The dubious trade of rechipping

By: Alan Bunting, Thursday, October 01, 2009,

Tags: Emissions, Engines, Legislation.

AutomotiveWorld.com

In an ideal world the exhaust emission limits now effectively enshrined in type approval legislation would apply throughout a vehicle's life. But, as pointed out previously in this column, enforcement of such a regime is, for practical reasons, not possible.

In-service verification of emission levels at say yearly intervals, coinciding with routine roadworthiness checks, clearly cannot match the accuracy and repeatability of type approval certification tests, the latter being carried out under what amount to laboratory conditions.

So a margin of exceedance - to use the legislators' word - has to be allowed, in Europe in some instances up to 100%. That is to say, once a vehicle has been registered, perhaps even before it has turned a wheel, it is able to emit up to twice the amount of NOx nominally permitted by law.

In-service verification of emission levels at say yearly intervals, coinciding with routine roadworthiness checks, clearly cannot match the accuracy and repeatability of type approval certification tests

That margin conveniently allows for deterioration of the engine and its emission-related auxiliaries through the vehicle's life. But, to environmentalists and bodies such as the European Economic and Social Committee (EESC), that permitted exceedance is to be deplored.

What the EESC might also have pointed out, but didn't, in its recent pronouncement, is the associated loophole through which truck and bus operators especially can get their new vehicles modified, as soon as they go into service, in order to enhance fuel consumption, critically at the expense of increased pollutant emissions.

Ever since electronically-managed fuel systems first appeared on diesel engines in the 1980s, it has been possible for those with the know-how, but invariably without the manufacturer's approval, to manipulate fuel metering and, more significantly, injection timing. The practice known as 'rechipping, that is replacing solid-state components in the fuel system's microprocessor, started with a demand from owners of gasoline-engined sports cars wanting higher performance. But it has now been taken up by small, enterprising, but arguably less than scrupulous, concerns targeting fuel cost conscious truck operators.

Though their promotional material seeks to blind non-technical fleet managers or owner-drivers with science, the rechippers' essential strategy on a diesel engine is to advance net injection timing. The word 'net' has to be included here because in a modern automotive diesel the timing is continuously adjusted to optimise engine efficiency through different combinations of load and speed, within the constraints imposed by type approved emission limits.

rechipping pushes NOx beyond certified (ie type approved) limits and, as such, eats into the in-service NOx exceedance margin

Bringing forward (ie advancing) the injection and hence the combustion process improves engine efficiency, which can be used to enhance fuel economy and/or performance. Most truck operators are happy to maintain existing performance and channel all the rechipping benefits into fuel economy enhancement - which happens also to cut CO2 emissions; PM (particulate matter) emissions are reduced at the same time.

But - and here is the crunch - those fuel economy benefits are gained at the expense of an inevitable rise in NOx (oxides of nitrogen) levels. That is to say, rechipping pushes NOx beyond certified (ie type approved) limits and, as such, eats into the in-service NOx exceedance margin. But because that margin has to be so generous, allowing for the relative lack of precision in on-board-diagnostic (OBD) NOx tailpipe sensors and testing station equipment, the rechippers can get away with their dubious trade.

For the owners of newer vehicles, an effective safeguard against rechipping is the certainty, if discovered at a routine dealer service or if an engine fault arises, of invalidating warranty cover. Looking ahead, as OBD sensors and test station emission measurements become more accurate and reliable, exceedance margins will be trimmed back. That will make back street rechipping progressively more impractical.

The opinions expressed here are those of the author and do not necessarily reflect the positions of Automotive World Ltd.

Published on Thursday, October 01, 2009