HOW TO USE THIS SECTION
This portion of article is used only AFTER you have checked the following
- Verify on-vehicle diagnostics work (if equipped). Perform DIAGNOSTIC CIRCUIT CHECK from BASIC TESTING article.
- Verify ECM and SERVICE ENGINE SOON light function properly.
- Verify no trouble codes stored, or only intermittent ones.
- Verify fuel control system operates properly. Perform FIELD SERVICE MODE CHECK in BASIC TESTING article.
- Perform fuel system pressure test.
- Visually inspection all systems.
After performing all checks performed, verify customer complaint and locate correct symptom among those listed in this article. Not all items listed under each symptom apply to all models and systems. These procedures will normally recommend testing of a system or component on vehicle, such as EGR, EST, TCC, etc. These are covered in the SYSTEM/COMP TESTS article.
Note. If ECM displays data, but engine fails to start, proceed to NO START - ENGINE CRANKS OKAY in BASIC DIAGNOSTIC PROCEDURES article.
POSSIBLE CAUSE & CORRECTION
Check the following
- Check fuel pump relay. Connect test light between fuel pump test terminal and ground or between fuel pump connector and ground. Turn ignition on. Light should illuminate for 2 seconds. If not, see FUEL PUMP RELAY in SYSTEM/COMP TESTS article. For location of fuel pump test connector, see COMPONENT LOCATIONS in SYSTEM/COMP TESTS article.
- Check for poor fuel quality or water contaminated fuel.
- Ensure TPS is not sticking or binding.
- Check EGR valve operation.
- Check for a leaking injector. Disconnect injector electrical connector at injector. Crank engine and watch for fuel leakage.
- Ensure coolant sensor circuit or coolant sensor resistance is not too high. See CODE 15 chart in TESTS W/CODES article or SENSOR RANGE CHARTS article.
- Check ignition system for a worn distributor shaft, bare or shorted wires, incorrect pick-up coil resistance, or loose ignition coil ground or moisture in distributor cap. Check for adequate spark using Spark Tester (ST-125).
- Check for shorts by spraying plug wires with a mist of water.
- Remove spark plugs. Check for wet plugs, cracks, improper gap, burned electrodes or heavy carbon deposits.
- Check for correct fuel pressure at all speeds.
- Check for a faulty in-tank fuel pump check valve. A faulty check valve will allow fuel in lines to drain back to tank after engine is stopped.
- Ensure correct PROM is installed in vehicle. Check with dealer for latest application information.
- Check for restricted exhaust system.
MISFIRE ISOLATION
- Start engine. Disconnect IAC motor. Using insulated pliers, remove one spark plug wire from a spark plug and ground it against the engine.
- Note engine RPM as wire is grounded. Reconnect spark plug wire. Repeat procedure for all cylinders. Stop engine and reconnect IAC motor.
- If engine speed dropped equally (within 50 RPM) on all cylinders, refer to ROUGH, UNSTABLE OR INCORRECT IDLE symptom. If there was no engine RPM drop or no excessive variation on one or more cylinders, check spark on the respective cylinder(s).
ENGINE WON'T START
| Possible Cause | Correction |
|---|---|
| No voltage to fuel solenoid | Check electrical connections |
| Restricted Air Filter | Check and/or replace air filter |
| Faulty glow plugs or glow plug controls | Check and/or replace glow plugs or controls. |
| Plugged fuel return system | Remove restrictions |
| No fuel to nozzles | Inspect fuel delivery system |
| No fuel to injection pump | Inspect fuel delivery system |
| Clogged fuel tank filter | Replace filter, see SYSTEM/COMP TESTS |
| Incorrect or contaminated fuel | Remove and replace fuel. |
| Incorrect pump timing | Reset pump timing, see SYSTEM/COMP TESTS . |
ENGINE WON'T START TROUBLESHOOTING
ENGINE STALLS AT IDLE
| Possible Cause | Correction |
|---|---|
| Incorrect slow idle adjustment | Reset idle adjustment, see ADJUSTMENTS . |
| Faulty fast idle solenoid | Replace solenoid, seeI - SYSTEM/COMP TESTS article |
| Plugged fuel return system | Remove restrictions |
| Glow plugs turn off too soon | Check glow plug system, see SYSTEM/COMP TESTS |
| Incorrect pump timing | Check and reset timing, see ADJUSTMENTS article |
| Limited fuel to injection pump | Check fuel delivery system |
| Air in injection lines to nozzle | Check line fittings |
| Incorrect or contaminated fuel | Remove and replace fuel |
| Faulty injection pump | Replace pump, see REMOVE/INSTALL/OHAUL |
| Fuel solenoid closes in RUN position | Check solenoid operation See SYSTEM/COMP TESTS |
ENGINE STALLS AT IDLE TROUBLESHOOTING
ENGINE IDLES BUT MISFIRES ABOVE IDLE
| Possible Cause | Correction |
|---|---|
| Plugged fuel filter | Remove restrictions and/or replace filter |
| Incorrect pump timing | Adjust pump timing, see ADJUSTMENTS |
| Incorrect or contaminated fuel | Remove and replace fuel |
ENGINE IDLES BUT MISFIRES ABOVE IDLE
ENGINE WILL NOT IDLE
| Possible Cause | Correction |
|---|---|
| Linkage binding or misadjusted | Remove binding and readjust linkage |
| Restricted Air Filter | Check and/or replace air filter |
| Defective injection pump | Replace injection pump, see SYSTEM/COMP TESTS |
ENGINE WILL NOT IDLE
FUEL LEAKS WITH NO OTHER ENGINE MALFUNCTION
| Possible Cause | Correction |
|---|---|
| Loose or broken fuel line or connection | Check all fuel line fittings and correct |
| Internal seal leak in injection pump | Remove and replace injection pump |
FUEL LEAKS WITH NO OTHER ENGINE MALFUNCTION
LOW ENGINE POWER
| Possible Cause | Correction |
|---|---|
| Restricted air intake | Remove restrictions |
| Plugged fuel filter | Remove restriction and/or replace filter |
| Improper throttle linkage adjustment | Adjust linkage |
| Improper fuel return system | Check fuel return system |
| Restricted tank-to-pump fuel supply | Check fuel delivery system |
| Incorrect or contaminated fuel | Remove and replace fuel |
| Restricted fuel tank filter | Replace filter |
| Nozzle or glow plug compression leaks | Check fittings and replace as required |
| Plugged nozzle | Remove restriction and/or replace nozzle |
LOW ENGINE POWER
ENGINE WILL NOT SHUT OFF WITH KEY
| Possible Cause | Correction |
|---|---|
| Injection pump fuel solenoid doesn't return to off position | Check solenoid operation, see SYSTEM/COMP TESTS |
ENGINE WILL NOT SHUT OFF WITH KEY
INTERMITTENT SIMULATION
To reproduce the conditions which create an intermittent fault so that it may be identified during testing, some of the following methods may be used
- Applying light vibration to components.
- Heating a component.
- Wiggling or bending a wiring harness.
- Applying humidity to a component.
- Remove or apply a vacuum supply source.
Monitor circuit/component voltage or resistance while attempting to simulate intermittent. If vehicle is running, monitor for self-diagnostic codes. Use the results of these tests to identify a faulty component or an area which should be checked closely for the problem.
To determine possible causes of an intermittent SERVICE ENGINE SOON light operation, check the following
- 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.
- Check for poor connection from ignition coil to ground or arcing at spark plug wires or plugs.
- Check wire from SERVICE ENGINE SOON light to ECM for short to ground.
- Check wire from ALDL "test" terminal for intermittent short to ground.
- Check for poor connections in ECM ground terminals.
- Check for loss of trouble code memory. To check code, disconnect TPS and run engine at idle until SERVICE ENGINE SOON light comes on. Code 22 should be stored and retained in memory when ignition is turned off. If not, ECM is faulty.
- 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.
- 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 silicone-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.
- Check for improper installation of electrical accessories such as auxiliary lights or 2-way radios.
- Ensure EST wires are kept away from spark plug wires, distributor wires, distributor housing, ignition coil and generator. Ensure ground wire from ECM to distributor or ignition module is connected to a good ground.
- Check for intermittent short to ground on terminal "B" (diagnostic enable) of ALDL or in SERVICE ENGINE SOON light circuit.
- On vehicles not equipped with a driver information center, check for intermittent wiring problem using Scan tester. See SCAN TESTER USAGE in appropriate G - TESTS W/ CODES article.