The Car Shuts After 6000 Rpm

[Stronzo]

hi everyone,

i have a harsh airflow drop after ~6300 rpm, at aproximately ~4,4v at Z32 MAF. It feels like i just lift foot of the pedal. When i look at the Datalogit charts i can see that the airflow drops earlier than boost.

I suspected the stock rubber suction pipe being sucked inside under boost and just changed it to a silicon type ebay item enforced with metal rings. I also changed the air filter to the new apexi panel filter in the stock box. but no use.

the cars still shuts after ~6300 rpm.

what else can it be? some kind of full-throttle compressor surge or what? is there any way to diagnose suction pipe sucking itself on the road without a dyno?

p.s. it`s rb25 with rb26 crank and rb26 forgies, hks 256/8,8 cams and GT2871R (without port shroud) running 0.8 - 1 bar boost.

thanks.

[GTRsean]

Check exhaust for restriction eg cat blockage? does boost drop off? timing etc.

[Stronzo]

Check exhaust? does boost drop off? timing etc.

boost drops _after_ airflow.

timing is ok.

exhaust... it`s a split dump pipe from ebay, frontpipe + decat pipe in one piece and fujitsubo exhaiust. the only new part is a splitdump but it seems ok. how should i check it?

[Stronzo]

and one more thing: usually the first run at is ok -- the car pulls ok to the redline. but other runs at 1 bar have this problem. On very hot days after traffic the problem appears even at 0.8bar.

[Spurdo]

i had a very similar problem and it turned out to be bad coils. gets worse as you run more boost, and the sudden drop is very violent, mine also performed slightly better in colder conditions.. if its the coils then you run the risk of doing damage to your bearings if you continue to drive it like this. whatever it is, stay off the boost/revs until its fixed

[Stronzo]

i have had problems with coils before -- this problems looks different. but thanks for reply.

[boostn32]

Knock sensors, you get 1 rev to red line then it will retard once its gets to a certain rpm untill the ignition is turned off then back on.

to check this, just turn engine off while moving then turn on again and rev right through to red line to see if its gone and then returns

on next gear rev to red line.

[JonnoHR31]

only with the standard ecu, the datalogit suggest the OP has a power fc, which doesnt do anything with knock readings other than show a number

dying coils do not kill bearings

[boostn32]

only with the standard ecu, the datalogit suggest the OP has a power fc, which doesnt do anything with knock readings other than show a number

you are correct Jonno. didnt even think that it could a power fc

[Stronzo]

yes, it`s power fc so there is no any R&R or any other safe modes.

[femno]

Faulty AFM?

Try swapping with another.

[Stronzo]

Faulty AFM?

Try swapping with another.

but what is it`s fault? its voltage is ok. it`s voltage drop is ok too as it follows real "pedal lift" effect. but thanks for advise - i`ll try to find another z32 afm.

[Stronzo]

ok let me ask in other way: is there anyone here running gt2871r or smth similar on rb25 with the stock rubber suction pipe (or silicon type from perfomancewise) and stock airbox? do you have any issues like written above?

thank you.

[BoostdR]

and one more thing: usually the first run at is ok -- the car pulls ok to the redline. but other runs at 1 bar have this problem. On very hot days after traffic the problem appears even at 0.8bar.

I think your on the money already. The intake pipe sucks in easier when its hot. I fixed this issue temporarily with some coat hanger wire wrapped around the intake pipe to keep it circular. The silicon intake pipe without rings fixed it and flows better. this was on a Rb25 with GT2835.

Edited August 23, 2010 by BoostdR

[wolverine]

ok let me ask in other way: is there anyone here running gt2871r or smth similar on rb25 with the stock rubber suction pipe (or silicon type from perfomancewise) and stock airbox? do you have any issues like written above?

thank you.

Yep HKS GTRS on S2 Stagea with K&N filter. The cut and insert solid pipe per rev210 and issue gone.

You still need to be mindful that the filter can be a restriction causing the pipe walls to suck in so the filter should be cleaned if dirty or replaced as needed.

[Stronzo]

Yep HKS GTRS on S2 Stagea with K&N filter. The cut and insert solid pipe per rev210 and issue gone.

You still need to be mindful that the filter can be a restriction causing the pipe walls to suck in so the filter should be cleaned if dirty or replaced as needed.

yes, thanks, as i wrote new apexi panel filter was just installed.