We have talked much about diesel fuel injectors and frequent issues, especially for the Doosan Bobcat D24 in our most recent blogs. We’ll now go over the 2.4L high-pressure pump out of the D24 engine which is one of the most common engines used in excavators, skid steers, and track loaders. The high-pressure pump for the D34 engine commonly used in skid steers, track loaders and steer loaders is another example similar to the D24 pump. Both pumps are almost identical though the D34 pump is used in larger machines. The D34 pump does not have an internal pressure relief valve compared to the D24 pump and is around 36,000 psi, so if too much pressure is created, the internal valve releases that excess pressure. Instead, the D34 has a high-pressure relief in the fuel rail.
When an issue arises with our high pressure fuel pump, we want to properly diagnose it. Common issues can include your machine saying that it has low fuel pressure, to check your fuel filter, etc. So how do you diagnose your D24 pump?
Well, let’s start by doing a quick deep dive into an important part of the pump. Starting with the lift pump, this section is what pulls fuel from our tank through our fuel filter and into the cavity of the pump. The lift pump is what charges and pressurizes the cavity to 86-87 psi with the rotary vane pump which maintains that pressure through a low-pressure relief which is set to 86 or 87 psi (depending on what your manual says).
(the vane pump can be found inside of the lift pump)
We recommend starting by removing the IMV Valve by using a T25 Torx Screwdriver and removing the two bolts. The IMV Valve is controlled electrically and is what controls the rail pressure. The 86/87 psi goes through the IMV Valve which regulates how much fuel goes to the high-pressure piston. Your D24 pump will have one piston on the top and one on the bottom.
IMV Valve: “The Inlet Metering Valve in the common rail fuel system regulates the amount of fuel in a fuel pump, conserving energy used by the pump in allowing only the required volume of fuel to be pumped through the system.” (Source)
Once removed, the valve will have a screen around it. That screen is the last line of defense before fuel gets to the fuel rail and injectors. You can reference the photo included below. To troubleshoot this, you will need to check the screen and look for any type of debris, metallic bits, dirt, etc. If you find anything here then let’s move on to step 3.
If you find any kind of debris in the screen of the IMV Valve, we want to further test the IMV Valve by driving 12V through the wire connector and seeing if the solenoid will slam shut. When you take away the voltage it’ll open back up. If the problem with your pump is that it is not receiving any rail pressure, by running the 12V on and off you may be able to free up the IMV Valve to get your pump up and running again. That’s how you test the IMV Valve.
If debris was found on the screen of your IMV Valve, it likely came from your pump's vane pump which pulls fuel from the tank through the filter and into the pump. To check the vane pump you will want to remove the outer cover around the lift pump.
Once the cover is removed, you can now see the vane pump section. There are four vanes here and if you found any debris it likely got stuck in either one of those four vanes. That debris will get pushed into the pump and move over to the IMV Valve which will then make its way up to the injectors and the entire fuel system. This step is important to check before replacing injectors; in order to know why those injectors failed in the first place. Next, pull off the entire vane pump section.
Let’s go ahead and move over to the engine side of the pump. Remove the three bolts located on the back side of the pump to access the gear. Once you remove those bolts you’ll be able to access the piston and pump head which can be removed for now. Once all of the scrap parts are removed you’re left with the main opening which include 4 corner holes and one main hole in the center. We sometimes find rusted dirt has gotten into these openings and can lead to a failed pump.
If you're finding that the pump is contaminated, the rest of the fuel system may also be contaminated. In order to check the fuel rail, find the pressure sensor and remove it. Grab a long swab and place it inside the port opening. Move the swab in circular motion. Once you remove the swab, check to see if any dust, dirt or debris is collected. If so, this tells us that the fuel rail and likely the injectors are contaminated.
As an alternative, you can also purchase a Fuel Pump Diagnostic Scanner online for about $100-$200 and test to see how the fuel pump keeps up with the rail pressure.
To check for a fuel injection pump leak, open the filler cap in your vehicle and start the engine. Once it's running, turn off the ignition key and open the cap back up. If the engine still runs after a few minutes, it means that there is air getting past and into the tank.
We hope this guide was helpful in giving you the basics on how to troubleshoot your pump and/or fuel system. Please reach out for additional questions or feedback. At the end of the day, we want to assist you in accurately diagnosing your parts in order to ensure that you’re attending to the correct issue in your fuel system.