runs rough when applying gas.

1998 GMC SIERRA
200,000 MILES
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MUZZLEFLASH120MM
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this happened suddenly, the truck went from having great power and smooth idle. to: rough idle and it feels like the truck is missing on 2 cylinders.(not positive of this but it feels like that) truck will still start, but when applying gas it gets rougher. so far my thoughts are !fuel filter. 2. bad coil pack. 3. timing slipped a tooth. 4. bad gas/ water in fuel. (i had just put in gas less than 8 miles before this happened.)
Mar 3, 2012 at 1:19 AM
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FIXITMR
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what motor?
Mar 3, 2012 at 2:39 AM
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MUZZLEFLASH120MM
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5.7 ltr. vortec
Mar 3, 2012 at 2:55 AM
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FIXITMR
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it's likely got spider injection which has poppet injector problems make sure your fuel pressure is OK. 58lbs and holds after pump turns off.
Mar 3, 2012 at 4:12 AM
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MUZZLEFLASH120MM
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ok, like i said, it runs. it has a feel like a bronco i had one time. the fuel filter clogged up and it had no power if you stepped on the gas and it felt like it was misfiring.
. this almost feels like the motor is out of balance when you accelerate.
Mar 3, 2012 at 4:20 AM
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FIXITMR
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CEL? codes?
Mar 3, 2012 at 4:49 AM
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MUZZLEFLASH120MM
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i will be taking it and having it run on a tester tomorrow. i havent tested it yet to see what codes come up. but i do know that when it fist started this the check engine light was flashing.

Mar 3, 2012 at 4:52 AM
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FIXITMR
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yah that's a misfire CAT warning damage may occur.
Mar 3, 2012 at 4:57 AM
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MUZZLEFLASH120MM
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i had the truck tested with an obd II tester.random misfire was what came up. compression tests show 150 in all cyl's fuel pressure is good. possible crank sensor failure? is it possible that the sensor needs to be shimmed?

Mar 13, 2012 at 3:54 PM
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MUZZLEFLASH120MM
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so far i have replaced the plugs, wires, cap, rotor. when first started after replacement the truck ran good. but this was short lived, obd test indicate random misfire.
Mar 13, 2012 at 3:57 PM
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FIXITMR
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is light still flashing?
Mar 14, 2012 at 6:54 PM
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MUZZLEFLASH120MM
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i swapped out the new aftermarket cap and rotor on the advise of a parts clerk. went to the borg warner set. who woulda thought brand new parts could be the problem. after the swap the miss is gone, and i had the codes cleared with an obd tester. still clear after about 20 miles driven.
Mar 14, 2012 at 7:03 PM
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FIXITMR
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yah i forgot about that bein SO COMMON and it is hard to believe! forums always say use delco parts.
Mar 15, 2012 at 3:41 AM
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MUZZLEFLASH120MM
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the parts were the o'Reilly auto parts stock brand. i have to wonder why they even carry parts that have this kind of record. (the clerk was at an O'Reilly's store)? btw thank you for your help, i now have a much better understanding of my trucks fuel/injection system.

Mar 15, 2012 at 4:55 PM
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RIVERMIKERAT
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Our pleasure. Thanks for letting us know you fixed the problem. Thanks for using 2carpros.com
Mar 31, 2012 at 11:08 PM