2500 SILVERADO, 454, 4X4

1994 Chevrolet Other

I sent my tuck in for repair of a timing chain the fixed it, it ran for about a half hr and it stalled. My truck will not start unless I unplug the map sensor and when I do that it runs rough now there telling me it has bent valves because of the timing chain going out, and that I now need a new engine

my Question is what could be wrong cause I don't understand why it won't start unless you unplug the map sensor and also if it has bent valves why it doesn't make any knocking noise or anything

also it has 240,000 miles but has been very well maintained
October 21, 2006.

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