It runs, it drives. It’s good.
So yesterday I mentioned an issue with the engine leaning out badly. As it turns out, this was due to the Injector Duty Limit being set down at 13%.
It should be set much higher, something around 85% is good. Basically, the injector duty cycle is a percentage of time the injector is supplied with power. 0% means it doesn’t open, and no fuel flows through the injector. 100% is wide open, and pouring fuel through it. 13% means it’s open a fairly small amount and letting only so much fuel through. As the fuel requirements increase, so does the injector duty cycle. More fuel, more duty. Capping the injector duty at 13% means that even if I told the engine to run richer, it physically couldnt as the injector would only ever pump in 13% worth of fuel. This results in a horrific lean condition as the air to fuel ratio starts to sway heavily towards lots of air and only a small amount of fuel.
This isn’t a setting I recall ever changing, so no idea why it was that low. This also meant that I didn’t know the setting existed. The awesome guys over in the Speeduino community had a look through my logs and tune file, and concluded that the duty limit was too low, and I should increase it. Sure enough, increased it to 85% and the engine revved out properly, and felt a lot better.
Today after work (at 9PM) I just couldn’t help myself. Before even thinking of dinner I jumped in the Rover, laptop in the lap of my lovely assistant, and off we went. We did a couple of laps around the neighbourhood to see what was up.
It’s REALLY hard to get into high RPM around the back streets, so it spent most of its time in the lower half of the map. I tried to cover as many cells as possible.
On the RH side of the picture there are two boxes. One with yellow/green and the other red/blue. The top one indicates the cells (a cell is each of the little squares in the map with a number in it) that I have entered into when driving (depending on revs and intake vacuum). The darker the green, the more time spent there. The lower box is the cell change. The red indicates leaner, blue richer. So the good news is that my VE table was quite rich, and its gradually leaning the map out for me. There is a small patch that wanted to go richer. I wasnt so sure on the big jump, so I interpolated it with the cells around it and smoothed it out a bit.
During the drive I was also logging to a file to review later. The one thing I wanted to look into was the Acceleration Enrichment. Upon giving it a whack of throttle the engine would bog and then catch up and off you go.
The vertical line in the middle is the current data being reviewed. The white line at the bottom that makes a HUGE jump upwards is injector Pulse Width. Pulse Width is similar to Duty, except it’s the measurement in milliseconds that the injector is held open for. The longer it’s open, the more fuel. A big spike like that means it’s asking to dump lots of fuel in a short time. This is reflected a short time later where the red line that overlaps the white one down the bottom takes a steep dive downwards. This red line is the O2 sensor reading. Lower is richer, so the engine goes horribly rich and bogs down.
You can see from the full screenshot above that this happens when the Throttle Position Sensor reading (which is the white line in the middle section) increases. Its seeing the TPS increase and thinks “hmmm, he’s put the hammer down, it needs more fuel”. This is the work of a badly tuned Acceleration Enrichment function. I have tweaked it a little now to hopefully pull some fuel out of it, but it’s recommended not to put too much work into it until the VE table is nice and tidy, as it’s all related and one will change the other.
So, todays conclusion?
Stunning. Already, even untuned, its running better and stronger than it did on the Lucas ECU. It feels like the engine has freed up; it’s much stronger to accelerate and feels like it has more power/torque. It revs out well, and just keeps pulling.
It does have this horrible resonation from the intake on deceleration through. It’s a really deep droning noise. Not pleasant, and I’ll need to look into what to do to shut it up.
I’m really looking forward to refining the tune and seeing how good I can make it. Theres still some serious work to be done, but it’s coming along well so far.