Volvo 850 strange boost problem

Post by **Clemens** » 17 Jul 2019, 15:44

the tps is quite cheap and easy to replace.

Jaumme · Post by **Jaumme** » 17 Jul 2019, 16:35

i cleaned the tps and the values are ok now they increase as you accelerate bettwen pin in the middle and the one on the side, but the boost issue is still present, nobody solved something like that?

Post by **erikv11** » 17 Jul 2019, 20:03

I once ruined a TPS because carb cleaner got inside of it when I was cleaning the throttle body. Not sure how/why but that ruined it.

Have you ever inspected the CBV diaphragm for cracks or tears? Most of them have a hole or two by now if they were never replaced. One way is to pull the CBV diaphragm and hold it up to the light to check, kind of a hassle.

Post by **Clemens** » 18 Jul 2019, 00:22

I can tell you what I did and it all didn't help:
- cleaned pcv
- new spark plugs
- new wires
- new cap
- new rotor
- swapped ignition coil from my superbly running 850R
- swapped tps from the R
- reset the pressure for the wastgate
- checked all hoses, replaced a broken boost pipe

what i have yet to do is to put in a new boost controller.

Post by **erikv11** » 18 Jul 2019, 00:50

Clemens wrote: 18 Jul 2019, 00:22 I can tell you what I did and it all didn't help:
- cleaned pcv
- new spark plugs
- new wires
- new cap
- new rotor
- swapped ignition coil from my superbly running 850R
- swapped tps from the R
- reset the pressure for the wastgate
- checked all hoses, replaced a broken boost pipe

what i have yet to do is to put in a new boost controller.

So the CBV is 23+ years old???!!! I replace it on every p80 turbo car. Well I inspect it, but that has always led to replacing it.

Jaumme · Post by **Jaumme** » 20 Jul 2019, 07:26

My cbv is holding vacuum perfectly I didn't pull it to inspect but it seems ok.
Today I adjusted the wastegate to spec and I got a faster spool but now the boost is unstable between 3k and 4k rpm it's bouncing back and forth between half white lane a 3/4 during that range. Should I pull the cbv to inspect it visually?

Post by **hausmeister** » 20 Jul 2019, 10:07

From the video it seems to happen when you get into boost... maybe simple overboost (boost control valve to slow to correct)?
Might also be an issue with the hoses or wastegate tension. if it is overboost you should feel the car surge (a bit)... if not it is something else.

You would do good to install an aftermarket boost gauge, if it is just for troubleshooting. It is a great help for this sort of issues. The volvo gauge is very sluggish and you can't really read it without uints, for troubleshooting I found it useless.

If the bcv/tcv is very old I'd replae it with a new one. the newer volvo parts work fine as well if you are willing to adjust the mounting etc.

Post by **erikv11** » 20 Jul 2019, 10:25

Jaumme wrote: 20 Jul 2019, 07:26 My cbv is holding vacuum perfectly I didn't pull it to inspect but it seems ok.
Today I adjusted the wastegate to spec and I got a faster spool but now the boost is unstable between 3k and 4k rpm it's bouncing back and forth between half white lane a 3/4 during that range. Should I pull the cbv to inspect it visually?

It's a tough call, if it holds vacuum well then it should be good still, I agree with that, but the symptoms ("boost flutter") do fit with a torn CBV. By looking at it you can rule out cracks in the folds but if you have other troubleshooting ideas maybe those should be higher priority.

Jaumme · Post by **Jaumme** » 26 Jul 2019, 19:20

Today I replaced the tcv, I installed a newer model (pierburg), the boost is no more spiking it keeps stable but I still see It a bit lowish, tomorrow will install a boost gauge and see how much it's really boosting.
How much psi should a t5 boost in normal conditions?

Post by **matthew1** » 27 Jul 2019, 18:29

11-12psi