Feck I am impressed!Eh up.
Not been doing much with the Disco for a bit other than a very low amount of miles (less than 3k a year for last couple years). I'm doing a lot more now and the last fill up was almost 150 quid so....
I've dusted off my gauge system again. I want to read the fuel injection quantity from the ECU so I can display a fuel economy figure calculated from that and RPM's.
Basically if I drive this thing like I would normally I get 320 miles to the tank !!! 320 reported miles, the tyres are 5% bigger circumference than stock so the mileage is under reported.
If I drive like miss daisy, I can get 470 to the tank - I think that having a big flashing MPG or litres per 100mk figure on the dash will help remind me to keep the foot steady with 2022's ridiculous fuel costs.
Anyhow, I've managed to get my electronics talking to the ECU, I just need to do some code tidy up now - and probably finish off adding the other physical instruments that I've been putting off for a while : R380 cooler, oil temp & pressure senders, LT230 Oil temp, Engine Oil temp & Pressure.
I also need to finally fit those blooming Sumo bars
Here's a photo of the bench test system:
I had been gifted an ECU previously that turned out to be toast, I snagged this one in the pic for 60 quid from a lad locally and it works a charm - I've got a logic analyser hooked up so I can simultaneously sniff the K-line & the Serial activity driving it from the microcontroller - which basically means I can figure out wtf is going on and that I'm getting stuff out of the ECU.
At the moment I'm wrapping this all up with the code that reads all the extra analogue sensors, but I might just release this as a stand alone fuel consumption system - be a doddle for anyone with a TD5 to use it then, and probably a lot cheaper than the competition. I think there's about 20 quid in parts for the ECU side of things - gets a bit more expensive when the analogue sensors and cabling/connectors are factored in.
MAD!Can someone with half a brain help me work through my maths
I want to be able to calculate a litres per 100 km figure (probably also MPG once I have it straight in my head).
In order to do this, I need to know the injected fuel per stroke, the vehicle RPM, and the vehicle speed.
There are probably a lot of ways to go about this and no doubt I've probably picked the hardest way or got it completely wrong
First I need to get to kilograms consumed per hour...
= injection quantity in mg * rpm * (number of cylinders / number firing per revolution) * minutes in an hour / milligrams per kilo
= injection quantity * rpm * (5 / 2) * 60 / 1000000
At idle my car is injecting 22mg of fuel at 750 rpm, plugging that through the equation comes to 2.475 kilograms per hour - assuming I'm reading the correct value from the ECU!
Next we need to workout what that is in litres. So average density of Diesel is ~ 0.85, obviously this varies with temperature and I could calculate it from reading the fuel temp, but it's only meant to be a guide not exact.
Therefore litres per hour = kg/h * 0.85
So at idle for me that's 2.475 * 0.85 = roughly 2.1 l/h
To see what that equates to per 100 km, and I know this is contrived because the vehicle is stationary, but I'm just using the above figured to sanity check my workings:
100/vss gives us the number of hours it takes to travel 100km
So if we multiply our Litres per Hour by this figure we get the number of Litres per 100km.
Assuming the vehicle was in gear and moving at idle and the injection quantity didn't go up due to load, and assuming I got 5kph for that rpm (utter bollocks figure), then:
100/5 = 20
20 * 2.1 = 42l per 100km
Probably not far off the truth at that speed
Do my working outs look about correct?
42l per 100km
duuhhh!OK I shouldn't have included the idle injection stuff at all, that was just me making sure the figures weren't wildly wrong. More interested in whether the conversions I'm doing make sense - I _think_ they're correct, but not many people out there are doing live calculations so most stuff on the internet is about working out fuel consumption after the fact based on miles travelled and how much the tank needs topping back up.
OK I shouldn't have included the idle injection stuff at all, that was just me making sure the figures weren't wildly wrong. More interested in whether the conversions I'm doing make sense - I _think_ they're correct, but not many people out there are doing live calculations so most stuff on the internet is about working out fuel consumption after the fact based on miles travelled and how much the tank needs topping back up.
Not sure I follow, do you mean the fuel map? I'm talking directly with the ECU and reading the actual injected volume of fuel at any given moment, so once this is in the car and not just hooked up to my bench ECU it will read the actual RPM, injection quantity, and Speed to do the calculations against.Can you see your map? and its different sections.
J
Not sure I follow, do you mean the fuel map? I'm talking directly with the ECU and reading the actual injected volume of fuel at any given moment, so once this is in the car and not just hooked up to my bench ECU it will read the actual RPM, injection quantity, and Speed to do the calculations against.
Ah OK I see, the injection quantity changes based upon driver demand (pedal). So, no it is not constant. I think the map on mine has it inject up to 85mg at full chat, but that is also at like 4500 rpm, so quite a bit of fuel.