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Direct Injection Vs Port Injection – Is It Better To Have Both?
You may have noticed a growing trend in new vehicles being made today, which is direct and port injection. You may be asking yourself what is the difference between direct injection vs port injection and which is better? This guide is designed to help you understand the differences between direct and port injection and which you want to get on your next vehicle.
Why do new cars use both direct and port injection? New cars use both direct and port injection because it limits the amount of carbon buildup that would typically occur with a direct injection engine.
Engines that use direct and port injection allows the engine to get the advantages of both injection technologies while removing the downsides of using direct injection only.
One area that direct injection only engines have weak points is in the area of carbon buildup. Because direct injection engines are injecting fuel directly into the engine cylinder they can’t clean the back of your engine valves. This can lead to carbon build up over time which can be an expensive repair job.
Port injection engines don’t have this problem because they spray fuel over the back of your air intake valves which helps clean carbon build-up from the back of your intake valves. That is why some vehicle manufacturers have started making engines with direct and port injection.
They can take advantage of the benefits of using direct injection technology in their engine while also helping prevent carbon build-up with port injection.
Depending on the capabilities of the engine it may use direct injection in conjunction with port injection or one or the other. Direct injection is better suited for wide open throttle to help reduce engine knock and provide more horsepower. Port injection is used under low loads to help use less gasoline.
What is Direct Injection?
If your car’s engine is a direct injection engine this means that it has fuel injectors that are installed directly inside the engine cylinder. Because the fuel is being injected directly into the engine cylinder it can use less fuel to ignite during the combustion process.
Using direct injection also allows your car’s engine computer to allow greater control of where and how much fuel is injected into the engine cylinder. This typically means that an engine equipped with direct injection will get better gas mileage than an engine equipped with port injection.
Direct injection is the newer technology and why it is also a factor in why newer cars may get higher gas mileage.
What is Port Injection?
With port injection, the fuel injectors are positioned on the air intake leading to each cylinder of your engine. As your engine sucks in air to later be compressed your fuel injectors will spray a fine mist of fuel that will eventually mix with the ambient air as it gets sucked into your engine.
This allows the air and fuel enough time to mix with each other as they are eventually sucked into the cylinder wall. That air and fuel mixture would then be compressed and then ignited to complete the combustion process of your engine.
Port injection is the other of the two injection technologies and has been around for quite some time.
What are the Benefits of Direct Injection?
With direct injection technology, the fuel injector is positioned in the engine cylinders which allow the engine computer to be able to adjust the fuel based on how the engine is operating. Under low loads, the engine can use less fuel to propel itself down the road effectively reducing fuel consumption.
Under high loads, the engine is also able to run efficiently by using a small amount of fuel to help with the combustion process. Direct injection actually works the best under high RPM high load situations.
While the fuel in a direct injection engine may not be mixed as well as on a port injection engine direct injection will allow the engine computer to better be able to handle whatever situation it is presented with. If your engine is running lean it can adjust quickly to help reduce the chances of engine knock.
Because the engine is able to better use its fuel it will typically be able to obtain a higher fuel economy than an engine with port injection. However, there are many factors besides the type of fuel injection that will go into how many miles per gallon your car will get.
Direct injection can also help prevent engine knock. Because direct injection technology is designed to be high compression engines it is the best fuel injection technology for forced induction engines. If your car is equipped with a supercharger or turbocharger it’s likely that your engine could benefit from direct injection.
What are the Problems Associated With Direct Injection?
One downside to direct injection only engines is that they can be susceptible to carbon buildup on the intake valves of the engine. Because direct injection engines won’t have any fuel sprayed over the intake valves of the engine carbon buildup will begin to occur over time.
If you don’t take care of the carbon buildup in your engine it can lead to more problems down the line. Cleaning the carbon buildup in your engine is not a cheap job either. Most shops have to walnut blast the air intakes of the engine to be able to remove the carbon buildup.
Walnut blasting your engine intake can cost thousands of dollars because of the time associated with disassembling the engine and the care it takes to remove the carbon buildup. To learn more about the problems that can occur with direct injection engines check out the video below.
What are the Benefits of Port Injection?
Port Injection has been around since the 80’s when they replaced carburetors as the go-to fuel injection method. Port injection shoots fuel into your air intake port that is then sucked into the piston to provide fuel for the combustion stroke of your engine.
The benefit of port injection is that it allows the air to mix with the fuel being injected evenly before it is fed into the engine cylinder. When the air and fuel mixture is evenly mixed it allows the combustion process to burn all of the fuel that is injected into the engine cylinder reducing carbon buildup from unburnt fuel.
With direct injection, the fuel has less time to mix with the air coming into the cylinder which can cause some hot spots to form inside the engine cylinder. Hot spots are not good because they can cause one area to get much hotter than the other surrounding areas instead of evenly heating the engine cylinder walls.
What are the Problems Associated With Port Injection?
There isn’t necessarily anything wrong with port injection it’s just that direct injection is the newer technology of the two. With port injection spraying fuel over the back of your intake valves, you don’t have to worry about carbon buildup in your engine as much as you would with direct injection.
Port injection only engines are being phased out in favor of direct injection engines because of the increase in mileage that can be achieved with direct injection. Port injection has worked well in engines for decades but eventually, it’s going to be replaced with direct injection engines or both direct and port injected engines.
Therefore there aren’t necessarily any problems with port injection it just comes down to how fuel-efficient automakers can get their vehicles before new regulations force them to be more fuel-efficient.
What is the Benefit of Direct and Port Injection?
One benefit of using both direct and port injection that most vehicle manufacturers won’t talk about is the reduction of carbon buildup. When an engine can use both direct and port injection systems it will greatly reduce the amount of carbon buildup when compared to just a direct injection engine.
With direct injection engines, the fuel is injected directly into the engine cylinders and doesn’t get passed over the intake valves of the engine. Because of this carbon buildup can occur on the intake valves of direct injection engines over time as the fuel has additives that are designed to help clean your intake valves.
Since no fuel is ever sprayed over the intake valves on a direct injection engine it doesn’t have a chance to clean the intake valves. With direct and port injection engines engineers solved this problem as fuel will spray onto the intake valves from the port injectors which will keep carbon build-up from forming.
Auto manufacturers were having issues with direct injection and carbon buildup in their engines so they eventually decided that it would probably be best to add back in port injection to help prevent carbon build up in their engines.
This was a good move for consumers because having your engine carbon cleaned is not a cheap fix. To remove the carbon buildup the top of your engine has to be removed to be able to access your intake valves. From there the mechanic can walnut blast the intake valves and intake to remove any carbon buildup.
This process can typically cost in the thousands of dollars because of the labor associated with disassembling the engine to be able to walnut blast your intake valves. To learn more about why new cars are using both direct injection and port injection check out the video below.
Related Questions:
What is the Difference Between Port Injection vs Direct Injection? The main difference between direct and port injection is where the fuel injectors are located in the engine.
With direct injection engines, the fuel injectors will be located within the actual engine cylinder. With port injection engines the fuel injectors will be located in the air intake of the engine.
Both technologies have their own benefits and downsides. If you have the opportunity to go with an engine that has both direct and port injection technology you can get the best of both worlds. While the engine may be a bit more complicated it will be able to take advantage of both fuel injection technologies.
Can You Prevent Carbon Buildup in a Direct Injection Engine? Some engines with direct injection technology may not have an issue with carbon buildup but there are plenty of cases with people having to have that carbon buildup removed.
This is a common issue with BMW and Audi direct injection engines that tend to pop up on higher mileage direct injection engines.
While you can do your best to help any new carbon buildup from forming you can’t really prevent carbon buildup from happening altogether in your direct injection engine. One thing that you can to to help carbon buildup is to buy an oil catch can or an air oil separator. 
Is Carbon Buildup In Direct Injection Engines A Common Problem? Carbon buildup within direct injection engines is somewhat common in certain car models. It’s best to do your research to determine if it’s a common problem on a car that you are looking at buying.
Keep in mind that it is something that typically happens in high mileage direct injection engines. Sometimes engines have to be carbon cleaned before even hitting 100,000 miles. It really just depends on how well your engine is running and how it was designed where you will have this problem or not.
This is what has somewhat turned me off from ever purchasing a BMW 335i or Audi S5. Both cars use direct injection technology and both have had issues with carbon buildup. Quickly searching on related car forums will provide you with ample examples of people having to carbon clean their Audi S5 or BMW 335i.
Are There Direct Injection Engine Cleaners? If you have been having issues with carbon buildup in your engine you may want to take your chances at trying an engine cleaner to help remove that carbon buildup.
If your engine has steadily been building up carbon on the intake valves of your engine it’s likely that any engine cleaner will have little effect on removing the carbon that has already started to line the internals of your engine.
If you were to use an engine and fuel injector cleaner for the life of your vehicle that may help reducing carbon build-up in your direct injection engine but you may still have the problem. Because the fuel injectors are in the engine cylinders they won’t be able to spray fuel over the intake valves of your engine to clean them.
Really if you wanted to try to help remove carbon buildup from your direct injection engine you would want to spray an engine cleaner directly into your air intake. That way the engine cleaner would be able to spray over the back of your intake valves helping clean them off.
Seafoam sells a product called seafoam spray that you can use a spray nozzle to spray the product into your air intake while your engine is running. This allows the engine to suck in the product into the air intake helping clean the engine. Just don’t overdo it as this can cause your car to die if you spray too much.
Is Direct Injection Better Than Port Injection? Direct injection is the latest fuel injection technology and while it can be considered a better technology than port injection in some regards it also comes with some downsides.
Direct injection allows the computer engine to better control of how much fuel is injected into each engine cylinder before the combustion stroke.
Direct Injection Vs Port Injection – In Conclusion
Hopefully, now you know the differences between direct injection vs port injection and what the benefits of each type of fuel injection technology are. While direct injection can make an engine more efficient it also has the downsides of creating more carbon buildup in your engine. Port injection is older technology but carbon buildup is less likely to happen with port injected engines.