1994 Volvo 850 Turbo - Loss of Boost

Lost240 · Post by **Lost240** » 22 Jun 2015, 12:10

Hi,
I am in the middle of restoring the family 1994 855 Turbo with 170K miles on it. We have owned this car since 1998 and it has always been maintained and has run well, but I want to give it a bit of an overhaul so it lasts another 170K.

Recently I have had the timing belt, water pump, oil cooler lines, knock sensors, rear calipers and brakes, front brakes, shocks and struts, and brake master cylinder all replaced. I also replaced the old ipd rear sway (rusted off) with a new one. The car rides better than it has in years, but could still be improved a bit.

I have noticed that the turbo does not boost the way it used to. On the gauge in the dash the needle only goes about halfway into the white at full boost. There is also a whooshing sound like I have an aftermarket intake installed, but that is not the case. Where could I be losing the boost from? What should I check for/replace?

Also, what else should I look at replacing to keep this on the road for another 100K? It is due for a tune up (plugs,wires, cap, etc..) and I know that will help as well.
I am already in deeper than I thought I would be but I have come this far so there is no turning back.

Sommerfeldt · Post by **Sommerfeldt** » 22 Jun 2015, 13:13

If you're hearing the turbo like you have an aftermarket intake w/o the airbox... check your intake right away. If the hose is broken or the airbox is leaking somehow, you're pulling either raw (unfiltered, dirty) air in, and perhaps unmetered as well. Those are both very bad, bad things.

That said, check intercooler for leaks and all intercooler hoses as well. The lower rubber hose from the intercooler gets particularly spongy if there's been a little oil and gunk spillage. I've put silicone hoses on all of the Volvos I've had - Samco makes a great set, though a little pricey. A leak in one of these hoses will also possibly account for your loss of boost.

- S

Post by **Ozark Lee** » 22 Jun 2015, 14:01

It is also at the age where everything rubber tends to rot. Check all of the vacuum lines from the turbo and the turbo control valve as well as the compressor bypass valve. To test the CBV draw a small vacuum on it and see if it holds. On your '94 the turbo control valve I think is the round one and it is mounted on the intake airbox more or less under the MAF sensor.

...Lee

Sommerfeldt · Post by **Sommerfeldt** » 22 Jun 2015, 18:09

Ozark is right - check all the vacuum hoses as well. Or just change them to silicone - age is not rubber's friend.
Even though the smaller vacuum hoses wouldn't account for the loud whoosing, they can definitely whistle and hiss, and cause the boost loss - I'm trying to chase down a whistling noise these days, but the only whoosing sound is my open air filter...

- S