Jump to content
SAU Community

Intake Plenum Question - Dropping Boost - Also Good Tools To Have When Owning Skyline For $29 !


Recommended Posts

Hi there,

I'm having a problem.

Just had a tune on the rb25det. Made 247rwkw at 18psi boost. Running great, power to the redline. After 1 week I have noticed boost is dropping off massively after 6000rpm.

Still hits close to the same peak but soon after the boost drops off to less than 5psi. I havent changed anything.

- Exhaust manifold looks ok (no broken studs or soot) so too does the manifold to turbo.

- Checked intercooler pipework. I have the metal piece in intake pipe so it shouldnt be sucking closed.

I got the tuner to have a quick look and he thought it may be the intake plenum gasket (between the 2 halves). It doesn't appear to be leaking at idle but might be under boost. There was a little oil around the join.

Anybody got any ideas? Have you had a similar problem?

Also, you need a ratchet spanner to take the top half of the plenum off (for the 5 bottom bolts). Crack it first with a normal spanner (otherwsie you break the ratchet). Also, wear gloves or wrap your hand in a towel when doing this. I sliced my hand open trying to crack one of the underneath bolts. That is by far the hardest part of the job. You have to disconnect the crossover pipe etc and take the throttle body off and hoses. Also, leave all hoses attached to the AAV at the back, just undo the 3 bolts holding it on.

The gasket is about $85 from nissan. Will get the part no. and add to thead. Anybody know if there are good aftermarket ones?

Hopefully the gasket will fix this problem. Can't think of any other potential problems. I thought exhaust restriction butthat wouldn't have been so sudden I think. The exhaust is 3-3.5" the whole way through with catco high flow cat.

Notice the oil residue? Any comments?

img0959oh9.jpg

Gasket in place:

img0962kt1.jpg

Gasket by itself:

img0963rm3.jpg

Oil in the ports is this normal? Looks dry? Is this a low point wear it rests?

img0961pc0.jpg

$29 Ratchet spanners. From bunnings. Good for a lot of things on the skyline. Should have had them a year or so ago!

img0967zh7.jpg

Edited by benl1981

Sure, but I didn't think it was necessary to the problem - I'm hitting close to 18psi and the boost drops off massively after 5500rpm to 6000rpm.. I have put up mods in rb25 turbo upgrade thread.

dyno result and mods

247.4rwkw

R33GTST

Z32 AFM

GCG High Flow - R33 exhaust housing (not vg30)

3" Batmbl bellmouth dump --> Catco Cat --> 3.5" Kakimoto with 2 mufflers

S15 injectors 450cc

Tomei Fuel Pump

Turbtech boost valve

18psi - running back to 16psi

Stock Airbox

450x300x76 FMIC (Justjap)

Theres a thread about GCG turbo's dropping boost

It was something to do with the wastegate actuator arm

That could be it

edit: http://www.skylinesaustralia.com/forums/R3...html&hl=gcg

Edited by r32woohoo

the easiest way to tell if the gasket was leaking would b 2 get a can of carby clean and start the vehicle up and spray around all the vacumn lines and gaskets and listen 2 the revs if there is a leak the revs will climb slightly.

I'm just thinking that maybe I should have blocked off the BOV first to test that. I can't really hear heaps of air escaping so I was thinking it may be the standard BOV venting back into intake (would make sense). Do BOVs fail like this sometimes? It was working fine for a week - now something has happened.

Anyone used gasket goo on their old gaskets? THinking of wacking it backtogerther with a gasket goo so I can check the bov..

Wont get the new gasket till Monday!

Edited by benl1981

Ok I'm waiting for the goo to dry so I can test it. I used a small smear of this all the way round.

The GOO

Seems like it bonds quite well. I know it's not really the intended use but if it works it works. If it works for a few runs then blows out Ill invest in a new gasket and washers

I have also put a 50cent coin between my BOV and the intercooler pipe (blocking it off). Will this do any harm to my turbo if I do a couple of runs at 18psi!?? I imagine the pressure build up on gear change and stalling on the compressor couldn't be good.

DisplayImage.asp.jpg

Edited by benl1981
GCG High Flow - R33 exhaust housing (not vg30)

I see your problem, a restrictive rear housing.

An aftermarket exhaust manifold might help your case a bit. All the same 247kW is a pretty decent effort out of gcg hi-flow, I'd leave it at that.

Edited by BAMR33

The easiest way to find the problem is going to be to pressure test your entire inlet tract, otherwise it could take ages to narrow it down.

Another QLD user (FineLine) has had a tester fabricated and it is a VERY handy little tool. It's simply a 6" length of 90mm alloy pipe (he has a Q45 AFM, so you'd need 76mm from memory) closed on one end with a tyre valve attached.

You simply remove your AFM, install the alloy tube in its place and slowly pressurise with a compressor up to your desired boost level (have someone watch your boost gauge!) It's amazing how many leaks you will find. Also, you aren't trying to listen for an air leak over a running engine which makes life a lot easier.

After a 2 day road trip my car started having trouble developing boost. It would build really slowly and eventually hit full boost near redline, whereas previously it would hit ~3300rpm. We pressurised the system and found 3 boost leaks in the turbo/cooler plumbing. It's impossible to find them when stationary because you can't make any boost, and all the clamps/hoses etc seemed fine from visual and manual inspection.

The owner was having idling issues the other day, he pressurised the inlet and found a hole in some flexible inlet piping and 2 leaking silicone joins. Fixed leaks/holes, fixed idle.

If you went to an exhaust shop or the like I reckon you could get one knocked up for ~$25 and it would pay for itself in about 5 minutes.

We didn't have the throttle open, but you obviously could if need be. We used an air compressor, but wait for the compressor motor to stop before you start working so you don't have to listen over the compressor noise.

The easiest way to find the problem is going to be to pressure test your entire inlet tract, otherwise it could take ages to narrow it down.

Another QLD user (FineLine) has had a tester fabricated and it is a VERY handy little tool. It's simply a 6" length of 90mm alloy pipe (he has a Q45 AFM, so you'd need 76mm from memory) closed on one end with a tyre valve attached.

You simply remove your AFM, install the alloy tube in its place and slowly pressurise with a compressor up to your desired boost level (have someone watch your boost gauge!) It's amazing how many leaks you will find. Also, you aren't trying to listen for an air leak over a running engine which makes life a lot easier.

After a 2 day road trip my car started having trouble developing boost. It would build really slowly and eventually hit full boost near redline, whereas previously it would hit ~3300rpm. We pressurised the system and found 3 boost leaks in the turbo/cooler plumbing. It's impossible to find them when stationary because you can't make any boost, and all the clamps/hoses etc seemed fine from visual and manual inspection.

The owner was having idling issues the other day, he pressurised the inlet and found a hole in some flexible inlet piping and 2 leaking silicone joins. Fixed leaks/holes, fixed idle.

If you went to an exhaust shop or the like I reckon you could get one knocked up for ~$25 and it would pay for itself in about 5 minutes.

I did something similar, but povo style. I removed one of the hoses on the plenum and pressurised the plenum with the TB closed. I sprayed soapy water everywhere and watched for bubbles. You can get a few psi even doing it this way and it was enough to tell me my IACV was leaking. (I had a problem with vacuum at idle decreasing over time to the point where the car couldn't cruise without miss firing badly)

Lazy bastards way is better as it does a better job of sealing the system.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • Place the new daughterboard in the case and mount it using the 3 small black rivets provided, and reconnect the 3 factory ribbon cables to the new board Then, use the 3 piggyback cables from the daughterboard into the factory board on top (there are stand offs in the case to keep them apart. and remember to reconnect the antenna and rear cover fan wires. 1 screw to hold the motherboard in place. Before closing the case, make a hole in the sticker covering a hole in the case and run the cable for the android unit into the plug there. The video forgot this step, so did I, so will you probably. Then redo the 4 screws on back, 2 each top and bottom, 3 each side and put the 2 brackets back on.....all ready to go and not that tricky really.      
    • Onto the android unit. You need to remove the top screen because there is a daughterboard to put inside the case. Each side vent pops out from clips; start at the bottom and carefully remove upwards (use a trim remover tool to avoid breaking anything). Then the lower screen and controls come out, 4 screws, a couple of clips (including 3 flimsy ones at the top) and 3 plugs on the rear. Then the upper screen, 4 screws and a bunch of plugs and she is out. From there, remove the mounting brackets (2 screws each), 4 screws on the rear, 2 screws top and bottom and 3 screws holding in the small plates on each side. When you remove the back cover (tight fit), watch out for the power cable for the fan, I removed it so I could put the back aside. The mainboard is held in by 1 screw in the middle, 1 aerial at the top and 3 ribbon cables. If you've ever done any laptop stuff the ribbon cables are OK to work with, just pop up the retainer and they slide out. If you are not familiar just grab a 12 year old from an iphone factory, they will know how it works The case should now look like this:
    • Switching the console was tricky. First there were 6 screws to remove, and also the little adapter loom and its screws had to come out. Also don't forget to remove the 2 screws holding the central locking receiver. Then there are 4 clips on either side....these were very tight in this case and needed careful persuading with a long flat screw driver....some force required but not enough to break them...this was probably the fiddliest part of the whole job. In my case I needed both the wiring loom and the central locking receiver module to swap across to the new one. That was it for the console, so "assembly is the reverse of disassembly"
    • But first....while I was there, I also swapped across the centre console box for the other style where the AV inputs don't intrude into the (very limited !) space.  Part# was 96926-4GA0A, 284H3-4GA0B, 284H3-4GA0A. (I've already swapped the top 12v socket for a USB bulkhead in this pic, it fit the hole without modification:) Comparison of the 2: Basically to do the console you need to remove the DS and PS side console trim (they slide up and back, held in by clips only) Then remove the back half of the console top trim with the cupholders, pops up, all clips again but be careful at the front as it is pretty flimsy. Then slide the shifter boot down, remove the spring clip, loose it forever somewhere in the car the pull the shift knob off. Remove the tiny plastic piece on DS near "P" and use something thin and long (most screwdrivers won't fit) to push down the interlock and put the shifter down in D for space. There is one screw at the front, then the shifter surround and ashtray lift up. There are 3 or 4 plugs underneath and it is off. Next is the rear cover of the centre console; you need to open the console lid, pop off the trim covering the lid hinge and undo the 2rd screw from the driver's side (the rest all need to come out later so you can do them all now and remove the lid) Then the rear cover unclips (6 clips), start at the top with a trim tool pulling backwards. Once it is off there are 2 screws facing rearwards to remove (need a short phillips for these) and you are done with the rear of the console. There are 4 plugs at the A/V box to unclip Then there are 2 screws at the front of the console, and 2 clips (pull up and back) and the console will come out.
    • So, a bit of a side trip, but one that might be interesting for people with JDM cars and japanese head units. I know @Pac previously posted about a carplay/android auto adapter he installed which used the AUX input, and @V35_Paul put in one of the Tesla style units that replace both screens. The option I went with was a Lsait LLT-YF-VER5.87_2 (https://www.alibaba.com/product-detail/Lsailt-8GB-Android-Multimedia-Interface-for_1601187633672.html). Price was $1,150 for a single unit although they are much cheaper if you are willing to buy 2....$857ea. Make you you get the version 2 not version 1, it is faster and has a better UI - this is the manufacturer listing: http://www.lsailt.com/product/348.html. BTW if you've never bought from Alibaba before, don't be concerned....these guys can't stay in business unless they are responsive, ship fast etc, they were excellent (probably faster shipping than most local places) So, this was my task for a lazy Sat afternoon....looks complex but was all done in a few hours (it probably helps that I had some of it apart before so it was a bit familiar). I also decided to add a HD USB drive recorded at the same time and the unit also supports an aftermarket reverse cam (if you don't want to retain factory) and also AV in and HDMI out It looks much worse than it is, in fact in was genuinely all plug and play (no custom wiring at all). This video was pretty good (skipped a few steps), unfortunately they are an Aussie seller but no longer sell this unit (I guess Carplay/AA adapters are easier to install and much cheaper) https://www.youtube.com/watch?v=T5hJfYOB8Dg
×
×
  • Create New...