I wish manufacturers would slow the rate of change in the vehicles they manufacture, but it is clear that is not going to happen. When you have been around as long as I have, one has seen so many changes that you have a hard time remembering the updates and changes from just a few months ago.
The transmission business is tough because, as you know, it is not just the transmission that you need to worry about. It is now the engine and its control system, ABS, Body system controls, Chassis controls, Communication systems, and countless other systems that can ruin your day.
A couple of months ago, we had the ATRA seminar in Houston. With Texas being the truck capital of the world, a lot of the interest from the attendees revolved around issues with GM, Ford, and Ram trucks. Like most seminars, when we were finished, several attendees stayed around to visit regarding issues they were having in their shops.
In Texas, Duramax diesel applications are as “common as dirt,” so almost every shop has one in for some sort of service. Like everything else, the Duramax has undergone tremendous change since its introduction a couple of decades ago. The gentlemen that wanted to visit were having issues with a 2020 Silverado with the Duramax 6.6L (L5P) engine and an Allison 10L1000 transmission. The RPO L5P engine introduced in 2017 is very different from the other Duramax engines you may have worked on.
Some major changes include:
- GM dropped the Garrett turbocharger and replaced it with a Borg Warner B2BV-70A fully electronic variable geometry turbocharger capable of up to 28 psi of boost with an exhaust brake feature similar to the previous RPO LML applications.
- GM dropped the Bosch fuel system it had used for years and switched to the Denso high-pressure fuel pressure system. This system Denso HP4 pump operates at 29,000 psi pressure and utilizes solenoid-type injectors rather than the piezoelectric type used previously. The new injector design can support up to 7 injections per cylinder per firing event to smooth engine operation.
- A new design function hood scoop was added. The new scoop supplies up to 60% of the air used by the engine.
- A ton of internal engine, turbo, drive shaft and torque converter update changes were introduced during the 2020 model year, so you need to pay attention to the parts you are using.
- The Allison 10L1000 was introduced in 2020, replacing the LCT 1000.
Fuel System Components:
FPR: One of the areas of confusion with the new fuel system revolves around using two pulse-width-modulated fuel pressure regulators, FPR 1 and FPR2.
FPR1 is located internal to the fuel injection pump and controls the amount of fuel entering the pump. The high-pressure fuel is distributed from the pump to the fuel rail and the injectors. When fuel temperature exceeds 46° F (8° C), FPR 1 controls the system’s fuel pressure.
FPR 2 is located in the rear of the driver’s side fuel rail and controls the amount of fuel returned to the tank. When the engine is off, FPR 2 opens, eliminating pressure in the fuel rail. System fuel pressure is controlled by FPR 2 when the fuel temperature is colder than 46° F (8°C) and when releasing the accelerator pedal.
A couple of common DTCs we see causing operation issues are P228A (FPR1) and P228B (FPR2). These DTCs indicate that the system is not developing enough fuel pressure for proper operation. Remember, FPR1 is the primary device controlling fuel rail pressure, while FPR2 is used to validate the values received from FPR1.
Fuel Pressure Sensors: The fuel pressure sensor is located on the fuel rail. It’s a dual variable sensor that varies its output with pressure. The sensor is fed 5 volts from the ECM, and the output from the 2 sensors are contained within the one housing. The sensor output voltage rises from each sensor as fuel pressure rises.
Fuel Pumps: 2 fuel pumps are used to provide pressure and flow for the fuel system. A variable speed low pressure, 3-phase electric pump is mounted in the tank while a high-pressure injection pump is mounted in the front of the engine under the intake manifold. The injector pump provides fuel pressure for the injectors. Some applications use a 3rd fuel pump to transfer fuel between tanks on multiple tank applications.
Fuel Filter: The fuel filter is located near the left frame rail and houses the:
- Fuel Temperature sensor
- Fuel heater and water sensor
- Fuel water separator
- Fuel filter
Fuel Injectors: The updated ECM-controlled injector design allows for multiple injectors firings per cylinder firing cycle. This allows the Duramax to lower engine noise compared to many engines on the market. Like many current transmission designs, the injectors act as fuel control solenoids, so they are flow tested, and their flow rates are used to determine the engine calibration used. The injector flow rate must be used to update the calibration when an injector is replaced. Like many transmission solenoids, a QR code is etched into the injector body, which you will use in conjunction with your smartphone QR reader app to ensure that you have loaded the correct flow rate information into the ECM. Like a transmission, the Duramax injection system is equipped with its own form of adaptive learning known as “Fuel Setpoint Adaption” (FSA). FSA is an algorithm used to calculate the flow rates through the injectors so that as the injector wears, the system can adjust for changes in injector fuel delivery rates.
So, what issues do we see with these newer design trucks?
Map sensor-related drivability issues: The map sensor is located on the intake manifold, so it is prone to soot and grime contamination which can lead to engine misfire, surging, DTCs and other drivability issues, which may be misconstrued as transmission problems. As this is an ongoing issue with this design, many in the aftermarket are installing a Map sensor spacer to reduce the likelihood of the issue occurring. The spacer moves the map sensor away from the EGR stream, which leads to the issue.
Fuel Injector #4 failure: This typically leads to P0204 and drivability-related issues. P0204 can be caused by a faulty injector but do not overlook the injector connector and its pins as they can be problematic. Keep in mind that GM issued a campaign recall related to the injector calibration in 2019, so make sure your customer’s vehicle has had the recall completed.
Fuel Pressure sensor issues: Issues include drivability and DTC-related symptoms. The issue is typically not the sensor itself but rather the harness and its pins.
Hood scoop debris: Early designs had issues with water and debris intrusion into the air induction system. Take a look back at your 2020 seminar for details on the issue.
Transmission failure: Clutch-related concerns are starting to occur, especially on applications with engine performance software installed, as I outlined in a previous gears article.
Like the folks in Texas, I am sure you, too, are seeing your share of Duramax trucks appearing at your doorstep. Hopefully, you will now better understand some of the changes and issues with the later model applications. Until next time remember, “Today is the tomorrow you worried about yesterday.”
