GEN 2 Engine backfiring?

[dude1782]

@Sasquatch77

 

[tightt]

Note, I would assume that this might be more prevalent with lower octane gas due to it's lower resistance to ignition.

Its actually quite the opposite. The higher the octane, the lower resistance to ignition. Thats why lower octane fuels have a higher probability of knock, which is pre-detonation (exploding prior to spark being applied). Higher octane fuels can make more power by advancing timing, getting the combustion closer to top-dead-center of the piston stroke and the result = more power/torque.

With that being said I agree with what you about unburnt fuel being the culprit of his backfires. The question is why an OE tune would be SO rich. I know that rich = safe, but if its TOO rich it can cause cylinder wall wash. Thankfully I'm sure its nowhere near that rich but still.

 

[psufan]

Its actually quite the opposite. The higher the octane, the lower resistance to ignition. Thats why lower octane fuels have a higher probability of knock, which is pre-detonation (exploding prior to spark being applied). Higher octane fuels can make more power by advancing timing, getting the combustion closer to top-dead-center of the piston stroke and the result = more power/torque.

With that being said I agree with what you about unburnt fuel being the culprit of his backfires. The question is why an OE tune would be SO rich. I know that rich = safe, but if its TOO rich it can cause cylinder wall wash. Thankfully I'm sure its nowhere near that rich but still.

I honestly think this might be an early morning typo on your part... but in the post that you quoted, I said that lower octane = lower resistance to detonation (which would be higher probability to knock). In your post, you said the higher the octane, the lower resistance to ignition, which is untrue (but again I think is a typo because everything else you said makes sense). In any case, I think we are both on the same page regarding the basics of octane lol.

In regards to the backfires, I don't know what air/fuel ratio the stock tune is tuned to run at; however, given that it's a relatively high performance turbo engine, I wouldn't doubt for a second that it's a bit rich for safety. That being said, even if it's not overly rich, you are still going to have some fuel dumped into the exhaust track when you lift during mid/heavy throttle use.

 

[tightt]

In your post, you said the higher the octane, the lower resistance to ignition, which is untrue

It was an early post but, from everything I know about octane and tuning my own vehicles, the higher the octane, the more is RESISTS knock. Its quite the opposite of what the general public believes to be true (that higher octane burns faster/more quickly). As I said, the higher octane helps resist early ignition (PRE detonation).

Here is a quick quote from hemmings:

"Higher octane gas is processed through additional steps that further refine the blend and cause it to burn more slowly than lower octanes"

"Because higher octane gas burns slower, it is more resistant to knock when subjected to higher RPM and cylinder pressures"


Edit: Yup...we're on the same page.

 

[derekg1988]

Anybody else had this issue. I was just driving this morning around 55 mph and Heard a pop. There was an older car one lane from me, don't know if it was him or not. It sounded like something had hit my truck. I pull over to check the body and found no evidence of anything hitting my truck.

 

[Raptoroperator]

Same thing is happening to me after every fill. Running premium and is backfiring when slowing to a stop. What is the issue with the evap system?

 

[Monster]

Looks like there are two posts about this. Anyway here is what I put in the other:
Add me to the list. Filled up 91 octane. Left station in sport mode and after my foot was off the gas for a few seconds, I heard the backfire around 40mph. I pushed the gas, let off and was able to make it happen two more times at that speed. Windows were down for the first time and so it was loud.

Don't think it has ever backfired before. Has 1400 miles. It happened again turning into my neighborhood. And two more times in the neighborhood. I was trying to make it happen.

 

[mhaynes772]

Happens to mine after fueling too. My truck is bone stock and I run only 93.

 

[df4801]

I would take it into the Dealer. Definitely not normal. I usually run 87 octane but have tried 93 also and there is no backfire with either after 4000 miles.

 

[Monster]

Drove it again today. Only seems to happen in sport mode.