Inside Your Car 24 April 2024

A guide to your diesel car’s suction control valve

In every diesel engine there’s a small but very important component known as the suction control valve (SCV). This often overlooked device regulates the flow of fuel with precision to ensure optimal engine performance. When your SCV is working its magic, your diesel purrs with efficiency and power. But, when the SCV isn’t functioning as it should, it can lead to issues like decreased fuel efficiency to rough idling or even engine failure.

Whether you're a seasoned mechanic or a diesel novice, this guide has everything you need to know about the diesel suction control valve. We’ll explore what the SCV is, what it does, telltale signs of a faulty valve, and how to check and replace this unsung hero of your engine.

What is a suction control valve?

This vital electrical device regulates the amount of fuel injected into the engine cylinders. It acts as a gateway, controlling the flow of fuel to ensure the engine runs smoothly and efficiently by adjusting the fuel supply based on things like engine speed and load. Having a well functioning SCV is essential for optimal engine performance and fuel efficiency.

What does a suction control valve do?

The SCV’s job is to adjust the amount of fuel that enters the diesel engine's fuel pump. So how does a suction control valve work? It works by opening and closing in response to signals from the engine control unit (ECU), controlling the fuel pressure and amount of fuel delivered to the injectors. This precise control ensures that the engine receives just the right amount of fuel for its needs, based on factors such as speed and load, optimising performance and making fuel last longer.

Finding the suction control valve location

You’ll usually find the SCV on the back of the fuel injection pump. However, the exact location may vary depending on different makes and models, so check your vehicle's manual. Or, simply drop into mycar and our expert diesel technicians can help you locate it.

Symptoms of bad suction control valve in your diesel engine

There are a few signs that your diesel car’s SCV is on its way out. Some of the most common symptoms of faulty suction control valve are:

Engine running rough
Issues with acceleration
Decreased fuel economy
Vehicle power is reduced

If you notice any of these suction control valve symptoms, then it’s best to get your car checked out as soon as possible.

What happens when an SCV fails?

If your SCV has failed completely, then fuel injection will stop, causing engine issues such as:

Surging
Limp mode activation
Stalling or stopping

If you notice any of these symptoms, bring your car to your nearest mycar mechanic to get it quickly sorted.

What happens when the suction valve is closed?

If the suction control valve is closed, no fuel can flow into the fuel injection pump. The liquid that remains in the pump starts to heat as it moves around in the pump casing without being circulated. This can lead to overheating and damage to the pump. A closed suction valve also causes a reduction in pressure, leading to the fuel injection pump cavitating—a process that causes significant wear and can result in costly repair issues if not addressed promptly.

Here’s how to test suction control valve

If you suspect that your SCV is faulty, you can test its functionality.

Here’s what to do for the check:

Disconnect the suction control valve connector.
Measure resistance between terminal No. 1 and No. 2. Standard value should be approximately 2.1 Ω (at 20 °C)
Inspect the SCV for physical damage or corrosion.
Connect a vacuum gauge to the SCV to check for proper vacuum levels.

If you're not confident working on your car's engine, it's best to seek professional help, so bring it down to your local mycar for assistance.

How to clean suction control valve in your diesel engine

Follow the below steps to do a suction control valve cleaning:

Remove SCV, retaining all seals.
Remove C-clip inside SCV.
Remove plunger and clean all debris out of it.
Check for scoring or damage.
Replace SCV.

How long do suction control valves last?

The lifespan of your SCV will depend on the amount of driving you do, and how hard it has to work. It’s recommended that you get your suction control checked and replaced every 60,000-80,000 kilometres. Regular maintenance and inspection can help extend the life of your SCV and prevent potential issues, so it’s a good idea to get your car serviced regularly.

Steps to do suction control valve replacement

If your suction control valve problems haven’t been solved with a thorough clean, or testing revealed your SCV has failed, it’s time for a new one. Here’s how to replace your suction control valve:

1. Remove the old SCV:

Disconnect the electrical connector from the SCV.
Use a wrench or socket to loosen and remove the bolts securing the SCV in place.
Carefully pull the SCV out of the fuel injection pump. Be gentle to avoid damaging the pump or surrounding components.

2. Install the New SCV:

Compare the new SCV with the old one to ensure they match.
Insert the new SCV into the fuel injection pump, aligning it correctly.
Secure the SCV in place with the bolts and tighten them securely.

3. Reconnect Electrical Connections:

Reattach the electrical connector to the new SCV.
Ensure the connector is securely in place and the wiring is not tangled or strained.

4. Test the SCV:

Reconnect the battery and start the engine.
Check for any signs of improvement in engine performance.
If everything is working correctly, turn off the engine.

5. Once you’ve finished installing the new SCV, a Fuel Pump Learning procedure must be initiated in the ECU.

Still not sure? Drop into mycar for help

If you're not sure about the condition of your SCV, drop into one of mycar’s more than 275 conveniently located stores for professional servicing, testing, or replacement. We offer a lifetime guarantee on all work performed on your car, so you can have peace of mind your ride is always in good hands.