Car jerking/bucking help please

[Iryoku]

When I floor the car and hit 4500-5000rpm's the car starts jerking/bucking. A/F ratio is good to go ( think). I dont see/hear any vac leaks (is there a certain way to do this?), what else can cause this?
what should i look for?


I cant figure out the problem.

Thanks in advance!

 

[Drift_SM]

do you ahve a blow off valve?...and if so are you venting it to atmosphere?

 

[lil' red dsm]

what is your boost set at? also, if you are using the stock blow off valve, is it crushed?

 

[Iryoku]

no blow off valve... any aftermarket pieces are listed in my profile.

no i dont think its crushed, no reason for it to be its been fine and i never touched it.

I am running 15-16psi

 

[lil' red dsm]

15-16 lbs. shouldn't cause problems with the fuel system you have. what mas are you using?

 

[lil' red dsm]

is the jerking/bucking like a jerk forward in acceleration or does it feel like the engine stumbles? from what gathered from your info, i would check your ignition components. my car would stumble after about 3500 rpm espescially when i would tromp on it. it turned out to be a $50 fix of spark plug wires.

 

[BOBS90TURBO]

Check for a boost leak, build a boost leak tester, and find it.

 

[BergayaJS]

no blow off valve...

Man I read this and for a sec I thought you were like one of my smartass friend who thinks his stock wrx turbo can hold the amount of pressure in it that he doesn't need a bov. then I read on.. aah !

oh btw ppl tend to overlook this but it might be ur gapping too?

 

[ddavisaf]

A) What kind of spark plugs do you have and what are they gapped at?
B) You've got a 255 lph fuel pump. Almost 3x more than stock. You need a fuel pressure regulator.

 

[Iryoku]

NGK 7ES spark plugs
fuel pressure regulator? what does that look like?

forgive me im still a newbie as you can tell

And i believe my plugs are gapped 2.8

 

[ddavisaf]

http://www.dsmtuners.com/parts/default.php?cPath=2_140_81

 

[Iryoku]

Is that whats causing the problem?

 

[Iryoku]

I just put my car back to stock boost 10psi i believe... and the bucking stopped. Anyone have any idea what that might mean? hehe

 

[KuZo]

You probably have a boost leak at a pressure above 10psi. Go through your engine bay and inspect each and every intercooler hose and tighten the clamps and see if your problem goes away.

Build yourself a pressure tester, that will tell you exactly where the leak is coming from.