Pro Mouse

iTrader: (15)

I had this posted in the tuning section and not getting any responses there so It all started after a good 24 hour rain I got 6 gallons of gas in my 408 last Tuesday night and when I pulled out of the gas station excellerated kinda hard (Not Floored) and BANG!!!!! I was Like WTF!?!?!?!? I blew my y pipe apart at the clamp so got Home tightened it back up.The Next day on my way to work I got on it a couple of times and it back fired through the exaust again Blowing Blackish grayish smoke.So I went to the auto parts store picked up some new plugs,2 Bottles of dry gas, and some Octane booster.Dumped it all in right on the spot.I took it easy on the car ,it seemed ok normal driving.So This weekend I put new plugs in it(Plugs were fine).So today I am at about an 1/8 th of a tank so I went to a gas station I Trust,Not where I got the gas last week,Put in a can Sea Foam and 7 fresh gallons of gas drove about 5-6 miles and Hammered it (Floored) and Bang!!!! It back fired through the Exaust Still!What could it be?it is only at 50% throttle or more. Keep in Mind that Prior to getting this gas ,I nailed it about a mile from getting to the gas station the Car was Fine.This is an OPEN LOOP TUNE with NO o2 sensers...Please Help!!!!

Isolde

iTrader: (4)

Possible causes include any or even all of the following: way too rich, spark too late, exhaust valve opens too early, exhaust valve burned, exhaust valve not fully closing, oxygen in headers.

Pro Mouse

iTrader: (15)

Yeah ,But after getting fuel? It was fine a couple of miles down the road before I got fuel

RedHotG8

iTrader: (1)

It's probably a coincidence that it happened after you got fuel. All the conditions that Isolde posted will cause backfiring in the exhaust.

thunderstruck507

iTrader: (18)

intermittent wire issue with a coil also a possibility...missing any? seem down on power?

if you had duals an easy way would be to swap coils from one side to the other and see if the pop follows

might get a spray bottle and shoot the header tubes one at a time, look for one that takes longer to evaporate

Pro Mouse

iTrader: (15)

Well It is Not an exhaust valve.I did log it but came up with very Little KR.Well I filled up with fresh gas and the problem did not clear up.Checked every thing under the Hood and then it Hit me!I took out my jumper for my timing tuner,took it for a test drive and NO MORE BACK FIRE and Power Back, HaHA!! I have had the car die completely on me with the timing tuner if it got wet ,but never in the six years have I ever had this problem.A circuit in the dam thing must have went bad in it causing me to have a really advanced timing.This is why I could not pick up the problem with my HP Tuners...I guess I need a new Timing tuner for my nitrous....