"Changing the chip" on the Ford EEC-IV system involves installing a device which intercepts the control signals issuing from the computer (mostly SPOUT for spark timing and the injector control signals) and re-maps them to a different set of calibrations. For an experienced tuner who knows how to balance performance with reliability, this allows far greater control over an engine. In addition, because the SHO has no mechanical distributor, this is the only way to change the base spark timing and/or ignition curve, as an experienced tuner might do to take full advantage of serious mods.
Hypertech and SuperChips
Chips are Hypertech and Superchips only business. This doesn't encourage a holistic approach to performance. That is, they may try to get improvement with calibrations that would be safer and more reliable to do with mechanical modifications. Scott Chan did a pretty good basic test of an example chip module.
I bought an aftermarket engine control PROM for my '91 SHO. The mid-range throttle response "seemed" better, probably due to the intake runners openning earlier. But how to measure the improvement? On the "test track", I ran a series of acceleration runs, 5 with the aftermarket chip, and 5 without. In order eliminate the variables of gearshifting and wheelspin, I timed the runs from a steady 25 MPH to 60 MPH in second gear. This corresponds roughly to 2500 RPM to 6000 RPM. This ignores the very upper end of the rev. range, but does cover most of the important range. Timing was by hand-held stopwatch.
The results were disappointing... the average time was 6.7 seconds for both configurations. Some may argue that hand-held timing is inaccurate, but basically the differences were imperceptible.
How did the chip perform in normal driving? Again, I was unable to feel any improvements. The one difference I did notice was a distinct engine knock when driving uphill on a hot day. Apparently the program overrode the knock sensor and advanced the spark too far. Because knocking, or detonation, can damage the engine, I immediately removed the aftermarket chip.
Lifetime Performance Modules
There are some tuners dedicated exclusively to the SHO. Specifically, the SHO Shop, Scott Performance (programmed by Ted Breaux) offer Lifetime Performance Modules that are tuned for the exact modifications on your car (if any) and can be reprogrammed to account for additional modifications free of charge (except for shipping).
Following is the instructions for installing a "Ted Breaux" LPM in a 5sp SHO.
5-SPD SHO INSTALLATION INSTRUCTIONS
Your new computer module is designed to provide trouble-free service for the lifetime of your car. Unlike the factory program, which is designed rather conservatively, your new software features:
1. Optimized fuel curve
2. Optimized spark curve
3. Optimized opening of the short intake runners
4. 8000 rpm rev limiter
5. Slightly raised idle speed
6. Improved cold start characteristics (some models)
7. Special options (as deemed necessary)
Because your module is programmed for your particular car, it will not be functional on most other SHOs. Should you make any significant hardware changes (exhaust, MAF, cams, etc.), please notify me so we can determine if reprogramming is necessary.
1. Open the hood and locate the negative battery terminal. A smaller black wire splits off of the large negative battery cable. Follow this wire to a cylindrical connector. Disconnect this connector. This removes the power to your computer (resets it) while keeping power to your clock, radio settings, etc.
2. Open glovebox, empty contents.
3. Simultaneously pull the two restraining tabs (on each side of the open glovebox) inward, such that the glovebox opens entirely and hangs downward. The computer is the shiny metal box just under the dash.
4. Using a 7.5mm (5.5mm for some later models) box end wrench, patiently remove the screw which anchors the white plastic bracket which sits directly in front of the computer. Remove the bracket entirely.
5. Peel back the sticker (remove the plastic cap on later models) on the computer housing to reveal the service port. Clean the contacts thoroughly with a paper towel, etc. to remove every bit of electrical grease. Be sure to clean both the contacts on top and bottom of the PC board.
6. Plug in the module. The module is in the correct orientation if the hand-written EPROM label can be read upright. Record the information I've written on this label, and keep it in your glovebox (the label may eventually come off). You may want to put a layer of electrical tape on the back side of the module and fold it under the computer.
7. Reconnect the computer power connector (under the hood). Turn the key to the 'ON' position. If the engine cooling fan does NOT come on, you are ready to start your car and test the new module. A few wide open throttle events are necessary for the computer to learn the new settings.
8. If I've sent you additional EPROMs, when you remove the module to switch chips, do so carefully, paying attention to install the new EPROM in the proper orientation as indicated on the PC board.
9. Remove the module and install the bracket if you have any warranty work done to the car.