1997 850 t5 boost issue

bigty69 · Post by **bigty69** » 28 Sep 2016, 19:27

I recently put a manual boost controller in my 1997 850 t5 wagon i have it set to 13-15 psi and it works awsome. I have encountered a problem though if you slightly ease into it. it accelerates just fine but if you out the pedal down and floor it it will go but it for a split second it falls right on its face and i lose boost and then it comes right back on. It doesnt hapoen when it shifts it shifts really smooth just wondering if anyone has had this problem or might know what the problem is.

Post by **kcodyjr** » 28 Sep 2016, 20:07

Funny, my 97 does that if I stab into the pedal too quickly. Goes like a raped ape if I ease into it.

I never did track it down, I just figured it was getting old.

Anyone have a theory? Something to do with sudden loss of manifold vacuum, maybe?

blkbeauty · Post by **blkbeauty** » 28 Sep 2016, 20:49

I have a 99 V70, had the same issue. I replaced the CBV, now back to normal from the start. A real PITA to replace on the car. The bottom bolt you have to access from the bottom of the car. I replaced all vacuum hoses to the turbo while doing that job.

bigty69 · Post by **bigty69** » 28 Sep 2016, 20:58

Im going to be deleting my cbv and installing a blow off in the short future regardless so i will see if it makes a difference. The only thing i can think of is when the boost comes on to hard it erratically opens for some unknown reason? Weak spring? diaphram? My cbv is healthy i believe it works good just not sure why it is causing this problem .

Bassse · Post by **Bassse** » 15 Oct 2016, 06:35

bigty69 wrote:Im going to be deleting my cbv and installing a blow off in the short future regardless so i will see if it makes a difference. The only thing i can think of is when the boost comes on to hard it erratically opens for some unknown reason? Weak spring? diaphram? My cbv is healthy i believe it works good just not sure why it is causing this problem .

What is CBV???? and PCV???

Post by **Ozark Lee** » 15 Oct 2016, 07:05

CBV is the Compressor Bypass Valve. Basically it limits the boost from the turbo by dumping air from the output of the turbo back to the input to the turbo if the pressure gets too high.

PCV is Positive Crankcase Ventilation. The PCV system provides an escape route for the pressure in the crankcase other than popping out an oil seal.

...Lee

Post by **mecheng** » 15 Oct 2016, 10:06

Why blow off valve, I believe it will throw codes because it will be looking for the boost. It keeps the turbo spooling well