Project Paw-Paw: Part 9

January 17, 2020
Story By
Mike McGlothlin

Big fuel, high oil volume, a sizeable turbo and a built transmission means nothing on a 7.3L Power Stroke if you can’t get everything to work in harmony. Like a custom-tailored suit, the perfect PCM calibration has to be built around each individual modification for a cohesive overall package. This specialized tuning is mandatory in order to: 1) get maximum performance out of all the power adders, 2) make the truck drivable given the extent of its mods and 3) keep the engine as safe as possible. Turning to one of the most reputable names in the industry, we enlisted Gearhead Sales for Paw-Paw’s tuning needs. For more than a decade, Gearhead’s calibrations have produced some of the most powerful, cleanest-burning and longest-lasting 7.3L’s in the diesel world.

Using the Hydra Chip platform from Power Hungry Performance, we’ll be able to navigate a host of custom-tailored Gearhead calibrations on-the-fly. With most of the PCM calibrating revolving around control and optimization of the HEUI fuel injection system, Gearhead built us seven custom-tailored tunes. Among them are two files designed specifically for towing, one for daily driving, a high-idle setting for quicker winter warm-ups, stealth mode for ordering at the drive-through and two performance calibrations. The latter files are the hottest in our arsenal and are fittingly referred to as “All Out.” They will be the tunes that get us the numbers we want on the dyno. For a glimpse inside the 7.3L tuning world and a deeper understanding of words like timing, pulse width and ICP, keep reading.

We’re just about ready to turn Paw-Paw loose. After we add a few peace-of-mind mods in Part 10, we’ll be loading up and heading to the dyno—followed by a trip to the drag strip.

The Hydra Chip

By far the most popular tuning platform used on ’94.5-’03 Fords, the Hydra Chip revolutionized 7.3L Power Stroke tuning when it was released back in 2012. It’s manufactured by Power Hungry Performance, but can be programmed with calibrations from any custom tuner in the aftermarket, so long as the files are produced using PHP’s Minotaur software. As we mentioned, our custom tuner of choice will be Gearhead Sales, a name we wholeheartedly trust in keeping the rods inside the block and the truck 100-percent drivable. Our favorite feature on the Hydra Chip is that once everything shown above has been installed, there will no longer be a need to pull the chip for calibration changes. Thanks to the optional USB extension cable (an additional $25) pictured on the far right, tunes can be added or removed using our own lap top.

Hydra Chip Price (w/optional USB extension cable): $434

Pulling the PCM

First and foremost, before you ever locate a 7.3L’s powertrain control module (PCM), make sure the truck’s keys are in your pocket. Leaving the key in the ignition during the chip installation process will fry the PCM. A lot of installers even take the extra step of disconnecting the batteries before getting started. The module nearest the driver side fender along the firewall is where you’ll find the PCM on all ‘94.5-’97 Fords. The center bolt for the wiring block and the two PCM grommet bolts call for a 10mm socket. In the truck, the emergency brake panel has to be removed (or at least loosened) to feed th e chip’s power cable into the cab (a 13mm socket is required there).

Required Work Performed On The PCM

The Hydra Chip itself piggybacks onto the PCM’s circuit board via the J3 data port, which means that nothing is done in the way of tuning by downloading through the OBD-II port. The chip, once attached to the PCM, essentially takes over. However, the chip can’t be connected until you remove the layer of silicone present on the circuit board’s edge from the factory, (hence the inclusion of the wire brush with the Hydra Chip). It was our preference to pull the PCM’s cover panel off in order to both clean the circuit board and to install the optional USB extension cable (again, so we can retune the chip without having to pull it). Also notice the four-digit code on the wire block connection point on the PCM. That’s the PCM code. It has to be given to your tuner in order to get your chip programmed correctly.

USB Extension Cable

With the chip attached, the J3 data port taped up to prevent moisture from getting in and the PCM reinstalled, the ribbon cable and USB cable were routed into the cab. The USB extension cable can be mounted anywhere you want, but we just left it zip-tied up and under the dash for the time being. While most reputable custom tuners will compose tunes that get you close to your horsepower and drivability goals right out of the gate, a few tweaks are practically inevitable if you’ve changed as many variables as we have throughout the course of an extensive build. Needless to say, we’ll likely be putting the extension cable to good use in the coming weeks.

Digital Display

After pulling the upper and lower dash panels, we were able to snake the Hydra Chip’s ribbon cable between the two and used the supplied Velcro to mount the digital display where we wanted it next to the steering column. The ribbon cable simply plugs into the bottom of the display. The display uses simple up and down buttons to navigate tuning files.

Hydra Flash

To communicate with the Hydra Chip, Power Hungry Performance’s Hydra Flash was downloaded to our trusty shop lap top. Hydra Flash is free to download, but is only compatible with Windows-based computers (sorry Mac fans). You may have noticed the Hydra Tuning Files folder below the Hydra Flash icon. That’s simply the result of our preference to download emailed tunes into a separate folder and then upload them onto the Hydra from there.

Injector Flow and How It Relates to Tuning

In the Excel document above, the injector flow data provided for a set of 400cc hybrid injectors equipped with 200-percent over nozzles (400/200’s) is shown. To be sure, our injectors are 350/200’s, but either injector is similar in terms of flow and operation, as are the key parameters required to get maximum performance out of them. If you look closely you can see that with the PCM commanding 3.0 milliseconds (m/s) of pulse width (also known as duration or injector on-time), the injectors flow more than 300 cc’s, so long as sufficient high-pressure oil can be maintained (3,000 psi). In our application, in which we believe the SRP1.1 is on the edge of the injector size it can support, Gearhead has drawn the line at 3.0 milliseconds of pulse width in our "All-Out" tunes. Though the full potential of the 350/200 hybrids won’t be realized, this limitation in tuning will work in our favor in helping to keep the stock bottom end alive with all the added power.

All Out Files: Unleashing the Hybrids

While your tuner may refrain from sharing trade secret tuning details, Gearhead was up front about the All Out files that were built for our application. For example, on tune number 6, 3.0 milliseconds of pulse width and a fairly conservative 14 degrees of peak timing is being commanded. However, that 14 degrees of injection timing advance isn’t available until 3,200 rpm. Limited timing at low rpm and a progressive ramp up in its advance keeps cylinder pressure from sky-rocketing (i.e. bent rods and other possible collateral damage resulting from too much torque). The small trade-off in low-end torque will more than be made up for with a solid horsepower number up top. In tune number 7, slightly more timing is on tap. In both All Out files, the torque converter locks at the bottom of second gear to get as much power as possible to the ground.

Dialing Back the Hybrids for Towing

At the opposite end of focusing primarily on making horsepower, we have two tow tunes (positions 1 and 4), with enough fuel pulled out of them to drop peak power down to roughly 350-400rwhp. As far as towing with big injectors is concerned, tuning is more important than an intercooler in terms of controlling exhaust gas temperature (EGT). Gearhead’s careful construction of these files included calling for much less fuel and holding off the transmission upshifts until later in the power band (to keep loads moving). Another scenario where dialing back the hybrids pays off is when you’re running a stock or smaller turbo and need to keep it alive until you can afford to upgrade.

400-ish HP Tow Tune

For lighter loads, Gearhead built us a crisp-shifting, custom tow tune with a modified converter lockup strategy. This file should yield approximately 400rwhp, 800 lb-ft of torque and will most likely be the one we use to pull our 10,000-pound toy hauler. It’s important to note that while we’re using seven tuning files right now, the Hydra Chip will hold up to 15 calibrations at any one time. On top of that, every Hydra Chip has a “Module Bypass” (00) and a “No Start” (nS) position built into it, so if you need to conduct any diagnostics or put your truck in anti-theft mode the Hydra has you covered.