Sinister_Z28

OK so i have a iron 408 i recently built and ive been slowly changing things and adjusting things as i get the cash. So i put on a LS6 valley cover and catch can as well as changing out the coolant bypass tubes. I also shaved the bottom of my ls3 intake manifold because it wasnt sitting flush on the head. So today i install the intake and new Ls3 coil packs that i bought a while back and hook everything up. So i start it up to check for leaks and it fires up and idles for like a minute then it backfires like out the exhaust. SO i shut it off and get out my code reader to see if there is one. Well i check and there are no codes and no SES light on so i fire it up again and same thing it idels fine then backfires then idles for a bit and backfires again. So i shut it off and do a quick check on my fuel injector plugs, my vaccuum lines on the back of the intake, drivers head grounds, and my coil pack wires. Everything looks fine so i fire it up one more time and it still back fires and idles fine. It revs like normal to so i dont think its a dead cylinder, " I had one right after i finished building the engine and the engine reved very lazy". Now i have a break in/ cruising tune and before i changed what i changed the car ran and idled perfectly. Now when my tuner put the break in tune on it my intake WAS NOT sitting flush with the heads and he said i needed to fix that. So could the tune be off now that the intake is sitting flush? Also the exhaust smells kinda rich but i can't really tell cause this is the first engine I've built by myself.

So id appreciate ur guys advice and opinions on this since I'm young and don't have a lot of experience in diagnosing backfires. Oh forgot to mention that the break in tune was done by a very reputable shop.

Sinister_Z28

Anybody?

Sinister_Z28

Update i started it up this morning after tightening up the AIR system and it idled and reved perfectly for about five minutes. I then restarted it a coulpe minutes later to recheck it and it start back firing again and sputtered when it first started. So i shut it off and rechecked for a code and i had a code for my bank 1 O2 Heater Sensor. Is this as simple as my O2 sensor went out because i know that can cause backfires. Again any opinions would be greatly appreciated.

wildcamaro

iTrader: (15)

Sounds like a tuning issue...

BanditDave

iTrader: (11)

You could have killed your O2 from an excessively rich condition...backfiring in the exhaust could be occurring from unburnt gas in the exhaust. You could try posting your tune if you have access to an HPTuners or EFI Live. You could also ask your tuner to email you the file and post it here for others to eval. You should also post up everything you can share about the set-up which will help with troubleshooting.

Dave

Sinister_Z28

I know but it didnt do any of this until i let i sit without starting for 2 months while i was researching and acquiring parts for the above mention task. Also i switched my coil packs from bank 1 and bank 2 and started it and the back fires were less violent and less frequent. After i switched the coil pack assemblies from bank 1 and bank 2 it only back fired within the first few seconds after it fired up and after i let it idle and warm up a little i slowly raised RPMs to 1500 and then completely let off and it went down to 900 RPMs had a small back fire then came back up to a 1000 RPMs where it usually idles at. I did that once more and got the same results. ALso i noticed it was sputtering a little bit but not enough to make the tack jump. Also i could hear a slight knocking noise but it didnt sound like a mechanical knock because i know what that sounds like. it almost sounded like it was in my exhaust on the drivers side. Last but not least i noticed when i shut it off that the drivers side header was like 3 times hotter than the passenger side. It was only on for a max of three minutes and the drivers side header shouldnt be that hot. Any ideas on what the problem is? Oh im also upgrading to TSP 1 7/8" long tubes and I'm replacing my O2 sensors so im hoping that might fix it but im all out of ideas on what it could be. Once again any help is greatly appreciated.

EricYJ-TA

iTrader: (10)

Try swapping the old coils back on ?

Sinister_Z28

Ok so i dont have access to a way to look at my tune. Now like i said earlier it only has a break in tune and not a full dyno tune. Basically i took the car to my tuner for a full dyno tune and he found to many issues for him to do a full dyno tune, i.e. leaking valve covers, intake not sitting flush, no pcv, he didnt like the way i had my ls1 coil packs mounted to my valve covers, and i had a dead cylinder in bank 1. So i found my dead cylinder was caused by a a broken peg in my #5 cylinder coil pack. So i bought new ls3 coils, mounts, and valve covers, as well as a ls6 valley cover, 2 ls2 coolant cross overs, catch can, ls3 coil pack wiring harness, and i milled the honey comb stuff down on the bottom of my ls3 intake so it would fit flush and seal. Then after i did all this i fired it up and i have the above said problems. Now i know i dont have a dead cylinder because i know what those sound, feel, and look like. The car/engine is a lq4 block bored out with a 4" stroker crank fully forged rotating assembly and ARP everything. the cam is a 236/242 113LSA+3 with 0.500" lift. Im running LSA heads with dual valve springs and titanium retainers toped off with a LS3 intake. Exhaust is stock manifolds and y pipe with a borla adjustable cat back. i have ordered and am waiting for my new headers to arrive and im ordering a TSP ORY and O2 sensors with extensions next pay check. It take time and budgeting to build a car like this at 19 on 9.50 a hour lol. Now back to the tune. My tuner said the break in tune was there so i could start and move the car, cruise it around the block to check things i needed to fixed to make sure there working properly and so i could drive it the day before i shipped out for boot camp. Basically my understanding is he tuned as much as he could without putting it on the dyno. Sorry for the 1000 questions but i dont have any one else to seek advice from.

Sinister_Z28

Good idea ill try that.

Sinister_Z28

Ok well i put the old coil packs back on and it purred like a kitten so i let it idle for like 5 minutes then i took it around the block and when i stopped at a light like 200 yards from my house i noticed it was smoking from the drivers side. So when i got back i shut the car off then i checked for codes and i had two. They were low voltage signals for both knock sensors and the knock sensors are brand new The only knock sensor related stuff re used was the little harness so i guess i should replace that? Now why is it smoking with these codes and no other noticeable issues?

Majestic9C1

iTrader: (19)

did the knock sensor harness get pinched at all when you put everything back on??

Are all the old PCV ports capped off at the back of the engine???

Sinister_Z28

Yep the only unused pcv port is capped. And im pretty damn sure i didnt pinch the knock sensor wires. But im gonna get a new knock sensor wiring harness.