Basic Checks

Ensure battery voltage is at least 11 volts with engine off. If battery voltage is not to specification, replace battery. If battery voltage is to specification, go to next step.
Crank engine. If engine cranks, go to next step. If engine does not crank, see in DIAGNOSIS BY SYMPTOM in appropriate TESTS W/O CODES article.
Start engine. If engine starts, go to next step. If engine does not start, go to step 12).
Remove air filter. Inspect air filter for excessive dirt and oil. Replace if necessary. Reinstall air filter if okay and go to next step.
Check air intake system between airflow meter and cylinder head for air leaks. If air leaks are found, repair as necessary. If no air leaks are found, go to next step.
Check idle speed. Start and warm engine to operating temperature. Place transmission in Neutral. Turn off all accessories. Connect a tachometer to terminal IG- of check connector. For location of check connector, see Fig 1.

Set tachometer to 4-cylinder scale. See IDLE SPEED SPECIFICATIONS table. If idle speed is okay, go to next step. If idle speed is not within specification, see DIAGNOSIS BY SYMPTOM in appropriate TESTS W/O CODES article.

CAUTION: DO NOT ground check connector terminal IG-. Damage to ignitor and/or ignition coil may result.

NOTE: Ensure tachometer is compatible with this system before use.

IDLE SPEED SPECIFICATIONS

Application

RPM

LS400 ⁽¹⁾

600-700

⁽¹⁾	If air intake temperature is less than 50°F (10°C), idle speed will be 750-850 RPM.

Check ignition timing. Start and warm engine to operating temperature. Ensure idle speed is within specification. Using a jumper wire, connect check connector terminals E1 and TE1. See Fig 3.

Connect timing light to No. 6 cylinder. Check ignition timing. See IGNITION TIMING SPECIFICATIONS table.

IGNITION TIMING SPECIFICATIONS (Degrees BTDC @ RPM)

Application	Specification
LS400	8-12 @ 600-700

Disconnect jumper wire. If ignition timing is not within specification, go to next step.
If ignition timing is within specification and a normal code is displayed by CHECK engine light, see DIAGNOSIS BY SYMPTOM in TESTS W/O CODES article. If a code is displayed by CHECK engine light, see appropriate code chart.

Fig 1: Locating LS400 Check Connector
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Ensure throttle valve is fully closed. Ensure continuity is present between Throttle Position Sensor (TPS) terminals IDL and E2. See Fig 2. Ensure engine valve timing is correct.

Fig 2: Identifying Throttle Position Sensor (TPS) Terminals
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Fig 3: Identifying Check Connector Terminals
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WARNING: ALWAYS relieve fuel pressure before disconnecting any fuel injection-related component. DO NOT allow fuel to contact engine or electrical components.
Check fuel pressure using Figs. 4 thru 8.

Fig 4: Fuel System Check Steps 1-3 Chart (1 of 5)
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Fig 5: Fuel System Check Steps 4 & 5 Chart (2 of 5)
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Fig 6: Fuel System Check Steps 6 & 7 Chart (3 of 5)
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Fig 7: Fuel System Check Step 8 Chart (4 of 5)
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Fig 8: Fuel System Check Steps 9-13 Chart (5 of 5)
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Check for spark. Remove coil wire from distributor. Using insulated pliers, hold end of coil wire 1/2" from ground. Crank engine. If spark is present, see DIAGNOSIS BY SYMPTOM in appropriate TESTS W/O CODES article. If spark is not present, see SPARK TEST in this article.