By Jim Kerr

Stumbles, stalls, hesitations, hard starting, lack of power, poor fuel economy: these vehicle problems can all be caused by deposits inside your vehicle’s engine. Clean up these deposits and your engine will operate much better. Let them build up more and you pay in aggravation and higher fuel consumption. Where are these deposits and what causes them?

There are two areas of the engine that are affected most by deposits: fuel injectors can build up gummy fuel deposits on the tips that affect fuel volume and spray patterns, and the back side of the engine valves can build up deposits that disrupt fuel and air flow into the cylinders and restrict exhaust gases as they exit. This happens in all engines, but some seem to be worse than others. It doesn’t appear to be the actual engine that is the cause. Rather, it appears to be caused by what we put in them – fuel and oil – and how we drive.

Fuel injectors sit down in the intake manifold, with their tips projecting into the engine’s intake runners. Fuel sprays from small holes in the injector tip and comes out in a fine cone-shaped mist. This allows the fuel to evaporate rapidly and be drawn into the combustion chamber when the intake valve opens. Every time the engine is turned off, heat from the engine rises and bakes the injector tips. Fuel remaining on the tip when the engine is turned off evaporates but leaves behind some of the heavier parts of the fuel, which forms gummy deposits. The fine mist spray pattern is disrupted by the deposits and instead fuel is sprayed out in a stream and possibly in the wrong amounts.

There are three things you can do to prevent this from happening: first, drive longer trips. Highway travel causes higher volumes of fuel to flow through the injectors, helping clean them. Secondly, use a quality fuel. All fuel manufacturers add injector fuel cleaning additives to the fuel, but the amount and type of additives varies with the fuel supplier. You may have noticed the Shell fuel advertisements on TV recently. They claim they specially formulate the fuel for Canadian climates and driving conditions. I can’t verify that Shell fuel does contain better additive packages, but I have noticed that some of my vehicles run better when filled with their fuel, and I have witnessed the effects of switching from one brand of fuel to another on the deposits found on the back of the valves. Use the right fuel and those deposits actually start to dissolve again.

Adding a fuel injector cleaner chemical to the fuel tank is a third way of cleaning up injector tips or preventing deposits from forming in the first place. Deposits on the back sides of engine valves are more difficult to remove. Some of these deposits are even difficult to remove with a wire wheel when the valve is out of the engine. The deposits disrupt fuel flow into the cylinders and can build up enough to block air flow, reducing engine power. Some manufacturers such as BMW have even specified service procedures to remove the deposits by blasting them with walnut shell. First the intake manifold is removed and the engine cranked over so the valve is closed. Then an adapter is bolted to the cylinder head that shoots walnut shell at the back side of the valves with air pressure. Walnut shell is used instead of sand blasting, as walnut shells won’t damage or erode fine metal finishes and if any small bits are left in the engine, they just burn in the combustion chamber.

These deposits are formed by oil film from the crankcase ventilation system, lubricating oil that seeps down the valve guides and gummy fuel that collects in the intake ports. Again, using a fuel that contains the right additives to clean these deposits is the easiest way of removing them, but it can take several hundred kilometres for the majority of the deposits to be removed even with good fuel. Because the engine valves are not easily visible, the only way to tell if your fuel is working well is to use a few tanks and see if performance improves. You will probably notice idling quality and fuel economy are the first things to change. Try one brand of fuel and then another. When you find one that improves engine operation, stick with it.

You may think that changing oil and replacing filters is all that is necessary to keep an engine clean, but preventing deposits from forming on injectors and valves will improve your vehicle’s performance and save some fuel money too.

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