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1997 850 t5 boost issue

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70

bigty69
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Year and Model: 1997 volvo 850 T5
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1997 850 t5 boost issue

Post by bigty69 » Wed Sep 28, 2016 7:27 pm

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.

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kcodyjr
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Year and Model: 1997 850 GLT
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Re: 1997 850 t5 boost issue

Post by kcodyjr » Wed Sep 28, 2016 8:07 pm

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?
1997 850 GLT sedan, 152K and WHOOHOO!
RIP 1996 850 wagon, 201K, hit by a runaway 4-wheeler
RIP 1996 850 GLT sedan 5spd, 260K, rearended someone
RIP 1986 245 boring, 200K, rusted beyond inspectability
RIP 1981 242 turbo 5spd, 300K, serious teenage crash

blkbeauty
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Re: 1997 850 t5 boost issue

Post by blkbeauty » Wed Sep 28, 2016 8:49 pm

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
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Re: 1997 850 t5 boost issue

Post by bigty69 » Wed Sep 28, 2016 8:58 pm

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
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Re: 1997 850 t5 boost issue

Post by Bassse » Sat Oct 15, 2016 6:35 am

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???

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Re: 1997 850 t5 boost issue

Post by Ozark Lee » Sat Oct 15, 2016 7:05 am

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
'94 850 N/A 5 speed
'96 Platinum Edition Turbo
Previous:
1999 V70XC - Nautic Blue - Totaled while parked.
1999 V70XC - RIP - Wrecked Parts Car.
1998 S70 T5
1996 850 N/A
1989 740 GLT
1986 740 GLT
1972 142 Grand Luxe

mecheng
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Re: 1997 850 t5 boost issue

Post by mecheng » Sat Oct 15, 2016 10:06 am

Why blow off valve, I believe it will throw codes because it will be looking for the boost. It keeps the turbo spooling well
1998 Volvo S70 T5 - SE - 240km - Sold July 2018
1997 Volvo 850 GLT - 190km
Boost is my drug of choice

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