Compression
Check engine mechanical condition with a compression gauge, vacuum gauge or engine analyzer. See engine analyzer manual for specific instructions.
| WARNING | DO NOT use ignition switch during compression tests on fuel injected vehicles. Use a remote starter to crank engine. Injectors on many models are triggered by ignition switch during cranking mode, which can create a fire hazard or contaminate the engine's oiling system. |
| Application | Specification |
|---|---|
| 3.5L | (1) 155-170 psi (10.9-12.0 kg/cm 2 ) |
| (1) Maximum difference between each cylinder should not exceed 25 percent. | |
| (1) | Maximum difference between each cylinder should not exceed 25 percent. |
ENGINE COMPRESSION SPECIFICATIONS
Exhaust System Backpressure
The exhaust system can be checked with a vacuum gauge or pressure gauge. If using a pressure gauge, remove oxygen sensor or air injection check valve (if equipped). Connect a 0-10 psi gauge, and operate engine at 2500 RPM. If exhaust system backpressure is greater than 1 3/4 - 2 psi, exhaust system or catalytic converter is plugged.
If a vacuum gauge is used, connect it to intake manifold vacuum, and start engine. Observe vacuum gauge. Open throttle part way and hold it steady. If vacuum gauge reading slowly drops after stabilizing, check exhaust system for restriction.
FUEL PRESSURE
Basic diagnosis of fuel system should begin with determining fuel system pressure.
| WARNING | ALWAYS relieve fuel pressure before disconnecting any fuel injection-related component. See appropriate RELIEVING FUEL PRESSURE procedure. DO NOT allow fuel to contact engine or electrical components. |
Relieving Fuel Pressure (Vehicles With Fuel Rail Test Port) -Disconnect negative battery cable. Slowly open fuel tank cap to release pressure in tank. To release remaining pressure in system, remove fuel rail pressure test port cap. Place open end of Fuel Pressure Release Hose (C-4799-A) in approved gasoline container. Connect other end of pressure release hose to test port. Fuel pressure will bleed-off into container.
Relieving Fuel Pressure (Vehicles Without Fuel Rail Test Port) -Disconnect fuel pump wiring harness connector at fuel tank. Start engine. Let engine run until fuel is exhausted and engine stops. Turn ignition off. Disconnect negative battery cable. Connect fuel pump wiring harness connector.
| WARNING | Perform fuel pump test with fuel tank at least half full. Before disconnecting fuel lines or fuel system components, relieve fuel pressure. See appropriate RELIEVING FUEL PRESSURE procedure. |
Ignition Coil Resistance
Ignition coil resistance test procedure is not available from manufacturer. Use IGNITION COIL RESISTANCE table under IGNITION COIL to determine correct coil resistance.
Scheme 15
- Remove ignition coil secondary cable from distributor cap. Hold end of cable 1/4" away from a known-good engine ground. Crank engine and check for spark.
- If spark is not constant or if there is no spark, go to step 4). If spark is constant, slowly move coil secondary cable away from ground while assistant cranks engine. If arcing occurs at coil tower, replace ignition coil.
- If spark is constant and no arcing occurs, ignition system secondary voltage is correct. Ensure secondary voltage reaches spark plugs, indicating ignition system is okay. Go to «MECHANICAL INSPECTION»(ref-11035-S32217792162000111000000) under PRELIMINARY INSPECTION & ADJUSTMENTS. Perform tests under «FUEL SYSTEM»(ref-11035-S24539853852000111000000).
- Ensure battery is fully charged (at least 12.4 volts). Connect volt-meter to ignition coil B+ (battery voltage) terminal. Crank engine for at least 5 seconds while checking voltage at coil terminal.
- If voltage remains near zero during entire cranking period, test Auto Shutdown (ASD) relay circuit. See appropriate «TESTS W/CODES - 3.5L»(ref-11020) article.
- If voltmeter reading is near battery voltage and then drops to zero after 1-2 seconds of cranking, test distributor reference pick-up circuit. See appropriate «TESTS W/CODES - 3.5L»(ref-11020) article.
- If voltmeter reading remains at or near battery voltage during entire cranking period, turn ignition off. Disconnect 60-pin connector from Powertrain Control Module (PCM), and check terminals for poor connections. (Scheme 15)
- Remove positive lead from coil. Connect a jumper wire between battery positive terminal and coil positive terminal. Using a specially constructed jumper wire, momentarily ground PCM harness connector terminal No. 19. (Scheme 16) Spark should occur when ground connection is disconnected.
- If spark occurs, replace PCM. If spark does not occur, ground coil negative terminal using specially constructed jumper wire. If spark occurs, repair open circuit in wiring harness. If spark does not occur, replace ignition coil.
Ignition coil resistance test procedure is not available from manufacturer. Use IGNITION COIL RESISTANCE table under IGNITION COIL to determine correct coil resistance.
Scheme 16
IGNITION COIL
| Application | Primary | Secondary | |
|---|---|---|---|
| 3.5L | |||
| Diamond | .52-.63 | 11,600-15,800 | |
| Toyodenso | .51-.61 | 11,500-13,500 | |
| (1) Resistance is measured at 70-80°F (21-27°C). | |||
| (1) | Resistance is measured at 70-80°F (21-27°C). |
IGNITION COIL RESISTANCE - Ohms @ 68°F (20°C) (1)
IDLE SPEED & IGNITION TIMING
Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see ADJUSTMENTS - 3.5L article.
SUMMARY
If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES proceed to appropriate TESTS W/CODES - 3.5L article. If no hard codes are found in self-diagnostics, proceed to appropriate TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO-START, etc.) or intermittent diagnostic procedures.