Mechanical Inspection: Compression

Ensure battery is fully charged and starter motor is in good operating condition. On 2.5L, disconnect ignition coil connector. On 4.0L, remove coil rail assembly to access spark plugs. On 4.7L, remove coil on plugs. On all models, clean spark plug recesses with compressed air. Remove all spark plugs. Remove fuel pump relay from power distribution center. See Fig 1 , Fig 2 or Fig 3 . Install compression gauge. Hold throttle in Wide Open Throttle (WOT) position. Using a remote starter switch, rotate engine 3 revolutions. Record compression pressure from third revolution. Continue test for remaining cylinders. See COMPRESSION SPECIFICATIONS  table for correct engine compression pressures.

Fig 1: Identifying Power Distribution Center (Cherokee)

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Fig 2: Identifying Power Distribution Center (Grand Cherokee)

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Fig 3: Identifying Power Distribution Center (Wrangler)

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