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Runs rough when applying gas.

Tiny
MUZZLEFLASH120MM
  • MEMBER
  • 1998 GMC SIERRA
  • 200,000 MILES
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.)
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Saturday, March 3rd, 2012 AT 1:19 AM

14 Replies

Tiny
FIXITMR
  • MECHANIC
  • 9,990 POSTS
What motor?
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Saturday, March 3rd, 2012 AT 2:39 AM
Tiny
MUZZLEFLASH120MM
  • MEMBER
  • 8 POSTS
5.7 ltr. Vortec
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Saturday, March 3rd, 2012 AT 2:55 AM
Tiny
FIXITMR
  • MECHANIC
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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.
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Saturday, March 3rd, 2012 AT 4:12 AM
Tiny
MUZZLEFLASH120MM
  • MEMBER
  • 8 POSTS
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.
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Saturday, March 3rd, 2012 AT 4:20 AM
Tiny
FIXITMR
  • MECHANIC
  • 9,990 POSTS
CEL? Codes?
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Saturday, March 3rd, 2012 AT 4:49 AM
Tiny
MUZZLEFLASH120MM
  • MEMBER
  • 8 POSTS
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.
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Saturday, March 3rd, 2012 AT 4:52 AM
Tiny
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Yah that's a misfire CAT warning damage may occur.
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Saturday, March 3rd, 2012 AT 4:57 AM
Tiny
MUZZLEFLASH120MM
  • MEMBER
  • 8 POSTS
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?
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Tuesday, March 13th, 2012 AT 3:54 PM
Tiny
MUZZLEFLASH120MM
  • MEMBER
  • 8 POSTS
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.
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Tuesday, March 13th, 2012 AT 3:57 PM
Tiny
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Is light still flashing?
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Wednesday, March 14th, 2012 AT 6:54 PM
Tiny
MUZZLEFLASH120MM
  • MEMBER
  • 8 POSTS
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.
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Wednesday, March 14th, 2012 AT 7:03 PM
Tiny
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Yah I forgot about that bein SO COMMON and it is hard to believe! Forums always say use delco parts.
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Thursday, March 15th, 2012 AT 3:41 AM
Tiny
MUZZLEFLASH120MM
  • MEMBER
  • 8 POSTS
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.
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Thursday, March 15th, 2012 AT 4:55 PM
Tiny
RIVERMIKERAT
  • MECHANIC
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Our pleasure. Thanks for letting us know you fixed the problem. Thanks for using 2carpros. Com
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Saturday, March 31st, 2012 AT 11:08 PM

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