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LOVE-OR-HATE CVT

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).

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