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Occasionally people talk about using an aftermarket chip in their car. What they really mean, is that they’re going to change their engine’s ECU programming. There was a time when actual chips were swapped, but that’s not really the case anymore. I don’t know who the first manufacturer was to put an end to this, but Porsche ECUs used to perform a hardware check when the car was first started. If the ECU determined some "other" hardware was present, ignition was retarded. Now, ECUs are simply reflashed. What does reflashing an ECU really do?
A few changes are advertised, but I’m unclear as to "why" for some of them. The usual changes are raising the redline, changing the fuel maps, removing the speed limiter, changing the ignition maps, and eliminating the adaptive throttle logic.
- Raising the ECU governed redline is possible, but this usually doesn’t do anything for increasing power levels. Look
at a dyno chart. At redline the power levels are usually dropping off, not increasing. There are also other things
to consider. One issue may be whether the rod bearings can take the increased stress. The same applies for the wrist
pins. If the engine in question is a 3.2 from a Porsche Carrera, the factory rod bolts are a definite issue. Porsche
factory 3.2 rod bolts are undersized and will stretch. Are they an issue here? At what RPM does the engine in
question begin to experience valve float? Are there clearance issues if the engine experiences valve float? Those
are questions that should be answered before exploring the physical limitations of the engine. Revving an engine
until something breaks is an expensive way to determine it’s boundaries. This isn’t all gloom and doom. There is an
upside to raising the redline. Just because raising the redline doesn’t change peak power levels doesn’t mean the
car won’t be faster. Depending on the gear spacing, up shifting at a higher RPM may result in the engine staying in
a rev range where it makes more power. This could result in better ET’s.
- Remapping a chip can also be used to change fuel delivery. This can be beneficial, provided the fuel can actually be
burned. The amount of fuel an engine can burn is limited by cylinder size, air intake, ignition system, port sizes,
exhaust tuning, and a host of other things. If one looks at a dyno chart with an A/F reading, some things can stand
out. When the A/F readings drop too low (increased fuel), the power level drops off too. Some go the other direction
and lean it out a little. Does that sound odd? It shouldn’t. Some boosted engines have been known to run very rich
with the factory settings. The factory settings for most boosted engines are rich because it’s safer that way. If a
boosted engine runs too lean, the power level drops off just before detonation and a holed piston. The correct
changes for a particular car may be easy to determine with an A/F gauge and a dyno. For an NA engine, the correct
direction is probably rich, but that may introduce another problem. At redline and wide open throttle, are the
injectors at maximum duty cycle? Maximum duty cycle is the maximum amount of fuel an injector can deliver. Injectors
are limited by physical dimensions. This is regardless as to what the ECU says. If the injectors are at maximum duty
cycle, larger injectors are typically required.
- If there is a speed limiter, that can be removed.
- Changing the ignition map is where most power claims come from. Manufacturers can’t say whether customers will have
access to 93 octane fuel all of the time, so they dial the timing back. Even with the knock sensors, the timing is
dialed back. That’s because in places like California, Nevada, and Arizona, 91 octane is the norm for premium fuel.
If the timing is set for 93 octane, and the 91 causes a ping, then the knock sensors will dial the timing back.
Knock sensors don’t just dial the timing back a little. They dial it way back to "this engine couldn’t possibly
ping at this timing" levels. If you have access to 93 octane fuel, then a reflash "may" be of some
benefit.
- Removing the ECU's driver adaptive throttle logic can be done with a reflash. Many Bosch ME systems have this built in, and resetting it to the base numbers can be good for 3 to 10 HP on back to back dyno runs. Of course, on a Mercedes-Benz, this can also be manually reset without reflashing the ECU.