Backfire/Misfire Under Boost

[zero_wheeler]

Couldn't find much info it, doesn't seem like a common problem.

Ever since I swapped the head gasket,turbos, and head studs, I've had this problem.
At first I just figured it was a problem with the tune because of the turbos, but it
just feels a bit deeper than that.

The car idles fine, Doesn't smoke or backfire, smells like its running fine, but all hell breaks out when you hit boost.

Any positive pressure at all the car starts to smell pretty rich, but it pulls just fine until 10psi.

Then anything over 10psi, it backfires, misses, and lets a massive backfire when I close the throttle.

I'm pretty certain the wastegates are set at 15psi, but I can't tell because anything over 10 it loses it's mind.

Anyways, They are HKS GTSS turbos, with a test pipe, 3.5in exhaust to a flow-through muffler. It's pretty loud.



The first things that come to mind are the tune and possibly the fuel pump, but the car ran just fine on 1bar
before the swap. but i've also read that if you swap the O2 sensors you'll get some nasty backfires. I feel like there's just alot of possibilities.

Any input is welcome, Thanks!

[Skym]

Gap down spark plugs to 0.8mm (stock spark plug gap of 1.1mm is too wide, unless have a upgraded ignition system) if engine is missing at higher rpm, boost levels, tune engine. But be aware the coilpacks could be damaged because of the missing (common for 2x coilpacks to fail when that happens), check them on bench with a multimeter (see engine? manual).

Also check the heat range of sparkplugs, go one colder if engine is running leaner. You should have a run in tune done.

[bobbo]

X2 for what Skym said. In addition I had a similar problem and it turned out to be the ignitor. Of course I figured that out AFTER changing out the coil packs, plugs, and the coil harness.

[frankydodo]

Gap down spark plugs to 0.8mm (stock spark plug gap of 1.1mm is too wide, unless have a upgraded ignition system) if engine is missing at higher rpm, boost levels, tune engine. But be aware the coilpacks could be damaged because of the missing (common for 2x coipacks to fail when that happens), check them on bench with a multimeter (see engine? manual).

Also check the heat range of sparkplugs, go one colder if engine is running leaner. You should have a run in tune done.

Coilpack resistance between pin 1 and 2 should be 0,6-0,9 ohm if i remember rigt!

Envoyé de mon SGH-I747M en utilisant Tapatalk

[zero_wheeler]

I'll give it a shot tomorrow and post up some results, might even be able to get a video. Thanks guys.

[zero_wheeler]

Played musical coil packs with some spares a friend had, tied with regapping the plugs cleared my high boost miss. Thanks guys

[Skym]

Good to hear.