Question about GMC C1500

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I have 250000 miles on this 4.3L "w" Vortec engine, I was going down the road and missing randomly then big backfire, won't start, I have changed everything I can think of like wires, rotor, cap fuel filter, fuel Pressure Reg, the injectors seem to be working fine, can I check the timing by # 1 cylinder TDC with rotor pointing to # 1 wire?

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If you have replaced the timing chain please disregard my answer, I'm risking my rating because I want to help you for free.
If the timing chain has not been changed that the problem might be an overstretched timing chain.

As timing chain accumulate mileage, chain stretch, sprockets wear out, and set the valves off timing. Most chains go up to 100000 miles or more, but not always. As a rule when there is more than about half inch of play between the gears on a V6 or V8, it is the time for a new timing chain and sprockets.
It is not unusual for a timing chain to accumulate 200000miles, but I remember a car, with broken timing chain, with only 160000miles on it, the valves were bent and a hole was put on the piston.

Signs of worn out timing chains are:
Rough idle.
Sluggish performance and poor economy.
Sudden engine performance change including the inability to start the engine.
Intermittent backfire through the intake manifold.
Inconsistent ignition timing or a clattering noise coming from the front of the engine.
It is a good idea to replace the water pump (coolant pump), and the thermostat while replacing the timing chain.
The cost of the replace of timing chain is at least +$1300, but if is to bad, we pull out engine and replace both guides. In this case might cost more.
Please do not be mad with me. I'm a certified dealer, and I'm trying to give you the necessary information to help you to deal with the problem.

Posted on Nov 03, 2010

  • global1207 Nov 03, 2010

    There is a very simple check for a loose timing chain due to a broken tensioner, worn gears, or a stretched chain. Pull the distributor cap and observe the rotor position. Put an appropriate socket on the crankshaft damper pulley. Slowly turn the crankshaft pulley in a clockwise direction. Watch the distributor and observe that the rotor is moving. Stop turning. Mark the damper pulley position with the chalk mark the crankshaft pulley and engine block. Very carefully turn the crankshaft in the other direction and VERY carefully observe the rotor in the distributor. The instant it begins to move STOP turning and mark the crankshaft position again. Measure the number of degrees of rotation of the crankshaft. If there is a lot of slop in the chain then you will have moved the crankshaft ten or fifteen degrees (or more) before the distributor rotor moves again.



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