Learn the importance of performing essential scan tool functions on common rail diesel engines

Diesel Injector Coding and Pilot Learning

Common Rail Diesel Injectors are manufactured with very tight tolerances, however, slight variations will always occur and as such all new injectors are tested and then stamped with a coding number which is used to inform the ECU how much compensation is required to achieve the optimum in lowering emissions and provide smooth running.

The injector coding number should be noted by the technician prior to fitting the new injectors and after replacement is completed the technician can then program in the new injector numbers to replace the ones previously programmed into the ECU

Injector programming can be carried out with high level Diagnostic Scan Tools such as G-Scan or Autocom ICON.

Care must be taken when reading the identification code stamped on the injector to ensure the correct number is entered into the ECU for the corresponding cylinder. Inputting an incorrect number or fitting the wrong injectors for the engine will result in the injector failing the programming procedure.

New Injector Calibration Data has been entered here. After pressing OK, the ECU will then check the number to complete the programming procedure

The actual number of characters to be entered will depend on the vehicle and can vary greatly.

If injectors have been removed from an engine and are to be reused, the injectors should be tagged to ensure they are being fitted back into the correct cylinders, alternatively, they would need to be recoded to the new cylinder in which they are fitted. Should a technician wish to swap injectors between cylinders to help diagnose a problem, the correct coding must be also changed with the injector to the new cylinder.

Pilot Injection

In order to reduce engine noise and exhaust smoke in Common Rail Diesel Vehicles, a small amount of fuel is injected through one or more small microinjections, also called Pilot Injection. These microinjections occur just prior to the main injection pulse. The actual number of microinjections will vary between vehicles or ECU Programs for a particular vehicle. The number of Pilot Injections will also depend on the running conditions at the time i.e. engine temperature, speed, load etc.

Microinjection learning maybe performed automatically whilst driving under certain conditions by the ECU monitoring changes in RPM immediately after pilot injection has occurred. The ECU can then increase or decrease the microinjection quantity to achieve the optimum quantity required.

As described below, a scan tool may also be required to perform Pilot Learning in some vehicles.

Injector Pilot Learning or Small Quantity Learning

Following Injector Coding or in some cases during routine servicing, manufacturers may require the technician carry out a procedure to teach the ECU the ideal Pilot Injection for the engine. This is called ‘Pilot learning’ or Small quantity learning’

The procedure for carrying out Injector Pilot Learning will vary, depending on the manufacturer. The exact procedure and pre-requisites must be met otherwise, the procedure will fail.  One example of Pilot Learning procedure requires the technician to enter Pilot Injector learning mode on the Scan tool and then accelerate the engine a number of times as per the manufactures instructions.

Performing Small Quantity Learning

Small quantity or Pilot Learning will be found in ‘Special Functions’ on G-Scan

Pilot Injection Testing may be performed on some vehicles in the G-Scan Actuation Test as seen below using the new G-Scan 2

Checking Injector Compensation Values in Data Analysis

In closed loop systems, the ECU will output ‘Compensation Values’ which can be read in the Scan Tool Data. The compensation values show any corrections required to obtain the desired fuel delivery. The closer the compensation value is to zero, the closer the delivery is to the optimum delivery.

As time goes by, injector contamination or other cylinder related problems will cause the compensation values to increase in either a ‘positive’ or ‘negative’ direction.

As long as there are no engine mechanical faults, higher than normal compensation values (+ or -) on one or more cylinders, usually indicate the injectors require service/replacement.

The Injector Compensation Values shown here show no major fuel problems in any cylinders.

Other on-car tests used to assist correct injector diagnosis, include:

• Carrying out a Power Balance, using the scan tool actuation test
• Testing Injector back-leakage using a Common Rail Injector Test Kit.