1997 Chevrolet Silverado random misfire

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  • 269,000 MILES

After replacing the CKM sensor and The CPK sensor. A complete tune up . The misfire still exists. Is there any way to manually adjust the timing? I have also checked the vacuum lines. I also replaced the fuel filter as well. The truck starts right up, stays running but does hesitate upon acceleration. It seems like the timing is not right but after replacing the two sensors there is no change except for a lighter wallet. Any Ideas?

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Friday, November 1st, 2013 AT 7:23 PM

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  • 29,782 POSTS

There hasn't been a way to adjust ignition timing for decades, even on vehicles with distributors. Those made adjustments for engine speed and load, and that's it. Your computer also takes into account coolant temperature, intake air temperature, transmission shift points, and a number of other factors. You aren't going to do anything to improve on it. Besides, adjusting ignition timing isn't going to fix the cause of a misfire. I'd start with the basics, meaning spark plugs and wires, but there is another rather common problem on GM vehicles. They don't install matched sets of injectors on the assembly line. Chrysler buys their injectors in flow-matched sets from Bosch and failures are almost unheard of. Ford also has very little injector trouble. With high mileage, some GM injectors will start to flow a little less making those cylinders lean. That can result in a misfire. You didn't list which engine you have or which injector system, but regardless, a '97 model is capable of telling you which cylinder is misfiring. The Check Engine light should be on though if the misfires were detected. I'd start anyway with having the diagnostic fault codes read if new plugs and wires don't solve the misfire. If there is a code indicating a specific cylinder is misfiring, swap that injector with one of the other ones, erase the code, then see if the misfire moves to that other cylinder.

If you don't have individual injectors, check the fuel pressure. Some GM engines will misfire or be very hard to start if the pressure is just a couple of pounds low.

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Friday, November 1st, 2013 AT 10:36 PM

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