In the actual tune-up operation, as in troubleshooting, the most important thing to do before starting the job is to get the customer's story. What particular problems has he or she been having with the car? Why was the car brought in for a tune-up? What are the specific complaints? The best tune-up job in the world can result in a comeback and an unhappy customer if the customer's specific complaints are not examined and corrected when possible. And, if the problem can't be fixed by a tune-up, the customer deserves a complete explanation of the reasons.
1. Test battery, starter, and ignition while cranking
Check the battery first to ensure that the car will start and that there is enough voltage for the ignition primary circuit. Remember that dirty battery terminals can make a good battery fail these tests. Clean the terminals and cables, if necessary. While cranking the engine to test the starter, make sure that there is secondary ignition voltage during cranking.
2. Test charging system
The charging system does not normally need repair as a part of tune-up, but you must know early in the procedure if it will need repairs and if it may cause ignition system problems. Check the alternator's current output and the voltage regulator setting.
3. Test overall engine condition and performance
This step tests the engine's mechanical condition as well as generally testing the ignition and fuel systems. These basic tests early in the job will determine if the engine can be tuned, or how much work is needed before a tune-up can start. Steps 1, 2 and 3 can be done quickly and easily with an oscilloscope motor analyzer and an infrared tester.
The engine condition and performance tests should include:
- Ignition primary circuit
- Ignition secondary circuit
- HC and CO emissions
- Spark timing controls
- EGR, PCV, and air injection systems, if needed
- Cylinder power balance
- Compressions (if balance test indicates a problem).
4. Service ignition systems and distributor
Shut off the engine for steps 4 through 7. The required ignition system service will vary according to the car. Breaker-point distributors get routine service. Solid-state distributors get repairs or replacement only as required. Step 3 will have revealed any ignition secondary service needed.
The distributor's dwell and advance mechanisms can be tested and adjusted with the distributor in or out of the engine. However, these tests and adjustments can be made more easily and accurately with the distributor removed from the engine and installed in a test machine.
Ignition system services may include:
- Breaker-point primary routine maintenance - points and condenser
- Solid-state primary troubleshooting and replacement as needed
- Secondary circuit parts replacement as needed - distributor cap, rotor, and cables
- Spark timing control service as needed - distributor advance units, solenoids, switches, vacuum lines, and other parts
- Breaker-point dwell adjustment
Steps 5 and 6 may be switched for convenience. While the spark plugs are out, you may want to check cylinder compression. However, the engine should be warm for an accurate compression test.
6. Service all filters
All air filters, fuel filters, PCV filters, and others must be serviced before the carburetor is adjusted.
7. Service PCV, EGR, and air injection
If step 3 revealed any faults in the emission control systems, repair them now that the engine has cooled.
8. Set ignition timing
Bring the engine to operating temperature for step 8 through 10. Adjust initial timing to specifications.
9. Adjust valves
Do this step only for engines that have mechanical valve lifters.
10. Adjust carburetor
Using the infrared analyzer if possible, adjust the idle speed and mixture according to the manufacturer's instructions. Some engines may not need an idle mixture adjustment as regular service. Usually, all filters are in place and the air cleaner is mounted during the step.
11. Retest
Repeat the basic engine performance tests as a quality-control check. You can compare these results to the step 3 test results to show the customer your work. The retest should include:
- Overall ignition performance
- Cylinder power balance test
- HC and CO emissions
Drive the car to be sure you and the customer are satisfied with your work. Some more advice on road testing is in order at this point. One quick lap around the block is not enough to check out a problem before service or as a quality control check after service. For a worthwhile road test, the engine should be brought to normal operation temperature. The test should include a stop-and-go city driving cycle and a period of cruising at highway speed. If the car has air conditioning, operate it during the road test. If a hilly stretch of road is available, include it in your route.
A complete road test can be performed in about 10 minutes. If possible, use the same route for all tests so that the performance of a car can be compared before and after service, as well as to the performance of similar vehicles. If your shop has a dynamometer, it can be used to simulate a road test.
