Well first off thank you for reading this, I can use any help that I can get.

I have an o4 evo 8 with injen uper intercooler pipe and hard pipe, aps 3" turbo back exhaust, hallman MBC and tune. I bought the car used, with these mods.

I have begun to notice that at WOT in 3rd or 4th gear from 3,500 - 5000 rpm I hear a load popping noise coming from the engine, it sounds like a firecracker exploding or what I would think a hose popping off under boost would sound like. This noise is sometimes a few pops in a row or just one pop. The noise is accompanied with a decrease in boost pressure for a split second then back to full boost which is 19 psi. I have not noticed a change in air/fuel during these events; although I can not entirely rule that out for I have only looked at the gauge once during an event. (happens fast and unexpectedly).

Could this be detonation, knock, a boost leak, or something else? Has anyone ever heard of this happening before? I am really worried and will no longer drive in boost, which royally sucks. It seems to only occur at 4 - 5k

EDIT: New plugs gapped at .024 corrected this.

 

Hook it up to an evoscan and see what the knocksum is. Thats what my tuners does...(I think I said it right...)

 

ya with ecoscan you could datalog it and see your knock sum, air/fuel, and everything else..i would give it a try if you have the hookup
good luck

 

any1 care to speculate on what it could be?

 

check to see if ur vacuum hose to ur fuel pressure rugulator is connected or not dryrotted or somthing. Take a quick look under the hood and see if anything is noticeable, and also like everybody else said, make a log of ur driving, see what ur knocksum and AFR's are! Good luck

 

You say that when you purchased the car it already came tuned for its current mods. So, who did the tune?

 

here is my dyno graph https://www.evolutionm.net/forums/sh...d.php?t=311392
im not sure who did the tune.

 

o had the p0300 random cylinder misfire a whiel back but the check engine light has never come back ion sine i cleared it. mayeb its a missfire..

 

I don't think you are going to hear knock that sounds like a firecracker.

more likely you are getting intermittent boost pressure release aka a popping leak.

like your hose can hold 18.5 psi but pops a leak at 19.

 

He could be hitting fuel cut and hearing backfires when i blew off my IC pipes it sounded like someone lit off a m1000 under my hood and the car pretty much was underivable until i popped it back on. So far I keep one 5/16's nut driver in my car for this purpose even with no popping off since the first one.

 

Is the popping occurring at the same RPM each time? Is it around 5900-6250?

edit: Sorry, I see the 3500-5000rpm comment. I would also look at the above rpm range for a tuning change.

 

It could just be misfiring issues. good luck

 

and where is the data log? or we just gonna say his plugs are fouled or need regapping.

 

That's peak torque area for sure and with boost turned too high, that would certainly aid in the misfire situation. The torque line vs whp line alone says to look at a misfire at peak boost.

 

Sounds like a regular misfire due to incorrect heat range plugs or too wide of a plug gap.
Get fresh plugs and set the right gap for your set-up.