Honda CRF250F - Fuel Injection
April 6, 2019 version




 Fuel Injection 

 Break In 

Click pictures to  supersize.

NOTICE    -    Bank Angle Sensor Ignition Cut-off System

Your motorcycle's banking (lean angle) sensor system is designed to automatically stop the engine and fuel pump if the motorcycle is overturned.

Before restarting the engine, you must turn the ignition switch (key) to the OFF position and then back to ● (ON). The engine will not restart until you perform this procedure.

Page 28 of the 2019 CRF250F Owner's Manual. 0750.2018.09.K

ramz note: the BAS (bank angle sensor) function check shows:
 Start the engine.
 Incline the bank angle sensor approximately 60° to the left or right.
 The bank angle sensor is normal if the engine stops after a few seconds.
Page 4-32 of the 2019 CRF250F Honda Service Manual 61K9900, September 2018
60° !?? I'm gonna have to disconnect the BAS when I ride the 'fun' trails.



CDI - Capacitive Discharge Ignition
DLC - Data Link Connector
DTC - Diagnostic Trouble Code
ECM - Engine Control Module
EEPROM - Electrically Erasable Programmable Read Only Memory
IACV - Idle Air Control Valve
MCS - Motorcycle Communication System
MIL - Malfunction Indictor Lamp
PGM-FI - Programmed Fuel Injection
SCS short connector - Service Check Signal short connector



BA sensor - Bank Angle sensor
CKP sensor - Crankshaft Position sensor
EOT sensor - Engine Oil Temperature sensor
IAT sensor - Intake Air Temperature sensor
MAP sensor - Manifold Absolute Pressure sensor
TP sensor - Throttle Position sensor

Not present on this model
ECT sensor - Engine Coolant Temperature sensor
O2 sensor - Oxygen sensor
VS sensor - Vehicle Speed sensor


CRF250F fuel injection

Motorcycle fuel injection systems are of 2 major types: open loop and closed loop. In closed loop, there is an O2 sensor in the exhaust port which feeds combustion values to the ECU, which then adjusts the fuel injection values to keep the engine combustion process near the stoichiometric air/fuel ratio, given by the chemical equation for combustion of a fuel in air. The chemically correct stoichiometric ratio for gasoline is 14.7:1 (14.7 times as much air as fuel, by weight). In open loop, there is no O2 sensor feedback to the ECU.

The stock CRF250F has an open loop system named PGM-FI. Open loop tuners are not necessarily poor tuners. There are open loop tuners on the market that are quite good.

EJK sells tuners for many motorcycle models. Their tuners are open loop and load-based. The EJK controller uses Load Based Technology which sets it apart from most of the competition. Most EFI controllers use what is called 'Alpha-N' Tuning Technology. Alpha-N tuning is associated with just using Throttle Position (TPS) and RPM as the factors to make tuning adjustments. Load Based Technology differs by using Rate, TPS and RPM as the key factors for adjustment. Load Based tuning allows a user to tune their vehicle for every gear and for all riding conditions. From EJK KEY FEATURES


PGM-FI Troubleshooting Information

This topic is covered in Chapter 4 of the Honda CRF250F Service Manual. I will cover a few brief points here.

When the ignition switch is turned ON, the MIL will come on, stay on for a few seconds, then go off. If the MIL does not come on, stay on for a few seconds, or does not go off, inspect the MIL circuit.

You can read out and clear the DTC using an MCS ($2400 at HelmInc, $1200 on eBay) or the relatively cheap SCS short connector ($20 at BikeBandit, Partzilla, Amazon, eBay).

busy busy
The MCS and in kit form.

The MCS is a meter or handheld computer that allows the service tech to readout the DTC, the freeze data, other current data, and the ECM condition. Most riders will not own one of these, nor have access to one.

I have the pdf manual: Honda Motorcycle Communication Interface, User Manual, Version 1.0, 22 pages. Nice read.

I went for the SCS short connector. It's nothing more than a female connector with a jumper wire installed which allows you to connect two pins in the DLC. You could do this with a short piece of wire, but be careful you don't short out anything else in there; the DLC has four pins inside it. You could also look for the female connector in an electronics supply store and add your own jumper - probably in the $5 range.

Essentially, you plug the SCS short connector into the DLC, then read codes from the MIL. The MIL blinks two numbers that indicate the DTC, and you refer to a table in the manual for instructions on what to do.

All of this information is covered in great detail in Chapter 4 of the Service Manual, 32 pages in all.



So what kind of open loop tuner is on the CRF250F and what can it do to adjust for riding conditions such as temperature, air density (elevation), and humidity. This next part is conjecture on my part; I wasn't on the CRF250F design team.

A look at the sensors can yield some clues.

BA sensor - Bank Angle sensor The BA sensor does nothing for tuning; it's there to shut the engine off if the bike falls down. Actually, the specs show that if the lean angle is 60 degrees or more, the engine will shut down.
No help here with tuning based on riding conditions.

CKP sensor - Crankshaft Position sensor The CKP sensor is the master timing clock for the whole bike. The sensor sends out a pulse every time the crankshaft completes a revolution, and at a particular time in that revolution. The ECM uses this timing pulse to insure that events happen at the time they are supposed to happen. Although this sensor is important, it doesn't vary to a measurable degree when riding conditions change.

EOT sensor - Engine Oil Temperature sensor The EOT sensor tells the ECM if the engine is cold or hot. The test procedure in the Service Manual only tests for a threshold value for voltage and resistance. This is consistent with cold and hot start conditions, and not an engine shutdown or warning if the engine overheats. Cold and hot starts are not riding conditions, so no help here.

IAT sensor - Intake Air Temperature sensor At last, something that changes as riding conditions change. It would be a good idea for the ECM to lean/richen fuel as temperatures rise/drop. But temperature is of lesser significance than elevation when considering riding conditions. This is good, as far as it goes.

MAP sensor - Manifold Absolute Pressure sensor I don't know enough about engine design and operation to know if manifold absolute pressure is a good indicator of pressure altitude. If it is, then here is the golden egg. If manifold absolute pressure also indicates exhaust flow, which I doubt, this could also compensate for muffler changes. Any engine gurus out there??

Here is what wikipedia has to say: Engines that use a MAP sensor are typically fuel injected. The manifold absolute pressure sensor provides instantaneous manifold pressure information to the engine's electronic control unit (ECU). The data is used to calculate air density and determine the engine's air mass flow rate, which in turn determines the required fuel metering for optimum combustion (see stoichiometry) and influence the advance or retard of ignition timing. A fuel-injected engine may alternatively use a mass airflow sensor (MAF sensor) to detect the intake airflow. A typical naturally aspirated engine configuration employs one or the other, whereas forced induction engines typically use both; a MAF sensor on the intake tract pre-turbo and a MAP sensor on the charge pipe leading to the throttle body.

MAP sensor data can be converted to air mass data using the speed-density method. Engine speed (RPM) and air temperature are also necessary to complete the speed-density calculation. The MAP sensor can also be used in OBD II (on-board diagnostics) applications to test the EGR (exhaust gas recirculation) valve for functionality, an application typical in OBD II equipped General Motors engines.

Sounds to me like this sensor is the absolute indicator of important riding conditions as far as fuel injection is concerned.

TP sensor - Throttle Position sensor The throttle position sensor tells the ECM how much you've turned the throttle, and thus how much fuel to inject. No help here with tuning based on riding conditions.

And that's it as far as sensors.


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