my f'n car, WILL NOT run under boost. as soon as i hit 6-7psi, it starts studdering/backfiring like a bitch. you would think this is pretty nasty, and i'd be throwing all sorts of codes.

wrong.

NO CODES.

I pulled my N249 and SAI out, and I get a code for the SAI, but that shouldn't affect boost. There are NO codes related to some system failing, or going out of parameters.

TOO MUCH F'N ADAPTION in the motronic. Its too willing to make the car run, even if its not running well.

anyway, if anyone can think of any sensors to log with vagcom to maybe figure this one out, post away. I'm clueless here, and Im starting to get pissed. This is my venting/asking for ideas thread. It goes in too many places to be assigned to another thread or post.

I need a good beer and a cigar....

 

what mods do you have and how are you controlling boost?

 

What are you monitoring so far - anything? I'd think that if you're going to break up under boost, you'd want to watch O2 sensor, MAF, injector duty cycle (if possible, log this along with boost pressure), timing, and det sensor. Something in that bunch has to be leaving a telltale that will give you a peek into what's going on.

 

Mods: HKS shroom filter, Forge silicone turbo inlet hose, muffler delete (only resonator can now)
As of this head gasket issue, SAI delete, N249 delete- diverter runs directly off manifold vac now. N75 is still wired in, as is N249, they just don't have vac lines hooked to them.

Controlling boost with a Hallman boost controller. Even a very slow roll on the throttle with boost only creeping up, the car studders terribly above 5psi, or occasionally from 0-5psi if the engine is under much load (like on a hill).

Its just like anti-lag. I actually held it under boost last night to see what it does. It kept missing, (boost gauge jumps from 5 to about 10psi when you do this), and when I let off the throttle, I got a decent fireball from the exhaust. (kinda neat to see glowing embers blast all over the highway).

Before holding it under anti-lag conditions, my only codes were SAI related, and evap related. After anti-lag, I also added misfire codes, but that makes sense for anti-lag, but not for this situation as a whole.

 

What do you have going on with the diverter valve? Is your timing dialed in......I remember you changed the head gasket?

 

DV is running right off manifold vac. pretty straight forward, actually, couldn't get any more simple.

as for timing, its good. I'm an F'n expert when it comes to timing belts, plus, it drives fine, just doesn't like boost.

 

Maybe a leak?

 

in my experience, nothing short of a hose coming completely apart would make it run that bad. Unfortunately, i loaned out my pressure tester and haven't seen it in a month, so I can't test it to confirm right now, but I've done a good visual, and nothing stands out.