Last Update: March 2, 2003
The boost gauge I want is on back order, so episode II is going to get completed in two parts. The two gauges I ordered are both from Auto Meter although I'm buying through Summit Racing. Specifically I bought two from the Cobalt series:
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Air Fuel Ratio |
Boost 30 in Hg.-Vac/30 PSI |
Mostly the gauging is going in to protect the engine and to help diagnose an intermittent rich mixture warning being issued by the computer every 50-100 miles or so. I suspect it's a boost artifact, but the gauges should help see when it happens at least.
Once again, the stock instrument cluster is documented in the images below before I start on changes. The v6 stock gauge cluster is dark faced with a 120 mph speedometer. Blue/green legends with red indicators.
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Part 1 - Fuel/Air Gauge
The first step is to take off the stock instrument bezel so I can run the necessary wiring down behind the dash to tap into the oxygen sensors in the EEC-V wire harness. Taps are also added to the dimmed dash light, chassis ground, and 12 volt power lines.
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After getting tapped into all of the harnesses on the car, I pinned an inexpensive molex style connector so I can remove the bezel in the future without doing anything drastic. Also while I was in the dash I added wiring for the boost gauge so I don't have to tear everything apart again when it arrives. You can see those provisions taped up in the coil in the first picture below. The fuel/air gauge itself gets press fit into a replacement bezel along with a toggle switch I'm adding so I can see the mixture readings from both exhaust manifolds.
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All this being done, I'm out of things to do until the boost gauge arrives. The half finished installation can be seen below.
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Part 2 - Boost Gauge
Installation of the boost gauge requires a little fabrication. There simply isn't anywhere to mount the vacuum/boost sensor unit under the hood without fabricating a bracket to keep it correctly oriented. After surveying the engine compartment for a suitable location, I decided to fix two problems at one time. The stock mounting bracket for the EGR vacuum switch and exhaust pressure sensors is far too close to the supercharger for comfort. Therefore the stock bracket is going to get reworked to fix the clearance problem and to accomodate the new vacuum/boost sensor as well.
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In addition to fabricating the new support bracket from aluminum, I stripped and repainted the stock bracket after drilling new mounting holes for the EGR vacuum switch and relocating the basic mounting pattern to the drivers side by about 3/4 of an inch. The finished parts, with a fresh coat of black paint, can be seen in the last photo above.
Now that there is a place to support the sensor, I tapped into the intake manifold vacuum line near the fire wall on the passenger side. This section of hose is sporting a hell of a lot of tees at this point, but it was the most exposed line (below left). The wire harness for the sensor which runs to the instrument panel is routed around and over the engine block with other wires and vacuum lines to a grommet in the firewall (below center). Some thoughtful Ford engineer left a nice plug here so I didn't have to get out my drill. A razor blade did a fine job of making a solid grommet suitable for passing wires (below right).
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Now, after finishing under the hood, the instrument panel needs to be pulled apart again. The boost gauge requires one electrical connection I hadn't planned for. The 12v power must be an "Always On" connection. Most 12v lines in the car are turned off during start to provide maximum voltage when cranking. However, the Autometer instructions warn that the gauge will miscalibrate if it's power is interrupted during start. So much for planning ahead. I eventually located an "Always On" connection in the harness for the main gauge cluster. This was a bit of a challenge since my diagram for the car didn't match the wire color coding actually in the dash. Some subtle changes were made in the '99 production break and my diagrams are based on the disassembly of a '95 mustang. Regardless, after some head scratching and a little time with a meter I found the wire I was looking for.
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Routing the wires around behind the bezel is a snap and that was that. The finished installation appears below.
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The boost gauge has blessed me with the knowledge that the engine still spends most of it's time in a vacuum. The supercharger doesn't drive it into positive pressure until after the bypass valve closes around 2000 RPM and boost climbs exponentially from there up to 9+ psi.
Since I'm a bit of a fanatic for numbers, I took my digital camera out for a ride and took some quicktime movies of the instrument cluster during a few wide open runs. Going back frame by frame it was easy to plot boost pressure against RPM and then fit a curve to the points. The resulting curve is below and gives a nice accurate way to find boost pressure at any given RPM on the current setup (Vortech Kit, Stock MAF, Stock Fuel System, Vortech Chip).
