Addressing GDI Issues

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Maintaining the Right Charge

Carbon buildup is just one common problem

BY BILL FULTON

GASOLINE DIRECT INJECTION (GDI) engines are becoming very popular on GM, Ford, Honda, Lexus, Hyundai, Kia models, as well as those by many European manufacturers. The reason some manufacturers are leaning toward GDI engines is because they offer an increase in fuel economy, lower emissions and an increase of engine torque and horsepower, even in small-displacement 4-cylinder engines. This occurs because the compression ratios can be increased, and the danger of detonation has been nearly eliminated.

As you already know, the GDI systems inject fuel directly into the combustion chamber instead of into the intake runners. The drawback here is that we no longer have the advantage that PFI (port fuel injection) systems offer where fuel was sprayed into the back of the intake valves, which supplied the solvent effect and kept the back side of the intake valves clean. Unfortunately, the GDI systems do not offer us this advantage. Oil vapors from the PCV system will accumulate on the back side of the intake valves which impedes the engine’s ability to breathe. The GDI engines that are equipped with variable valve timing systems can suffer from these valve deposits due to the valve overlap that occurs at off-idle conditions. This easily occurs on GDI engines when the car owner ignores the oil change intervals, or the wrong API and SAE spec oil is used.

Virtually every GDI engine manufacturer I have researched highly recommends premium synthetic oils. The owner’s manual would be the go-to place for this information. Ford, for example, will actually recommend 10,000 mile oil change intervals. Remember, this applies to normal driving conditions and we know that there is no such thing as normal driving conditions on America’s roads. And second, most of us technicians would never agree to that extended oil change interval.

Two manufacturers — Ford and Lexus — have addressed this problem by equipping some of their GDI engines with an additional PFI injection system. The PFI injectors are pulsed under certain engine conditions which allows the solvent effect on the back of the intake valves. It is critical here that the car owner is aware of the importance of using a brand of fuel known as Top Tiered Gasoline. You can do a Google search for Top Tiered Gasoline and find out what brand of fuel meets these standards.

Carbon buildup on the back of the intake valves has been a major issue for the manufacturers of GDI engines. The carbon deposit problem can be attributed to vaporized oil from the PCV system. See Fig. 1. Some Lexus dealers include a can of MOA on every oil change from the folks at BG Products. This formula helps prevent this oil vaporization problem that occurs at higher engine temperatures. Ford, for example, has never addressed this issue nor does Ford recommend intake cleaning procedures or any fuel additive to aid in preventing the carbon buildup problem.

Another problem GDI systems can suffer from is carbon buildup in the compression ring land areas which can prevent the compression rings from expanding, causing a reduction of compression. See Fig. 2. This problem is not unique to GDI engines. I have seen this problem many times on high mileage PFI engines. I have personally done the intake cleaning followed by a 30-minute cold soak period on high mileage PFI engines and gained 20 to 30 PSI increase in compression values. I have always allowed a cold soak period to allow the chemical to break the molecular bonding on the carbon. Both problems are a direct result from the car owner ignoring proper oil change intervals and using lower quality fuel.

I have always endorsed intake cleaning even as an annual maintenance procedure. The danger here concerns doing the procedure on turbo-equipped engines where carbon could break off and enter the turbo blades. (Chemically cleaning through the intake system will have little effect on the extreme carbon buildup problem seen in Fig. 1.) The folks at BG Products have a kit to address these concerns. See Fig. 3 and Fig. 4.

The procedure requires removing the intake manifold. On the intake valves that are closed, insert a few ounces of chemical known as 44K. After a few minutes of cold soak use the large wooden toothpicks to break away the carbon. The kit includes a wire brush to scrub the back of the intake valves and the intake runners, and there are a bunch of wire ties in the kit. They can be inserted into a drill with the pointed end inserted in the drill to scrub the intake runners. Obviously this procedure is going to be labor intensive.

Those of us who have a bore scope can easily confirm the carbon problem.

Once the carbon is broken loose be sure to blow the loose carbon out. You would need to do this to prevent carbon from entering the turbo blades on the turboequipped engines upon engine start up.

A mechanically driven, electronic controlled, high pressure fuel pump driven from the camshaft is the heart of the system and will generate fuel pressure exceeding 2,000 PSI under WOT conditions. The injectors pulse fuel into a pressurized combustion chamber.

A 12 volt injector will not generate a strong enough magnetic field to pulse fuel into this pressure environment, or to overcome the high fuel pressures in the rail. The GDI injectors are supplied with a 65 volt charge from capacitors inside the PCM or a FICM module found on the Honda V-6 engine.

When specifically addressing these systems, fuel pressures on the low side and the high side under all operating conditions need to be monitored. The GDI systems will have a low side fuel pressure sensor and a high side fuel pressure sensor. It’s obvious that if the low side fuel pressure is too low, then the high side fuel pump cannot perform properly. The good news here is that both the low side fuel pressure sensor and high side fuel pressure sensor can be easily monitored via scan data.

The high pressure pump is mechanically driven by lobes on the camshaft. The GM systems use three lobes on the camshaft while Ford uses four lobes. Most other manufacturers use a three-lobe camshaft. The high pressure pump is mechanically connected to the camshaft with a cam follower. There have been many cases where the cam lobes are worn along with the cam follower. If you replace the high pressure pump, use a magnet to pull the cam follower out and inspect for wear. Fig. 5 shows some examples of worn cam followers. You can be assured when noting this that the lobes on the camshaft are also worn and the camshaft would need to be replaced.

One of the first things to do when a GDI vehicle comes in with a lack of power complaint is to check the oil level. If the oil level is over full, this could be a strong sign that the high pressure pump is internally leaking fuel into the crankcase. If this occurs it also means the high pressure pump may not be able to generate enough high fuel pressure under heavy load, which is going to indicate lean fuel trim values and a loss of power.

The low side fuel pump provides low side supply pressure to the high side fuel pressure pump. Most of these low side fuel pumps are electronically controlled by a fuel pump control module. These pumps are not supplied with a constant voltage source. The GM fuel pump control module bangs the fuel pump 25,000 times per second, while the Ford fuel pump control module bangs the fuel pump 6,000 times per second with hot run voltage. Both fuel pump control modules receive a duty cycle signal from the PCM. As the engine load increases, the PCM will increase the duty cycle command to the fuel pump control module. This data is available via the scan tool. As the duty cycle command signal from the PCM increases, the fuel pump control module increases the on-time to the fuel pump. The low side supply fuel pressure is normally in the 50 PSI range, while the high side pressure will be in the range of about 500 PSI under idle or light load conditions. The high side fuel pressure will proportionally increase as engine load increases. During WOT conditions the high side fuel pressure can easily exceed 2,000 PSI. In the event of a hard failure of the high pressure pump, these systems are actually designed to start and run just from the low side supply pressure — although not really well.

If the high pressure pump is changed, always inspect for any wear on the cam follower, and never reuse the high pressure line that connects the high pressure pump to the injector rail. If the high pressure fuel sensor is removed from the rail it is highly recommended to replace it. Keep in mind that there is extreme pressure in the rail, so bleed off the fuel pressure before breaking the high pressure line. This could be done by removing the fuel pump fuse or the fuel pump relay and then starting the engine. When the engine runs out of fuel and dies it would be safe to break the high pressure line.

The P1219A or P1219B are common DTCs on these systems. The code is for individual cylinder fuel control. Take a look at the enable criteria for the P219A or P219B code in Fig. 6.

The code does not point to a specific cylinder but rather to which bank the rich condition occurred in. The PCM does not have the ability to identify what cylinder is causing the rich condition. Every time I

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