POWERSTROKE 6.4L AND FUEL TRIM


The Powerstroke 6.4L is now over 11 years old now and more are probably entering your drive in service

facility with issues. Fuel mileage complaints are very common along with regeneration issues.

The question questions asked many times over is how frequent should a regeneration take place. This is a

difficult questions to answer since there are so many variables.


​I have always stated that the proper function of an aftertreatment system is based on the condition or operation of the engine itself. The frequency of regeneration events are affected by low compression, boost leaks, excessive oil consumption, injector and fuel pressure issues. Driving conditions and habits contribute as well.   


Fuel Trim, better seen on a scan tool as SFT, has been around gasoline engines for a long time. Closed loop fuel systems used on these applications were equipped with oxygen sensors to inform the engine computer or ECU when there was excessive or reduced amounts of oxygen in the exhaust. In turn the ECU would command more or less fuel by changing the pulse width to the gasoline fuel injector. Open loop meant there was no feedback from the oxygen sensor due to the fact that the sensor was too cold or the engine may have been too cold. Heated oxygen sensors have aided in faster warm up to attain closed loop faster in order to maintain fuel control and economy.

Diesel engines incorporate similar controls with common rail injection. In is important to note that common rail fuel strategy takes place changing fuel pressure and pulse width. Programming in the ECU allows for constant fuel delivery changes due to engine load and speed. At idle the 6.4L engine management ECM (engine control module) uses the crankshaft position sensor (CKP) to measure the angular velocity of each power stroke of each cylinder in its firing order. The main input for short term fuel trim (SFT) is the CKP sensor. Oxygen sensors are not used in diesel engines for closed loop fuel control. In making it easy to understand, the sensors such as the engine coolant temp (ECT), the Manifold Absolute Pressure (MAP), the Inlet Air Temperature and other sensors inform the ECM in order to start fuel injection and program a desired amount. When the engine reaches operating temperature over 185 degrees F, the ECM will observe the angular velocity of the crankshaft at idle. As the engine crankshaft is rotating, the ECM knows its position thanks to the Camshaft Position Sensor (CMP). The ECM monitors the angular speed as each cylinder fires in its firing order. Number one fires, number two fires and so on in its firing order. The ECM assimilates if there was too much or too little angular speed and will adjust fuel timing, pulse width, fuel pressure to balance all cylinders to contribute equal power. Let’s say number 4 cylinder is weak due to lower compression. The ECM will add more fuel to that cylinder to increase power. On the other hand if a cylinder has too much power contribution due to excessive carbon buildup on the top of the piston, this will add more compression. The ECM will reduce fuel to this cylinder.

It is a form of a closed loop system since the CKP is providing feedback to the ECM if there is too much or too little power contribution from all cylinders.

You as the technician can view individual fuel trim (SFT) on the scan tool such as the IDS on Powerstroke 6.4L engines. It is important to emphasize that engine must be at operating temperature and at idle. This can be used to interpret if there is a compression issue, an injector issue or mechanical issue.

The scale Ford Motor Company uses on these engines is a percentage. The common specification is plus or minus 10 percent. Observe the chart below

​FUEL ADDITIVES FOR DIESEL AND COMMON RAIL FUEL SYSTEMS

When diagnosing fuel, smoke, or frequent regeneration issues, you can observe where the fuel setting is at. If the percentage is over plus or minus 10 percent, then that means there is an issue. If the fuel injectors are contaminated, the programming will add more fuel.  You can diagnose but ensuring that desired and actual fuel rail pressure are correct and that there are no fuel contamination issues.  In other words, you have checked the basics of common rail engine diagnosing.

Let’s role play, you are diagnosing an issue with frequent regenerations, you have checked all the basics, you can observe SFT and verify that all cylinders are in specification. If you have an issue can one cylinder with excessive change in fuel trim contribute to frequent regenerations? Remember that we have diagnosed many diesel issues by the amount of smoke that is visible. Diesel Oxidation Catalysts and Diesel Particulate Filters have masked or cleaned the exhaust thus causing frequent regenerations. Analyze the SFT and confirm if all fuel trims are within specification.

Please keep in mind that excessive crankcase blowby gases can contaminate or coat the catalyst substrate and cause regeneration issues. Turbochargers with oil leaks will contribute as well.

TECH TIPS

CUMMINS 6.7L COMMON RAIL

Dodge Cummins Training, Tech and Tips

The CR injectors on a 5.9L can be misleading and the software for diagnosing is not the best. Due to the fact there are many unauthorized reman fuel injectors sold, you can have smoke issues, fuel economy down and other driveability issues and diagnostic trouble codes (DTC) set. 

You get what you pay for! Buy quality Bosch injectors. 

Tip one- on a 5.9L, run the engine at idle. Snap the throttle, if the RPM stays high then drops, you have ball and seat erosion in the injector. Injectors will need replacement. Once you snap the throttle, ... more ... 

DOC AND DPF PRESENTATION - A QUICK REVIEW

Scan tools, Programming and Diagnostic information

There is a variety of scan tools that can work with a Dodge Cummins CR. The OE service scan tool is the

WiTech. There has been numerous updates to WITech but the program is basically the same. You can see

information on WiTech at www.kb.dcctools.com.

Here are a few basic tips.

  • When you read about Dodge Cummins 5.9L, there are many versions. There has been the 5.9L Cummins with the VE Pump, then the VP44 Pump and the CR systems. CR stands for Common Rail. 
  • What is Common Rail? It means there is one rail which delivers fuel pressure to all injectors. This fuel pressure can vary from 3500 psi to 28,000 psi. 
  • When diagnosing any drivability problem confirm using an appropriate scan tool the desired or set point fuel rail pressure to the actual fuel rail pressure. 


Programming

When programming a truck, especially the PCM/ECM, you will need the SKIM code. This is a four digit numerical code that will be needed to complete the programming or reprogramming process. This cannot be attained by the scan tool. There are tools sold that can read SKIM codes. You can also contact a Dodge Dealer if the parts rep is willing to give it to you if you provide them the last 8 of the VIN number.

The frustrating thing is that we did see over 70% difference between pre and post NOx sensor readings. All was good in the program but it needed updates for the message to erase. Please note that after the NOx sensor was replaced, there were no DTCs. There was a SCR light on the instrument cluster but no MIL light. Just the messages about Exhaust Fluid.

Lesson? As we have seen already on Ford Powerstroke 6.7L, the Duramax LML 6.6L may often require reflash of the ECM when there are no DTCs and a SCR light on. Procedures do call for the Reductant Fluid Quality Test to be ran but if no success and there are no DTCs, reflash ECM and run again.

Note that the SCR light simply is telling the technician that the ECMs program is not satisfied with the NOx reduction attained. 


KNOW YOUR MESSAGES AND LIGHTS!


Do you know why there is no check engine light and codes set when a SCR light is on?


We just finished with a 2012 GMC Duramax LML where the reductant fluid quality test was timing out and causing headaches after the installation of one of the NOx sensors. There were no diagnostic trouble codes (DTC), the vehicle was displaying the Exhaust Fluid Quality Poor message and derated to 55 mph.

I read and followed the diagnostic procedure over and over plus read on service information on what techs were discussing regarding this issue. We were on the third quality test which can take up to 70 minutes which times out with no reason given in the PIDS. As I have instructed on this issue, we had to have it reflashed with the latest files from GM. Once flashed, ran quality test again and within minutes, it passed and messages all gone.