J ,, these days ot'heightened environ-I rn"ntul consciousness the motor in-

I dustry is taking a bit of a pounding.I Vehicle exhaust emissions are apretty hot issue right now and it's on thecards that ever-tightening controls inthis area will be a major considerationfor many years to come.

At present the best weapon in the ve-hicle manufacturer's armoury, for thefight against emissions, is the computer-controlled engine management system.When all is said and done the friendlyold carburettor, even in its mostadvancd form, is a relatively crude me-chanical device. Its function is to controlthe relative amounts of fuel and airbeing delivered to the engine to ensurecorrect and efficient running.

However, you may be surprised tolearn that, in most cases, a carburettorcan only be expected to be doing its jobproperly at half-a-dozen or so pointsacross the rev range. At all other timesthe unfortunate truth is that it is deliver-ing incorrect quantities leading to badnews on the emissions front. The an-swer, of course, was to develop a way ofcontinually monitoring and adjustingthe fuel and air supply which is exactlywhat we have today.

Good managementThe thinking behind engine manage-ment was to produce a system thatwould overcome this inefficiency and

create a way of controlling accuratelyboth the fuelling, so that precisely theright amount of fuel was delivered, andthe ignition timing throughout thewhole rev range. In this way emissionsof carbon monoxide and nitrous com-pounds could be kept to the absolureminimum and the engine could run atits peak performance at all timeseveryone was happy!

However, the manufacturers sooncottoned on to the fact that they nowhad the means conveniently to tailor theperformance of an engine to meet anyparticular market requirement if, forexample, they were looking for highsales to company car fleet managers,then fuel economy was a vital consider-ation and the system could be pro-grammed to produce excellent mpgfigures.

This was obviously great news for themanufacturers themselves but it alsohad an interesting knock-on effect inthe after-sales market too. This 'pro-

grammability' of the on-board comput-ers proved to be an irresistibletemptation to electronics wizards likePeter Wales. He immediately saw thepotential for modifying the manufac-turer's programmes to unlock the fullpotential of an engine's performancecapabilities. The re-chipping industrywas born!

Peter went on to form DetectionTechniques Ltd (Buckingham Indus-trial Park, Buckingham MKl8 lXJ, Tel:0 2 8 0 8 l 6 7 8 l o r 8 1 5 8 3 8 , F a x : 0 2 8 0816764) who are now at the forefront ofthe industry. With his experience andexpertise it was obvious that Peter wasthe man to talk to for an insight into thecurrent state of play.

Detection and coruectionMy introduction began with an explana-tion as to how the management comput-er, which runs other vital systems suchas ABS braking as well as the fuellingand ignition settings, exercises its con-trol. Now, I'm no computer expert but,from what Peter said, it appears that thewhole system stands or falls on theinformation held in one tiny memorychip. This is just a standard microchip,like those found in any personal com-puter, which is crammed full of figures.About 32,000 in fact!

These figures make up the program-ming instructions for all the computer's

Subtle badging is often the onlyway 0f tellin0 that a Gat hasbeen rc-clripped.

WITANDAND GHIPSPARI I Pictures by Chris Erahan

Re-chippirg o modernPnrformance cor must surelybe the most cost-nffuttiae wo)of sign?ficantly improaingits Pnrfurmonce.Chris Graham d,is c ou erswhat's inaolaed,.

functions and they can be displayed on ascreen once the chip has been 'read'by uspecially adapted computer. Peterloaded up a sample chip and, sureenough, the said figures appeared onthe screen after a few seconds. I mustadmit that they meant very little to mebut, within a moment or two, he wasable to recognise important sequencesof numbers which he explained werecalled maps.

The maps relevant for tuning pur-poses are the fuelling and timing mapswhich, in the case of the Bosch manage-ment system, take the form of 72 by 12number grids. They contain the manu-facturer's chosen performance settingsfor varying conditions. In addition theprogramming also allows the enginemanagement system to take care ofother variable factors such as air tem-perature, battery voltage and enginetemperature. These are important toobecause they can all cause fluctuationsnecessitating changes in the fuelling andtiming settings to maintain efficientrunning.

Peter picked out a fuel map and dem-onstrated how altering various figurescould affect the running of the engine.Changes made to the maps will governhow lean or rich the engine is runningat any one point in the rev range. Care-ful analysis will identify exactly when inthe engine's power curve it starts to runlean or rich and corrective adiustmentscan be made.

On the cheaper management systemsthere are usually separate fuel maps forthe engine at three different throttlesettings idle, part-throttle and fullthrottle - and two timing maps for eachthrottle setting. This makes a total ofnine to be assessed although Peter add-ed that he rarely fiddles with the idlemaps because these are usually perfectlyadequate.

The inside 0l a typical engine management computel.

48 CAR MEGHA]'||CS JULY 1e91

The more expensive systems, asfound on BMWs for example, arerather more complicated with threemaps for the part-throttle setting (light,medium and heavy), and there can befour or five completely different fuell-ing/timing map sets for use in differentcountries! In such cases Peter's first jobis to find out which ones are actuallycontrolling the engine at the time of thetest. The manufacturers, of course, donot provide any help in this respect! Al-though the control box in a BMW 535manual may look the same as the one inthe auto version, the engine will be run-ning on different maps. If the automaticis switched to the 'sport' mode then itwill switch to yet another programmemap to advance the ignition for greater

performance. It's a very complex busi-N C S S .

So far, though, everything seemed tomake reasonable sense but it got a gooddeal more involved when Peter went onto talk about cars fitted with catalyticconverters. The management systemson these need to be more complex still.For the set-up to work at all there mustbe no unburnt fuel or air passing out ofthe system through the exhaust - itmust be what's known chemically as stoi-chiometric! Only after complete com-bustion, with no air or fuel left over, willthe catalytic converter function proper-ly to convert the carbon monoxide (CO)into carbon dioxide and the nitrouscompounds into nitrogen. Running onleaded petrol is a definite'no no'with a

The staff at Detection lechniques are a Gross between m0t0l mechanics and electronics engineers.While coats abound!

Beneatn the protcGtiue tap6 fiides lhe all-poweilul mem0ry Ghip.It's hard t0 [slieue that something this small can haue such aninlluential eflect 0n the peilomance 0l a m0t0r Gat.

converter because the lead will simplyclog it up.

To achieve stoichiometric combustionunder all conditions the computer hasan oxygen sensor placed in the exhaustpipe to measure the waste gases. Its re-cordings lead to changes in the amountof fuel being supplied and so the correcrbalance is maintained by continualadjustments which reflect changes inengine setting made by the driver.

Iweaking techniqueAs I've already mentioned, the motormanufacturers make full use of theirability to pre-programe an engine's per-formance levels to best suit theirintended market. However, in manycases these limitations can lead to rather

boring and even unsatisfactory per-formance if you are an enthusiasticdriver.

Often you will find that the enginehas been set to run so weak in the mid-range (presumably to save fuel whencruising) that if you suddenly put yourfoot down there's nothing there! Thesolution is to re-programme the fuellingmap so that the engine runs slightlyricher in the mid-range. Because of theextra richness already there the mixturewill not go too weak when more airarrives after you press the accelerator.The result wi l l be instant response.

Another neat little trick the manufac-turers adopt is to programme in anoverrun cut-off which effectivelyswitches off the engine when you takeyour foot off the accelerator. Althoughproving a good fuel saving device, thedown side of this type of control is that itcan often cause all sorts of lurching andhesitation problems, particularly whenyou're driving around town in heavytraffic. However, Peter says that by asimple alteration to just two figures inthe memory chip the problem can besolved. The cut-off action is removed sothat every time the accelerator or pedalis re-applied the engine respondsinstantly rather than having to switchitself back on again with the associatedlurch.

Another point worth noting is thatmost performance cars are set up, bytheir manufacturers, to run fairly richwhen on full throttle. This is not idealbut is done in a bid to aid mid-rangeacceleration. If it was not the case thensudden acceleration from the mid-range (which is set lean anyway) wouldweaken the mixture too much and the

Ihe engine management in the new Caualier SRiis lound behind the side panel in tfte driyer'slootwell. This convenient location means thattfie cu can be made t0 pefiorm significanflybetter without euen opening tne [0nnel!

engine would falter. Therefore, by mak-ing the full-throttle map over-rich, themixture strength is increased as soon asthe throttle is fully opened and theengine is coaxed through the lean sportwithout hesitation. However, this is allvery well until the engine is run for anytime at full throttle. Under such circum-stances the mixture quickly becomes toorich and performance suffers. This canbe put right by leaning off the mixturewith adjustmenrs to the full-throttle fuelmap.

Ihe proof of the puddingThere is no question that DetectionTechniques are totally confident aboutall the conversion work they undertake.They fully appreciate the imporrance ofwhat they are doing and the seriousnessof the consequences should things gowrong. It's a business in which cornersjust cannot be cut although, unfortu-nately, there are those around todaywho are prepared to take the risk.

If a customer arrives in the DetectionTechniques workshop with a car that isnew to them then they will have to startfrom square one with a look at what's onthe engine management's memory chip.The contents will be read and copied onto their computer to provide a workingcopy. From this the control maps will beidentified, analysed and then the busi-ness of alteration will start.

The car is put on the rolling road andconnected up to the main computer andthe analysis machinery so that prelimi-nary CO and timing measurements (tak-en at half-a-dozen points across the revrange) can be made. Then, by a compli-cated process of elimination, the func-tion of each map is determined. This isdone by making deliberately exagger-ated alterations to each one in turn andnoting the effects these have on the run-ning of the engine.

Having established this then the finetuning can start and it takes about sixhours to completely re-tune an enginefrom scratch. After they have producedwhat's considered to be the definitive setof fuelling and timing maps, copies aremade of the chip and rhey are testedextensively on other similar engines. Ifthe reports on performance are unani-mously good then the chip can be mar-keted. However, if there arejust one ortwo that do not produce the sameimprovements as those seen on the orig-inal test car then more developmentwork is done to find out why.

In Part 2, next month, we shall take alook at the practical results of DetectionTechniques' tuning packages on bothnormally aspirated and turbo cars. Alsowe shall be considering the cost, to theowner as well as to the engine, of suchmodifications.This computer is used t0 tead cnips and altet tne ptogamming they contain.

JULY 1991 CAR MECHAI{IGS 49