Car bogging when full boosting dont know how to isolate problem

[r33rb25]

I have a 94 R33 GTS-t with an RB25 and i recently just put a FMIC on and installed a Greddy Profec spec 2 boost controller and turned the boost up to 1 bar was running perfectly fine for a few days and then just last night started bogging while in full boost it is all good up untill about 4500 rpms and doesnt even happen all the time it started with just one initial cut before it started boosting but now has developed into this no smoke comes from the exhaust please help =( i miss boost

[archaeic_bloke]

2 suspects, Air Flow Meter or intercooler piping leak.

start by inspecting all the pipes from turbo to intake and look for any cracks, splits, or holes in the pipes and hose couplers.

[Nismo_line]

probably the ic pipping, one of the claps probably wasnt tight enough and the pipping popped loose

[r33rb25]

well i was thinking about the ic piping but i dont seem to have a boost leak at all like my guage isnt registering that unless if it wouldnt show there? and also by airflow meter do you mean the MAF sensor?

[r33rb25]

and the noise the car makes sounds like a rev limiter almost but still boosts through it =/ i dont get it as i do not have a rev limiter and am still running the stock ECU i was wondering if my car wasnt up for the 14 lbs or somethin my supporting mods list include
Apexi super suction kit
FMIC
Greddy Profec spec 2 boost controller
Stock turbo
Downpipe
Hollowed cat
Full 3" exhaust
Walboro 255
300zx fuel filter

[archaeic_bloke]

yea that sounds a lot like a MAF (air flow meeter) or boost leak problem.

Does it bog down only on boost?

[Skym]

Boost cut (fuel cut, just like stock revlimiter) is similar and is related to MAF.

If engine goes flat and struggles to accelerate, stock ECU is probably pulling ignition timing due to detecting knock. Stock R33 ECU tune doesn't like much over 10psi and cold night doesn't help.

[r33rb25]

yea its only when im boosting and usually starts at 4000 rpm till about 5000 n when 5 hits most of the time it pulls like crazy again n like i said it was all good up until last night the first few days with the boost up was perfect

and i wonder if it is an ECU problem when i looked at my ECU it says Impul on it i did a little research and i guess its a japanese aftermarket chip for advanced timing and blah blah but ultimately doesnt do that much for me i guess

[dan5050]

spark plug gap! could be with the added boost your blowing the spark out at top end. Check the gap. Stock setting is .8mm i think so if it's already at that go a little bit smaller and see how she runs

[r33rb25]

so i turned the boost down to 10 psi n it made a promising difference bogs way less but issue is still there the only thing im having problems understanding is that it was running perfect for the first few days at 14 psi but then the issue came out of no were same fuel n everything

[DarkCaporaL]

Check your plug gaps as advised above.

[Skym]

Sparkplugs can make engine feel flat when worn out / not the correct heatrange (burns the tips and produces bigger gap). Did this on my car with only intake, exhaust.

If between 4000-5000rpm, VVT might be switching over at that point. I noticed that drop in torque on alot of RB25DET dynochart's with stock cams at around 4000-5000rpm and tune didn't seem to solve it.

Was browsing the Tomei catalog and found this article that mentions fitting their brand of cams solves the drop problem when switching and explains how adjusting VVT affects powerband on SR20DET (I assume RB25DET is similar) -

http://www.tomei-p.co.jp/_2003web-catalogue/064-065_camshaft.html

According to Tomei 1000-4500rpm with stock RB25DET cams (roughly compare to chart, dyno plot shape in above link) -

http://www.tomei-p.co.jp/_2003web-catalogue/e090_camshaft-specs.html

[r33rb25]

soo i went out and bought a brand new set of NGK iridiums today gapped them all perfectly to .8 and still sale problem im aiming more towards a MAF problem now could it be shot? i have the Apexi super suction kit and maybe when i capped the intake line that ran to my acuator when i installed my boost controller i didnt plug it well enough? or does that line from the intake need to run somewhere?

[r33rb25]

the only time it has any studder is from 4-5000 but then from 5-7000 pulls HARD again like no hesitation

[DarkCaporaL]

Did you clean your MAF like the first few post advised? It may just be dirty...get some MAF cleaner of eletrical contact cleaner and spray it down.