Direct Injection: Efficiency at a Price
And, it’s probably your faultby Matt M., on
For a while now, direct injection (DI) engines have been all the rave: boasting better efficiency, more power, better economy. Sounds wonderful, right? Who wouldn’t want that? Well, DI engines have a dirty, dirty little secret that you will not discover until you are deep into a relationship with them. DI engines have much higher maintenance requirements and associated costs. If you ignore those requirements, the cost is going to compound itself many times over in the form of major repairs. If you’re thinking you’re going to save a few bucks at the pump, you had better save those few bucks because you’re going to need them..
What is a Direct Injection engine? How do I know if I have one? Why would a car company do this?
|Fuel Delivery in a Direct Injection System|
First, please know that this was not an evil car manufacturer plot, they HAVE to find ways to make cars more efficient from an emissions standpoint. You can easily look up your make and model to find out whether its engine is DI.
Chances are if you have an Audi or VW less than 10 years old, you have a DI.
The same is true of most of the newer Japanese and Korean models. For example, the Hyundai GDI trim level cars? Yeah, GDI means Gasoline Direct Injection. Some companies call it different things, all trying to be special… but if you put a wig on a pig and name it Chad, it’s still a pig. Oink.
|Start of Direct Injection Combustion|
Direct injection is when fuel is injected directly into the combustion chamber of an engine.
It used to be that most engines were what is called “port injection” or PI for short. This is where the fuel injectors spray fuel into the intake ports of the cylinder head to mix with air and then is drawn over and around the intake valves and into the combustion chamber. The reason many companies have switched to DI over PI is because DI makes for a much cleaner burn and less atomization of the fuel to create a more controllable combustion cycle. In normal speak, this means that a car can get better gas mileage by wasting less fuel.
|Visual Representation of Port Injection|
There are, however, a handful of problems with DI and one of them is potentially your fault. The first one is injector failure. It’s more common on DI cars then PI, because the injector is IN the combustion chamber, meaning it is exposed to high temperatures, pressure, and carbon buildup that occurs naturally in a compression cycle. This can lead to failures in the DI injectors such as clogging, damage, and failures from rapid heat cycling.
The second problem is less obvious. A piston in a cylinder has rings on it that seal it to the cylinder wall but still allow it to move. The upper rings keep the combustion on top of the piston, and the lower rings keep the oil on the sides and under the piston for cooling and lubrication. It’s not 100% and over time compression leaks past the rings into the crankcase and the oil can leak up into the combustion chamber. This compression leak down, as it is called, has to be vented or it can pressurize the engine’s crankcase (where all the rotating bits are) causing all sorts of problems. This is where the vehicle’s PCV (positive crankcase ventilation) system comes into play. It basically consists of a “check valve” that bleeds off this pressure, unburned fuel, and oil vapor (remember this part) and recycles it back into the vehicles intake system. Wait… what? Yep, this is part of emissions requirements, and they can’t just let it vent into the atmosphere. Plus, a catch can to corral this hodgepodge would be very difficult to service. This “recycled” mixture of gas, oil, and air gets piped back into the intake manifold to be cycled through again.
|Carbon Buildup in a Direct Injected Engine|
Have you ever stood in a kitchen that doesn’t have a ventilation system? The walls kind of look grimy and it’s impossible to clean off once it has built up over time. That same problem occurs in DI engines.
Oil vapor likes to get caught on anything, and it gums up the manifold runners and the top of the intake valves.
So, over time the tops of the valves get gummed up and eventually lead to problems because they are so dirty that they can’t seal anymore. Remember from before about how the PI engine sprays fuel before the valve? This fuel tends to clean things as it passes over them including the buildup on the ports and the valves. As this is less efficient for mileage and power, it is certainly a win in the form of longevity.
Car companies have realized this is a problem and are now starting to do engines that are both DI and PI, but that doesn’t address the fact that millions of cars have been sold with this problem. Combine this with the fact that turbocharged DI cars compound the problem even more because turbochargers are lubricated with oil, and over time, can start to leak some of that oil into the intake as well.
|Carbon Buildup in a Port Injection System|
Now the most interesting part is that a lot of this for some people is actually their fault.
If you have a DI car, it probably uses synthetic oil. All synthetic oils are NOT alike.
They have a rating system and bases them on what called “Noack evaporation loss.” Basically, it measures evaporation loss at standard operating conditions.
|NOACK Volatility Rating|
Essentially: every time you delay an oil change, you are compounding the effect. Every time you do budget maintenance with cheap deals on oil from your local oil change place, you are compounding the effect. Most service companies have deals with oil manufacturers to use that brand of oil. Oils, especially synthetic oils, are NOT all made with the same quality. This is not something that most brands want public, so it’s not like they advertise “our synthetic is the cheapest and the worst for your car so come put some in your car, ya cheapskate.” It is, however, common sense that the cheaper the brand, the less quality you’re going to get. This is true in basically all things, so why would it not be true in your car? There is so much information on what is good and what is not online that you can take 5 minutes and save your self some headache down the line.
Use the right oil, on time, every time because cars get much more finicky and manufacturers are using thinner and thinner oils that are great for efficiency, but bad for longevity.
The days of skipping oil changes or being thousands of miles late are becoming punishable by engine death.
This also applies to what type and brand of fuel you use. If you’re filling up at the cheap gas station to save a few cents on fuel, you are also compounding the problem. Not all gasoline is created equal so you should decide if saving a little bit right now is worth spending a whole lot later. Do not be afraid to throw some fuel system cleaner in there from time to time, too. (Again, know your products and use as recommended).
The next thing you can do is keep up on your preventative maintenance. Most cars come with a book full of information on recommended service. If you can’t find yours, chances are it’s available online for free. Keep to the schedule and do your recommended maintenance. Most companies know this is a problem and have contingencies to deal with the issues, but you have to bring your car in BEFORE there is a problem.
It’s not all bad: DI is a wonderful thing for the combustion engine from an efficiency standpoint and for performance reasons. As companies start to make less fuel go further, we must make adjustments to how we use (or abuse) our cars. We cannot complain about the environment and expect all these companies to make changes while expecting our experience to remain the same. Most companies have found ways around this problem in the past few years so if you have a brand-new DI car you will probably be all right, so long as you follow the above advice. If you have an older DI car and have not been taking care if it properly, good luck to you and fingers crossed.