New cars, old me­chan­ics

Mod­ern ve­hi­cles are highly com­plex, and de­spite train­ing ses­sions run by the in­dus­try, few me­chan­ics man­age to stay up to date. Jake Venter re­ports.

Farmer's Weekly (South Africa) - - Motoring - FW

There was a time when the av­er­age farmer could get a re­luc­tant en­gine to start by us­ing one or two ba­sic tricks.

If churn­ing the starter didn’t bring joy, a re­luc­tant ve­hi­cle could of­ten be coaxed to life with a push. If that didn’t help, the next step was to re­move the air-cleaner to see if the car­bu­ret­tor’s throat was wet, then pull off a spark plug lead while the starter ro­tated the en­gine to see if there was a spark.

Only if these meth­ods failed would a me­chanic be called in. The lat­ter would re­peat the above pro­ce­dures be­fore bring­ing the tools out. Those days are long gone. You can­not check on fuel reach­ing the en­gine in a fuel-in­jected en­gine, and if you check for a spark in the way men­tioned, the high-volt­age elec­tronic ig­ni­tion cir­cuit may well suf­fer a volt­age spike that could dam­age the en­gine con­trol unit (ECU).

Us­ing the starter mo­tor for a long pe­riod or push­ing the car for more than a few paces would most likely re­sult in raw fuel reach­ing the cat­alytic con­verter (CAT). When the en­gine fi­nally starts, this could see the CAT over­heat­ing and self-de­struc­t­ing.

Em­ploy­ing jumper leads is so risky that the Bosch hand­book states that they should be used only in a real emer­gency.

Many peo­ple, even some me­chan­ics, are un­aware of these re­stric­tions to time-hon­oured pro­ce­dures, as well as many other new de­vel­op­ments. The re­tail mo­tor in­dus­try and ma­jor mo­tor and com­po­nent man­u­fac­tur­ers or­gan­ise reg­u­lar talks and train­ing ses­sions to cor­rect any bad habits. I’ve at­tended some of these and of­ten found them poorly at­tended.

One of the prob­lems is the fact that many older me­chan­ics think they are suf­fi­ciently ex­pe­ri­enced and in­formed. An­other is that very few me­chan­ics are true au­to­mo­tive en­thu­si­asts.

For many years, I or­gan­ised a Me­chanic of the Year com­pe­ti­tion for a na­tional mag­a­zine. There were sep­a­rate cat­e­gories for ama­teurs and qual­i­fied me­chan­ics, and I in­vari­ably found that the ama­teurs knew more about ‘au­to­mo­tive the­ory’ than the me­chan­ics!

TO­DAY, MANY WORK­SHOPS USE DI­AG­NOS­TIC CON­SUL­TANTS

MOD­ERN FAULT-TRAC­ING

Fault-trac­ing on to­day’s cars is such a com­pli­cated pro­ce­dure that many work­shops em­ploy spe­cial­ist di­ag­nos­tic con­sul­tants to de­tect any elec­tronic mis­de­meanour. They use a lap­top com­puter and/or a code reader, and the model-spe­cific set­tings and pro­ce­dures are a few sec­onds away on the In­ter­net.

So let’s look at all the new com­po­nents and ideas that an old, re­tired me­chanic has not seen: • The ECU con­trols all the en­gine func­tions and op­er­ates on a very low 0,015 amp cur­rent. As noted, it can be dam­aged by a volt­age spike or even by a dam­aged HT lead.

• The CAT can eas­ily be dam­aged not only when ex­cess fuel gets in­side, but when a com­pres­sion test is car­ried out with­out first de­ac­ti­vat­ing the fuel pump re­lay.

• The knock sen­sor warns the ECU when the com­bus­tion is ir­reg­u­lar so that the ig­ni­tion tim­ing can be re­tarded. The sen­sor is very frag­ile and can eas­ily be dam­aged if dropped dur­ing re­place­ment.

• The lambda sen­sor mea­sures the oxy­gen level in the ex­haust pipe and trans­mits a sig­nal to the ECU. This then com­putes how much fuel to sup­ply for the next com­bus­tion event. The sen­sor can be dam­aged by ex­ces­sive heat, car­bon build-up, or even chem­i­cals in the anti-freeze if this leaks into the com­bus­tion cham­ber via a blown cylin­der-head gas­ket. • Fi­nally, torque-to-yield bolts are still rel­a­tively un­known, es­pe­cially among the back­yard brigade. The spec­i­fi­ca­tions for these re­quire a low torque plus an an­gle through which the wrench has to be ro­tated to achieve the cor­rect torque. This will en­sure a high clamp­ing force but cause the bolt to stretch per­ma­nently so that it can­not be re-used.

• Jake Venter is a jour­nal­ist and a re­tired en­gi­neer and math­e­ma­ti­cian. Email him at ja­cob­ven­[email protected] Sub­ject line: Mo­tor­ing.

THOMAS KAROL

ABOVE: As ve­hi­cles and their com­po­nents be­come ever more so­phis­ti­cated, me­chan­ics find it in­creas­ingly chal­leng­ing to keep abreast of new tech­nol­ogy. It also means that trac­ing and re­pair­ing faults is risky, as dam­age can eas­ily oc­cur un­less the me­chanic knows ex­actly what to do.

JAKE VENTER

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