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Old 01-30-2013, 08:15 AM   #1
MentalGuru OP
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CRF250L Engine Control Details and Tech thread

Here goes....

The injection system on the CRFL is designed using automotive technology. It is a basic open/closed loop speed density system.

I'm very experenced with this style system... I have 20 years of experence with this type of fuel injection and engine controller diagnosis, programing and custom tuning.

I can try explain how the system operates so everyone can understand.

I'm used to using the standardized automotive abbreviations. So keep that in mind.

MAP = Manifold Absolute Pressure Sensor can also read barometric pressure
TPS = throttle position sensor
CTS = Coolant Temperature Sensor
O2 = Oxygen Sensor
IAC = Idle Air Control valve/stepper motor
CKP = Crankshaft Position Sensor
IAT sensor = Intake Air Temperature sensor
AI/02 = Air Injection Oxygen system valve/sensor

ECM/PCM = Engine/Powertrain Control Module
DLC = Data Link Connector
DTC = Diagnostic Trouble Code

Honda calls it a PGM-FI system.

OBD is On Board Diagnostics.

Open loop is when the engine is running on base programing.

Closed loop is when the engine is monitoring the sensors and adjusting as needed to maintain the desired air/fuel ratio.

Adaptive memory is the computers ability to adapt to and remember what is needed to achieve the desired air/fuel ratio in closed loop mode. It has the ability to add or subtract fuel as needed. There are two types of adaptive memory, long term and short term. Long term memory is stored memory about what was needed and short term memory is what is needed at that moment. The computer uses short term memory to establish it's long term memory.

The MAP sensor is used to read Barometric pressure at key on then. This would be how the PCM checks altitude. It monitors engine vaccum which it used to determine engine load by comparing it to the TPS reading. It can also sense alititude change at WOT if programed to...

The TPS sensor tells the computor what position the throttle is in. It's as simle as that.

The CTS is just as simple, it monitors the coolant temperature for the PCM.

The O2 sensor monitors the oxygen level(air/fuel ratio) in the exhaust so the computer can adjust as need when in closed loop mode.

The CKP sensor identifies the crankshaft position, RPM and can be used to sense when the engine fires.

The IAC is a air bypass valve that is used to control the engine speed at idle. The throttle body allows a pre determine amount of air past the throttle blade and the IAC controls the extra need to reach the correct idle speed and prevent stalling. I'll add more details about this later since stalling it is a problem.

The IAT monitors the air temperature going into the engine. Cold air is denser and has more oxygen in it. It is used in combination with the other sensor values to help determine the correct air/fuel ratio.

The lack of the cam sensor and 1 wire narrow band O2 sensor shows me it is basically an early type automotive system. That means the PCM is most likly a PROM type instead of a EEPROM type.

Here's the difference.

PROM is programable read only memory type controller.

EEPROM is eletronicly erasable programable read only memory type controller. This means can be reprogramed/flash programed.


This type of system doesn't do to much OBD so it is easier to trick it as needed. This also makes diagnoising and testing easier for the average backyard tech.


More to come...

MentalGuru screwed with this post 01-30-2013 at 01:43 PM
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