Unlocking the Hood: An Engine Troubleshooting Guide

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Higher gas prices, increasing repair costs and required emissions testing are important reasons for today's vehicle owners to test and tune their cars to keep them running smoothly. Computerized cars may seem scary to first-time D-I-Y'ers, but with a little basic knowledge you can learn that troubleshooting and tune-up is easy and fun! This article is designed to teach you about the new engine technology and the new test equipment for troubleshooting computer-controlled cars. Armed with this knowledge, you can help yourself "unlock the hood" of newer cars and save money on vehicle repair costs. This article is divided into 6 sections:
 
  • Description of computer-controlled engine systems 
  • DIY Tips 
  • Trouble Codes 
  • Sensor Tests 
  • Engine Tests 
  • A simple reference chart listing common engine problem symptoms and the tools used to diagnose and repair.
 
A) Unlocking the Hood: An Engine Troubleshooting Guide
 
Computerized Engines Offer New Challenges
Over the past 15-20 years mechanical engine controls have been replaced by vacuum, electronic and most importantly, computer controls. It is normal to be uncertain about working on a computer-controlled engine at first, because it is new and different. But with just a little time, education and experience, "high tech" becomes easy and safe. Remember how quickly we learned the new technology of VCRs, microwave ovens and personal computers? 
 
The Computer 
  • Controls the fuel injectors (delivers gas to the cylinders replaces the carburetor) 
  • Controls engine idle speed 
  • Controls spark advance timing (replaces function of vacuum and centrifugal advance in distributor)
  • Controls emission control devices, such as EGR valves
 
Computer-controlled engines and older engines have one thing in common: they both experience breakdowns that can be tested and repaired with simple troubleshooting steps. 
In the early '80's, car manufacturers added computer controls to vehicle engines in order to meet Federal Government economy and emission standards. A computer-controlled engine is basically the same as earlier types. It is still an internal combustion engine with pistons, plugs, valves and cams along with associated ignition, charging, starting and exhaust systems. Only the engine control systems have changed, and they have become computer-controlled. If the vehicle problems do not relate to the computer-controlled areas previously mentioned, you troubleshoot and fix them the same way you always have! 
 
Problems in the computer-controlled system are usually due to bad sensors (which tell the computer what is happening to the engine), bad actuators (the computer-controlled devices that affect engine operation, such as fuel injector) or bad wiring/poor connectors. The computer itself rarely goes bad. Actron's owner manuals are a good reference source, as they are fully illustrated and easy to understand. They clearly show how to test and tune today's cars using Actron test equipment. You can refer to these manuals for specific applications and test and replace many of these components yourself with the proper Actron equipment -- saving yourself time and money!
 
B) Unlocking the Hood: An Engine Troubleshooting Guide
 
DIY Tips
If your car was manufactured after 1981, chances are good it has an on-board computer and requires one or more of the Actron tools for computer-controlled vehicles.
 
Some of the benefits of do-it-yourself maintenance: 
  • Save Money
    Save the high cost of labor by doing it yourself.
     
  • Save Time
    Do the work on your time and at your location. 
     
  • Be a Smart Consumer
    Protect yourself by diagnosing the problem before taking the vehicle into the shop. Be equipped with knowledge about your car.
     
  • Better Gas Mileage
    A properly running vehicle uses less gasoline by running more efficiently. 
     
  • Pass Emission Tests
    Poorly tuned vehicles may fail state emission testing, requiring costly repairs. 
     
  • Sense of Pride and Enjoyment
    Knowing you have the skill to "Do-It-Yourself"
 
C) Unlocking the Hood: An Engine Troubleshooting Guide
 
Engine Computer Trouble Codes
The engine computer can do special tests to diagnose vehicle problems prior to making DIY repairs or taking the car into a professional shop. Test results are reported as numerical "trouble codes". Use a Code Scanner or Scan Tool to obtain trouble codes quickly and easily. The owner’s manual for the manufacturer specific code scanners (GM, Ford and imports) includes detailed test instructions and over 300 trouble code definitions. The Autoscanners include a CD-ROM with over 5,000 code definitions.
 
Recommended Tools:
  • SUPER AutoScanner Kit CP9150
  • SUPER AutoScanner CP9145
  • SPANISH OBD II AutoScanner CP9138S
  • OBD II AutoScanner CP9135
  • PocketScan Code Reader CP9125
  • Honda/Nissan/Toyota Code Scanner CP9025
  • Ford Code Scanner CP9015
  • GM Code Scanner CP9001
 
D) Unlocking the Hood: An Engine Troubleshooting Guide
 
General Sensor Tests 
Computer-controlled engines require good, working sensors. Severe performance problems can result when sensors fail. Check sensors for proper operation. 
Recommended Tool:
  • AutoTroubleShooter CP7677
  • Ignition Module and Sensor Tester CP9087
 
MAP, MAF and VAF Sensor Tests:
Critical MAP (Manifold Absolute Pressure), MAF (Mass AirFlow) and VAF (Vane AirFlow) sensors must be kept in reliable working condition.
Recommended Tool:
  • AutoTroubleShooter CP7677
  • Ignition Module and Sensor Tester CP9087
 
Ignition Module Test
Faulty ignition modules can cause no-start problems. Check modules for proper operation.
Recommended Tool:
AutoTroubleShooter CP7677
Ignition Module and Sensor Tester CP9087
 
E) Unlocking the Hood: An Engine Troubleshooting Guide
 
Basic Tests Anyone Can Do on a Computer-Controlled Car
Before we describe the tests for computer sensors, it is vital to remember that many important checks can still be made the old familiar way. The basic engine has not changed and the computer does not control everything! 
 
Compression Test
Use a compression gauge to test for proper compression in each cylinder. Improper compression can cause rough idling or running, backfiring and poor fuel economy. Can also be used to test valve problems, piston rings and timing chain.
Recommended Tools:
  • Professional Compression Tester CP7828
  • Compression Tester Kit CP7827
  • Stem Compression Tester CP7821
 
Engine Vacuum
Use a vacuum gauge to test for proper intake manifold vacuum at idle. Improper vacuum can mean problems with ignition timing, piston rings, valves, valve timing, valve springs, valve guides, manifold leaks and some carburetor adjustments. Even small vacuum leaks can cause hard starting, stalls, and poor engine performance. 
Recommended Tools:
  • Hand Pump / Brake Bleed Kit CP7835
  • Hand Vacuum Pump CP7830
  • Vacuum/Pressure Tester Kit CP7803
 
Check/Adjust Basic Engine Timing
Correct timing is essential to maintain top performance. Timing refers to when the engine tells each spark plug to fire. A chart under the hood of most cars shows what the timing should be at various RPM levels. Use a timing light to set the timing on any engine (computer-controlled or not) that has a conventional distributor ignition system. Timing cannot be manually adjusted on cars with distributorless ignition systems, but it is important to check computer timing to see if it might be the cause of engine problems. Use an advance timing light such as the Timing Advance Analyzer CP7519 to check whether the computer is "advancing the spark" according to spec as engine speed increases. 
Recommended Timing Lights:
  • DC Power Timing Light CP7520
  • Timing Advance Analyzer CP7519
  • Chrome Inductive Timing Light CP7515
  • Inductive Timing Light CP7504
 
Vacuum Leak Test
Leaky vacuum lines can cause problems for any engine. A vacuum pump can be used to check vacuum lines as well as vacuum-operated solenoids and switches. 
Recommended Tool:
  • Hand Pump / Brake Bleed Kit CP7835
  • Hand Vacuum Pump CP7830
  • Vacuum/Pressure Tester Kit CP7803
 
Remote Starter Switch
Start, crank or "bump" engine while under hood. Useful for compression tests, checking camshaft or crankshaft sensors and adjustment work on valves, distributor or camshaft. 
Recommended Tool:
  • Remote Starter Switch CP7853
 
Battery Voltage Test
Low batteries can cause intermittent problems well before the battery completely dies. Battery voltage should be at least 12.4 volts. Use a voltmeter or battery load tester to check. 
Recommended Tools:
  • AutoTrouble Shooter CP7677
  • Digital Multimeter CP7676
  • Digital Multitester CP7674
  • Digital Multitester CP7672
  • AutoAnalyzer CP7665
  • Battery Load Tester CP7612
  • Battery/Alternator Tester CP7611
  • Dwell/Tach/Volt Analyzer CP7605
 
Cranking System Voltage Test
The cranking system requires at least 8-1/2 to 9 volts to start the engine. Use a voltmeter to test cranking system voltage. 
Recommended Tools:
  • AutoTrouble Shooter CP7677
  • Digital Multimeter CP7676
  • Digital Multitester CP7674
  • Digital Multitester CP7672
  • AutoAnalyzer CP7665
  • Dwell/Tach/Volt Analyzer CP7605
 
Lighting System Voltage Test
Use a voltmeter to test lighting systems. 
Recommended Tools:
  • AutoTrouble Shooter CP7677
  • Digital Multimeter CP7676
  • Digital Multitester CP7674
  • Digital Multitester CP7672
  • AutoAnalyzer CP7665
  • Dwell/Tach/Volt Analyzer CP7605
 
 
F) Unlocking the Hood: An Engine Troubleshooting Guide
 
Troubleshooting Reference Chart
Engine Component or FunctionRecommended Actron ProductTest Selection/Range
Air Temperature Sensor/SwitchDC Power Timing Light CP7520
Timing Advance Analyzer CP7519
Chrome Inductive Timing Light CP7515
Inductive Timing Light CP7504
Crankshaft degrees
Battery and Charging VoltageBattery/Alternator Tester CP7611LED Voltage indicators
Battery ConditionBattery Load Tester CP7612Load Test
Battery VoltsAutoTrouble Shooter CP7677
Digital Multimeter CP7676 
Digital Multitester CP7674 
Digital Multitester CP7672
AutoAnalyzer CP7665
Battery Load Tester CP7612
Battery/Alternator Tester CP7611
Dwell/Tach/Volt Analyzer CP7605
Volts:
Digital - 20V
Analog - 16V
Cam Position SensorIgnition Module and Sensor Tester CP9087"Test" light blinks or On/Off
Charging System VoltsAutoTrouble Shooter CP7677
Digital Multimeter CP7676 
Digital Multitester CP7674 
Digital Multitester CP7672
AutoAnalyzer CP7665
Battery Load Tester CP7612
Battery/Alternator Tester CP7611
Dwell/Tach/Volt Analyzer CP7605
Volts:
Digital - 20V
Analog - 16V
Cranking System VoltsAutoTrouble Shooter CP7677
Digital Multimeter CP7676 
Digital Multitester CP7674 
Digital Multitester CP7672
AutoAnalyzer CP7665
Dwell/Tach/Volt Analyzer CP7605
Volts:
Digital - 20V
Analog - 16V
Computer Advance TimingAdvance Inductive Timing Light CP7519Verify degrees advance with advance knob
Coolant Temperature SensorIgnition Module and Sensor Tester CP9087"Test" light changes brightness
Crankshaft Position SensorIgnition Module and Sensor Tester CP9087"Test" light blinks or On/Off
Cylinder CompressionProfessional Compression Tester CP7828
Compression Tester CP7827
Stem Compression Tester CP7821
PSI or kPa scale
DC Idle Speed Control MotorIgnition Module and Sensor Tester CP9087Manual contains test instructions
EGR Valve Position SensorIgnition Module and Sensor Tester CP9087"Test" light changes brightness
Engine Computer Trouble CodesSuper AutoScanner Kit CP9150
Super AutoScanner CP9145
OBD II AutoScanner CP9135
SPANISH OBD II AutoScanner CP9138S
PocketScan Code Reader CP9125
Import Code Scanner CP9025
Ford Code Scanner CP9015
GM Code Scanner CP9001
Manual contains test instructions
Fuel PressureProfessional Fuel Pressure Tester Kit CP7838
Multiport Fuel Injection CP7818
GM TBI CP7817
Vacuum & Pressure Tester Kit CP7803 (Mechanical Fuel Pump)
0-100 psi

0-100 psi
0-60 psi

0-10 psi
GM C-3 Mixture Control SolenoidDigital AutoTroubleShooter CP7677
Dwell/Tach/Volts Analyzer CP7605
Dwell / 6 cylinder
Ignition ModuleIgnition Module and Sensor Tester CP9087Manual contains test instructions
Knock SensorIgnition Module and Sensor Tester CP9087"Test" light blinks
Mass Airflow (MAF) SensorIgnition Module and Sensor Tester CP9087"Test" light changes brightness
Manifold Absolute Pressure (MAP) SensorIgnition Module and Sensor Tester CP9087"Test" light changes brightness
Monitoring Engine Speed (Tach or RPM)Super AutoScanner Kit CP9150
Super AutoScanner CP9145
Digital AutoTroubleShooter CP7677
Digital Multimeter CP7676
Dwell/Tach/Volts Analyzer CP7605
Appropriate menu selection
Appropriate menu selection
Tach: Range to match speed measured
Monitoring Engine VacuumVacuum Pump/Brake Bleed Kit CP7835 
Hand Vacuum Pump CP7830
Vacuum & Pressure Tester Kit CP7803
Inches or kPa scale
One-man brake bleed operationVacuum Pump/Brake Bleed Kit CP7835 
Brake Bleed Kit CP7840
Hand Vacuum Pump CP7830
Instructions included with kit
Oxygen SensorIgnition Module and Sensor Tester CP9087"Test" light switches On/Off
Ported Vacuum SwitchDigital AutoTrouble Shooter CP7677
Digital Multimeter CP7676
Digital Multitester CP7674
Digital Multitester CP7672
AutoAnalyzer CP7665
Ohms/200
Start or "bump" engine while under hoodRemote Starter Switch CP7853Push button
Throttle Position SensorIgnition Module and Sensor Tester CP9087"Test" light changes brightness
Vacuum leaksVacuum Pump/Brake Bleed Kit CP7835 
Hand Vacuum Pump CP7830
Vacuum & Pressure Tester Kit CP7803
Read vacuum on gauge
Vacuum-operated solenoids, etc.Vacuum Pump/Brake Bleed Kit CP7835 
Hand Vacuum Pump CP7830
Vacuum & Pressure Tester Kit CP7803
Component operates when vacuum applied
Vane Air Flow (VAF) SensorIgnition Module and Sensor Tester CP9087"Test" light changes brightness
For acceptable test readings, consult your vehicle's service manual. Service manuals are available from the vehicle manufacturer or your local public library.