Skoda Rally Blog

At the end of this week is one of the things I hate about cars.  It’s MOT time.  And obviously amongst the many other things that are tested, the car’s emissions are scrutinised.  Which means that it needs to run properly and use the right amount of fuel to give a nice clean exhaust.  Or something like that.  Anyway, while the car fired up last weekend, there is a lot more to it than that; the right amount of fuel is needed for the car to not only pass an MOT but also to make decent power, to protect the engine’s internals (too little fuel and it will run too hot, possibly melting a piston; too much and the oil will be washed off the bores leading to engine wear), and to make the car driveable.

So, with that in mind, all the mapping gear was connected up; there’s a sensor which is in the exhaust which measures the air/fuel ratio, and in addition there is another box which measures the engine speed and the throttle opening.  It also measures G force forwards and backwards and side-to-side, but that’s just an amusement for me rather than anything I make use of.  All of this data gets recorded as I drive the car, and then can be downloaded to the laptop to set the map up – this needs to be done several times due to the changing conditions and that things don’t react quite as you’d think; the more you learn about how engines work the more you realise they are really, really complicated things and there is a great deal happening all at once.

But that’s by the by; I didn’t get to do any driving yesterday as I’d made myself ready to do it and… the recce car battery was flat!  So that meant a few hours on charge as pushing it out of the way is definitely not an option at the moment.  But once all was well this morning, I fired up the Felicia and took to the road.  Well, I say that, it was more a case of car spluttering into life against its wishes, and then me having to cajole it into even moving a foot.  Looking at the meter, the mixture was massively lean, so there was next to no power.  I reversed out of the drive (with one of my neighbours giving me that look) and then got the car going forwards, and started recording.

And then for some reason I lost my mind.

I live on a road which is alongside a dual carriageway.  And for some unknown reason instead of sticking on my road, I went onto the dual carriageway, and as soon as I did, the car died.

Completely.  I was 20 yards onto the road, and no way back.  After what seemed like an eternity,  I got it to fire up but it didn’t want to move, and despite me having put my hazard warning lights on, people clearly weren’t paying much attention; getting rear ended wasn’t on the menu but was looking likely, but I managed to get enough fuel in to at least move the car; this involved pushing the accelerator repeatedly (which injects more fuel momentarily) which at least did enough to get the car moving, and then round the roundabout at the bottom and the same going up the road; here was where the close ratio box really paid off as I could at least do a semi-sane speed and as it was a Sunday morning the traffic wasn’t bad, so I got round the roundabout at the top and back home without too many problems.

So, stop the recording, and then time to re-do the map.  Which I’d thought was straightforward, but when I went to do it I realised that I’d completely forgotten all the tricks I was using to make the process quick.  Rather than entering the values into the logging software, doing the calculations and then manually re-entering the new values, I had come up with a system which used a spreadsheet to keep the values in, and using Notepad++ to edit the output from the logging software to be changed into the DTA Map format.

Thing is I had no idea what I’d been doing, and I’d not made any notes.  So I spent nearly an hour reinventing the wheel before being able to do what I’d been doing simply, and then saw that the engine was taking in a LOT more air than the last one; this is a GOOD thing as it’s more efficient and should mean more power in the future.  But the idea now was to make it driveable – after all, it had been almost unable to move itself.  And the log made why quite clear:

Early Map, lean as anything with mad throttle movements.

The pink line is the mixture, and ideally it would be around the middle of the graph (top to bottom).  The black line is the rpm of the engine, and the other line shows me repeatedly hammering the throttle as it was the only way to get enough fuel into the engine at all.  Not good! Even the first mapping change altered the way the car behaved completely – it was much. much better already.  This meant that firstly I could venture out on to the main road without risking death, and secondly that I could then use a wider range of throttle openings and engine speeds.  After another short drive, more changes, and then a longer drive, this time about 15 minutes, with the car behaving much better, aside from an occasional misfire.

Back onto the PC, more changes made (this time over most of the used rev range and throttle openings, as I’d been careful to use as many combinations as I could do), and a more drivable car again; another longer trip was much better, except again there was a low-speed misfire.  This was not down to mixture as I could provoke it at will and looking at the meter (and indeed looking at the log afterwards) showed that the mixture was spot on, so I suspect that either the coil pack or the spark plug leads are on the way out; above 2500rpm the car was running cleanly and smoothly, and feeling really good.

By way of comparison to the log shown above, here’s one of the later ones, and you can see that the mixture is much closer to where it should be (around the middle, but that’s dependent on speed and throttle to a degree), and no longer is the throttle being pressed maniacally.

Later map, things looking far nearer being right.

So, it’s time for a new coilpack and plug leads; this is one of the original parts that I got from “the idiot”, and as all the other parts from “the idiot” have been sub-standard, it’s something I’d rather eradicate before looking any further.  And once I’d removed the coil pack, I saw that it was dated 2001, so it’s probably time for a replacement; I doubt he fitted it new!

Time to check other things for the MOT, so I checked the lights and so on, all was well, and then cleaned the poor thing inside, and tested the new Peltor intercom with the extension leads for the first time.  OK, it was wallet-meltingly expensive, but it really is fantastic; I could hear everything said with perfect clarity.

And that’s how it stands.  The MOT is on Friday afternoon, but I have a busy week until then, so I may get a chance to drive the car with the new coilpack before Friday afternoon, hopefully that will clear the problem along with some nice new plug leads, and maybe even a set of plugs – the boat is well and truly pushed out.

As an aside, when I was driving the car on the last mapping run, I drove past Canford Arena, which is the service area of the Sunseeker.  And said to myself that it just might happen.  I’ve made great strides forward with my back this weekend, having had a couple of terrible days this week, so hopefully they were a glitch rather than a trend.  Here’s hoping.