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LOUD exhaust backfire after head/cam install....????

phat_ridegt

TCG Elite Member
Sep 16, 2007
3,351
2
Ottawa
LOUD exhaust backfire after head/cam install....???? SOLVED

so im working on a buddies truck its an 05 4x4 gmc truck. we swapped in a low mile 5.3 that i put a 220r cam, and prc stage 2.5 cnc heads. also put pacesetter lt headers. currently its setup open headers because i need to get it to the exhaust shop to mate it all up. every time i start the truck it backfires like a shotgun.

i know its open headers but ive never ran into this before. I don't have a base tune in the truck because i can't even get it running long enough to do anything with it. i dont have much experience tuning ls motors. anyone have any suggestions on what to change right off the bat? stock intake and injectors for now. my concern is i'll tow it to the exhaust shop and then still wont be able to drive it home.....
 
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phat_ridegt

TCG Elite Member
Sep 16, 2007
3,351
2
Ottawa
installed that ground strap and a new battery terminal bolt (which was stripped) and it seemed to run a tad better but it still backfired and stalled. it starts back up but just wont fire. smells like raw fuel. think im going to tow it over to the exhaust place next week and get that finished up and see what happens. fml lol
 

phat_ridegt

TCG Elite Member
Sep 16, 2007
3,351
2
Ottawa
so ive been talking with jim at speedinc, and he said the tune shouldnt stop it from running with stock maf and injectors. so i decided to hold the throttle open a bit and when its over 1300ish rpms, it runs fine. no backfiring at all. its picking up a misfire on one cylinder so im going to solve that first but it seems maybe the misfire in combination with the open headers is my problem......hmmmmmm
 

phat_ridegt

TCG Elite Member
Sep 16, 2007
3,351
2
Ottawa
fwiw

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1
 

Shibby50

TCG Elite Member
Mar 30, 2008
5,005
74
Braidwood, IL
Put something on after the headers. I found out the hard way you need at least "10 of tubing after the o2 sensors or they read the air coming in the other way. It ran fine for a min. Took it to the track and barely got it off the trailer. It would idle fine around like 1-1300 anything over it was shit and if I let off it would die. Put the mid pipe on and all was right in the world.
 

Gone_2022

TCG Elite Member
Sep 4, 2013
13,094
7,525
Hook the exhaust up first..... Then I am guessing it has not been tuned yet? If not the car may die as soon as it tries to go into closed loop. Same thing happened with my Camaro. Ran ok during warm up open loop. As soon as the warm up cycle completed boom it would die.
 
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