Engine - ECU and Engine Control
Upgrading the engine control system, even with a completely stock engine, can yield significant performance
improvements. The Geminis raced in Japan under Group N rules were restricted to completely stock engine and
internals, but were allowed unlimited changes to the engine control system. Even with inlet air restrictors,
they managed 30+% power increases with 1991 technology.
The Geo Storm uses a GM P4 ECU and complete cadre of GM sensors common to LT1/LS1 and HEI ignition GM cars.
These ECUs are flash programmed, meaning that there is no preprogrammed chip to be removed and replaced. Instead,
they have a little hard drive which is loaded with the control program specific to the engine being used.
The factory ECU has serious limitations. The fuel delivery curve and ignition timing curve are Siamesed together
and the computer is not able to adjust these two independently from each other. This means that for a set point
in fuel delivery, there will be a set point in spark timing, which will not be adjustable or responsive to
conditions such as engine load, speed, blended fuel composition (10% ethanol), etc.
The factory tune of the ECU is also set extremely conservatively. The fuel curve runs the air fuel ratio rich
to the point of slobbering gasoline, as if to plan in a redundancy to cover for complete fuel system failure.
Really squeezing more power out of the engine involves leaning out the fuel mixture and advancing the ignition
timing curve, which would require a knock sensor and a wide band O2 sensor, two things the factory computer
system does not have.
Because of these issues, reprogramming or reflashing the original computer will not yield much improvement. The
Elan-Scan system, popular with the Lotus Elan owners, has proven itself to be a complete waste, due to the above
described lack of flexibility in the GM P4 ECU. Generic reprogramming from a mail-order company such as Superchips
and Everest Chips, have proven an even greater waste, because not only can the system not control the parameters
that need to be changed, the reflash is done without the computer attached to the running vehicle, making it
impossible to even see the adjustments needed to improve the programming.
The best solution is a stand-alone computer system, which completely replaces the original computer, and allows
for programming the fuel and spark curves using a laptop computer. Analog systems should be avoided. Digital
operates faster and more smoothly. Neither Haltech nor Megasquirt are recommended for these reasons. Both have
proven fraught with problems due to their antiquated analog based systems, lack of compatibility with the
existing vehicle control system, and lack of the required sensor inputs.
Isuzuperformance offered a complete, plug-in-and-play, digital system with the ability to operate multi stage
nitrous, sequential fuel injection, and coil-on-plug ignition conversion.
Batch Fire to Sequential Injection Conversion
The original fuel injection system in the Geo Storm is batch fire, meaning that the fuel injectors are wired in
pairs, which fire twice per cycle. This means that a lot of fuel is wasted by spraying it at the wrong time.
Wasted fuel in the intake system causes the engine to run rich and respond sluggishly and lethargic.
Converting the system to sequential firing, so that each injector fires once per cycle, and fires at the optimum
time for the best power, improves throttle response, fuel efficiency, and power output.
This is controlled by the ECU, and is another reason to make a careful choice of which programmable system to
The digital system from Isuzuperformance is sequential fire capable.
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