It’s been an exciting weekend.

Posted on September 7th, 2003 in Opinion by Julian Edgar

It’s been an exciting weekend.

Genuinely exciting.

I have been testing one of the projects from an electronics book I am doing with Silicon Chip Publications. I’ve been selling work to Silicon Chip, an Australian electronics magazine, for a long time – in fact something like a decade. Over that period I have written many articles about car electronic systems, in addition to covering topics as diverse as electric lighting technologies and washing machines.

But what I have been testing over the weekend is all about modified cars.

It began when about six months ago I had a discussion with the publisher of Silicon Chip, Leo Simpson. He asked: how would I like to come up with all sorts of ideas for electronics projects that could be applied to high performance cars? After I devised the concept, the magazine’s chief electronics designer – an unsung genius called John Clarke – would do the hard work (including building the prototype) and then I’d do the on-car testing. And after we’d got a bunch of projects together, they’d be published in a magazine-style book.

Sounded good to me.

Click for larger image So Рback to this weekend РI spent the daylight hours working with my fiancé Georgina, as she punched the keys on the digital hand controller and I drove the cars and offered advice. The cars were (sequentially) my 1988 Nissan Maxima V6 Turbo import and then my 1998 Lexus LS400. We were tuning the air/fuel ratios using a brilliant new DIY kit interceptor designed as part of this electronics book. The kit is likely to be stocked by Jaycar Electronics and should be well under AUD$200 (maybe even only $150!); the ability to fine-tune the air/fuel ratios is quite extraordinary.

Injector swaps, airflow meter swaps, tweaking the high load mixtures – all are possible. And then add to that the fact that the interceptor will work with 0-5V (common airflow meters), 0-12V (less common airflow meters) or 0-1V (oxygen sensor signals) and you can see why I am excited.

On the Maxima the interceptor (which we’ll call a Digital Fuel Adjuster, or DFA), worked perfectly. Two changes were made to the mixtures of the Nissan – leaning out the full-load mixtures (which were typically over-rich), and tipping-in a bit of extra fuel as the car came onto boost. At full load we changed a 6000 rpm 11.2:1 to 12.5: 1, at a full-load 5000 rpm we went from 11.3:1 to 12.7:1 and at 4000 rpm we leaned from 11.7:1 to 12.6:1. As the car came on boost we went from a near-stoichiometric 14.5:1 to a much more power-friendly 12.9:1.

And yes, the car sure responded.

But not content with that we also upped the boost, firstly from a standard 0.4 Bar to 1 Bar, then back to 0.6 Bar (the intercooler was getting a bit too hot at 1 Bar!). And both times we were able to tune the mixtures to suit – with all testing being done on the road. And that’s not only the full-load mixtures, but also the part-throttle air/fuel ratios (out of closed loop, of course).

The Lexus was a bit trickier – as with any prototype testing, we found that a few changes to the kit would need to be made. (These alterations might add – er – $4 to the price…)

Click for larger image

One interesting thing we found is that the Lexus stays in closed loop until quite high loads, but we were still able to alter full-load air/fuel ratios from around 11:1 to typically 12.5:1. Interestingly, the peak injector duty cycle (displayed on a digital meter which is another DIY project from the book!) dropped from 74 to 65 per cent. 0-100 km/h times showed an improvement of about 2/10ths of a second, but the important stuff is that even on a sophisticated car like the Lexus (four oxygen sensors…) we were still able to change high load mixtures seamlessly and with absolute smoothness.

No driving glitches here.

And the Autronic air/fuel ratio meter that we were using for all this testing? Funny thing is that we borrowed it from a company that has its own sophisticated interceptor, a product that in some ways this cheap DIY project will be in competition with…

ChipTorque has developed the Xede, which in addition to fuelling changes can also do timing and boost control – and other things as well. But Lachlan Riddel – head honcho of ChipTorque – and his chief tuner Matthew Spry were fascinated by my plans for a budget DIY kit interceptor; interested enough to make available the company’s Autronic air/fuel ratio meter for a weekend of testing.

The unkind could suggest that they wanted to see the testing fail in the most glorious way possible, so that they could say “Told ya!”. But I don’t think that is true: instead I think it more likely that despite some minor commercial conflicts of interest, the technicalities just entranced them to a degree that they wanted to become involved. And to be honest, their product can do infinitely more than the tested prototype kit – and for the dollars being asked, you’d hope so!

So right now I am putting the prototype DFA through its paces on a long-term test: the device will stay in my car from hereon. The electronics project book – still to be named – will be sold through the AutoSpeed shop, in addition to newsagents here in Australia and New Zealand, but realistically the publication is still about 6-8 months away.

But hey, I just had to share that excitement. Real-time tuning the air/fuel ratios with a digital hand controller – and the whole lot a kit costing under two hundred Australian bucks…

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