In your Diesel Car Magazine there are a lot of claims made for chips that make diesel engines more powerful and give better fuel mileage, and a lot of other claims. Are these all true, and are these conversions worth the money? I have a 2015 Golf TDI, and the Volkswagen dealer claims that any kind of chipping will void the manufacturer’s warranty. I have subscribed to your magazine for four months now and I am very impressed with it. I reside in the USA, in Munster, Indiana, approximately 25 miles from Chicago Illinois. Thanks in anticipation!
James Gullicks

Glad to hear that you are impressed with Diesel Car – we do our best! You ask two questions, I guess – does diesel electronic tuning work, and what about the warranty? Well, electronic tuning does definitely work, but I have some special qualifications to make regarding your situation in the USA. The basic software that controls engine settings, and in particular fuel injection settings, is set on the conservative side, to take account of all conditions, fuel quality, and driving styles. There are certain settings, such as turbocharger boost, fuel injection pressure, and fuel injection timing that, with skilled attention, can be optimized (spelt with a “z” just for you – we spell it “optimised”) to the benefit of torque output and power. Recognizing (there I go again!) that this is possible, and not in any way dangerous, we can observe that some basic engines are available with different power outputs – the VW Group 2.0-litre TDI has been offered with outputs of 109, 118, 138, 148, 161, 168, 175, 181 and 187bhp. The significant differences between these power outputs are mostly down to fuel injection and turbocharger settings. So anyone tuning your Golf engine (148bhp?) will only be doing something similar to what manufacturers are doing to get higher outputs. Admittedly some engine and running gear components might also be up-rated on higher power engines, maybe clutch, brakes, wheels, tyres (tires!) etc., but obtaining the higher power output is not that difficult. Good tuners do the job better than poor tuners, and this applies to both add-on boxes and full software rewrites, or chipping as it used to be called. The name chipping comes from the early days when the master chip, the ECU, or the injection chip, were actually removed from the car and replaced with a modified item. Nowadays, tuners can access the chip through the engine diagnostic port and actually change the software settings. Add-on boxes are plugged into the injection circuit and fool the signals being sent to the injection pump and injectors – basically into delivering more fuel, for which generally there is an excess of air to burn. If it’s overdone (and the same applies with chipping or rewrites) then too much fuel and not enough air can create black smoke and a badly running engine, but any good tuner will be well aware of this. Good tuners are those with a good history and not fly-by-night operators who come and go from the market. In your case, I am aware that Superchips are present on the US market and have a long-running good reputation. They are also the official tuners to the UK Volkswagen Racing Team, who have run tuned Golfs and other models in saloon car racing in the past. But if any other companies that you see advertising in Diesel Car are operating in the USA, then you could look at them also. The Superchips website has good information and will tell you how much extra performance you might expect.
Regarding manufacturer warranty, many garages recognise that such things happen and “turn a blind eye” when warranty issues might arise, other than something obvious like a totally blown engine. So if you drive sensibly, the risks of any problems are small. If you know how to drive a diesel engine properly, you will already know that the useful performance comes at relatively low engine speeds, and there is no reason to over-rev any tuned engine, because it’s just not necessary, or the least bit sensible. The reason for the continued popularity of the add-on boxes – in spite of their relative lack of sophistication – is that they give decent results, and in many cases you can remove the box when the car goes in for servicing, so nobody knows anything about it at the garage! There is also the issue of insurance, which in the UK is fairly important. You probably need to notify your insurer if you have an engine tuned, and some insurers may just take note and accept the modification, others may charge an extra premium, and some may decline altogether, meaning that you would need to find another insurer who will be happy to insure you.
I think that covers the essential issues of tuning, except maybe to mention that you often obtain a modest improvement in fuel economy because the greater torque output means that the engine is thermodynamically more efficient. And unless you use all the extra performance all the time, you will get better economy – often because you can pull a higher gear in many situations, and overtake other cars without a down-change.
But now to the the reservations regarding diesel in the USA. Much of your diesel fuel over there is poor compared with European diesel fuel. The cetane value of US diesel is low, meaning that the combustion efficiency is impaired because the base crude oil in the fuel is inferior to European crude. If you are thinking of tuning your Golf, and maybe before you think of tuning it, you should look at using diesel fuel additives. That will raise the cetane value, contain detergents to keep your injection system cleaner, and give you better all-round performance without any engine tuning. If you need any more advice on this, come back to me. I’ve now researched and established that Deuce Juice is a suitable diesel additive, which I have found you can get from Rollin’ Smoke Diesel in Michigan City 46360.
Best regards,
Doctor Diesel