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9-5 boost gauge tap (again) - help needed Posted by Peter [Email]  (#2804)  [Profile/Gallery]
(more from Peter) on Wed, 2 Oct 2002 08:03:35
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I installed a boost gauge in my '99 9-5 last month and thought all was well until my indy mechanic pointed out I'm not reading vacuum at idle. Here is what I've found, and can someone suggest the best line to use:
First tap: Source line runs from base of throttle body to a sensor at the top of the firewall. From the other side of this sensor, another line runs to the BPV. Added 'y' for the gauge on the intake side. Readings: 0 at idle to 12 psi at full boost (Abbott ECU). Mild accel = 5 psi. Moderate=8-10.
Second tap: Looking at engine from front, on right side of intake manifold is a vertical black fitting with 2 lines (it is in front of the line for the brake master cylinder): one goes to fuel bar, other goes a number of places out of sight. Tapped into fuel bar vac line. Readings: -18-20 in Hg at idle, as much as -25 in Hg while coasting (decel.). But mild-moderate accel only gets needle up to -10 to 0 in Hg. WOT under load will rise to 12 psi, but it doesn't stay there as it did in the first location. Rarely above 0 under normal driving. Seems wrong.
Third tap: Someone had mentioned the line to the BPV. Although it appears to be the same source as the first tap, but after a sensor, I tried it. At idle, 0. Accel some and let off gas, it spikes to -20 in Hg, but immediately returns to 0. I did not drive with this one, so don't know what kind of boost is recorded.
First appears to have a check valve that prevents vacuum.
Second seems to under-read boost, but shows great vacuum.
Third appears to limit vacuum to a burst to trigger BPV - didn't check boost readings here.
Ideas on best line to use - either these or another?
Anyone know where the Aero or later 9-5's take their source?
Also, unlike the earlier 2.3L, these do not appear to have an unused tap on the manifold - at least I couldn't find it.
posted by 57.68.12...
, Wed, 2 Oct 2002 08:03:35 <-- Viewing This Message, Wed, 2 Oct 2002 20:55:54
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