Proper Boost Measurements

Here's the interesting part…SOMETIMES for some reason I only get 8psi of boost, other times 11psi. During shift the boost spikes to 15-17psi.

Boost

What are the proper boost measurements for your volvo?

Proper boost measurements for your volvo:

  • Warm Idle: 18 inches of mercury vacuum
  • Cold Idle: 16 inches of mercury vacuum
  • WOT (Wide Open Throttle) 2,000 RPM: ~5 PSI boost
  • WOT 3,000 RPM: ~15 PSI boost
  • 75mph @ 3,000 RMP: ~10 inches of mercury vacuum
  • Between Shifts: 0 (atmospheric) due to the bypass vale venting manifold pressure to keep the turbo spooled

MVS Forum Member nobbie_nz asks:

Hi guys, all the way from New Zealand 🙂 Have just hooked up a temporary boost gauge on my new 950R 1996 AUTO and I have made some interesting findings.

After hooking up an Autometer boost gauge my vacuum at idle is around 15-17, during deceleration (no throttle) i get 20. Do you guys still think I have a vacuum leak? or do these numbers sound normal?

Now heres the interesting part…SOMETIMES for some reason I only get 8psi of boost, then other times I get 11psi??? During the shift from one gear to another the boost spikes to around 15-17psi (auto box) – please note this is BETWEEN shifts when the boost spikes.

The other thing that happened was that in 2nd gear at wide open throttle boost is at 11psi and then when the car changes to third the boost drops to only 8psi and feels quite sluggish.

Any ideas on what might be the problem here….I did some research on the site and read a little about wastegates?? but not sure if the wastegate would be the problem??

feedback and thoughts really appreciated 🙂

Cheers
Rob

MVS Forum Member MadeInJapan replied:

Everything sounds fairly normal unless your ECU has been chipped. Other than that, I hope you meant 850 and not 950.

MVS Forum Member nobbie_nz added:

Right, i think im a little thick lol…having never owned a turbo car…something just dawned on me.

If the car downshifts to a lower RPM then the boost will start lower and then rise. IF the car downshifts to higher RPMs then the boost will be higher.

So…when changing from 3rd to 4th (auto) I would assume its normal for the boost to drop from 11psi to 6psi when it goes from high revs 3rd to lower revs 4th. The boost would then rise with the revs as the car gets faster.

Have I just solved my weird problem? or is this not normal 😉

Proper Boost Measurements

3 Replies to “Proper Boost Measurements”

  1. Just replace the mass airflow sensor in my car. Hand to unplug it to drive. When I re-connected it the car cut off. Been to auto repair shops nobdy is getting it. can you help me.

    1. I had the same Issue on my 98 v70, I drove around with maf unplugged, I bought a new one and it would start then die and would not run, I started looking around for air leaks and sure enough there was one of the tubes off and I recconnected it and car started up and ran wierd for a minute. I shut it off disconnected battery and reset the computer by taking possative and negative cable and connecting then together off the battery for 30 minutes , then reconnected to battery started it up car did idle funy for a minute then after idling for 2 or three minutes I took a 30 minute drive and its ran great. Its been about two months now and all is good.

  2. Try and disconnect the + and – battery cables then clamp them togheter ie no juice to the car with a clamp or vise grip (not to hard) for 10-20 min and reconect. this will often work to reset many control modules ,done it on door, brake,interior ect modules. theh reconnect battery cablel adn restart car. the car can relearn the new part. Volvo want’s to sell yuo a software program, which you might need if this does not work. check other forums I just saw this old post so good luck.

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