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Boost pressure too low

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1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
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Matt88ch
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Boost pressure too low

Post by Matt88ch » Wed Feb 15, 2017 6:56 am

I have a 2000 S70 glt se lpt, i have the Bluetooth obd adapter and torque pro app. When I have the vacuum/boost gauge the highest boost I've reached is 3.6 I read stock psi for the stock lpt should be 6-7 psi...I'm thinking vacuum lines must be old and brittle or maybe have a hole? Any ideas or recommendations are appreciated. Thanks guys.

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Re: Boost pressure too low

Post by erikv11 » Wed Feb 15, 2017 8:19 am

The torque app is just calculating the boost, it's not actually reading it. The word on the street is those calculated numbers are not very reliable. But if none of the narrow rubber vacuum lines have been replaced in 17 years, I would swap out every one of them. It's cheap and not too much hassle, pick away at it over one or two weekends. The boost will probably improve if you do.

Another thing to watch for is a hole in the CBV diaphragm, again very common for a 17 year old rubber part that constantly flexes back and forth. But you would usually notice that while driving - I would start with replacing the lines.
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rspi
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Re: Boost pressure too low

Post by rspi » Wed Feb 15, 2017 2:43 pm

You really need to install a boost gauge to see what the real pressure is.
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Matt88ch
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Re: Boost pressure too low

Post by Matt88ch » Wed Feb 15, 2017 5:44 pm

Yeah I'm planning on getting one this weekend....I have no check engine light so I know it's not a big problem, I was just curious on what the psi was and when I saw 3.6 it got me thinking about the vacuum lines...Although I did replace some but not all. I'll try to do the rest this weekend and post up my psi after I get a real boost gauge. I always thought that the OBD2 port w the adapter would give me a accurate reading, but I guess nothing beats a good old boost gauge tapped into the vacuum lines. Thanks guys

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Re: Boost pressure too low

Post by abscate » Thu Feb 16, 2017 2:46 am

Your 2000 has an actual manifold pressure sensor that ypu can access by obd, I don't know if your software supports it though.

The turbo control valves (TCV) also get tired with age..it's a fairly fast duty cycle solenoid (100Hz?) so it is harder to diagnose without fancy stuff. I started seeing BMWs in my rear view after I replaced mine at 140k
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Matt88ch
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Year and Model: 2000 S70 glt se
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Re: Boost pressure too low

Post by Matt88ch » Thu Feb 16, 2017 6:43 pm

abscate wrote:Your 2000 has an actual manifold pressure sensor that ypu can access by obd, I don't know if your software supports it though.

The turbo control valves (TCV) also get tired with age..it's a fairly fast duty cycle solenoid (100Hz?) so it is harder to diagnose without fancy stuff. I started seeing BMWs in my rear view after I replaced mine at 140k
Is to possible to test the tcv...I have a spare one from my parts car maybe I'll swap it and see if it makes a difference, thanks bud

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Re: Boost pressure too low

Post by abscate » Fri Feb 17, 2017 10:09 am

You need some pretty good equipment to test a TCV - usually you replace on age (10 years/100k miles)

The coil resistance test doesn't tell you much, spec is 29.7 Ohms with no error bars given.
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