Backfire/misfire after LT headers

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Dec 25, 2015 | 07:12 PM

JacobChevys

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From: West Coast

Backfire/misfire after LT headers

Installed 1 7/8 Pacesetter LTS, with their ORY pipe. Upon first startup and drive I noticed the car run extremely rich and misfired and backfired. Engine when cold runs smooth for about 1 min then will backfire(gun shot like a .22) and is down on power considerably. Upon first inspection The back two plug wires got ripped. So, I put in all new set of TR55 plugs and MSD 8.5mm wires next to eliminate those, so no chance of a cracked plug or ripped plug wires and I have checked numerous times making sure all the plug wires are secured clicked onto plug and coil.
Got a code reader, Am getting p0300 and p0154(bank 2 sensor 1) along with the EGR and AIR codes after they were blocked off. So I changed the 02 sensor on bank 2 sensor 1. After 5-10 min of idling p0154 code never came back but was still misfiring.

After new plugs, wires, 02 sensor, Codes are p0300 and the EGR and AIR codes I forgot which ones.
Havn't driven for more than 10 minutes cause the misfiring and backfires would be so bad. I can also tell its coming from the passenger side of the engine. So finally pulled all the plugs. 1,3,5,7 are all firing clean. Plugs 2 and 4 are soaked in gasoline almost fouled. 6 and 8 still look brand new.

Ive checked all electrical connections, coil harness, 02 harness, everything is where it should be with no damage. Maybe Im missing something? Kinda stumped here.

If the 2 plugs in back (6 and 8) have no fuel and are not firing. Could the fuel injectors (6 and 8) be bad? Missing connection? Grounding out?

Thanks in advance and Merry Xmas!

Dec 25, 2015 | 07:15 PM

JacobChevys

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From: West Coast

I should also state the car ran how it should prior to LT install. Never a misfire. Never any SES lights, engine is bone stock and never been opened. Besides a lid and free mods I recently did. Have owned car for almost 4 years. First serious bolt on mod are these LT headers...besides rear gears. I need to fix this issue so I can drive my car again!!!!

Dec 25, 2015 | 07:21 PM

JacobChevys

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I can also post pictures of the plugs if that would help someone diagnose. Plugs 2 and 4 are literally wet and black.... 6 and 8 look brand new.

1,3,5,7 all seem to look be running perfect.

Dec 25, 2015 | 07:24 PM

JacobChevys

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If someone can move this to the engine section.. I would appreciate!!!

Dec 31, 2015 | 10:14 PM

RollinSScamaro

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Try unplugging your MAF and see if it gets any better.. if not maybe a bad coil or something? No misfire codes?

Jan 1, 2016 | 02:07 PM

Mongoose350

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From: Dallas Texas

Be sure you don't have any vacuum leaks. There is a hose for the pcv system that connects to the rear of the valve cover on the passenger side.

Apr 9, 2016 | 11:44 PM

gwtt

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From: So cal

Have you checked fuel pressure? I got dirty gas in the tank. Would idle fine but taking off and climbing the slightest of hills would fart stumble. Couldn't drive it on the fwy. Got misfire codes. Put a fuel pressure gauge on it and would have proper pressure at idle but soon as you got off idle pump couldn't keep up and drop pressure