Ccc Carburetor Tests W/o Codes Cadillac Brougham I

HOW TO USE THIS ARTICLE

This article is to be used only AFTER you have checked the following

1. Verify the on-car diagnostics are working by performing appropriate DIAGNOSTIC CIRCUIT CHECK chart for that system.
2. Verify that the ECM and "SERVICE ENGINE SOON" light are functioning properly.
3. Verify that there are no trouble codes stored, or only intermittent ones.
4. Verify that the fuel control system is operating properly by performing appropriate SYSTEM PERFORMANCE CHECK chart. See appropriate TESTS W/CODES article in this section.
5. Perform a careful visual inspection of all systems.

After all checks have been performed, verify customer complaint and locate correct symptom. Check items indicated under that symptom. Not all items listed under each symptom apply to all models and systems. These procedures will normally lead you to a component system on vehicle, such as EGR, EST, TCC, etc. These are covered in component system charts. These charts are listed with a "C" before the number of the chart (C1A, for example).

INTERMITTENTS

"SERVICE ENGINE SOON" light comes on but does not stay on. A stored code may or may not exist.

POSSIBLE CAUSE & CORRECTION

To track down possible causes of an intermittent "SERVICE ENGINE SOON" light, check the following items

1. Check for poor mating of one connector to another. Terminals may not be fully seated. Check for improperly formed or damaged terminals. Check wire to terminal connections.
2. Check for poor connection from ignition coil to ground or arcing at spark plug wires or plugs.
3. Check wire from "SERVICE ENGINE SOON" light to ECM for short to ground.
4. Check wire from ALDL "test" terminal for intermittent short to ground.
5. Check for poor connections in ECM ground terminals.
6. Check for loss of trouble code memory.
7. Check for electrical system interference caused by a defective relay or an ECM driven solenoid or switch which may cause a sharp electrical surge. This type of problem will normally occur when faulty component is operated.
8. Check for aftermarket parts which may not have been produced to manufacturers' specifications. Solenoids without original -equipment diodes for circuit protection and HEI-EST module or voltage regulator using transistors instead of silicon -chip circuitry may possibly cause voltage surges (up to 300 volts) in ECM wiring, causing temporary ECM shutdown. ECM shutdown is a normal response to system overvoltage (over 16 volts on most models). ECM will repower when condition ceases to exist. This could cause a flickering "SERVICE ENGINE SOON" light with no codes set in memory.
9. Check for improper installation of electrical accessories such as auxiliary lights or 2-way radios.
10. Make sure that EST wires are kept away from spark plug wires, distributor wires, distributor housing, ignition coil and generator. Make sure that ground wire from ECM to distributor or ignition module is connected to a good ground.
11. Check for intermittent short to ground on terminals "B" (diagnostic enable) or "D" ("SERVICE ENGINE SOON" light) at ALDL.
12. Check for intermittent wiring problem using "Scan" tester. See SCAN TESTER USAGE in this article.

NO START - ENGINE CRANKS OKAY

This is defined as engine cranks properly, but does not start. Engine may fire a few times.

Check the following items

1. Perform appropriate DIAGNOSTIC CIRCUIT CHECK for that system.
2. Make sure proper starting procedure is being used.
3. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at both distributor cap and spark plugs.
4. Remove air cleaner and check carburetor choke valve, vacuum break(s), linkage and unloader operation. Choke valve should move smoothly, be closed when cold and open when hot.
5. Check for presence of fuel by noting carburetor accelerator pump operation. Look for gasoline squirt in carburetor bore while quickly opening throttle lever. If no squirt occurs, check for: fuel in tank, carburetor fuel inlet filter dirty or clogged and float needle for proper operation. Check for fuel pump pressure of 5.5-6.5 psi (.39-.46 kg/cm 2 ), fuel pump capacity of 1/2 pint in 15 seconds (idling) and fuel pump vacuum of at least 15 in. Hg (50.7 kPa). If there is a pump squirt, crank engine and check for flooding. If engine is not flooding, check ignition system. See appropriate component CHART C4 for that system.
6. Remove spark plugs. Check and replace as necessary.
7. Remove distributor cap and check for moisture, dust, cracks, burns, and arcing to ground through coil mounting screws or rotor.
8. Try to turn distributor shaft by hand. Drive gear pin may be broken.
9. After starting engine, perform appropriate SYSTEM PERFORMANCE CHECK for that system.
10. In very cold temperatures, check that oil is the proper viscosity and that crankcase oil is not contaminated with gasoline.

HARD START - COLD

Engine cranks, but does not start for a long time. Eventually, engine does run. If engine starts but immediately dies (as soon as key is released from start position), see NO START - ENGINE CRANKS OKAY.

Check the following items

1. Perform appropriate DIAGNOSTIC CIRCUIT CHECK and SYSTEM PERFORMANCE CHECK for that system. Be sure driver is using proper starting procedure.
2. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at both distributor cap and spark plugs.
3. Check for air leaks at carburetor mounting and intake manifold.
4. Check wires for pinches, cuts, and proper connections.
5. Check choke valve, throttle and fast idle cam for sticking. Replace any malfunctioning parts. If caused by foreign material and gum, clean with non-oil base solvent.
6. Check choke and vacuum break operation adjustment.
7. Check EGR valve system for faulty operation that could cause valve to stick open. See appropriate component CHART C7 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
8. Check float level using external float gauge. Adjust float to specification, if required.
9. Check carburetor fuel inlet filter. Replace if required.
10. Check ignition system. See appropriate component CHART C4 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
11. Check distributor for worn shaft, bare and shorted wires, pick-up coil resistance and connections, loose ignition coil ground, and moisture in distributor cap.
12. Remove spark plugs and check for wet plugs, wear, improper gap, burned electrodes or heavy deposits. Clean or replace as necessary.
13. Check ignition timing and adjust if necessary.
14. Check fuel pump pressure, volume and vacuum.

HARD START - HOT

Engine cranks, but does not start for a long time. Eventually, engine does run. If engine starts but immediately dies (as soon as key is released from start position), see NO START - ENGINE CRANKS OKAY.

Check the following items

1. Perform appropriate DIAGNOSTIC CIRCUIT CHECK and SYSTEM PERFORMANCE CHECK for that system. Be sure driver is using proper starting procedure.
2. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at both distributor cap and spark plugs.
3. Check wires for pinches, cuts, and proper connections.
4. Check choke valve, throttle and fast idle cam for sticking. Replace any malfunctioning parts. If caused by foreign material and gum, clean with non-oil base solvent.
5. Check choke and vacuum break operation adjustment.
6. Check EGR valve system for faulty operation that could cause valve to stick open. See appropriate component CHART C7 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
7. Check for carburetor flooding.
8. Check float level using external float gauge. Adjust float to specification, if required.
9. Check carburetor fuel inlet filter. Replace if required.
10. Check for obvious overheating problems.
11. Check EFE valve operation. EFE valve should be open. See appropriate component CHART C9 for that system.
12. Check ignition system. See appropriate component CHART C4 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
13. Check distributor for worn shaft, bare and shorted wires, pick-up coil resistance and connections, loose ignition coil ground, and moisture in distributor cap.
14. Remove spark plugs and check for wet plugs, wear, improper gap, burned electrodes or heavy deposits. Clean or replace as necessary.
15. Check ignition timing and adjust if necessary.

STALL AFTER START - COLD

This condition is with engine in warm-up mode at room or outside temperature, within 3 minutes after start. Vehicle stalls after brief idle, dies as soon as any load is placed on engine (such as A/C turned on or transmission engaged) or dies on initial driveaway. If symptom is present when vehicle is both cold and hot, go to symptom STALL AFTER START - HOT.

Check the following items

1. Perform DIAGNOSTIC CIRCUIT CHECK and SYSTEM PERFORMANCE CHECK for that system.
2. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label (in engine compartment).
3. Make sure hot air tube is connected to air cleaner.
4. Check for proper operation of THERMAC.
5. Check choke valve, throttle and fast idle cam for sticking. Replace any malfunctioning parts. If caused by foreign material and gum, clean with non-oil base solvent.
6. With engine off, check all choke adjustments, including vacuum breaks and TVS if used.
7. Check carburetor accelerator pump operation.
8. Check fast idle speed and curb idle speed if applicable.
9. Check EFE valve for proper operation. EFE vacuum valve should be closed when cold. See appropriate component CHART C9 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
10. Check choke and vacuum break operation adjustment.
11. Check EGR valve system for sticky operation that could cause valve to stick open. See appropriate component CHART C7 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
12. Check ignition timing and adjust if necessary.
13. Check for poor or contaminated gasoline.

STALL AFTER START - HOT

This condition is with engine in warm-up mode at room or outside temperature, within 3 minutes after start. Vehicle stalls after brief idle, dies as soon as any load is placed on engine (such as A/C turned on or transmission engaged) or dies on initial driveaway.

Check the following items

1. Perform DIAGNOSTIC CIRCUIT CHECK and SYSTEM PERFORMANCE CHECK for that system.
2. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label.
3. Make sure hot air tube is connected to air cleaner.
4. Check for proper operation of THERMAC.
5. Check choke valve, throttle and fast idle cam for sticking. Replace any malfunctioning parts. If caused by foreign material and gum, clean with non-oil base solvent.
6. With engine off, check all choke adjustments, including vacuum breaks and TVS if used.
7. Check carburetor accelerator pump operation.
8. Check fast idle speed and curb idle speed if applicable.
9. Check EFE valve for proper operation. EFE valve should be open. See appropriate component CHART C9 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
10. Check choke and vacuum break operation adjustment.
11. Check EGR valve system for faulty operation that could cause valve to stick open. See appropriate component CHART C7 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
12. Check ignition timing and adjust if necessary.
13. Check for poor or contaminated gasoline.
14. Check for obvious overheat condition.
15. Check for overcharged A/C system.
16. Check operation of power steering cut-out switch.

HESITATION, SAG OR STUMBLE

This is defined as a momentary lack of response as accelerator is pushed down. It can occur at all vehicle speeds. Usually, it is most severe when first trying to make vehicle move. Occasionally, this condition may cause vehicle to stall.

Check the following items

1. Perform DIAGNOSTIC CIRCUIT CHECK and SYSTEM PERFORMANCE CHECK for that system.
2. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at both distributor cap and spark plugs.
3. Check wires for pinches, cuts, and proper connections.
4. Make sure hot air tube is connected to air cleaner.
5. Check for proper operation of THERMAC.
6. Check float level using external float gauge. Adjust float to specification, if required.
7. With engine off, check all choke adjustments, including vacuum breaks and TVS if used.
8. Check carburetor accelerator pump operation.
9. Check fast idle speed and curb idle speed, if applicable.
10. Check EFE valve for proper operation. EFE valve should be closed and electric heater should be on. See appropriate component CHART C9 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
11. Check vacuum hose to pressure sensor for leaks, restrictions and proper connections (should be manifold vacuum).
12. Check EGR valve operation. See appropriate component CHART C7 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
13. Check TPS adjustment. See 5.0L (VIN Y) CHART C2F. See the CCC 5.0L CARB TEST/CODES article in this section.
14. Check canister purge system. See appropriate component CHART C3 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
15. Check for open ignition coil ground and for intermittent ECM ground.
16. Check engine ignition timing.
17. Check for poor quality or contaminated gasoline.

VEHICLE SURGES

Engine power varies under steady throttle or cruise. Feels like vehicle speeds up and slows down without changing position of accelerator pedal.

Check the following items

1. Perform DIAGNOSTIC CIRCUIT CHECK. Perform SYSTEM PERFORMANCE CHECK for 5.0L (VIN Y) engines.
2. Check operation of thermostatic air cleaner damper door.
3. Check that Park/Neutral switch is properly adjusted. See CODE 24B chart for carbureted systems.
4. Check for intermittent open or short to ground in Torque Converter Clutch (TCC) or HEI by-pass circuits. See appropriate component CHART C8 - TORQUE CONVERTER CLUTCH or appropriate component CHART C4 - HEI-EST CHECK for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
5. Check for proper operation of canister purge system. See appropriate component CHART C3 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
6. Check for proper operation of ESC system. See appropriate component CHART C5 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
7. Check for proper operation of EGR system. See appropriate component CHART C7 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
8. Make sure that initial ignition timing is properly set.
9. Check for adequate spark output using Spark Tester (ST-125).
10. Check O2 sensor for lead or RTV sealant contamination. This will cause a false high voltage signal to ECM. ECM will respond by leaning air/fuel ratio.
11. Check in-line fuel filter and replace if dirty or clogged.
12. Check fuel for water contamination. On carbureted models, check fuel pressure, volume and fuel pump vacuum.
13. Remove spark plugs and check for wet plugs, cracks, improper gap, burned electrodes or heavy carbon deposits. Also check condition of distributor cap, rotor and spark plug wires.
14. Check A/C for excessive charge.
15. Check for restricted exhaust system.

LACK OF POWER OR SLUGGISH

Engine delivers less power than expected. Little or no increase in speed when accelerator is pushed down.

Check the following items

1. Perform DIAGNOSTIC CIRCUIT CHECK and SYSTEM PERFORMANCE CHECK for that system.
2. Check that air filter and fuel filter are not plugged. Replace if necessary. Check for incorrect fuel pressure. On EFI vehicles, see appropriate component CHART A7 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
3. Check for proper operation of thermostatic air cleaner damper door.
4. Check for proper float level using external gauge (carbureted).
5. Make sure that initial ignition timing is properly set.
6. Check for proper operation of TCC system. See appropriate component CHART C8 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
7. Check ESC system for excessive retard. See appropriate component CHART C5 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
8. Check EST system for proper operation. See appropriate component CHART C4 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
9. Make sure that EGR valve is not open all the time. See appropriate component CHART C7 for that system.
10. Check for proper operation of EFE valve (carbureted).
11. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See appropriate CHART B1 - RESTRICTED EXHAUST SYSTEM CHECK for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
12. Check charging system output. Repair charging system if voltage is less than 9 volts or more than 16 volts.
13. Check MAP or pressure sensor output. See appropriate component CHART C1-D for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
14. Using Spark Tester (ST-125), check for available secondary voltage.
15. Check engine valve timing and compression.
16. Check engine for a worn camshaft.

ENGINE BACKFIRES

Fuel ignites in intake manifold or in exhaust system making a loud popping noise.

Check the following items

1. Check for proper valve timing.
2. Check engine for sticking or leaking valves.
3. Check for fuel or water in vacuum hose to MAP sensor. Also check for restricted hose.
4. Using Spark Tester (ST-125), check available output voltage of ignition coil.
5. Check for crossfire between spark plugs, distributor cap and spark plug wires.
6. Check for an intermittent ignition system problem.
7. Make sure that initial ignition timing is properly set.

ROUGH, UNSTABLE OR INCORRECT IDLE

Engine runs unevenly at idle. If bad enough vehicle will shake. Idle may vary in RPM. Engine idles at incorrect RPM.

Check the following items

1. Perform DIAGNOSTIC CIRCUIT CHECK. Perform SYSTEM PERFORMANCE CHECK for 5.0L (VIN Y) engines.
2. Make sure that throttle linkage and/or TPS are not sticking or binding.
3. Make sure that initial ignition timing is properly set.
4. Check engine idle speed, both base idle and ECM idle.
5. Check Idle Air Control (IAC) system. Check for foreign material in IAC bore. See DIAGNOSTIC AIDS in CODE 35 chart or appropriate component CHART C2 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
6. Check for proper operation of EGR system. See appropriate component CHART C7 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
7. Check ISC/ILC operation. See appropriate component CHART C2 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
8. Check P/N switch circuit. Also make sure that P/N switch is properly adjusted. See appropriate component CHART C1 (EFI) or Code 24B chart (carbureted) for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
9. Check power steering pressure switch circuit. See appropriate component CHART C1 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
10. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See appropriate CHART B1 - RESTRICTED EXHAUST SYSTEM CHECK for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
11. If rough idle only occurs when engine is hot, check PCV valve for proper operation, check evaporative emission control system, check for proper spark plug gap and check engine compression.

ENGINE WILL NOT IDLE

Defined as engine starts okay, but dies at idle. Engine will run if accelerator is held at part throttle.

Check the following items

1. Perform both DIAGNOSTIC CIRCUIT CHECK and SYSTEM PERFORMANCE CHECK for that system.
2. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label.
3. Check for air leaks at carburetor mounting and intake manifold.
4. Check carburetor for flooding.
5. Check float level using external float gauge.
6. Check engine idle speed, both base and ECM controlled.
7. Check EGR system. See appropriate component CHART C7 for that system. See the CCC 5.0L CARB TEST/CODES article in this section. Check for loose valve or sticking plunger. The EGR system should not function at idle. Pulse width modulated systems do not work in Park or Neutral.
8. Check carburetor idle adjustment. If unable to adjust, check carburetor idle system. See appropriate component CHART C2 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
9. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See appropriate CHART B1 - RESTRICTED EXHAUST SYSTEM CHECK for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
10. Check spark plug condition and gap.

POOR FUEL ECONOMY

Fuel economy, as measured by an actual road test, is noticeably lower than expected. Fuel economy is noticeably lower than was on this vehicle at one time.

Check the following items

1. Check for proper operation of thermostatic air cleaner damper door. Also check for a clogged air filter.
2. Check cooling system thermostat for proper heat range and operation.
3. Check coolant sensor for shift in calibration. Use temperature-to-resistance chart in Code 14 or 15 chart.
4. Make sure that speedometer is properly calibrated.
5. Check engine compression.
6. Check for dragging brakes.
7. Check A/C for "full time" operation.
8. Make sure that initial ignition timing is properly set and check for proper EST and ESC operation. See appropriate component CHART C4 and C5 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
9. Check for proper operation of Torque Converter Clutch (TCC). See appropriate component CHART C8 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
10. Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See appropriate CHART B1 - RESTRICTED EXHAUST SYSTEM CHECK for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
11. Check oxygen sensor for silicone or lead contamination.
12. Remove spark plugs and check for wet plugs, cracks, improper gap, burned electrodes or heavy carbon deposits.
13. Make sure that speedometer is properly calibrated.
14. Check engine compression.
15. Check for dragging brakes.

ENGINE DIESELING/RUN-ON

Engine continues to run after ignition is turned off but runs very rough. If engine runs smoothly, check ignition switch.

Check the following items

1. Check for binding throttle linkage.
2. Check IAC system. See DIAGNOSTIC AIDS in appropriate CODE 35 chart or component CHART C2 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
3. Check ILC for proper operation. See appropriate component CHART C2 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
4. Check engine for overheating.

DETONATION/SPARK KNOCK

A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with amount of acceleration.

Check the following items

1. Check for obvious overheating problems.
2. Make sure that initial timing is correct.
3. Check TPS adjustment and operation.
4. Make sure that ESC system is operating properly. See appropriate component CHART C5 for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
5. Make sure that EGR valve is not open all the time. See appropriate component CHART C7 for that system.
6. Make sure that TCC system is operating properly. See appropriate component CHART C8 for that system.
7. Make sure that correct PROM is installed in ECM.
8. Remove carbon from engine with top engine cleaner.
9. If excessive carbon exists in combustion chamber, check for excessive oil burning due to leaking valve guide seals.
10. Check for incorrect basic engine parts such as camshaft, cylinder heads and pistons.
11. Check that PROM in vehicle is correct for that vehicle. Check with dealer for latest application information.

EXCESSIVE EXHAUST EMISSION (ODORS)

Vehicle fails emission test. Vehicle may also have excessive "rotten egg" smell (hydrogen sulfide) being emitted from exhaust pipe.

Check the following items

1. Perform both DIAGNOSTIC CIRCUIT CHECK and SYSTEM PERFORMANCE CHECK for that system.
2. Check for lead contamination of catalytic converter. Look for removal/tampering at restrictor in fuel filler neck.
3. If emission test shows excessive carbon monoxide (CO) and hydrocarbons (HC) emissions and vehicle also has excessive odor being emitted, check all systems and components that could cause engine to run rich. See DIAGNOSTIC AIDS in appropriate CODE 45 chart for that system. See the CCC 5.0L CARB TEST/CODES article in this section.
4. If emission test shows excessive oxides of nitrogen (NOx) emissions, check all systems and components that could cause engine to run lean or to run too hot. See DIAGNOSTIC AIDS in appropriate CODE 44 chart for that system. See the CCC 5.0L CARB TEST/CODES article in this section.

SCAN TESTER USAGE

Note. Prior to connection of scan tester to vehicle, diagnostic system should be checked to determine if system is operating properly and if information received by scan tester will be accurate. This is done by performing appropriate DIAGNOSTIC CIRCUIT CHECK for that system. If vehicle does not pass diagnostic circuit check, information received by scan tester may be invalid.

CCC Scan tester is a specialized tester which, when plugged into ALDL, can be used to diagnose on-board computer control systems by providing instant access to circuit voltage information without need to crawl under dash or hood to back-probe sensors and connectors. Scan testers cut down diagnostic time dramatically by furnishing input data (voltage signals) which can be compared to specification parameters (see SCAN DATA tables). They also furnish information on output device (solenoids and motors) status. Status parameters, however, are only an indication that output signals have been sent to devices by the ECM. It does not indicate if devices have responded properly to that signal. This will need to be verified at output device using a voltmeter or test light.

Note. Code 12 should always exist when ALDL is grounded with key on and engine not running but may not be indicated by all makes of scan testers.

If trouble codes are not present, this is not an indication that there is not a problem. CCC related problems are about 20 percent codes and 80 percent driveability. Sensors that are out of specification WILL NOT set a trouble code but WILL cause driveability problems. Use of a scan tester is easiest method of checking sensor specifications and other data parameters. Tester is also useful in finding intermittent wiring problems by wiggling wiring harnesses and connections (key on, engine off) while observing data parameters. See SCAN DATA tables in this article.

Note. Information obtained by scan tester is only as accurate as the tester itself. If erroneous voltage signals are suspected, it will be necessary to verify tester information using a digital voltmeter and wiring schematic. If non-existent codes are in evidence, turn ignition off, remove tester, turn ignition on and ground ALDL "test" terminal. If same codes are not flashed by "SERVICE ENGINE SOON" light that were indicated by scan tester, tester cannot be used on vehicle and information obtained by it will not be guaranteed accurate.

FULL FUNCTION CARBURETOR - SCAN DATA SPECIFICATIONS

Note. Information contained in the following table is typical of readings taken on vehicle with engine idling, upper radiator hose hot, closed throttle, transmission in Park or Neutral, "closed loop" status achieved and all accessories off (except as noted in tables). Data parameters are updated every 1 1/4 seconds. On systems using P-4 computers, parameter updates are virtually instantaneous. Not all devices & systems are used on all models.

FULL FUNCTION CARBURETED