DEFINITION: This involves a steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases. The exhaust has a steady spitting sound at idle or low speed.

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Were the Preliminary Checks performed?

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Go to Step 2

Go to Symptoms - Engine Controls

Test the ignition system output voltage for all of the cylinders using a spark tester.

Is spark present on all of the cylinders?

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Go to Step 3

Go to Electronic Ignition (EI) System Diagnosis

1. Inspect the spark plugs for excessive wear, insulation cracks, improper gap, or heavy deposits.
2. Measure the resistance of the ignition wires. Replace any ignition wires that have a resistance greater than 30,000 ohms.

Did you find and correct the condition?

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Go to Step 4

Go to Step 5

Repair or replace any components as needed.

Did you complete the repair?

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System OK

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With the engine running, spray the ignition wires with a fine water mist to check for arcing and shorting to ground.

Is a repair necessary?

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Go to Step 6

Go to Step 7

Replace the ignition wires.

Did you complete the replacement?

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System OK

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1. Perform a cylinder compression test.
2. If the compression is low, repair the engine as needed.
3. Inspect for proper valve timing, bent pushrods, worn rocker arms, broken or weak valve springs, and worn camshaft lobes.
4. Inspect the intake manifold and the exhaust manifold passages for casting flash.

Is a repair necessary?

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Go to Step 8

Go to Step 9

Repair or replace any components as needed.

Did you complete the repair?

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System OK

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1. Inspect the fuel system for a plugged in-line fuel filter.
2. Inspect the fuel system for low fuel pressure. If the fuel pressure is less than 379-393 kPa (55-57 psi), service the fuel system as needed.
3. Inspect for contaminated fuel.

Is a repair necessary?

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Go to Step 10

Go to Step 11

Repair or replace any components as needed.

Did you complete the repair?

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System OK

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1. Disconnect all of the fuel injector harness connectors at the fuel injectors.
2. Connect an injector test light to the harness terminals of each fuel injector connector.
3. Note the test light while cranking the engine for each fuel injector.

Does the test light blink for all of the fuel injectors?

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Go to Step 13

Go to Step 12

1. Repair or replace the faulty injector drive circuit harness, the connector, or the connector terminal.
2. If the harness, the connectors, and the terminals are OK, replace the engine control module (ECM).

Did you complete the repair?

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System OK

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Measure the resistance of each fuel injector. The resistance will increase slightly at higher temperatures.

Is the injector resistance within the specified range?

11.6-12.4 ohms

Go to Step 15

Go to Step 14

Replace any fuel injectors with a resistance that is out of specifications. Refer to Fuel Injector Balance Test with Special Tool .

Did you complete the replacement?

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System OK

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Perform an injector balance test.

Is a repair necessary?

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Go to Step 16

Go to Step 17

Replace any restricted or leaking fuel injectors.

Did you complete the replacement?

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System OK

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1. Inspect for electromagnetic interference.
2. Monitor the engine RPM with a scan tool.

Does the scan tool RPM change greatly with little change in actual engine RPM?

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Go to Step 18

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1. Inspect the routing of the ignition wires.
2. Inspect all of the ignition system grounds.
3. Correct the routing or repair the ground connections as needed.

Did you find and correct the condition?

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System OK

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