(GDI) is a fuel injection system that sprays gasoline, directly into the combustion chamber.
So, (GDI) uses a separate fuel injector, for each cylinder.
As a result, this allows for direct access, to the combustion chamber. So, the only thing going through the intake manifold and the intake valves, is air.
Now, with (GDI), the fuel enters each cylinder, as a high pressure mist. Then, uses computer controlled electric injectors, to spray fuel into the cylinders.
Consequently, the computer controls, all aspects of the (GDI) system. So, with all the different running conditions, the computer will decide, when to inject the fuel.
The Benefits, Of The (GDI) System
First, you have better fuel economy, with less overall emissions. As a result, this leads to better engine performance.
So, the engine makes more power, and uses less fuel from:
- Spraying fuel directly into the combustion chamber, as compression is building.
- As well as, during and after initial combustion.
So, engines with (GDI) can tolerate, extremely lean fuel mixtures, (up to 40:1). Even under light load, and cruise conditions. The net result, is typically 15 to 20 percent, better fuel economy.
So, this new system closely controls the fuel mixture, at just the right moment. Also, (GDI) engines can handle higher compression ratios. As a result, (GDI) engines, usually produce more power.
The Disadvantages, Of The (GDI) System
So, the big disadvantage of (GDI), is carbon building up, on the back of the intake valves. This can throw a computer code, and result in an engine misfire or a ignition failure.
Also, the actual cost of this system, tends to be higher. Because, the fuel pump, must be capable of very high pressures.
All this has led to the engine, needing to drive the fuel pump. So, the main reason we are seeing vehicles on the market with (GDI), is tighter fuel economy standards.
So, (GDI) Requires, Extremely High Operating Pressures, (up to 2200 PSI).
(GDI) needs more fuel delivery pressure, to overcome compression pressure, inside the cylinder. As a result, it needs to deliver a higher volume of fuel, in a shorter period of time.
The higher injection pressure also helps, to atomize the fuel into small droplets. So, it will mix better with air, for more complete combustion.
So, How Does (GDI) Create New Problems
Along with many automotive innovations, comes a new set of problems.
First, higher cylinder temperatures and pressures, released into the crankcase, accelerate oil vaporization. Eventually this causes oil droplets, to coat the intake valves. Also, with (GDI) systems fresh fuel, is not sprayed onto the intake valves.
As a result, the valves are no longer cleaned or cooled by the fuel.
Secondly, it can cause piston rings, to become stuck into their lands. And, if the engine uses low tension rings, the sludge can prevent them from properly sealing. As a result, that can cause sludge and fuel deposits, to bake onto the top of the piston.
Since inception, (GDI) engines have had known problems with, carbon building up. One of the problems is cooked fuel deposits building up, and fouling the injectors. As the deposits accrue over time and mileage, the timing can also be altered. Carbon building up on the back of the valves, can alter ignition timing, and the firing order.
The carbon also acts as an insulator, so the valves can heat up and fail. Over time, the carbon can fall off the valves and make its way, to the bottom end of the engine. As a result, causing wear on the moving parts.
Carbon deposits may flake off and pass through the combustion chamber, and into the exhaust. So, if the engine is equipped with a turbocharger, there is a chance the carbon, could damage the turbine fins in the turbocharger.
The problem tends to be worse in (GDI) engines, that are used mostly for short trips. Because, the intake valves, never get hot enough, to burn off the deposits.
How To Clean This New Fuel System
Some of the choices may include:
- Use a chemical cleaner sprayed into the throttle body or intake manifold, directly into the intake ports.
- Remove the intake manifold and spray solvent, directly into the intake ports in the cylinder head.
- For extremely heavy carbon deposits, it may be necessary to remove the cylinder head to clean the valves.
Conclusion
So, port injection, is much better than the old carburetors, and throttle body systems. But, just can’t match the power and economy, produced by (GDI). As fuel costs increase, the difference in manufacturing cost between port, and direct injection systems will diminish.
BY DANNY BENDER
