Why do Touareg common rail engines require more care?

Hi Baraza,

Thanks for your informative page in DN2. Two quick questions:

1. What is the meaning of “common rail engine” in VW Touareg?

2. Why do vehicles with a common rail engine require more care than other engine types?

Thanks in advance,

Charles

1. The common rail feature in an engine is a type of direct injection fuel delivery system involving much higher nozzle pressure (up to 1500psi) as compared to what used to be called direct injection (but nowadays distinguishable as pump-duse) in which a fuel pump serves unit injectors.

In a nutshell, common rail works like this: there is a fuel rail which serves all the cylinders (hence the name common rail). Fuel is delivered into this rail at very high pressure to enable easier and more efficient atomisation of fuel.

The injectors in each cylinder are fed fuel from this rail and while early versions of common rail engines used mechanical actuation of the injectors, more contemporary engines use solenoids and piezoelectric valves (piezo electricity is created by pressure or impact). This electronic activation enables the fine tuning of injection pulses and fuel quantity for more efficient running.

Look at it this way: You have a line of houses. On one end is a water reservoir. The water is delivered to these houses by a main pipe running past all the houses into which water from the reservoir is forced, either by a pump or by gravity. Each house has its own pipe connected to the main one, and these pipes terminate in the taps inside the house and these taps are opened by the house occupants every time they need water.

The water reservoir is the fuel tank. The main water pipe is the common rail. The individual house pipes are the injectors, and the taps are the injector nozzles. The solenoids or piezoelectric valves are the people who open these taps at the time of need.

To put things in perspective, we need an analogy for the pump-duse system. We still have a water reservoir on one end of the line of houses, but in this case each house has its own pipe going straight to the reservoir. In pump-duse, we have what are called unit injectors, combining an injector nozzle with its own injector pump.

Fuel reaches each unit injector by means of ducts machined into the cylinder head. Since the unit injector has its own injector pump, fuel arriving at the injectors is under lower pressure; pressurisation for atomisation is done by the injector pump. This is unlike common rail, where the fuel has to be pressurised while still in the rail.

Each system has its pros and cons, but these are becoming trickier to justify or dismiss as electronic systems take over more and more control of vehicle systems, but as it is, common rail engines are more the norm for both petrol and diesel engines.

2. I would not say common rail engines require “special” care compared to unit injection engines, but given that pressurisation of the fuel starts at an earlier stage, then it is harder to isolate a fuel pressure issue in case one of the injectors gets clogged or cracks (a very unlikely occurrence).

Also, the unit injectors are cooled and lubricated by the fuel itself, eliminating the need for these additional systems. And there is no need for high pressure fuel pipes, reducing risk of pressure-associated problems.

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Hallo Baraza,

I recently acquired the latest Toyota Premio model in the market but I have an issue with my eldest son, who apparently has forged a spare key.

I fitted the car with a secret switch but he discovered it. Disconnecting the battery does me no good. Can you advise me what I could disconnect to prevent the car from igniting?

Eric

What you need to do is confiscate his key and teach him the importance of respecting other people’s property. However, mine is not a parenting column, but a motoring one.

If he found the first cut-out switch, then most likely he will find any others you may choose to install. So it might be time to do things the way Mr Bean does because the situation is desperate. Remove and hide the battery in a different location. This is very tiresome and risky because some cars actually need the ECU (electronic control unit) to be mapped again if the battery is removed.

You could also fit a padlock-secured dead bolt on the driver’s door, but this will tarnish your car’s otherwise pristine appearance. How about a steering lock? Or gear lock? Or both? Aftermarket high-strength steel affairs that are also key operated and are hard to pick open.

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Hi Baraza,

I have a question concerning the Toyota IST 2005 model 1298cc. Is it possible to change its gearbox from automatic transmission to manual transmission? I am used to manual transmission as it gives me more control compared to automatic transmission, where gears shift on their own.

What implications will it have on the overall performance of the vehicle? Will it affect the vehicle negatively or positively and what are the costs of acquiring and replacing the transmission system?

Max

It is possible to swap an automatic transmission with a manual one. Performance implications are dependent on the ratios in the new gearbox, but the general prognosis is good: it should improve, if not for anything then for the use of a friction clutch and a lighter transmission.

If the transformation is done properly, then your car will not be negatively affected. The exact costs of acquiring and replacing the transmission are unknown to me but what I know is that some of this can be off-set by selling the auto-box. That way the net cost will be low.

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Hi Baraza,

I am a mechanic and regular reader of your column. I own a Peugeot 504 pick-up and its consumption was terribly excessive. I modified its carburettor and it now drives at 13km/ltr.

My questions are:

1. Can I sell my idea to global manufacturers? And how can I contact them because I have tried it on the Internet but it is complicated.

2. Do you think this idea can bring carburettor vehicles back in the market?

3. Can manufacturing a complete product and selling it locally be marketable.

Innovative Mechanic

1. You can sell your idea to global manufacturers, but whether they will actually buy it is a matter of conjecture. I cannot speak for them and I do not know how good your idea is (I am not being nasty, but for all I know you could be using a smaller jet in the carburettor to reduce fuel consumption. Also you have not clarified if your modification has any implications on power or torque).

Contacting them is complicated, mostly because none of these people are based in Africa, let alone Kenya, and ours is an irrelevant market so they are not likely to get excited about news from this corner of the world. When I say ours is an irrelevant market, what I mean is that we do not buy new cars in numbers large enough for our opinion to matter on the world stage.

The only manufacturers whose ears I have (internationally, not locally) are Jaguar-Land Rover, General Motors (to a small extent), and hopefully Mahindra by the end of the month. I cannot promise to push your idea forward you because my line of work does not allow me to: it will conflict with my objectivity/neutrality.

2. To be honest, no. Carburettors, while cheaper, have been superseded by EFI (electronic fuel injector) systems and are, thus, crude by virtue of design.

3. This calls for market research and analysis before a decision or solid answer can be arrived at, which is a whole other line of work.

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Hello Baraza,

I am a regular reader of your column. Being a woman, I am very concerned about my tyres. I need your advice on the best tyres in the market.

I drive a Nissan B14 and one of the tyres has been losing pressure at a high rate. My mechanic checked for any punctures but it does not have any.

Luckily they are tubeless, but every week I have to make sure that they have enough pressure. And since I do not want to have any issues, I want to replace two of them. What would you recommend? I am looking for quality and value for my money. I am not sure what brand my current ones are as they came with the car when I bought it.

Miss Problematic Tyres.

If the tyres themselves are fine, then the valves/nozzles are leaky. One of the cars I use on a regular basis actually has that problem, but on a smaller scale in that I do not have to check the tyres weekly.

I would say replace the valve (the teat-like thing that one uses to pump up the tyre) but this is not as easy as it sounds and it could actually ruin an otherwise serviceable tyre. Another word of advice that I may give but not fully stand behind is to “grin and bear it” — Pump up those rubber rings weekly.

Now, sadly for you, I cannot do product endorsements right now. It calls for very extensive research, which no one seems interested in funding (but I am very interested in actually doing it) and if I fund it myself on my current salary, then I will die a debt-ridden and bankrupt man. I have not given up on that quest yet, though.

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Hello Bwana Baraza,

I own a Toyota Corolla 110 but I intend to buy a new car at the end of this year, God willing.What is your preferred choice between Toyota Noah and Toyota Wish?

I personal I prefer Wish but my wife and children prefer Noah. Their happiness is my priority. Your quality advise will be highly appreciated.

Best regards,

Nassir

My preferred choice? That would be the Noah, for two reasons: the Noah offers more space and practicality, but more importantly, there is no love lost on the Wish from me, not for any solid reason except that it is a bit unsightly and is used (mostly) by those with over-productive loins. Mostly. Not always.

The Noah still wins either way because you have actually answered your own question. You say your family’s happiness is your priority, and your family has a thing for the Noah. So make them happy and get a Noah.

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