1995 Ford Mustang GT Tune Up - High Maintenance Project Redheaded Step Child Part 2

Last month in Part 1 of Project RSC, we treated our '96 Mustang GT just like a red-headed stepchild, yanking it fresh from the orphanage and plunking it on the dyno without care or concern for its well being. The proverbial competitive father, we expected our child to rush out and hit home runs, score touchdowns, and win races, all without so much as a decent warm-up. Hardly the makings of a good parent!

I have to take the blame for this one. Being in an all-fired-out hurry to demonstrate the worth of the neglected mod motor, I forgot that this car has delivered some 200,000 miles of faithful service. It's all I can do to stop from turning myself into child services. But as adults we learn from our mistakes, so we take a step backward in part here by providing RSC with some much needed TLC in the form of maintenance items. In fact, some components even cross the line between maintenance and high performance (we here at MM&FF always plan ahead).

While the 4.6 Two-Valve was performing admirably, we decided to give the motor a quick once over. First up was a compression check. We also took a look at the color and condition of the oil, but since it was due for a change, we opted to step up to a synthetic blend (our boy deserved nothing but the best).

The compression check was performed by removing all the spark plugs (something already on the to-change list) and inserting the compression tube down in the plug hole. We also took the liberty of disconnecting the injectors to eliminate fuel flow to the cylinder during cranking. With the throttle held open, we cranked over the motor using the starter eight or nine times in a row. The compression gauge was used to determine how well the cylinders were sealing (though a leakdown is more accurate).

Since a number of factors contribute to actual reading (static compression, cam timing, and ring/valve seal), what you are looking for is consistent readings from all cylinders. It is not uncommon for all the cylinders in the right bank to produce one number and all the cylinders in the left bank to produce another. This is an indication that the cam timing is off side to side. Our compression test revealed the motor was still plenty peppy (but by no means excessively powerful), with readings of 125 psi per cylinder.

With a seemingly healthy candidate (we expected as much given the dyno numbers from last issue), we turned our attention to the fuel system. Because of the excessive mileage, we decided to check the injectors for leakage and/or clogs. In most cases, injector problems are caused not by excessive use but rather by lack of use. Injectors sitting idle (filled with fuel) for extended periods allow deposits to form. These deposits can clog, alter the spray pattern or stop the pintle from sealing, causing the injector to leak when fully closed.

The injectors were removed along with the fuel rail for installation onto the ASNU injector cleaning/flow test machine. The first order of business was to test the injectors for leaks, which was a simple matter of hooking up the injectors and applying pressure. The injectors all checked out perfectly. Next, we flow tested all eight injectors to both verify the flow rates and measure the flow balance between them. Ideally, all the injectors flow exactly the rated amount (19 lb/hr). Excessive or insufficient flow from one injector can play havoc on the air/fuel, as the computer will adjust by leaning out or richening up the mixture. Having seven cylinders suffer for the misgivings of one is obviously not good for performance. Thankfully, all the injectors from RSC received a clean bill of health.

Before reinstalling the stock injectors, we took the liberty of replacing the factory (non-adjustable) fuel-pressure regulator with an adjustable unit from Accufab. While proper tuning is best accomplished via the programming (a custom chip), the adjustable fuel-pressure regulator may come in handy if we are testing a component(s) and do not have access to programming. Of course, the Accufab adjustable fuel-pressure regulator will only allow us to make global changes in the air/fuel mixture, as we can't change the air/fuel at predetermined rpm points, only a broad change throughout the rpm range. Still, it is nice to have the ability to richen up the mixture even if only temporarily until we can employ the SCT tuning software. For now, the fuel pressure was set at the factory pressure reading of 43 psi.