924Board.org

[klec]

Hi!

After reconnecting the boost gauge (VDO), I noticed that it shows quite strange readings. Earlier gauge at idle and quiet driving fluctuated around -0.5 bar to -0.6 bar (~7-8psi). Now readings on the gauge looks like this:
1 ) After start and "in-place" such as standing at a traffic lights, approximately: -0.6 bar (IMO ok)
2 ) Under a load, at the second gear (fast driving): from 0.2 bar up ( ok)
3) Safely adding gas: from -0.6 bar to 0.1 bar.
4 ) After releasing the pedal: -0.9 bar !
5 ) During a quiet drive: from -0.6 bar to -0.9 bar !
6) Adding some power in a hot car (at ease, idle): -0.6 bar to -0.9 bar !

In the case of driving in the city rarely when I press the gas so that the gauge showed something more than... 0 bar. Earlier it shows readings like: 0 to 0.5 bar.

So I have a high vacuum (almost 1 bar, which is ~14 psi), earlier the boots gauge does not come down more than -0.6 bar (except for releasing pedal during rough driving).

I think something is wrong:
1) with a boots gauge, or
2) turbocharger / wastegate?

I hasten to explain that the car accelerates as before, i.e. from ~3500 rpm objects in the mirrors are losing.

Thanks for your help!

Regards!
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931, 1979, Diamantsilber metallic

[morghen]

I also get -0.5 to -0.6 bar at idle with a warm engine.
With a cold engine (first 60 seconds) i get -0.4 and -0.5bar.

Under load the boost goes over 0 bar around 2000 RPM
If i let it rev to say 3500 RPM under load(fast driving or normal driving) and then release the pedal, the readings will be -0.7 to -0.9 bar depending on how fast i was going.

During a quiet drive as you say, i dont get boost either.

With the car standing if i rev the engine more than 2500-3000 RPM the readings will be 0 bar, and then when i release the pedal the boost will drop to -0.7 to -0.9 bar for a short while and then it goes back to -0.6 bar.

From what you say, the car behaves in the right way, maybe it does not produce so much boost...for that you need to drive in 4th gear on an open road at 1500 RPM....floor it and when you reach 2000RPM you should already have 0bar to 0.2bar....when you reach 3500-3800RPM you should have max boost (0.7bar on a stock 924)
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Supercharger and EFI kits
https://www.the924.com

[klec]

[morghen]

So if you rev it up on the road, boost goes to 0.7bar and then release the pedal while in gear, its normal to have -0.9 until you press the clutch pedal or you stop. But after the engine reaches idle it should go back to -0.6bar
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Supercharger and EFI kits
https://www.the924.com

[9xx]

Similar experiences with you guys. I have the VDO bar gauge also.
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Mikko

All gone: 931 '82 Alpine White, original option "220" G31 with LSD + 3 x 944

[klec]

So it is verified - those are valid boots readings for 931.
Thanks!
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931, 1979, Diamantsilber metallic