What Is the Cause of Hard Starting in Diesel Engine?

Weather conditions can do bad things to our vehicle. One of those things is a hard start on a diesel engine, but do you know the reason for this? Let us find out.

So what is the cause of hard starting in a diesel engine? The answer is not limited to one. There are many reasons like a fault in glow plugs, bad starter, bad injector, and many more.

We will list below all the possible reasons. Keep reading and enjoy.

What Is the Cause of Hard Starting in Diesel Engine

Reasons Why Is Diesel Engine Hard to Start

Here are some reasons why your diesel engine is hard to start.

1. A Faulty Glow Plug System

If there is no slow cranking, you might have to consider a faulty glow plug system. Most of the cars have glow plugs. These glow plugs assist the vehicle on cold starts.

A timer and a relay power these glow plugs. These will course a voltage to the plugs. The voltage must be turned off once the timer has run out.

But there are other instances where the relays will stick, resulting in the continuous feeding of voltage to the glow plugs. In return, the glow plugs will burn out. In average weather, this issue will not likely cause the diesel engine a hard start, but it will be if the temperature will drop.

If there are burned-out glow plugs in your vehicle, your diesel engine will be harder to start. This will get worse if the temperature drops. You can check the glow plugs by measuring their continuity or resistance.

If you are experiencing a hard start on your diesel engine, your glow plug module can fail to turn on the glow plugs. This is especially true if the weather is cold.

You can check the glow plug module using a voltmeter. It would be best if you replaced any glow plugs that were necessary replacements.

2. Problems With Stalling

There must be a lubrication problem in your injector pump if your diesel is stalling when you are decelerating. You need to check first the idle speed above all else. If the idle speed is low, it will keep the pump governor from recovering.

The pump governor must recover enough to prevent the engine from stalling when you are decelerating. If you also make the metering valve or plungers inside the pump stick, the diesel will still stall from the water in the fuel.

The pump must be cleaned and replaced. However, you can try to add additives first. If it will not work, have the pump removed, cleaned, or replaced.

3. Problems With The Injector

A diesel injector requires more pressure than a standard gasoline engine. However, the pressure can decrease over a long period. You need to check if there are any damages or issues with the injector.

Your injector can have varnish deposits, clogging, leakage, and wears. You can check if an injector is terrible on a diesel engine. You can use a digital pyrometer.

You can use this to check the operating temperature of the cylinder. If there is a lower temperature reading than the other cylinders, then this is a weak cylinder. Your injectors might be dirty if you will experience a rough idle or a loss of power.

You will also see white smoke from the exhaust. You need to check for the resistance of the glow plugs. You also need to check for the temperature of the cylinders.

4. Fuel Delivery Problem

The timing of the injector must be accurate for an engine to start correctly. You need to check visually if timing marks are lined up. If you notice that the timing is off, you can check on your vehicle’s manufacturer’s timing procedure.

Your car will have a hard start if there is air in your fuel. If there is air in the fuel, the engine will die after you start it. It will also be difficult again to start.

Air can come in the fuel and can make your engine hard to start. You can check if the air is the problem. You can install a clear return hose on the return side of the injection pump.

After that, you just have to crank the engine and observe the line. If there are air bubbles, the air bubbles will enter the inside of the pump. If you also have a clogged pump, this can also make your engine hard to start.

Related: Diesel Hard to Start After Sitting

How to Start Diesel Engine More Easily?

There can be a few tips on how to start your diesel engine quickly. You need to use glow plugs and block heaters. These two will start the diesel engine in cold weather.

Glow plugs will do their job of heating the internal combustion chamber. After this, the condition will be suitable for compression and ignition. You may also install a second battery.

You need to ensure that you have a fully charged battery. If you do not have a fully charged battery, it is always advisable to install a second battery. This second battery will be for the glow plugs.

Your glow plugs will not do their job if there is some serious juice on the car’s battery. You also need to change your oil regularly. If your oil is thicker, a diesel engine will have a hard time starting.

You can also turn off all unnecessary accessories. It would help if you conserved all your batteries to turn off all accessories that you will not use. Turning on and using accessories are getting energy from the battery.

It is also essential to use the correct diesel fuel. You can also use winter fuel additives. This additive will be added to your fuel. You need to mix this additive into your fuel.

hard starting diesel engine


In summary, this is not an unusual situation. Many drivers have experienced a hard start on their diesel engines. In sipping fuel, diesel can be a handful.

Though diesel is very popular for trucks and pickup trucks, diesel also has a lot of issues. One of these issues is having a bad start.

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My name is Hank, and I've been in the automotive industry for 27 years. I've been working in my own auto repair shop for the last 13 years, and now I want to help you here, on my blog. Let me know if you have any questions. Read more