I was driving down the road in my 2000 Jeep Grand Cherokee Laredo 4.7 L V8 Power Tech. It lost power, backfired and stopped running. I thought the timing chain broke . I pulled it home and took it apart to see the timing chain. It has 3 chains, the left and front chains are tight and the right chain is a little loose. I can move the loose chain about a 1/2 inch . So can you help me please.

RESPONSE

MEASURING TIMING CHAIN WEAR

NOTE: This procedure must be performed with the timing chain cover removed.

1. Remove the timing chain cover.
2. To determine if the secondary timing chains are worn, rotate the engine clockwise until maximum tensioner piston extension is obtained. Measure the distance between the secondary timing chain tensioner housing and the step ledge on the piston.
3. The measurement at point (A) must be less than 15mm (.5906 inches)
4. If the measurement exceeds the specification the secondary timing chains are worn and require replacement.

ENGINE TIMING – VERIFICATION

CAUTION: The 4.7L is a non free-wheeling design engine. It is an interference engine. Therefore, correct engine timing is critical.

NOTE: Components referred to as left hand or right hand are as viewed from the drivers position inside the vehicle.

NOTE: The blue link plates on the chains and the dots on the camshaft drive sprockets may not line up during the timing verification procedure. The blue link plates are lined up with the sprocket dots only when re-timing the complete timing drive. Once the timing drive is rotated blue link-to-dot alignment is no longer valid.

Engine base timing can be verified by the following procedure:

1. Remove the cylinder head covers.
2. Using a mirror, locate the TDC arrow on the front cover. Rotate the crankshaft until the mark on the crankshaft damper is aligned with the TDC arrow on the front cover. The engine is now at TDC
3. Note the location of the V8 mark stamped into the camshaft drive gear. If the V8 mark on each camshaft drive gear is at the twelve o’clock position, the engine is at TDC on the exhaust stroke. If the V8 mark on each gear is at the six o’clock position, the engine is at TDC on the compression stroke
4. If both of the camshaft drive gears are off in the same or opposite directions, the primary chain or both secondary chains are at fault.
5. If only one of the camshaft drive gears is off and the other is correct, the problem is confined to one secondary chain.
6. If both camshaft drive gear V8 marks are at the twelve o’clock or the six o’ clock position the engine base timing is correct. Reinstall the cylinder head covers.

Engine Warm-Up Mode This is an open loop mode. The PCM adjusts injector pulse width and controls injector synchronization by controlling the fuel injectors ground paths. The PCM adjusts ignition timing and engine idle speed. The PCM adjusts the idle speed by controlling the idle air control motor.

Engine Timing The PCM cannot detect an incorrectly indexed timing chain, camshaft sprocket, or crankshaft sprocket. The PCM also cannot detect an incorrectly indexed distributor.(*)