It’s not just a Jeep thing!
By Clinton Brett.
A worn low-pressure supply pump can leave a common rail diesel stalling when hot and refusing to restart. Clinton Brett walks through the diagnosis on a Jeep Grand Cherokee WK2 and why the lesson applies well beyond the Jeep badge.
A couple of technical bulletins aside, I’ve never written a Jeep article. That’s largely because non-specialist workshops rarely take them on. Still, the Grand Cherokee became a dream car for plenty of Australians and New Zealanders after its 2011 launch campaign.
The popular model was the Grand Cherokee (WK2) 3.0 CRD V6, fitted with the VM23D (EXF) 177kW engine and later the VM44D, across 2011 to 2021. Early on they came with a long list of issues. I was working at Frizelle Gold Coast VW Commercial at the time, which also held the Jeep franchise. The Jeep techs were working around the clock on warranty claims covering most of the engine and other drive components.
One component that rarely gave trouble was the Bosch fuel system, which I rate as the best diesel fuel system manufacturer.
The fault in this article isn’t a Jeep fault. It’s the failure of the electric low-pressure fuel supply pump, a component common to many common rail diesel systems. Depending on the vehicle, it can sit on the chassis rail, within the fuel filter assembly or inside the fuel tank. Some OEMs, such as BMW, run one in the tank and another on the chassis.
They eventually wear out and will completely shut down the engine, preventing it from restarting. Some of you may have read my previous articles, where I mention that a CRD can run without the aid of an electric supply pump and you can simply connect a separate fuel supply to get it started and running. Today, there is a mixture across the diesel car park. But in my experience diagnosing Jeeps and affiliated vehicles such as Fiat/Chrysler, they are 100% dependent on this in-tank pump. Depending on the model, they require a minimum feed pressure value to ensure the engine starts and runs without faults or failures.
Symptoms: The vehicle would stall occasionally, especially after driving, when the engine was warm. Difficulty starting would occur more often when warm and when the fuel tank level was less than half.
Diagnosis and early detection of the fault: Before replacing the pump, check the other parts of the low-pressure fuel supply system that may stop it supplying adequate pressure. As mentioned previously, this model will not operate on a separate fuel supply.
The ECU has a strategy in place to monitor the rail pressure when the ignition is switched on. The in-tank supply pump will be active immediately to produce enough pressure for the monitoring system to enable full starting and running of the engine.
Jeep fuel filter low pressure pump
If the pressure is below the minimum desired fuel pressure, the ECU will prevent power supply to the injectors, preventing the engine from starting. We have found 3.5 bar to be the approximate minimum fuel pressure required to meet the strategy. This is not the exact specification, as we can only provide the minimum pressure that has been determined by previous cases. But don’t lock this pressure in for all CRD low pressure fuel supplies. We diagnose a similar problem on the Mitsubishi Canter and it requires 4.1 bar exactly.
Placing your finger over the fuel pipe outlet, activating the pump and splashing everyone with diesel is not a reliable monitoring system.
To confirm the low supply pressure meets its 3.5 bar minimum, install an inline pressure gauge between the fuel filter and the tank, preferably a liquid filled gauge with a range of 0 to 20 bar.
Turn the ignition on or, if possible, use your scan tool to activate the in-tank pump and observe the pressure. It should reach this minimum of 3.5 bar within a couple of seconds.
If there is a lower reading, the engine may still start and run, but this will depend on how much fuel is in the tank at the time. A higher level increases the head tank weight, assisting the flow of the fuel and increasing the pressure by way of gravity. In other words, the higher the fuel level, the more push the fuel has behind it.
Low pressure pump passenger side chassis rail
Another test that can help confirm the in-tank pump has failed is a current draw test. Using an amp clamp at the pump relay or the pump itself, the amperage must remain at approximately 3.5 amps when active. The pump can be found on the passenger side chassis rail.
If there is no amperage draw at all, confirm there is a good quality power supply to the in-tank pump. If not, start checking the power at the pump and work your way back to the fuses and relays. Carry out a continuity test and confirm adequate battery power and quality earths. Some vehicles use an activation switch as part of the driver’s door to assist pre-priming.
For testing the electrical circuit, refer to HaynesPro WorkshopData, component H2, fuel pump with level sensor.
Solution: Once the pump has been confirmed as failed, remove it and replace it with a genuine part only. Remove the entire tank for a full clean.
Special notes: Most in-tank pumps require minimum pressure to prevent failures of the main system. Low pressure can be caused by contaminated fuel such as water or petrol. If this were to enter the high-pressure system, major damage is likely to occur.
Haynes Pro Wiring Jeep I Source: HaynesPRo Workshop Data
Often there is no filtration before these pumps, so the average life of these supply pumps is approximately 150,000km to 200,000km. As preventative maintenance, I strongly advise replacing these supply pumps every 150,000km.
Clinton Brett is the owner of Diesel Help Australia. dieselhelp.com.au
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