Turbo pressure sender.

[balto8]

My turbo pressure gauge on the dash has been acting funny lately.

It's normal behaviour, at least what it did before, was to stay on 0 while being on idle, moving around the negative zone when acceletaring gently and then pushing up to a max of 0.5 bar when the turbo is on it's highest pressure.

Now it's on max negative pressure when idling, when I throtle gently its comes for a while to wander through the negative zone, and if I push the turbo it moves to the positive areas but somehow lower that it did before.

The car hasn't lost power. I't pushes as before. I've tried 3 diferent turbo gauges and they all act the same. Have tried following the tube that comes from the back of the pressure clock on it's way down and back of the glovebox ( LHD), then it reaches a T connection at the lower right side of the central console. From the T joint there'es one tube movin backwards to some control unit right behid the ashtray. Then there's another that goes front and dissapears into the engine bay, but I can't see where it ends. Is there any scheme with the path of this sender tube?

Feeling with the fingers I could sense some vacuum sucking from the modulator valve, part 3435269 n 9 on the scheme. DOn't know if that's normal, all tubes were ok.




Anyone with an idea of what i'm looking to?

[jamescarruthers]

http://www.volvo-480-europe.org/forum/v ... dle#p26187

According to the above, Negative pressure at idle is normal

[balto8]

" Watch the needle of the turbo-pressure gauge:
-engine off: 0 bar (between white and orange)
-start engine: needle drops to -1 bar
-engine idle: -1 bar
-when driving slowly at constant speed: needle in white area between -1 and 0 bar
-when you touch the accelerator, the needle has to react inmediatly (by going up)
-when you floor the accelarator the needle will (in a few seconds) climb up to half way the orange area (if chip tuned up till the end of the orange area). You should feel the difference in acceleration with your 480es, some even feel the difference between RON95 and RON98 petrol. "


It did not behave like this before. Do all versions of turbos do the same. Mine is a june 1991..... So either something's has gone wrong now of it has been self-fixed?

I'll continue to look into this.

Anyone with a modulator valve, (part 3435269 n 9 on the scheme) for sale?

Best.

[Robou]

There is no sender or the like. The tube with the T joint goes to the gauge and the ECU and comes from the inlet manifold.
The turbo actuator valve has it's own connection.
Check the tube on leaks. But somehow a leak would also have it's influence on performance of the car, as the ECU doesn't get the right information about the boost. And you claim it's like before.

[balto8]

That's precious information.

So is it this rigid tube that departs from the upper left side of the inlet manifold (looking from the front of the car)?

[balto8]

I am quite sure that the regulator valve of the turbo has some kind of leak as I'm sensing this slight vacuum on my fingers when I put the on the back of the sensor plus a slight "shhhh" coming from it.

Have found a later valve (3460502) from chasis 567600 wich is in apareance equal to my older valve model (3435269) , up to 567599 chasis number. Th only external difference seems to be that T joint at the lower tube, absent in mine.

Should I give it a try or is it a "don't even try" situation here. Could I cause any damage to the turbo system?

[Robou]

It seems you haven't a problem with the turbo gauge at all, your regulator valve needs to be replaced. I do not understand what you mean by placing your finger on the back of a sensor, but if it is the same as the regulator, it should be absolutely leak free.
I am not aware of any different types, they may have changed the part number for the same device, but I'm quite sure they are interchangeable.
And the T joint I refered to is in the pipe to the gauge and the ECU, which runs from the inlet manifold under the right fender to the inside.
The nice collection of T joints in the picture probably comes from a diy project. Here the regulator is connected to the air inlet of the turbocharger, I wouldn't know of any reason to share this information with any device.
I'm quite sure your statement the car was running as before was incorrect.

[balto8]

Thanks for clearing this.

What I meant ( sorry for my poor explanation) is that putting my finger on the back of the valve I could feel some sucking on my finger. I wasn't sure if the valve should be completely airtight.

And I agree on your explanation point by point that the car was delvering a little less that originally, but sometimes it's hard to tell if you've lost some torque. Just wasn't sure.

So I will replace and come back with results.