Please explain why certain manufacturers such as Toyota, Nissan and Subaru continue to supply the world with vehicles tted with continuously variable transmissions (CVT).
I know that Audi has stopped tting CVT to its vehicles and that may indicate that it’s aware some motorists detest an automatic box characterised by an awful whining noise. I have also not come across any motoring journalist who has anything good to say about this type of transmission. Can you please explain why manufacturers persist with the CVT? GEOFF EVANS Johannesburg In theory, a CVT is the optimal type of transmission, as the internalcombustion engine’s speed can be xed to optimise fuel economy or torque and power output. It has fewer moving parts than other transmissions and is more compact. CVT s can also offer a wider gearing range than most conventional transmissions.
The disadvantages are that there is always slip between the (metal) belt and the pulleys, resulting in heat generation and therefore energy wastage. The feeling of a clutch slipping is another negative that many drivers dislike. Some manufacturers (such as Subaru) are now calibrating the belt to move in a stepped manner, mimicking the gearshifts of a conventional transmission. Although this enhances driver enjoyment, it lessens the ef ciency gains of continuously moving the gear ratios while the engine speed remains constant.
A CVT is actually well suited to normal, sedate driving. The whine is present only under heavy acceleration.
THE WRONG FUEL
Reading the article The wrong stuff in May 2017, no mention was made regarding the danger of using lead-replacement petrol (LRP) in a vehicle designed for unleaded petrol. I presume that the catalytic converter would suffer a meltdown?
Human-brain fade accepted, lling a vehicle with the wrong fuel from a lling-station pump could be eradicated given a little co-operation between motorvehicle manufacturers and petrol companies. All new vehicles should be tted with a shortrange (25 mm) transponder in the fuel ller ap (coded to identify the type of fuel used by the vehicle), while all petrol pump nozzles should be tted with a receiver (coded to identify the type of fuel being dispensed). If the two codes do not match, no fuel is dispensed. Problem solved.
This is not rocket science. The technology has existed for some time as petrol pumps must be activated by a transponder carried by the pump attendant while some receivers are already on the pump nozzle. Older vehicles could be retro tted by aftermarket transponders epoxied to the fuel ller ap and create some jobs in the process. What are your views on the proposal? PAUL BUBEAR Lakeside You’re correct that using LRP in an unleaded vehicle damages the catalyst. This “catalyst poisoning” can also happen to the lambda or oxygen sensors in the exhaust. The result is compromised emissions control, bad running and a lit engine-check lamp in the instrument cluster in the case of a complete failure.
Your idea of the transponder
is a workable solution, but to get the buy-in from all parties would be near-impossible (who drives the incentive and who pays for what?). The human factor is always present and there will be instances where the transponder is not fitted (or fails to be recognised). In this case, an override function must exist and this is where the problem lies. Pump attendants may choose to use the override function all the time rather than trying to fix problems with the system, putting us back at square one.
Some manufacturers (such as Ford) offer a fuelling mechanism that mechanically prevents the wrong nozzle from entering. Ultimately, however, the onus is on the vehicle owner to check that the correct fuel is used.
PETROL SOUNDING LIKE A DIESEL
I own a 2009 1,3-litre (fuel injected) Mazda2 with 58 000 km on the odo. A problem has emerged where the engine sometimes sounds like an clattering diesel. I always switch off the engine immediately and, when I try to start it again, it does not fire at all. After I leave the car for about an hour, it will start but runs rough for about five seconds and then picks up speed and runs completely normal again.
What causes the engine to sound like a diesel, and can it be damaged? I have been told that the engine is probably flooded, or that the timing belt may have stretched. Surely the last suggestion is nonsense, as it does run perfectly normal at times? GEORGE MAWSON Table View We doubt the engine is flooded, as this rarely happens with fuel injection and you would probably have smelled the unburnt fuel from the exhaust after cranking. If the noise is combustion related, then it may very well be a sparktiming issue. We would propose taking the vehicle for an onboard diagnostic check to see if there are any fault codes stored in memory that point to a sensor problem.
Our guess would be that there is a problem with either the cam or crankshaft pick-up sensor, which is responsible for the phasing and timing (spark and injection) of the engine. If the sensors do not provide a clear signal to the ECU during cranking, the ECU may not inject fuel or fire the spark plugs and causing the non-start situation. Or, a faulty signal may cause incorrect timing and cause the rough running you mentioned. When the signal is fine after a few rotations, the timing is correct again and the problem disappears.
We agree a stretched cambelt is unlikely and belts cannot stretch like chains. There is a possibility that the engine can sustain damage if the timing is incorrect, especially at higher loads.
VIVARO FLEET PROBLEM
We have some petrol-engined Opel Vivaros in our vehicle fleet and many of them exhibit recurring problems where they stall, cut out or misfire. They have repeatedly been in for servicing and repairs, but the problems persist.
Our staff members are concerned for their safety, as their vehicles often stop in unsafe or crime hotspots, leaving them vulnerable. There is also the other issue of losing power steering and brake servo when the engine cuts out, resulting in a coasting vehicle with much reduced braking and steering performance. Are you aware of an issue with these vehicles and, if so, do you know of a fix? TREVOR RENNISON Cape Town We are slightly perplexed that many of the vehicles on the fleet exhibit this issue, as it rules out the odd loose electrical connection or sensor problem. A common denominator may be a fuel station. Please drain a sample of fuel from one of the problematic vehicles and have it tested, especially for water content. If you look at a fuel sample in a glass container, you should be able to spot the water at the bottom (water is heavier than fuel and does not mix).