mechanic"
episode WKM-101 |
|
|
|
advertisement
|
Diagnosing the Problem It has been determined that the hesitation and stalling problems in the 1993 Taurus are likely due to the fuel delivery system. Diagnostic tools have been obtained to help narrow down the problem before any actual repairs can begin. Following are the steps that Weekend Mechanic host Bruce Bonebrake follows to help diagnose the exact problem. To verify the suspected fuel injectors as the cause of the problem, the test rule out other factors such as the ignition system, sparkplug wires, fuel-system pressure and power supply to the injectors. Important: Included below are the steps in this automotive procedure as shown in the episode. These steps are general guidelines that are applicable to most vehicles. With any particular vehicle, there may be procedures, specifications, settings, tolerances, components, etc. that are specific to that vehicle. Always consult your vehicle's service manual when undertaking significant automotive repairs. Safety Alert: Fuel-related projects require a well-ventilated work area.
Materials: RPM meter
Spark tester
Fuel-pressure gauge
Noid light
Extra-long screwdriver
Shop rag
Steps:
- The first step is a thorough visual inspection under the hood (figure A). Check vacuum hoses, electrical harness and other visible components to see if there are any obvious problems like loose hoses or connections. On our vehicle, the inspection indicated that the PCV valve was old, and in need of replacement, and the retaining nut on the intake manifold needed tightening. It's also a good idea to check the air filter. Typically, air filters should be replaced about every 30,000 miles. The air filter on our vehicle was clogged and in need of replacement.
- The first diagnostic test is the performance of a power balance on the ignition system. This will help rule out the ignition system as the source of the problem before moving on to the fuel system. Six small lengths (about 1-1/2 inches) of vacuum hose are cut and each is placed on a cylinder -- with one end on the plug wire and the other on the distributor cap. With those connected, a ground-probe is connected to ground and an RPM-meter is connected to both ground and the negative side of the coil. The RPM reading is then monitored for each of the cylinders. As the probe is brought in contact with each cylinder (figure B), the rpm gauge (figure C) is checked. In each instance, there should be an RPM drop. If there is no change when the probe is brought into contact with any of the cylinders, an operational problem associated with that cylinder is indicated.
- In this test, it was determined that one cylinder on the Taurus was not operating properly. The might be caused by a sparkplug wire or sparkplug. A spark tester is used to check the sparkplug and wire. Attach the plug wire to the terminal end of the spark tester, and the clip to a ground point. If the wire is OK, a spark should be visible in the tester-indicator (figure D) when the ignition is turned on. In our test, the wire was found to be OK. The sparkplug was then removed to checked for condition, and was found to be OK. These tests ruled out the ignition system as the source of the problem, providing further evidence for the fuel delivery system.
- To begin diagnosis on the fuel system, the fuel pressure is checked first. Identify the fuel port on the fuel rail (figure E). The fuel port is where the fuel-pressure gauge will be attached.
- With the cap on the fuel port removed, attach the fuel-pressure gauge to the port (figure F). Use a shop towel around the valve to catch any fuel that may be expelled and avoid fuel from spilling onto the engine exterior.
- Check your vehicle's manual for proper fuel pressure for your vehicle. On ours, the manual gave a range of 35 to 45 PSI -- a range typical of most American vehicles. With the fuel-pressure gauge securely attached to the port (figure G), have an assistant start the engine and check the gauge readout. The acceptable readout on our test (figure H) indicated that the fuel-pump, lines and fuel filter are all OK.
- The next step is to check whether the injectors are operating. One technique is to use a long screwdriver as a makeshift "stethoscope" to listen to the sound of each injector as the car is running (figure I).
- Safety alert: Use caution when performing this test, making certain to stay clear of belts, moving parts, the electrical terminals at the rear of the alternator, etc.
- With the engine running, rest the tip of the screwdriver directly on the injector (figure J) and listen at the handle of the screwdriver. If the injector is working properly, a series of crisp "clicks" should be audible through the screwdriver-"stethoscope."
- One of the injectors in our test was making only a weak, irregular click, and another was making no sound at all -- indicating problems of varying degree with those particular injectors.
- To test and rule out the connections leading to the injectors, unplug the injectors (figure K) exposing the electric solenoid connection.
- Connect a noid light tester to the injector plug (figure L) and, making certain that the tester wires are out of the way of belts or moving parts, start the ignition.
- With the ignition running, if the noid light flashes, this indicates that the injector is receiving electrical pulses. The pulsing light in our test (figure M) indicated that the injector was receiving power, giving further indication that the injector itself is the cause of the problem.
In the segment that follows, the injectors are removed, cleaned and tested.
RESOURCES :
The Complete Idiot's Guide to Trouble-Free Car Care
Author: Dan Ramsey
ISBN: 0028635833
Alpha Books
Auto Repair for Dummies
Author: Deanna Sclar
ISBN: 0764550896
Fuel Injection: Installation, Performance Tuning, Modification
Model: 0879387432
Author: Jeff Hartman
Motorbooks International (MBI Publishing)
|
)
)
)
)
)
)
)
)
)
)
)
)
