Beginning of the diagnostic procedure we put on the diagnostic computer and compare the actual reading of the cam adjuster on bank 1 and bank 2 cylinder head to specification. we watch to see how far the ecu adjust the timing retard and advance. We scan the ecu for dtc's and if we find a cam position code and a correlation problem between the cam and crank between either of the two cylinder heads we know the timing has jumped, broken guides, collapsed tensioners, or possible stretched timing chain. Most common problem on the 4.2 engine is broken guides and valve adjuster assembly not working properly.
step 2 - 4.2 diagnostic part 2
The next step in the diagnostic procedure is to remove the two cylinder head valve covers and the rear cylinder head timing chain covers. We install the timing tools at the correct position and if the tools don't lineup or fit then we do a visual inspection on the two cylinder head timing chain components and main chain components. When a problem is found visually it is always recommended to do the full timing chain service.
step 3 - 4.2 diagnostic part 3
It is then required to remove the engine and remove the rear main timing chain cover. Do a visual inspection on all the timing chain components and look for broken guides, defective tensioners, stretched timing chain, sludge buildup, and defective adjuster. When the oil changes are not done at 5000 miles, the engine starts to buildup sludge and this can cause the tensioners to collapse and fail, cam adjusters to fail and not allow them to advance and retard the timing when the ecu demands a action, and guides get worn out excessively to the point that they become weak and bridle and break into multiple pieces which can cause a oil restriction anywhere in the oil lubrication system leading to more damage in the engine. Because of the correlation problem between the cam to crank we also do a cylinder leak down test to check for bent valves.
step 4 - 4.2 repair procedure
It is highly recommended to do the full timing chain service which includes replacing the timing chains, timing chain tensioners, timing guides, cam adjuster solenoids, and the cam adjuster on each cylinder head.