I have an ODB 1 supercharged 540I/6 (E34 1995 if that matters) that was hitting 10 PSI of boost relatively easy last summer. The car has been sitting for a while, and the boost was barely touching 5 PSI when I drove it last week. The vacuum gauge at idle was reading 22~ HG.
I took the post-inlet (supercharger) pipe out and found major leaks that called for complete replacement and audit of piping. While I pressure tested the new intake of the vehicle, I want to be extra careful and ask a couple of questions before going for a test drive.
The car now reads 18 HG at idle. To my understanding, a drop from 22 to 18 HG is significant, and I assumed that the adjustment indicated that the leaks were properly addressed. After reading some articles, I'm no longer sure if that's the case since a lot of material points to another direction.
- Does the fact that I have a Supercharger impact this in any way? Since the air no longer leaks out, would it do a better job of counterbalancing the manifold pressure?
- Would the decreased reading make sense if the DME and MAF were not fully reset to re-calibrate the MAP, etc.?
- Any other ideas or suggestions why HG would drop at idle if let's say the leaks were actually fixed 100%?
Edit: TLDR; if the supercharger is pushing air at idle (creating additional pressure) sans any leaks then in theory the vacuum would be better balanced with pressure – there before a drop in HG would be observed. That's my theory right now.
Thank you!
