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 97 vortec misfires and backfires??

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1969starcraft
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PostSubject: 97 vortec misfires and backfires??   January 15th 2010, 8:29 pm

Hi my 97 gmc vortec 5.7 will idle awesome and runs good except it pops about 4 times when it shifts, mostly from 2nd to 3rd. It also backfires at highway speed randomly every half mile to mile some times less. The backfires will make the truck jerk a little. If i have her at full throttle it will never do any of this and it still has a lot of power all the time. The symptoms also dont start until the engine is warm, and with the 6 inch lift i get about 12 mpg which i think might be normal. Im thinking its a timing problem or maybe a sticky valve. What do you guys think? any help is appreciated greatly.
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merlin5577
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PostSubject: Re: 97 vortec misfires and backfires??   January 15th 2010, 9:23 pm

Sounds like your ERG valve is sticking. Is your check engine light on? What are the codes?

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-Robert.
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2011 Volkswagen Jetta TDI 2.0L 6A
2010 Chevrolet Malibu LT 2.4L 6A
2003 Chevrolet Silverado LS 6.6L 5A
1997 GMC Suburban SLT 5.7L 4A


"If you dont stand behind our troops, feel free to stand in front of them."

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1969starcraft
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PostSubject: Re: 97 vortec misfires and backfires??   January 15th 2010, 9:29 pm

yes engine light is on and its just throwing the random misfire code and emissions code.
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merlin5577
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PostSubject: Re: 97 vortec misfires and backfires??   January 15th 2010, 9:39 pm

Let me guess PO300? Thats the random misfire code. And IIRC PO460 is the emissions code.

================================================
-Robert.
My Fleet;

2011 Volkswagen Jetta TDI 2.0L 6A
2010 Chevrolet Malibu LT 2.4L 6A
2003 Chevrolet Silverado LS 6.6L 5A
1997 GMC Suburban SLT 5.7L 4A


"If you dont stand behind our troops, feel free to stand in front of them."

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1969starcraft
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PostSubject: Re: 97 vortec misfires and backfires??   January 15th 2010, 9:42 pm

Im not sure of the numbers i just took it to autozone and thats all they told me when they scanned it.
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merlin5577
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PostSubject: Re: 97 vortec misfires and backfires??   January 15th 2010, 9:48 pm

My 97' did the exact same thing you've described, so i'd be willing to bet those are the codes. The miss fire is the EGR valve. Its an easy fix, 2 bolts, 1 plug, voila', done. The 'emissions' code that causing the poor fuel economy is the oxygen sensors. Again, its an easy fix, just unplug, unscrew, and voila'. Problem is which oxygen sensor is causing the problem. Without a Tech-II scan tool, you wont be able to narrow it down. So best bet is to replace all four, thats what I did.

================================================
-Robert.
My Fleet;

2011 Volkswagen Jetta TDI 2.0L 6A
2010 Chevrolet Malibu LT 2.4L 6A
2003 Chevrolet Silverado LS 6.6L 5A
1997 GMC Suburban SLT 5.7L 4A


"If you dont stand behind our troops, feel free to stand in front of them."

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1969starcraft
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PostSubject: Re: 97 vortec misfires and backfires??   January 15th 2010, 9:57 pm

Ok cool thanks, and i only have 2 oxygen sensors left and someone cut off the catallatic converter so im guessing thats why i have that code showing. Is there a way to test that the egr would be wrong with it or just trial and error, il pry just replace it anyway though. I plan on putting on one of those 2 in 2 out cats and two flowmasters this spring when i pull it out of the snowbank so i hope that helps to.
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merlin5577
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PostSubject: Re: 97 vortec misfires and backfires??   January 16th 2010, 9:16 am

Yup, no cats or oxygen sensors will contribute to your problems. One everything is back to factory you should be all set. As for the EGR valve if its the factory one from 97' best just to replace it.

================================================
-Robert.
My Fleet;

2011 Volkswagen Jetta TDI 2.0L 6A
2010 Chevrolet Malibu LT 2.4L 6A
2003 Chevrolet Silverado LS 6.6L 5A
1997 GMC Suburban SLT 5.7L 4A


"If you dont stand behind our troops, feel free to stand in front of them."

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1969starcraft
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PostSubject: Re: 97 vortec misfires and backfires??   January 25th 2010, 9:10 pm

Well i unhooked the battery to shut my service engine soon light off and then while the truck was running i unplugged the egr valve and the light came back on instantly. Would this mean that the egr valve is still good or not have anything to do with it. If i dont unplug anything the light wont come on for a while while im driving it, so unplugging the egr valve is what turned the light on right away.
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007jimmy
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PostSubject: Re: 97 vortec misfires and backfires??   January 26th 2010, 2:10 am

it wouldnt have anything to do with it.. it probley saw a vaccum leak and thats why the light came back on..
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1969starcraft
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PostSubject: Re: 97 vortec misfires and backfires??   February 24th 2010, 7:42 pm

I think its fixed. I unplugged the EGR valve and plugged it back in and i finally got a chance to take it out on a dry road and it ran perfect. I did all i could to try to get it to pop and it wouldn't. I hope that fixed it somehow, it didn't make sense to me but it seemed to have done the trick. I also put on a new PCV valve and gromet because the old one kept falling out because it was worn out.
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merlin5577
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PostSubject: Re: 97 vortec misfires and backfires??   February 25th 2010, 12:06 pm

Its weird how some times things just work themselves out. Glad you back up and running.

================================================
-Robert.
My Fleet;

2011 Volkswagen Jetta TDI 2.0L 6A
2010 Chevrolet Malibu LT 2.4L 6A
2003 Chevrolet Silverado LS 6.6L 5A
1997 GMC Suburban SLT 5.7L 4A


"If you dont stand behind our troops, feel free to stand in front of them."

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