Boost issues..

[dundoot]

ok guys, interesting scenerio... Ive got a gts-4 with rb20det, just had fresh headgasket done and rb25 turbo rebuilt, installed... all was well.

now the other day i was driving and noticed a whole lot of lag... strange lag...

normally the car was reaching full boost at like 2800 rpms

Car accelerates and bost gauge will read upto 0 almost right after take off.... no boost through most of the rev range... then at like 4700ish- 5200ish boom Full 10 psi of boost.... seems like it comes on Crazy hard and holds to red line... then i let off throttle and when i apply throttle again it takes at least 25 30 seconds before it will read positive boost again...even if the car was already revving at say 4500rpms

no smoke, ticks, sqeals, nadda... car runs awesome except the late boost?

rb20 no fun when turbo doesnt perform

Ive check boost leaks, timing, turbo for any signs of a problem(it was just rebuilt) all came back fine.. could it be TPS maybe?

I'm stumped

[Collector1313]

hey

how long did it run good for after the build ?? Was the lack of boost right away or was it after the "break in period" ??
I dont know much but it almost sounds like your actuator (maybe) is it after-market or oem

[dundoot]

car drove excellent, was getting boost almost instantly. build was complete as of the week of jan 2011. maybe 2500 kms since then..

lack of boost is just in the last 2 days... and its not all the time... sometimes it just gets up and goes.... then 10 seconds later its a biotch to get into boost... but yet no smoke out the back or anything, even if im goin wot and still not getting boost... i would have expected it to be thick black smoke or something? thats why i was thinkin tps maybe? just not gettin right signal?

atomspheric bov cause this due to rich point off throttle?

I have yet to check the compression, but i will if i cant figure it out before the weekend. i think its gotta be something small... one of them easy fixes...
also was thinking maybe sticky wastegate flapper? again ill have to dig into it to check that.

I'm thinking out loud..

[dundoot]

actuator is from the original oem rb20 turbo that came off the motor.

[Collector1313]

no, with the tps the car would run like a bag of ****, up and down fluctuation i would think (most cars do). Its easy make a mark on your tps and lossen the bolts and turn it a bit while idling it should bring the idle up or down, if it does the tps works. Also what kind of kms did you put on ?? was there enough time for the gaskets to seat (all gaskets) before you brought the boost up over oem gasket seating requirements ?? Just asking because Im trying to pin point your problem. And it idles smooth now but just has boost problems ??

[johnZ32]

Could be a sticky throttle body. may be worth cleaning it just because?

[Collector1313]

not that I know it would make a difference with the actuator but Adam At Feast told me when I bought my HKS2540 I could use my stock actuator, but.... I would have internal boost limitations if I did not install a uprated adjustable one
So I think it could be possible your asking your boost controller for power that cant be given for the weak actuator.
Just a quick guess, because if your engine is running fine it has to be something to do wit the boost control system
How is it on a lower boost setting ??

[dundoot]

no boost controller.... just wastegate pressure. rb20 wastgate is 10psi vs the rb25 gate which is 6 or 7..

I'm running a r34 turbo with rb20 wastegate.. pressure is 10 psi. gaskets are all good from the looks of it..
i put about 2500 kms on it since jan. car was under the knife because it had a bad HG...
i got a new to me cylinder head and had it machined flat, installed arp headstuds...oem gasket kit.
put the car back together... all was right in the world lol.

now no boost til say 4500-5000rpms... and the car still runs idles fine except no boost til 5k...baffling.

not to mention, like i said before there are times i still get full boost at 3k its just not consistant... was thinking its running super duper rich but now thinkin wastegate issue.

vac is setup, one line from intercooler pipe to wastegate.
ill check and clean the tb, wen i get sum time

[johnZ32]

shouldn't there be a vac line that goes from back of the intake mani to the Wg?

[Collector1313]

Baffling for sure, I would think your fuel system is also still supplying fine as well, your not demanding crazy fuel all the time.
I have one last question, does it run better when it is colder out side or warmer, it would make a difference is your running a bit rich or lean.

someone on here will come to your aid soon, and it probably be something small that got overlooked
or the wastegate or actuator is not doing what its supposed to
Mean while I will search aswell to see what I get, keep me posted on here we can keep this topic going until someone that might know sees it

[dundoot]

yea, thanks guys, i just got home from work, ill take a peek and see what i come up with.

weather it runs better in cold vs hot, i would say normally runs way better in the cold than hot summer air... but this problem came up as bc got hit with a wickad arctic storm.. first night the snow came... so we could be on to something there.

[johnZ32]

im up in kelowna and my car tends to run like poop until it fully warms up and even then it sometimes does weird things.

[beacher1B0]

Could u borrow a spare rb20 or even 25 wastegate actuator from a friend/member? Try it out and see what happens. And just out of curiousity where did you source boost for your wastegate actuator?

Could u get intouch with someone with a Nissan Consult Plug and software(ie Scantech)
and get them too hook your car up and then take it for a ride? Get a look at what your ecu is seeing.

Have u checked for codes?

[M13]

your waste gate might be stuck open or there's an exhaust leak before turbo.


(that is, if you have no massive boost leak, but since your car is running fine before boost, that can be ignored for now)

[Skym]

I would think stock ECU is protecting engine.

If it comes and goes in 10sec or so, I would say stock ECU is detecting knock and switching to knock maps which injects more fuel to protect engine and then switches back to main maps when it doesn't detect's knock. Also when knock is detected, ECU can retard ignition timing. RB20DET actuator is 12psi when bench tested and that's testing 2x of them, same result. On cold night boost level can spike and engine can run lean enough to make engine knock. More so on low octane gas which has a lower resistance to knock. Have to remember you have a bigger turbo that pushes more air than stock turbo.

If you look through Nistune tuning software, probably notice knock count figure going through the roof.

My advice is fit a upgraded fuelpump, injectors, Z32 MAF + Z32 MAF plug and retune stock ECU with Nistune.