searched and am still lost, bucking really badly

[HOOKSH]

installed new UICP with HKS SSQV about a month ago, and was running 14b @ 8psi. was running great, really smooth, good pull for only 8psi, no problems at all. so i turned it up to 14psi, pulled pretty hard, but at about 4500-5000 it started bucking, but it isnt fuel cut because it keeps on pulling through it. i had a CEL a few months back P0400 i think, EGR flow fault. so i was planning on getting the EGR valve checked, but then the CEL went away, and i wasnt having any problems so i didnt bother with that. if i go about 80% throttle, probably about 10-12psi, it pulls really hard, and runs PERFECTLY smooth, no issues at all. any ideas? im gonna check for IC leaks tonight, but if 8psi runs perfect, i dont think itll be that. MAS should be in good shape. the only thing i can think of is either a bad EGR valve, or possibly a bad TPS. plugs and wires are both brand new, and didnt help at all, went with NGK BPR6ES plugs gapped to .028" any help would be great, sorry about being longwinded, but im just stressin it cuz im trying to sell the car, and i looked thru about 5 pages of a search on bucking and found so many diff things i didnt know where to start. somebody please help me

 

[boosted95]

I'd do a leak test first, it's most likely the problem.

 

[HOOKSH]

that doesnt sound too far fetched, but why not at 10psi but at 14 its so bad? just seems like a boost leak would hurt performance at any boost level, but 8psi is perfect. you dont think EGR valve would do that? i read in the haynes manual but im not even sure what the EGR valve really does, so im not sure how i can tell if thats the problem. or maybe TPS? im not sure how to test these things, so hopefully someone knows the best way. ill definetly do a leak test though, but i dont see how that could be it.

 

[BUCK]

that doesnt sound too far fetched, but why not at 10psi but at 14 its so bad? just seems like a boost leak would hurt performance at any boost level, but 8psi is perfect. you dont think EGR valve would do that? ill definetly do a leak test though, but i dont see how that could be it.

Because it's NOT LEAKING AT 8-10 PSI! Whatever seal is leaking fails at the higher pressures.

 

[blackGSX2g]

Is your BOV recirculated? If not, then that could be the problem. 8psi might not be enough to open the first of the two chambers on the HKS SSQV, but once you turn it up to 14psi, the pressure leaks out some air. Also, some leaks in your system will only show up past a certain boost pressure, I knew a guy who's stock uicp hose leaked only past 18psi, so I'd go with boosted95 and try a boost leak test and pump it up past 14psi and see what leaks,

 

[HOOKSH]

Just to let you all know, i just let it sit for a few days while i was waiting on new lugs so my shitty ones wouldnt let my wheel try to fall off again. Then i jumped in it the other day, drove it easy, tried to keep it under 50% throttle to keep boost level down, then i got on it the other day not even thinking, went WOT and pulled to like 6500 and never bucked once. I was like WTF? it was really weird, but i havent had any problems, the DSMs got me beat again with weird problems. Thanks for all the help though guys, if it comes back, ill def do a leak test 1st.

to all the people here on Tooners that actually help