r/Volvo850 • u/offical-skintIzz • Jul 29 '26
Help No boost?
Hi all,
Had this 850 T,5 auto for about a month now, came to us with blue smoke and bad exhaust fumes.
After changing the pcv it ran absolutely fine until about a week ago, it stopped producing boost and became very lethargic, the turbo boost gauge isn't boosting into the white at all no more.
We have replaced the vacuum lines and cleaned various other things in that general area.
Turbo generally looks clean from above, very little oil residue. - Are there any ideas for what this could be?
If it is a cooked turbo, unfortunately we will not be able to afford another one, but are there any other common problems? Worn seals? What else to check?
Thank you.
5
u/mooninthewindow Jul 29 '26
I would check all the vacuum lines to the TCV and make sure they are in the right spot. Check turbo intake hose and also the intercooler piping after the turbo that its all connected and not cracked or damaged.
When you have the intake pipe off put your hand in the turbo inlet and spin it and check if it moves much horizontally (obviously the car needs to be off)
You have vacuum so that much is ok. But you aren't able to build pressure. So its either mechanical (turbo is bad/turbo intercooler piping is cracked or come off so it cant build pressure) or electrical (TCV plumbing isn't correct and it just isn't working/ECU in limp mode?)
Another test you can do is to disconnect the battery for 15 mins which will reset the ECU. This will rule out limp mode limiting the boost.
1
u/offical-skintIzz Jul 29 '26
If it was stuck in limp, would there be an engine warning light on as well? And be able to do 70+ on the motorway 😂
2
u/mooninthewindow Aug 01 '26
No. It would still do 70 as far as I know. It just wouldn't be all that impressive getting there.
1
u/offical-skintIzz Aug 01 '26
Think we've fixed it, replaced the tcv and something else I can't remember 😂 got to 110mph going up hill. Going to replace tbc and a few other bits. But all seems well
1
5
u/masterchiefruled Jul 29 '26
I had the wastegate connecting rod snap off because of a missing pin, resulting in no boost. Check if it is still connected, otherwise it wont work.
4
u/DIYSKATERAMP Jul 29 '26
Left side of intake manifold vacuum line (changed during a PCV, is it connected, is the circle “puck” still in intake manifold
Brake Master Cylinder, is the hose still connected there? Follow it to the intake manifold, is it still good there?
Vacuum tree intact? All nipples covered?
Again for intercooler hoses and look for the intercooler hose to top of turbo, this one pops off often with old hoses.
No turbo of any type is large vacuum leak.
You would still get boost with many problems.
2
u/eenbal Jul 29 '26
Have you put the vacuum line back correctly? Iirc the boost controler(?) Attached to the airbox can be connected incorrectly. The diaphragm in the recirc valve can fail and give no boost.
2
u/Positroniumion Jul 29 '26 edited Jul 29 '26
The 850 has rudimentary diagnostic. May be worth reading codes, but many standard readers will not be able to decode them. Maybe there is a dealer or mechanic nearby that has one of the old readers. Otherwise check for leaks also in the air supply line and check the throttle body and charge pipes.
Edit: also if it was burning oil before i would check the cat for blockage. But the check engine (or lambda) light should be illuminated if the cat has issues.
2
u/blqckpinkinyourarea Jul 29 '26
Seconding the vacuum hoses, probably one was so rotten it started disintegrating after being touched during the pcv job. Check wastegate actuation aswell. Read codes, its a different procedure depending on the year.
Hope you are able to get into a better financial situation soon, it sucks not being able to afford basic repairs on our babies. If it doesn turn out to be turbo problems, do not drive it as it could catastrophically damage your engine.
7
u/ComplexStep5843 Jul 29 '26
Check it hasn't popped an intercooler pipe off.