S2 Stagea Boost Problem

[pixel8r]

i think anyone who doesnt own a rs four s should mind their own business as half of this post is a discussion about the diff between a s and a rsfour .

heh real nice.

i fail to see how a boost issue MUST be specific to it being a manual. It could be, but surely we who own (or have owned, as in my case) an s2 RS4(V) can at least offer to help.

The boost solenoid is not complicated at all. Its just bleeding off pressure in order to lift the boost pressure by 2psi after 4500rpm. I'm not sure if this is how it works in the manual versions, but this is definitely what the solenoid does in function.

The vacuum lines just plug into different points on your intake, and also the wastegate actuator. The wastegate actuator then just measures the amount of pressure in the vacuum line. It will open the wastegate when pressure reaches 5psi, and will close it when its below that. Bleeding some pressure off as the solenoid does, will cause the wastegate to see LESS pressure, and thus stay closed a bit longer. If you bleed too much pressure off, by bypassing the solenoid and using too wide a hose, the wastegate actuator may never see 5psi and will stay closed, resulting in "unlimited" boost as mentioned in an earlier post. This is bad.

When the wastegate is closed, the boost pressure keeps building up. When its open, it stops the boost pressure from continuing to build up (ie. because the air is now escaping), and the boost pressure may even fall a little (as it will with a stock engine).

A common problem with these cars is that the wastegate sometimes can get either stuck open, or the spring may weaken and it will creep open rather than staying closed right up to 5psi. In both cases, it will not build boost or may build boost slowly or just slower than it should.

Hope this helps.

[morm]

After a year of searching this problem still not totally fixed, after fuel pump swap, mechanic changing all relevant sensors from our cars R34 to c34 then adding NISMO fuel pressure reg, running on dyno (mixtures are good), fault is much better. Car is detonating occasionally causing the ECU to put the car into the knock limp mode, this limp mode does not bring up an engine check light. Has anyone else had issues like this? I am still trying to find root cause, not just work around yet. Thanks also to those who posted!

[KiwiRS4T]

Have you thought of getting a Nistune chip? Without that your car can't really be tuned at all.

[wolverine]

Have the coil packs been looked at yet?

[morm]

In case anyone is interested, the problem was blocked injectors causing knocking. I replaced them with new ones and car has been flawless since.

[H@ME]

Hey guys,

 

stagea - s2 rb25det

 

just done head gasket and timing kit etc

car has high flow turbo, fmic, bleed valve and exhaust and nistuned

Car back up and running fine but NO BOOST at all - as in it drives n/a fine boost gauge comes up to the 0 but not even 1psi of boost...

ideas?

[KiwiRS4T]

How fast does it go? Is it boosting but the gauge is dead?

If really no boost you have dead turbo, incorrectly plumbed bleed valve, stuck or maladjusted waste gate or (most likely) massive leak.

If you can't find the leak by following the path around to look for a missing clamp etc the best way is to pull the turbo outlet pipe off and make up a plug with a tyre valve in the middle. If it won't hold say 20 psi you should easily be able to tell where the air is escaping.

[H@ME]

Thanks for the reply. Should not be a dead turbocharger. It was perfect prior to me doing the head gasket etc.

i removed the wastegate circlip and operated by hand it opens and closes fine.

removed the intake pipe and spun the compressor wheel by hand - spins freely no issues.

ill make a boost leak tester and check for leaks shortly - a big leak would make the car run rough yes?? Runs perfect doesn’t drop idle etc just no spool.

[KiwiRS4T]

Don't forget

incorrectly plumbed bleed valve or maladjusted waste gate

and another possibility, faulty BOV (if in doubt try a run with it blocked off).

[Turtle tickler]

On 23/11/2010 at 11:23 PM, morm said:

After a year of searching this problem still not totally fixed, after fuel pump swap, mechanic changing all relevant sensors from our cars R34 to c34 then adding NISMO fuel pressure reg, running on dyno (mixtures are good), fault is much better. Car is detonating occasionally causing the ECU to put the car into the knock limp mode, this limp mode does not bring up an engine check light. Has anyone else had issues like this? I am still trying to find root cause, not just work around yet. Thanks also to those who posted!

Hey mate, having similar issues to you.. While in this limp mode you were still able to freely rev it up (past 3-4k) as if it wasnt in a "limp home" mode?

[morm]

The car ran fine, boost was less. I changed injectors with new OEM injectors and car is fine. I had injectors cleaned and flow tested. There was large differences in flow, both at low flow and high flow which I suspect caused detonation and lower boost 'limp' mode. The car is a factory 2000 RS4s. This is my experience and what worked for me (fixed issue).

[Turtle tickler]

Yeah sounds exactly like what I got going on at the moment. Will have to pull the injectors and get them cleaned and tested. Hopefully that's it ahahah, thanks legend

[Ben C34]

On 8/7/2023 at 5:29 PM, Turtle tickler said:

Hey mate, having similar issues to you.. While in this limp mode you were still able to freely rev it up (past 3-4k) as if it wasnt in a "limp home" mode?

Do a proper boost leak check man. That's pretty much exactly what happens when a coupler has popped off. Also solid chance it's crusty old ( or new ) coils

[Turtle tickler]

Definitely not a boost leak, can pull over turn the car off and on and it runs fine. Could be coils I will look into it, pretty sure they were replaced last year sometime by the previous owner with split fires

[morm]

The injectors were the last thing I did and and no issues since.