Skoda Rally Blog

If you’ve never built a car or messed around with the engine on one, it’s fairly easy to think that they just run without any real effort.  Unfortunately, the cars that you drive every day that start up on cold mornings, run economically and go well when you hit the loud pedal actually hide many, many hours of development.  Not only on the mechanical parts that whizz round the engine for thousands of hours without letting go, but also on the systems on the car that put just the right amount of fuel into the engine, and then light that fuel with a carefully timed spark.  There are many things that can go wrong with this – too much fuel and you’ll have a car that is expensive to run, chokes people behind it and damages the internals of the engine.  Too little fuel and it will run too hot and possibly burn holes in the pistons.  If the spark is too late, you don’t get as much power as you could do.  If it’s too early, you can create massive pressures inside the cylinders and damage the pistons and other parts.  It’s quite amazing that modern engines run as well as they do.

Why am I telling you this?  Well, the thing is if you change any part of the engine’s internals (cam, head, valves) or external bits (exhaust, inlet filter, etc), then it means that all the old settings are now going to be at best wrong, and at worst disastrously wrong!  So whenever a new-spec of engine is built, it’s time for the engine to be set up.  Back in the old days with a distributor and carburettors this was a majorly long-winded process, and always involved many compromises.  But with fuel injection and electronically controlled ignition, it is at least something which can be done without dismantling the fuel system to make a change; all you need is a laptop!

The engine on the Skoda uses two main things to control the fuel – the engine speed and how far open the throttle is.  Once it knows that, it looks up how much fuel to put in.  Fairly simple.  But this isn’t something you can do blindly, you need tools to measure what’s happening at the current time, so you can alter the settings to the correct values.   Handily I already had one of them, a sensor which goes in the exhaust, and from the gases coming out of the engine works out the mixture of fuel and air that was just burned.  All I needed to add to that was something that would measure the engine speed and how far open the throttle was, and then I’d be in business.

Luckily the people who make the meter mentioned above also thought of this, and made a little box which attaches to it, and which can measure several other things at once.  Unluckily, no-one seemed to have them in stock, but an afternoon of searching finally turned up someone who had one in stock (and only one!), and I got that sent down.  £180 which is a lot for a little black box, BUT it should make this job much easier.  In the past we’ve done this by me driving the car at a specific speed and throttle opening with Paul noting down the meter reading on paper, and working from that.  This should mean it can all be recorded just in normal driving.  An hour spent adding a new sensor to a spare throttle body and another hour doing some wiring extensions saw the car all set up and ready to map.

Last time I’d driven the car, it was really not that happy.  This morning I took it up the road just to see how it would go, and it was much better within minutes – I think it was dodgy old fuel that was causing the poor running as once it had warmed up it drove pretty well; well enough for me to go up and down the dual carriageway outside a few times before coming back, and then downloading the log to the laptop.  This highlighted two things – firstly that the mixture wasn’t too far off, and secondly the person who had chosen the values of the lookup table’s columns had made things difficult for me as some odd numbers had been picked.  I decided to change this to make it easier to do in future, which meant an hour or two adapting the contents of the old table to the new values; let’s just say I know a LOT more about Excel than I used to, and also if I wasn’t as good at working with files and making macros I’d probably still be entering the 560 new values needed for the car to run!

With the new settings in, the engine ran well, and was starting to free up; before it wouldn’t tick over and now it was happily ticking over too fast.  A 20-minute drive saw nothing untoward (although it is quite a rattly beast), and with a rev limit of 4000 and throttle limit of “about half” there was lots of data in the right area to work with.  Because of the way it works, it’s very quick for the computer to then come up with new fuelling figures (you tell it what you want to see and what you already have, and it works out the values for you), so although I’ve not changed anything since that long run, I’m sure that the new table will improve matters greatly.

At the moment the car looks like one of those pictures you see of a new model being tested as there are cables from under the bonnet going into the passenger compartment, and when it’s running the passenger seat is full of meters, cables and laptop.  I’m back to work this week, so I’ll have less time to do much on the car, but it should hopefully have a few runs in the evenings and see the low-speed and low-throttle running sorted out and as it should be.  Once the engine is a bit freer (with a few more miles on it, say 2-300) then I can give it some more revs and more throttle and fix those areas too.  And see if it goes better than the last one!