Ask an expert

I intend to replace my Toyota Carib with a Toyota Nadia. I hope to select from a D4 Engine & VVTI engine.

Can you please advice on the following:

* The differences between the two engines
* How to tell which is a VVTI engine
* Is there a location where the VVTI sign is printed/engraved?

Julius

From the "Ask Jack" archives - 8 November 2009

The Toyota Nadia is a good replacement for a Carib.

The two engine types are quite different however. While both have similar internals, the big difference is the way the fuel is injected into the engine.

With the VVTI engine, fuel is injected into the inlet manifold to mix with the air prior to entering the combustion chamber.

In the D4 engine, fuel is injected under very high pressure into the combustion chamber itself (direct injection). During the combustion process, air is compressed and at a very precise moment fuel is injected directly into the combustion chamber. The idea behind this concept is to allow the engine to run leaner producing less emissions and lower fuel consumption.

In theory the D4 engine is very good and is an advancement on the VVTI however, history has shown it does not take much to upset the engine performance and issues such as surging, rough idle and engine stutter are not unusual.

Unfortunately these problems are not that easily sorted out with little product knowledge on these engines available within the industry. This often leads to expensive, unnecessary and time consuming repairs.

VVTI stands for "Variable Valve Timing Induction". This engine type is a lot more conventional and improves performance by optimising valve timing. It is a proven system, effective and very trouble free.

The D4 can be recognised by a large plastic cover over the engine with embossed D4 lettering.

If I recall correctly, the VVTI engine has the lettering cast into the aluminium rocker cover on top of the engine.

Does this mean that do not go for buy a toyota car with D4 engine? For example Toyota wish had two types of engine the vvti 1800cc and D4 2000cc? Which one should I choose for piece of mind car?

Yes, the 1.8 is a similar engine fitted to NZ New Corollas and has a great reputation. The 2.0 D4 does not enjoy such a good reputation. Go for the 1.8.

Just to make things trickier,The Toyota Avensis 2L engine is D4 and VVtI.as shown on the cam cover.

VVT-i just refers to Variable Valve Timing - intelligent. A D4 engine can still have that feature. The 2.0 litre D4 engine (Direct Injection) is what concerns us.

I've been wondering though, why Toyota has decided to put the D4 technology into the new 86/BRZ ?

Or does this surging problem disappear when you use the highest premium octane 98 ?

Technology is ever evolving and we're told the D4S system fitted to the Toyota 86 / Subaru BRZ (which is essentially a Subaru boxer engine) has been significantly refined since the early Toyota D4 system. We're told the D4S system in the 86/BRZ uses conventional port injection at start up and low rpm (where the richer running created much of the problem with the previous D4 system), then utilises direct injection at high rpm.
Therefore, while it's early days for the new system, we can only assume that the engineers have refined the technology to overcome the problems that were associated with D4 (direct injection) systems of the past.
Definitely, high octane fuel with the D4 system is a must.