Boost drop to 7psi and exhaust note change occasionally

[swanson-07]

Hey, ive got a 2000 BE5 Legacy - RevC

Got no CEL, but sometimes under boost I only get 7psi and a different sound out of my exhaust. Normally id get 15psi on both turbos, done it for 6months or so but its starting too annoy me. the other thing i noticed is secondary normally comes in at 4500rpm but when its down to 7psi it comes in at 5000rpm. any ideas

Ive replaced air intake pipe, o2 sensor, spark plugs, coils, intake manifold gasket ect.

Runs 110% when its boosting the 15psi best car in the world to drive then boom it cuts to 7psi. tends to be under load, eg; 4 or more people in the car or 5th gear up a steepish hill

[kamineko]

sounds consistent with limp mode due to knock or overboost. do you use 98 or 95 fuel?

[94 Leone]

It still revs over 4,5 though. Limp mode usually limits?

[Joker]

stickey ECV?

use a can of upper cylinder cleaner maybe?

[Guest]

Lower boost means slower to spool due to wasting so much ex gas.

[swanson-07]

Use 95 Fuel because thats the best in Picton

limp mode shouldnt let secondary come on tho?

[swanson-07]

Ive got to replace the AVCS as that was the last code I ever had and it just went away.

So you reckon pull off the EVC and clean it up?

[A_J_T]

 kamineko said:

sounds consistent with limp mode due to knock or overboost. do you use 98 or 95 fuel?

+1

Mine would do that when all i could get was 95 and the weather was warmer. it will be going into limp mode due to knock detection.

Limp mode on mine would simply limit boost to 7psi. no Cel nothing.

[Rosssub]

AVCS? Limp mode from knock will alter timing, fuelling and give WGSP. It wont stop TT changeover happening. 95 ron/5th gear/steep hill/full car.

Your exhaust note is changing because the WG is opening. Low boost before changeover, means less boost during and slower spool after changeover.

How's your air filter?

How's your fuel filter?

What condition is your TMIC in?

How many km's?

Have you ever used upper cylinder cleaner?

Have you ever replaced the knock sensor?

Can you here it pinging when you labour it?

[Andy_Mac]

Didn't think 3rd gens had avcs

[swanson-07]

Air Filter cleaned 2 weeks ago

Fuel filter i haven't looked at tbh

TMIC is in good condition same with hoses

189,000km

replaced knock sensor last year

never used upper cylinder cleaner

Nothing goes ping, it has full boost 80% of the time then it'll be 15psi then suddenly drop to 7psi for maybe 5-10mins of driving then go back to normal. its not a sudden drop as in throw your head forward it just simply feels slower then you look at the gauge and it reads 7psi

[Rosssub]

2 cans of upper cylinder cleaner might help slightly, by cleaning out some of the crud from your combustion chambers. Especially if you've never used it, or run a venting BOV. Also wondering if changing to cooler plugs might help, guessing your using stock BE/BH 6 heat range.

[94 Leone]

He meant iacv i know it doesnt have avcs; we changed the cambelt two weeks ago ☺

[swanson-07]

Gonna do the iacv next, then fuel filter, then silicon inter-cooler pipes. thinking there isn't enough flow for the 15psi so i limits itself back to 7psi?

[boon]

 swanson-07 said:

Gonna do the iacv next, then fuel filter, then silicon inter-cooler pipes. thinking there isn't enough flow for the 15psi so i limits itself back to 7psi?

Silicon hoses won't to anything, the ECU is pretty dumb for the most part, it has no idea about flow etc. There's no feedback apart from the exhaust O2 sensor about what actually happens to the air after it goes past the AFM.

[swanson-07]

replaced the 02 sensor last year.

its just weird that I have no CEL and my boost occasionally drops

[Rosssub]

As said, because of the 95 ron your ECU is detecting knock, then going into limp mode and giving waste gate spring pressure of 7psi.

Changing to cooler spark plugs will lower your combustion temps by 70-100'c, lessening the chance of pre-detonation/knock. If your currently running the BE/BH plug BKR6EIX, then try the cooler BKR7EIX.

Upper cylinder cleaner will remove the carbon build up in your 180,000km combustion chambers, lowering your CR closer to where it used to be. 1mm of carbon on top of my piston heads raises my compression ration from 8.0:1 up to 8.4:1. Which would make it prone to knock/pre-detonation.