Why has it gotten such a bad reputation?
Of course there is now the VVT-i D4, the latest mass extension of the `Direct Injection’ engine technology. VVT-i D4 is an upgrade of Toyota’s award-winning Variable Valve Timing with intelligence (VVT-i) engine. But that is a discussion for another day.
Today, we are prompted to discuss an engine-type that has attracted a little bit of flak on the street; the D4 engine. Is it really as crappy as some car brokers and street vehicle mechanics claim? Absolutely not.
It appears, from our research, that although the D4 engine is about two decades old and has been overtaken by the types we mention above, it is relatively new and uncommon on the Uganda market where Electronic Fuel Injection (EFI) rules.
Since the motorcar was invented, the challenge for engineers has been how to make an engine that delivers the highest mileage and speed at lowest fuel consumption. Issues of quality and quantity of emissions have become an issue lately.
The D4 direct injection engine is, in fact, a variant of the ultra-efficient Gasoline Direct Injection (GDI) engine first popularised by Mitsubishi in the mid-1990s. The GDI was itself a variant of the EFI.
In Uganda, the most popularised D4-(GDI) vehicle is the Toyota Premio. I have met owners of this popular car who confess to almost collapsing after their mechanic opened the bonnet and swore they had made the mistake of their life by buying a D4 engine car.
My advice would be to ignore the doomsayers.
In reality, the differences between the EFI and GDI are really technical but they revolve around attempts to bypass the old technology of engines mixing fuel and air and burning it in the cylinder efficiently and with minimal CO2 emissions.
An excerpt from an expert website says: “In GDI engines, petrol is directly injected into the cylinder, eliminating many of the hitherto restrictions on combustion control, such as the impossibility of adding fuel after the induction valves were closed. By achieving precise combustion control that is free of restrictions, the GDI delivers a previously unseen combination of fuel economy and power.
In conventional engines, fuel and air are mixed outside the cylinder. This ensures waste between the mixing point and the cylinder, as well as imperfect injection timing. But in the Toyota D4 engine, petrol is injected directly into the cylinder with precise timing, eliminating waste and inefficiency.”
So why are the D4s so unpopular if they are that superb?
It all starts with maintenance.
I follow a lot of online car forums. In one thread, a driver of a Toyota Premio with a D4 engine complained about the engine going off instead of idling when he did 100kph for some time and then either slowing down or braking. He suspected it had to do with ignition, sensors, or fuel filter. He was frustrated because he had to restart every time.
As anyone who follows these forums knows, not all offers of advice are to be taken seriously. But a comment from someone called Gregory, from somewhere in our lovely land, caught my eye.
He wrote (with some of my edits): “Simple; that is just a semi-clogged fuel system caused by contaminated fuel. The sensor heads are partially covered by dirt, carbon, etc. It can easily be rectified by simply cleaning the fuel system around the engine compartment by qualified personnel.”
Then he offered some tips for all D4 car engine owners:
Maintenance must be observed for day to day running:
Blow air cleaner element to keep enough aeration through
Maintain a standard minimum level of fuel in the tank i.e. not run empty tank all time.
Another useful thread I picked recommended use of iridium plugs that have to be changed in time i.e. at below 60,000kms, and use of synthetic engine oil to be changed after about 10,000kms, and keeping an eye on the timing belt.
“Regular service and quality fuel will make the engine last for long. Attend to it quickly if there are signs of over-heating. It’s a powerful modern engine that is fuel economical. Its problems are with its sensors; Oxygen sensor, fuel pressure sensor, and ignition timing sensor.
Those of course might not be solutions to your D4 engine problem. But at least you now know that the D4- (GDI) engine is not as crappy as some people claim it is.