Losing Boost After 4500 Rpm.

[Simmo1985]

I've got my turbotech boost controller set to 10psi, and it worked great for about a week. Now when accelerating past 4,500rpm boost drops noticeably to about 5psi (although the gauge shows 5psi it doesn't even feel like it's making that much boost). It's a really noticeable drop off in power.

I took it to the mechanics the other week and wouldn't you know it, the car worked fine when I was there.. but the problem is back now. Any suggestions of where to look? Will it just be a leak in the vacuum line?

Problems driving me nuts.. boost seems to work and pull fine prior to hitting those higher revs, like the additional pressure is causing a leak???

[R33GOD]

i have the same problem which is my plenum gasket.. i wouldnt imagine it would be stuffed on that low of boost but you never know

[Cubes]

When I removed my plenum to inlet manifold gasket I noticed it had been leaking.

When refitting inlet manifold/plenum/throttle body gaskets I gave them a spray with Hylomar just incase.

Using Hylomar also helps should you have to pull it apart again; it prevents gaskets ripping etc so you can save a few $$ and reuse.

[tezflow]

When I removed my plenum to inlet manifold gasket I noticed it had been leaking.

When refitting inlet manifold/plenum/throttle body gaskets I gave them a spray with Hylomar just incase.

Using Hylomar also helps should you have to pull it apart again; it prevents gaskets ripping etc so you can save a few $$ and reuse.

could you haer a sucking sound coming from the plenum when it was leaking.

[Simmo1985]

could you haer a sucking sound coming from the plenum when it was leaking.

I can hear a sucking or hissing type sound coming from my plenum at the moment. Didn't know what it was though, just thought it may have been normal. Guess my plenum is leaking then?

Edited October 7, 2007 by Simmo1985

[R33GOD]

yep theres ur problem

have fun tryin to take it off. its a pain in the butt.

[Simmo1985]

Would a leaking plenum cause any other problems? Just trying to figure out if that is in fact the problem, because the car drives perfectly normal otherwise.

Edited October 7, 2007 by Simmo1985

[Cubes]

could you haer a sucking sound coming from the plenum when it was leaking.

No strange sucking noises apart from the usual idle sssshhh noise

I think mine was only leaking on boost as it didn't cause any strange idle issues or afm readings.

[R33GOD]

when there leaking bad you will notice your idle dropping pretty low.

[EVL-R33]

i got this same problem, i hear a loud hissing like noise come from the plenum at high boost and notice my PSI drop from 20 to 15.. I still haven't got around to pulling the plenum apart and changing the gasket, but i'm pretty sure thats the problem..

[benl1981]

I think I have a similar problem. Had it tuned running 18psi no worries but after a week of driving it doesn't seem to hold boost. After 6000rpm the boost drops from 18psi to about 5psi. I can't hear any strange noises though..

I dont think its the inlet sucking closed as I placed a metal pipe in part of it. It looks a little weepy round the plenum gasket. Hopefully thats it..

ANYone got the part no. for R33gtst?

Edited January 29, 2008 by benl1981

[benl1981]

Would you normally hear a leak? Boost is dropping pretty quickly after 6000rpm..

[GeeTR]

Not to be a party pooper, but hold up. To loose half your boost pressure outa leak from a gasket... i would think there would be a VERY prominent noise under load.

[benl1981]

What do you think then? Hopefullly not head gasket or something..

Might get the mechanic to put it on the dyno and then we can see

[Cubes]

Get it on the dyno; watch what the afr's, afm volts and possibly duty cycle does depending if it has been tuned the way it currently is.

[benl1981]

I know the AFM voltage is down on what it usually is. Usually got to 4.44v now only 4.3v..

[benl1981]

The mechanic reckons I should just change the gasket without even running it on the dyno. They reckon theyve seen a lot of this on the rb25s. It isn't always that easy to hear apparently - and under load there is so much air floating around there with the fan going etc..

Will have a bit more of a check myself..

Nissan want $85 for one! There was a little oil residue around the join. We cleaned this off but there isn't really much coming back. Might run it up onto boost a few times and check again. I did a few 0-100km/h runs the other day which may have blown it apart..

Edited January 30, 2008 by benl1981