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Discussion Starter · #1 · (Edited)
Hey,
I was raising this topic several times among others, but've never posted how the problem exactly sounds like.
Maybe someone had the same issue and got it solved. Sadly my mech doesn't want to cooperate.

Actually:
- got new exhaust manifold gasket & got it planned (don't mind it - it repaired one rocket-whistle at cold start, but not this one)
- got ordered two check-valves (evap/brake booster) and will try it on


Circumstances when it happens:
- Accelerate more than 30% throttle
- It does not happen only in the turbo RPM's range, little hiss also happens when in neutral (First rec.)
- The best environment to hear is tunnel or driving next to metal barrier (Second rec.)
- You won't hear the hiss when standing opposite to the car's hood.
- Hiss comes from rear of the engine/exhaust. You have to lie down to hear the problem.
- When you release the throttle there is a sound like remaining pressure exits (any valve?)


First recording is at idle, cold start, when I can also hear the hiss.
Second recording is running at 3rd gear, near metal barrier.

1 - https://drive.google.com/file/d/1OGlPYnVKZceRDhQWtDFJDOBRldBvuHHv/view?usp=sharing
2 - https://drive.google.com/file/d/15wqpt3MENuimelqpaLt73B8Fs72Nct0S/view?usp=sharing
 

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Impossible to say from those clips, but since you don't mention any check-engine indication, we can assume it's not a gross air leak. That pretty much leaves the CBV valve, which can become torn in these cars. Do you have trouble building any boost?
 

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Discussion Starter · #3 · (Edited)
Impossible to say from those clips, but since you don't mention any check-engine indication, we can assume it's not a gross air leak. That pretty much leaves the CBV valve, which can become torn in these cars. Do you have trouble building any boost?
There are no codes related to such issues. Only software incompatibility and clutch position sensor faulty signal/signal too low.

If you mean accelerating - at the moment car is jerking a bit and sometimes stalls for a while, but as I mentioned somewhere, when I disconnect MAF car runs completely different and accelerates like new. I am going to check how will it run if I would change MAF to different new one. It doesn't cost me, will try in meantime anyway.

Also when I release the throttle strong jerk happens almost all of the time. It is sometimes as strong as when you ride on first gear and have fun with depressing and releasing the throttle. Seems like car does not release power delivery slowly, but drops to zero immediately and then the jerk happens. It happens when strong boost takes place.

What other symptoms would be for failing CBV?

Edit:
Look what I've found. One of guys post somewhere about CBV replacing.
If suspecting CBV for lost boost as I did in my case, I found the my problem was in one the vacuum check valves for the EVAP circuit rather than the CBV. Purge valve on the EVAP circuit draws vacuum from 2 possible sources : fresh air pipe just ahead of the turbo and manifold. There are a 1 way check valves for each vacuum source. Mine manifold one was broken (internal diaphragm broken when I cracked it open, actually repaired it with a bicycle tire patch kit). This means turbo inlet was draining the intake manifold pressure. It was kind of random depending on how the broken diaphragm behaved.

So in my case... I kind of had a giant "compression bypass" going on where intake manifold pressure was reduced by the turbo. Doing more or less what an open CBV does :) Anyhow, my CBV was good. You can hear the diaphragm open/close at 5psi vacuum (vacuum hose right at intake manifold, easy access
Do I match it well?

What I've also discovered brake booster buzzing some time ago - after cleaning CEM and connecting battery again.
https://www.youtube.com/watch?v=yIk_aePgzJI
Here is video showing how the brake booster buzzes. In my case it was the same sound, but it was only happening when I hit the brake pedal. Hit brake > one second noise > hit again > one second noise etc.. I noticed it is disappearing after first trip, but never before.
Over this weekend problem appeared again, but after trip again went over.

I found out it could be leak or maybe has to do with the check valves also? <green>
I was scared when I heard this first time and thought - oh my god, did something good to my car and other thing started working faulty.

One more - hisses when engine is hot seems to be not as loud as when the engine is cold. When we got engine really hot it was not as easy to notice as in a normal operating temperature. So it can be some metalic problem.
 

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You're on the right track. Let us know what you find.
 

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Discussion Starter · #5 ·
Fresh:
This evening I noticed that car runs worse than in latest days.
I had an idea to check OBDII for trouble codes and got new one - P0299 Turbo / Supercharger Underboost Condition (wow! - finally it has been thrown and appeared caused by those leaks?!)

As far as I read - it can be caused by TCV, hoses etc. So here is the question - is it related to mentioned leaks problem or is it another **** happening..

For now I am waiting for CBV - actually have two intake check valves, TCV and waiting for CBV. Will collect all of them and go check hoses for leaks + changing all those little valves. :(
 

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The generic "P" codes aren't particularly helpful for pinpointing issues to a part. You need the Volvo DTCs.

That said, an air leak will generally throw a check engine indication, due to the lost air. A CBV issue won't, because no air is being lost, just boost going round and round.
 

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Discussion Starter · #7 ·
https://imgur.com/a/QoKyBpu

I found that hose on PCV is loose and I can easily move it up and down. Picture of the valve above. Could there be any leak caused by this? The movement is limited, but kinda noticeable.. more than two mm's.
 

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That vent can be a problem on older cars, which have a earlier design. The valve can stick open and allow air to go both ways, which can sometimes cause this kind of thing. It's not a big deal that the pipe moves, that's normal.

It's not easy to replace, but maybe worth it. You need to disconnect the rubber line, then use a deep socket to remove the valve and that pipe together. Then, you need to remove the pipe from the valve, assemble it on the new part, and put it all back.

As a quick check, you might try clamping the rubber hose and listen if the sound changes. If not, well, keep looking.
 

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Discussion Starter · #9 ·
Problems with stuttering, stalling etc. were probably caused by MAF. I went into new one and everything works well.
Now have to care for whining. On Monday I'll go with new bracket to the hose I mentioned above. Is there such a pressure it can whine/whistle over there?
 

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Is there such a pressure it can whine/whistle over there?
It's possible. As I suggested, pinch off the hose and see if things change.
 

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Discussion Starter · #11 · (Edited)
1) PCV Hose - Tried this today.. spent like 2 hours hanging on the engine. Clamp used on hose is this one-time use type. Tried to put another flat screw driver type clamp, but without success. It's too strong to put it together after opening it (I tried doing this without destroying actual bracket and putting another without taking out the hose).

2) Check Valves - Can't take the hoses from intake check valves. They are sitting tight as hell. Any ideas? There are no clamps, hoses are firmly seated on the valves insets.
I think I'll have to let mechs do this job... no chance to try the ideas myself in those outside open air conditions.
 

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Discussion Starter · #12 ·
Guys, got question. Met today exhaust specialist to check my exhaust/cat area if there are no any leakings.

He told me everything is OK and once I told him that the rest was also triple checked (hoses, valves etc.) he got his concept that too much air could cause those hisses.

Is there any possibility that too much air (above some acceleration %) could cause such noises? There is a chance I've got ECM mapped (I've got CEM-3A00, which could point to modified software).
It could have sense, but is there any logical deduction for this case - is it physically posible?

IMHO It would cause power loss and feeling that there is not as good mixture combustion when accelerating. Wouldn't it?
 
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