28/09/2020
Shogun Power Loss: EGR Valve Mystery Solved
Many drivers of the 2008 Mitsubishi Shogun have reported an intermittent but severe loss of engine power, often occurring at specific points during a journey. This frustrating problem, where the engine runs but lacks any significant oomph, can eventually become a constant issue. If this sounds familiar, you're not alone, and the good news is that the solution might be simpler – and cheaper – than you think.
The root cause, as discovered by one Shogun owner, often lies within the Exhaust Gas Recirculation (EGR) system. This system is designed to reduce harmful emissions by routing a small amount of exhaust gas back into the inlet manifold. However, when the EGR valve, which controls this flow, becomes sticky with tar and carbon deposits, it can malfunction. In the case of a sticky valve, it can remain open when it shouldn't, leading to a dramatic drop in performance. This happens because it allows oxygen-depleted exhaust gases into the inlet, and more critically, it allows the boost pressure built up by the turbocharger to escape directly into the exhaust system, rather than into the cylinders. This effectively creates a large 'hole' in the intake system, mimicking a turbo underboost situation, and can often trigger diagnostic trouble code P0299 (Turbo Underboost), even if the turbo itself is perfectly healthy.
Understanding the EGR System
The EGR system is a crucial component in modern diesel engines, aimed at curbing the production of nitrogen oxides (NOx). NOx gases are formed at high combustion temperatures. By recirculating a portion of the exhaust gas, which is relatively inert and cooler than fresh air, the overall combustion temperature is lowered, thereby reducing NOx emissions. The EGR valve is typically an electronically or vacuum-controlled valve that opens and closes based on engine load, speed, and temperature. In many vehicles, including the Shogun, the EGR system is often integrated with a cooler (a small heat exchanger) to further reduce the temperature of the recirculated gases.
Symptoms of a Faulty EGR Valve
The symptoms described – intermittent or constant loss of power, particularly under acceleration, and the potential for a P0299 code – are classic indicators of a malfunctioning EGR valve. Other potential symptoms include:
- Rough idling
- Increased fuel consumption
- Engine hesitation
- Check Engine Light illumination
The intermittent nature of the problem, as described by the original poster, is often due to the valve being 'sticky'. Temperature plays a significant role; the valve might stick open at a specific engine operating temperature, only to free up later, or vice versa. This temperature sensitivity can make diagnosing the problem challenging without a systematic approach.
DIY Diagnosis: The Foil Trick
A clever and cost-effective way to diagnose if a sticky EGR valve is the culprit is by temporarily blocking the EGR flow. This can be done using a piece of thick aluminium foil. Please read the following steps carefully and ensure you are only blocking the EGR pipe.
Step-by-Step Diagnostic Procedure:
- Access the EGR Pipe: Remove the plastic engine cover to gain access to the engine bay.
- Locate the EGR Cooler: Look for a small, radiator-like component situated on the exhaust side of the engine, typically above the turbocharger. This is the EGR cooler, which uses engine coolant to reduce exhaust gas temperature.
- Identify the EGR Pipework: The EGR cooler will have at least two pipes connected. One pipe will come from the exhaust manifold (carrying hot exhaust gases), and another will run across the engine towards the inlet manifold assembly. It will also have coolant pipes connected to it.
- Create a Temporary Blockage: Focus on the pipe that runs *away* from the EGR cooler towards the other side of the engine. At the point where this pipe connects to the EGR cooler, there are usually two bolts securing the flange. Slightly loosen these two bolts. You need to create a small gap between the pipe flange and the EGR cooler housing. The pipe has some natural springiness, which should help you pull it up slightly. If it's too stiff, you might need to locate and loosen a clamp further along the pipe's length to give it more play.
- Prepare the Foil Gasket: Take a piece of household aluminium foil and fold it over several times (around 8 layers is usually sufficient) to create a thick, robust gasket. Cut it to a size that will completely block the opening in the EGR pipe when inserted into the gap you created.
- Insert the Foil: Carefully push the folded foil gasket into the gap you created between the EGR pipe and the EGR cooler.
- Secure the Pipe: Gently re-tighten the two bolts. Do not overtighten, as this could damage the flange or the cooler housing. Just make them snug enough to hold the foil in place for a test drive.
Test Drive:
With the foil in place, take your Shogun for a test drive, ideally replicating the conditions under which you normally experience the power loss. If the power returns and the engine performs as it should, it's highly likely that your EGR valve was indeed sticking open and causing the problem.
The Fix: Cleaning or Replacing the EGR Valve
If the foil test proves successful, it's crucial to remove the foil and properly reassemble the EGR pipework. Leaving the foil in place will disable the EGR system permanently, which can lead to other issues and increased emissions. The proper fix involves cleaning the EGR valve mechanism or, if cleaning is ineffective, replacing the valve.
Steps for Cleaning:
- Locate the EGR Valve Unit: Follow the EGR pipe from the EGR cooler to its destination on the inlet manifold. The EGR valve is typically mounted here and often has an actuator (which looks like a small motor) on its rear end.
- Remove the EGR Valve Assembly: Carefully unbolt and remove the entire EGR valve unit from the inlet manifold.
- Clean the Valve Mechanism: You will likely find that the valve mechanism inside is heavily coated in thick, black tar and carbon deposits. This residue is what causes the valve to stick. Use a dedicated turbo cleaner or a strong throttle body cleaner to thoroughly clean the valve and its seating. A stiff brush or some gentle scraping with a plastic tool might be necessary to remove stubborn deposits. Ensure the valve can move freely.
- Reassemble: Once clean and dry, reassemble the EGR valve unit back onto the inlet manifold.
- Reconnect Pipework: Reconnect the EGR pipe to the EGR cooler, ensuring the original gasket (if present) is reinstalled or replaced, and tighten the bolts securely. Reinstall any clamps you loosened.
When to Consider Replacement
If, after thorough cleaning, the EGR valve still sticks or if the electronic actuator appears damaged, replacement of the EGR valve assembly may be necessary. Consult your vehicle's service manual or a qualified mechanic for the correct part number and installation procedure.
Preventative Maintenance
While the EGR system is designed to reduce emissions, it can paradoxically lead to performance issues due to the nature of its operation. Regular servicing and the use of quality diesel fuel can help minimise the build-up of deposits. Some drivers opt for professional EGR cleaning or even blanking plates (though blanking is illegal for road use in many jurisdictions and can cause issues with modern engine management systems). However, for most owners, a proactive approach to cleaning the EGR valve when symptoms first appear is the most practical solution.
Frequently Asked Questions (FAQs)
Q1: Will blocking the EGR pipe permanently fix my Shogun's power loss?
A: No. Blocking the EGR pipe is a diagnostic test. While it temporarily resolves the issue caused by a sticking valve, leaving it blocked can lead to increased emissions, potential MOT failure, and may trigger other engine management fault codes.
Q2: Is it safe to clean the EGR valve myself?
A: Yes, for many DIY mechanics. However, it requires careful handling of engine components. If you are unsure about any step, it's best to seek professional help.
Q3: What is P0299 code?
A: P0299 is a diagnostic trouble code that indicates "Turbocharger/Supercharger 'A' Underboost Condition". It means the engine's computer is detecting that the turbocharger is not producing the expected boost pressure. A sticking EGR valve can cause this by allowing boost pressure to escape.
Q4: How often should the EGR valve be checked?
A: There's no fixed interval, but if you notice any of the symptoms mentioned, it's a good time to inspect it. Regular maintenance with quality fuel can help prolong its life.
By understanding the function of the EGR system and performing this simple diagnostic test, Shogun owners can effectively identify and rectify a common cause of power loss, saving time and money on potentially unnecessary repairs.
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