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ML 320 CDI - Engine fails to start despite cranking


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Greetings, everyone.

The engine is turning over but fails to ignite and begin running.

High pressure pump has been replaced.
Fuel Pressure Regulator (FPR) - Replaced Crankshaft sensor - Replaced

The pressure at the high-pressure pump is still insufficient to initiate the car's operation.

I am rapidly depleting my available choices. Does this problem indicate a malfunction in the Electronic Control Unit (ECU)?

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Do you have information on the fuel delivery pressure from the tank to the high-pressure pump (HPP)?

There are two methods for verifying this: using a gasoline pressure tester or using a Xentry machine.

It seems that you are randomly replacing components without doing a thorough examination. The costliest and exasperating method of repairing an automobile.

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Based on the information provided in his profile, it can be inferred that he has an ML320CDI, which is most likely a W164 model.

The crank pressure is inconsequential as the High-Pressure Pump (HPP) has previously been changed and the engine is still not starting. It is essential to first examine the fuel delivery pressure originating from the tank. The required pressure is 3.8-4.2 bar. If you do not possess it, it will not start even after an extended period of time.

In my experience, every 642 I've seen that didn't start had worn injectors. Typically, they have misfires and emit smoke, but they consistently initiate.

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Indeed, the W163 model was never equipped with a 6-cylinder diesel engine. I apologise for my mistake.

Was the gasoline quantity valve replaced with the high-pressure pump?

What was the cause of the problems? Which codes, if any, are activated?

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Prior to Christmas, the AA service arrived and affixed a scanner to the vehicle, diagnosing the issue as either the Fuel Pressure Regulator (FPR) or the High-Pressure (HP) pump. I substituted it, but it failed to initiate. Due to the absence of a fuel pressure gauge, I have taken the initiative to send it to a specialised Mercedes-Benz service. The fuel pressure was assessed and found to be significantly low at the high-pressure pump. Thus, it was substituted. Despite the previous attempt being unsuccessful, they proceeded to replace the crank sensor, since it is known to be a potential cause of engine failure to start. However, the issue persisted and the engine still did not start. That is the extent to which it progressed.

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I am unaware of any diagnostic equipment that can definitively determine the failure of a high-pressure pump (HPP).

I recommend that you thoroughly retrace your steps and conduct a comprehensive diagnostic from the very beginning. Alternatively, the garage may also be responsible.

Is there a pressure gradient present in the tank during delivery? If the answer is affirmative, proceed. If not, then you are experiencing a problem with the gasoline pumps located within the tank.

If the answer is affirmative, what is the magnitude of the rail pressure? The pressure should exceed 280 bar. If the answer is true, proceed and examine the injector leak off. If not, it is necessary to determine the cause and examine the rail pressure monitoring system to verify the accuracy of the data it provides.

There is an evident oversight there. Every reputable shop should have a fuel pressure tester.

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This morning, I informed them about the injector leak. I was informed that the pressure at the gasoline filter was satisfactory, thus I disregarded the possibility of a malfunctioning tank pump. However, I will still make a note of this information. Thank you.

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Once again, could you please clarify the meaning of that? When there is a fuel pressure of 2 bar, gasoline will leak out in various places, creating the illusion of sufficient fuel pressure. However, the current power level is insufficient to sufficiently activate the High-Pressure Pump (HPP) and provide optimal rail pressure. Therefore, it is necessary to quantify it. A delivery pump with low power may still provide enough pressure, but it may not reach the desired level of effectiveness.

Have you ever depressurized a tyre by releasing a Schrader valve at around 30 psi? It forcefully pushes your hand away. Three times the pressure is required to initiate the HPP system, which is crucial for its operation.

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