1995 S4s Won't Build Boost, Loud Whooshing Under Load- Blow off valve or wastegate?

[Bomb Factory]

I have a very well sorted and maintained S4s (Thank you Bruce Tatusko!).  I have only put about 200 miles on it since purchase.  It runs really well and had no issues.  I have been slowly pushing the car harder as I get used to it.  On my interstate high speed drive yesterday I think something changed.  On any throttle position it wont build boost past about .5 bar.  The car has a red race chip which should allow it to hit 1.25 bar I've been told. When it gets to right below .5 bar there I hear a loud whooshing which I am sure is excess pressurized intake air being blown out, and the boost falls to 0. Nothing else seems out of whack.  The car runs fantastically but I want my extra boost!  I have done some research on this issue and that allows me to report the following:

Blow off Valve- the car has a Samco Sport blow off valve.  It appears to be non adjustable and externally vented.  I am not sure how many flappy things it has- likely one.  PO does not know when it was installed but he had the car for 17 years so it is at least that old. I know the valve was working before because I could hear the slight "chuffing" sound on my shifts.  I was told that the hoses for these valves can be an issue- coming loose and such and this could cause the inability to build boost.  I did a visual inspection and mine appear to be quite tight.  All looks normal on visual.

Turbo housing and wastegate- I have only done a visual on this system- there is no rust or corrosion.  I tried to actuate the wastegate with my hand - moving the bar that goes from the capsule to the housing.  Stiff resistance there, could not get it to move. Unsure if that is normal or not. The issue would be if it were stuck open, not closed.  I could also not make it rattle but maybe I need to have it running and get someone to hit the gas?  I was by myself so I could not do that test.

Check engine light- I verified that this is not burned out.  It has not come on at all.  I read that if it is on the ECU will not allow full boost.

A clue? - The only other potential clue is that I did manage to blow a shift on the interstate and went from 5 to 2 instead of 4.  I realized it before I let the clutch all the way out and fully loaded the drivetrain.  The tach pegged at redline for a fraction of a second and I pushed the clutch back in fully and let the revs drop.  I felt no adverse effects from this mistake. It probably could have been a disaster if I had let the clutch out fully.  I was doing about 80 MPH.  I wonder if the quick hit to redline could have blown out a seal or something that contains turbo pressure?

Two things I am going to try now-

1. Removing the blow off valve and seeing what happens.  I will need to get a new hose and figure out the right way to cap or restore the vac lines to stock.  Once off, I'm on the fence about replacing it- if I do I will use a more modern one that is adjustable and has two flaps.  Ill make that call once I remove it and see what happens.

2. Testing the wastegate function- I found instructions for doing this on the tech talk site and I am capable of doing this test.

This is my first post and I am hoping to tap into the collective wisdom of everyone here for some guidance.  Starting with any other ideas that I might have missed here.

I cant say enough about my S4s.  It is a real joy to drive.  I read all kinds of stuff before I got it about what people dont like when driving it.  I fit fine, I can see behind me fine, the shifter is not a Ferrari - but it works fine- although 3 to 2 can be a bit indirect.

Thanks in advance.

-Charles Handler

 

 

 

 

 

 

 

 

 

[Sparky]

Plenum gasket?

[tomcattom]

Have you checked the wastegate solenoid is (still) working? Without that in theory max boost should be 0.65bar if the actuator is correctly set.

Does the car still have a cat fitted? Might be worth checking it's innards haven't disintegrated. I lost all boost on my S4s last week and it turned out to be a blocked cat.

P.s. if the gear shift is indirect it might be time to renew the translator bearings and joints on the gearbox end of the shift cables, assuming they haven't already been done recently. Renewing them transformed the gearshift on mine.

[Barrykearley]

Just had a new exhaust fitted ? You sure they haven’t left the pipe from the turbo to the chargecooler loose while they were moving stuff around?

[jonwat]

3 hours ago, tomcattom said:

P.s. if the gear shift is indirect it might be time to renew the translator bearings and joints on the gearbox end of the shift cables,

Does the S4s the have the translator? 🙄

[Sparky]

Yes.

[Erikl]

I had an old BOV go bad, is your idles still OK?  If the boost/vacuum line to the back side of the BOV split, the BOV would hold a little boost with the spring and then be pushed open - this would whoosh.  You would have a vacuum leak that might upset the idle.

I think it would keep whooshing though as long as the turbo was spinning?  Maybe the computer sees the drop in boost and opens the WG?  

 

[Bomb Factory]

Thx for the good ideas.

Exhaust not new, PO installed it years ago.  It is a Larini single exit with a Larini cat.  It is stainless and in nice shape so Im not sure how likely the cat is plugged but I will check this first.  I plan to unbolt the cat and do a visual as well as blow some air through it to see if it is clogged.

I have not been able to locate visually the charge cooler but I have not tried very hard yet! All I can see are the pipes- I am going to get it on the lift though so I can look more carefully then.

I'm going to order a regular hose to replace the bov and see what happens. 

The vacuume lines coming off the BOV are a bit hard to trace as I am still getting familiar with the engine area and it is very tight in there.  Where could I find a diagram that shows which ones are typically added for a BOV and what stock config should look like?

Thx!

 

Charles

[Sparky]

So, you haven't checked the plenum gaskets?

[Erikl]

The Charge Cooler is the big red box on top of the motor.

[Bomb Factory]

Have not checked the plenum gasket.  What would the best way to do that be?  Push air through it somehow?  I guess is starts with making sure the fasteners are tight.  Advice on that is appreciated.

I didnt realize the intercooler was the red box on top.  I am still learning my way around.  Ill check that out.  I did see that there is a little rubber bushing where it is attached to the motor and I can woggle the red box back and forth a bit.  My thought was that the rubber bushing was there to help it flex due to vibration.  Am I off base here?

I'm used to working on American v8s in giant engine bays- this is a new situation for me.

-Charles

[Sparky]

If I'm understanding your description of the issue, it sounds like you're leaking boost, so the issue is likely between turbo and plenum. You have 2 hoses, 2 plenum gaskets, a chargecooler and the BOV.  I've seen a few like this and it's often either loose hoses or breached plenum gaskets.  In one case, the chargecooler mountings had failed and it pushed itself off the top hose.

So, the easy stuff is to check hose clips and ensure the chargecooler is secure.  I would then replace plenum gaskets.  Difficult to see if they're breached, and you'll probably damage them on removal.  Could be the BOV but I doubt it.

The other thing to check (but this wouldn't sound like leaking boost - more a sucking sound) is your airbox to turbo hose.  These can lose integrity and sometimes collapse with turbo demand.

[andydclements]

I recall having a boost leak, turned out to be one of the silicone hoses having slipped slightly (less grippy that original rubber ones), but the problem was a PITA to find as you cannot easily replicate it whilst looking at the engine. perhaps time to dust with a tiny amount of talc (using a brush not throwing copious amounts about) and having driven, look for where the talc has been blown away.

[Bomb Factory]

@andydclements I was definitely informed that the BOV hoses can slip.  Mine seem quite firmly in place.  But I am going to take a deeper look and I can have a mate stand over the motor while I rev it and get boost flowing.

@Sparky

Is there a reference you can point me to in regards to the process for changing intake plenum gaskets and a good supplier for them? Ive changed many gaskets so its not about the basics but more any specific things to know when doing the service on this car.  Ive not learned my way around it yet.  First thing I need to shrink my hands.

 

 

 

 

[drdoom]

Welcome Charles!

You clearly are acquainted with wrenching so forgive this if redundant - it's all alloy one works with on these machines so watch the torquing levels. I'm not familiar with your series but would look for a leak on the pressurized side of the intake only after checking BOV function. Perhaps a broken spring within that?

Cheers

[Sparky]

Are you in the US?  If so, JAE.  Stand to the right of the engine bay and you will see the 10x 13mm bolts securing the plenum. 2 gaskets: 1 large rectangular and one roughly oval for the curved pipe.  That's it!

[andydclements]

I'm struggling with memory but I seem to recall you'll not get a lot (if any) boost under zero load (or close to zero), you'll get the engine speed but that will require mimimal air & fuel and so produce only small amount of exhaust gasses to drive the turbo.

[Erikl]

I believe Andy is correct, my experience agrees, would be nice if it would build a little boost in that scenario.  Make checking and testing easier.

[Bomb Factory]

I guess I can just replace the gaskets anyway.

I am checking the cat first and foremost as well as second deeper look at all the BOV hoses etc.

Is there an upgraded plenum gasket set?  And if so where to procure?

[snowrx]

Simple flat gaskets for the plenum, #46 and #53, you could cut them yourself if you had to.

I would rule out a BOV problem before I went after the gaskets.

[Bomb Factory]

After a busy few months I was finally able to get back on the diagnosis of my boost leakage.

I took a look at the cat which seemed fine but while I had part of the exhaust off- I just went ahead and removed the cat.  I live in Louisiana and we dont have any inspections to worry about.  I figured it would add a tad better flow - less restriction.

I test drove the car and the issue is not solved.  When you push the revs hard - during prime turbo time the boost hits .5 bar or so and there is a loud whoosh- which is not the same sound as the blow off valve makes- and the boost gauge falls to 0 and then starts its journey to build back up again once the throttle is applied again or pushed further.

Now that the cat is off it seems that there is more cackling and a bit of popping when I lift off the gas after accelerating.  None of it sounds bad per say- Ive had lots of cars with glass packs or even no mufflers at all and the noise is similar. But I want to be sure it is not a sign of something being wrong.  This being my first car of this type- and having only logged a hundred or so miles with the car- Im still a newby.

My next step in diagnosis is to map out all the blow off valve/turbo piping and vac lines to make sure I know what is going where and what its function is.  Then I can try removing the blow off valve and replacing with a new piece of hose that spans the gap left between the charge cooler and the air intake.  I dont want to just start pulling stuff off until I know what all the connected lines do and where they go.  This process will also allow me to do a more thorough inspection of the tubes, clamps etc.  From my visuals thus far- all seems snug and tidy.  Maybe I will find a break or loose fitting that I missed before.

I have all the service manuals for the car- binders of them- but would like to ask here if anyone has a nice, easy to follow map of the vac lines that relate to the turbo and the installation of a BOV that is not adjustable and externally vented (as mine is).  I am sure I can find it but I appreciate the collective wisdom of this group in shortening my research process.

thx

Charles

 

[jonwat]

9 minutes ago, Bomb Factory said:

a nice, easy to follow map of the vac lines that relate to the turbo

Should be a diagram stuck underneath the boot lid, just look up 

[Sparky]

Have you checked the plenum gaskets yet?

[Bomb Factory]

No havent checked the plenum gaskets- I know you are urging me to do so.  So I will do it.  Are you suggesting a visual inspection without taking the manifold off?  If so I reckon I better get some new gaskets no matter.  Do you recommend a good source for those?  I recall its a two part gasket?

 

@jonwat  Could it actually be that easy?  Certainly a good place to begin the journey.

cheers!

[jonwat]

10 minutes ago, Bomb Factory said:

Do you recommend a good source for those?

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