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Fuel Injection: Retrospective...

It is now almost a year since I embarked on my conversion to fuel injection and with a decent mileage completed since ( a total of 38 ½ hours of running time), I'm in a good position to compare the engine with when it ran on carburettors.

Would I do it again? Absolutely

Would I use the same ECU again? Yes, the DTA system works very well.

Would I now choose to run an engine on carburettors? Not likely.

One of the best (though not entirely unexpected) improvements has been fuel economy which has gone from about 25mpg to slightly over 30 mpg. There are two main factors in my conversion that contributed to this improvement:

•  Previously I was running with mechanical advance only (i.e. using a distributor with no vacuum advance signal input)

Additional timing is now added under light loads by the ECU which improves overall efficiency. Admittedly this could have been achieved by using a different distributor, but not with as much control.

•  Previously the engine was jetted on the rich side to ensure it wasn't lean at wide-on-throttle (wot)

The ECU allows more precise control of fuelling - and in a non-linear way too. So the low throttle input half of the map is programmed for fuel efficiency with Air-Fuel Ratios (AFR) leaner than 12.5:1 (the ratio generally agreed to give maximum power; 14.7:1 gives total fuel burn; leaner than 14.7:1 is achievable at light loads); and the high throttle input half of the map is programmed for maximum power with safely rich values. Better still, for zero throttle input settings, where the cars engine is on the overrun, fuel can be cut from the engine altogether; fuel does need to be reintroduced to ‘catch' the engine before it stalls so I only did this above 1500 rpm.

Other improvements include better driveability at lower rpms (the engine is benefiting from the additional timing advance), smoother idle at a constant rpm with engine hot or cold, better hot starting (no heat soak into the carburettor fuel bowls as there aren't any), more consistent running in different weathers (ECU adjusts fuelling for ambient temperature) and reduced maintenance (blocked idle jets are a thing of the past).

I can't think of anything that is worse than before but I'm still adjusting the engine for cold starting, and probably need another cycle of winter to get this completely right for my engine – however the Weber 40IDF carburettors didn't even have a choke so even where I am now with my setup is a big improvement.

I'm also finding that, thanks to the wideband o2 sensor I fitted, the engine is (almost!) fine tuning itself and I haven't found the need to visit a dyno. After a long run, you can hook up a laptop, view the average fuel corrections the ECU made to the programmed fuel tables to obtain the target air fuel ratio, manually edit any stray values, and then make the corrections permanent in the tables. Of course, this assumes that you have chosen the correct target AFR values in the first place….

So, on this positive note, I end my series on fuel injection – I hope it has inspired others to take the plunge.