Cleaning intake valves, using crushed walnut shells!

By Chris Dekker

 

During the 1980s, there was an important shift in the automotive industry: carburetors were out, and fuel injection was in. While a carbureted engine basically sucks in a stream of liquid fuel, a fuel injected engine uses an electronic fuel injector (which is controlled by a computer) to deliver a burst of high-pressure fuel mist at precisely the right moment. Think of a Windex bottle; the stream setting mimics a carburetor, while the mist setting is your fuel injector.

Most fuel injected engines from the last 20 years use port fuel injection, where fuel is injected upstream of the cylinder into the intake manifold. The fuel spray is carried past the intake valve, and into the cylinder (where it is burned) by the flow of air into the cylinder. Remember this part about fuel passing through the intake valve, as it gets important later!

Liquid gasoline has a hard time burning; it’s the vapor that really gets things going inside your engine. The mist delivered by a fuel injector atomizes easier, and burns more completely. This more complete burn – combined with the improved control from having a computer running things – translates into better fuel economy and decreased emissions. Now imagine that we could take that mist from your Windex bottle, crank the pressure way up, and shoot that pressure through tiny holes so small that the human eye can barely see them. The fuel spray would be super fine; how well would that burn?

 

direct injection

This idea is part of a new technology called direct injection. Direct injection also offers another advantage: it delivers its super-high-pressure fuel spray directly into the cylinders of your engine, right beside the spark plugs. Compared to port injection, direct injection offers even better control of the combustion event, and even better performance. Gasoline direct injection (GDI, for short) is getting more common in our industry, as car manufacturers continue to chase better fuel economy and cleaner emissions. GDI can help a small engine to make as much horsepower as significantly larger one, as Ford has demonstrated with their popular Ecoboost engines.

 

airdrie auto diagnostics

 

However, moving the fuel spray from the intake manifold to inside the cylinders had an unexpected conseqeuence: bad deposit build-up on the intake valves. It turns out that the continuous fuel spray onto the intake valves in a port-injected engine did a good job keeping them clean. Deposit build-up on the intake valves of GDI engines has become a big problem; causing misfiring, hard starting and poor performance.

 

carbon buildup valve

This nasty build-up is composed of:

  • Carbon from the combustion of fuel, which is pushed back out of the cylinders.
  • Trace amounts of engine oil that leak past the valve seals, or are carried into the intake manifold by the crankcase ventilation system.
  • Exhaust soot that is recirculated back through the intake manifold by the EGR (an emissions control) system.

 

This all combines to create a rock-hard, clumpy layer of junk on the intake valves that gets thicker and thicker over time. Eventually it builds up to the point where airflow through the valve is restricted, or the valve cannot open and close properly.

The photo above is from a Mazda that we serviced this week, and is the worst example of this build-up that we have seen to date. This engine had less than 150,000 kilometers on it, and a bad misfire that was due in part to the valve issues. With this Mazda, we decided to do a little experiment. As GDI becomes more common in our industry, so too do the problems with intake valve deposits. Several companies have responded with various products designed to clean off these deposits, including CRC with their GDI-specific “Intake Valve Cleaner”. But do any of them work?

Most of these products are a liquid designed to be “fogged” into the intake manifold as the engine runs, where they will travel through the intake valves and hopefully remove some of the deposit build-up as they pass by. The trouble with these products is that you normally never get to see how well they work (or don’t work), since the valves are hidden deep inside the engine. With this Mazda, we had the intake manifold removed and full access to the valves – so we decided to try several popular products to clean the valves directly. We chose CRC Intake Valve Cleaner, Sea Foam Motor Treatment, ACDelco Cleens Combustion Chamber Cleaner, and a last-minute crazy idea: Wipe-Out, a very powerful gun cleaner designed to remove carbon and copper fouling from rifle barrels.

airdrie auto repair

 

First we sprayed each of the valves with one of the cleaning products, let them soak for a couple minutes, then blew out the intake runners with compressed air. Initial results were disappointing: none of these products magically dissolved or removed any of the build-up through contact with the valves alone. Experience told us not to expect this anyways, but it would have been nice!

Next, we tried a longer, ten minute soak and then a good scrubbing with a small toothbrush before blowing out the ports again. A tiny amount of deposit was removed from each valve, with all of the products working about the same, but we were barely making a dent. We could tell that completely cleaning the valves this way would probably take days; not an economical choice for the customer!

It was the end of the day, so we decided to fill each intake port with cleaning product and let the valves soak overnight. The next morning, we gave each valve a good picking-at with a dental pick, and then a scrubbing with the toothbrush before blowing out the ports. The Wipe-Out seemed to work the best, but barely. We were hoping that “thinking outside the box” would produce an industry-leading breakthrough here, but it was not meant to be. All of the products loosened up an outer layer of the build-up, but 80% of the deposits remained.

One important note: Most of these products are designed to work in the presence of heat on a running engine, which should make the carbon build-up easier to remove. This was impossible with the engine disassembled, of course. However, we’d like to believe that if overnight soaking, scrubbing and brushing will not remove much of the build-up, 2-3 minutes of misting onto the valve will not work either.

At this point, it seemed that the various cleaning products, like much of the snake oil bottles on the parts store shelves, were a chemical solution to a mechanical problem, and just weren’t going to work. No chemical was going to remove these deposits, and pulling the cylinder head to remove the valves would cost thousands of dollars. There had to be a better way. It was after a little research that we came across another popular solution: sand-blasting the valves with crushed walnut shells.

 

airdrie car repairs

 

The crushed walnut shells are abrasive enough to remove the deposits, but not enough to remove metal from the valves or cylinder head. After a quick phone call, we had a big 30 pound bag of crushed walnut shells to play with, and decided to try this technique out. Now, we were making progress! It still took a lot of careful work, but the sandblaster did a nice job of cleaning the valves.

The walnut shell grains proved a bit too large for our recovery system to handle, though. A few hours later, poor Richard had walnut shells everywhere – in his hair, his clothes, and even his nose – but the Mazda had some much better looking valves!

 

airdrie auto service

 

The crushed walnut shell technique offers a good value in that it’s much more effective than most cleaning methods, and still relatively quick; definitely the way to go in a case like our Mazda here.

Having fixed this one, our focus now shifted to preventing this problem in the first place. Would some of the commercial cleaning products work better if used every 10-20,000 kilometers, as maintenance to prevent this build-up? Is this a service we should be recommending to our customers who own direct-injected vehicles?  We don’t want to sell a product that our customers will not receive a substantial benefit from. Continued research over the coming months should give us these answers, and we look forward to sharing more with you!

 

Leave a Reply