Some MPG results.

[Dom B]

It's a really nice idea, but as it's not a simple mathmatical relationship between the two signals I suspect it would end up being pretty expensive: you're basically talking about a lookup table, which means we're talking a microprocessor unless one of our amazing analogue gurus wants to chip in!? (CHIP in? Geddit!?)

I think i could do it with a PIC chip. I think it would have enough internal memory not to need another eeprom chip for a seperate table. If we keep it simple i could make the tank have 255 correction points i think. Once we have mapped one car it can be programmed into all of them. The chip only costs a couple of quid. Could probably make a circuit board and enclosure ready to go all in for maybe £30-£35 ish.

I will probably be doing it for mine anyway as the gauge really makes me feel guilty lol so i will post any results if i manage to get it working.

Winding the rheostat as a real hit and miss affair. I have a friend who worked for delphi and they had a master calibrator gauge that they used the data for a cnc winding machine to make the coil variable spacing very accurately. I could probably do it on the cnc lathe but i don't fancy that as a job. Probably be a real pain getting it right.

A easier solution might be to experiment with a few resistors soldered to the other side of the rheostat coil in tactical places to 'trim' the winding. You could leave the original coil intact. perhaps variable resistors could be used and tweaked to get the settings then change them for fixed values once measured. I do think the electronic method is easier though.

[Turbo_Steve]

A PIC is exactly what I was thinking! LOL

If you can get a board made up with a PIC, input and output drivers and programmed up for £30, I would imagine you will get a fair bit of interest from within the club: the fuel gauge is just laughable as it is.

[Dom B]

What sort of resolution do you think we need to feed the gauge.

At first i thought 1litre or 0.5litre would be to coarse but then i thought that would still give you around 32 needle points for 0.5l resolution or approx 16 points for 1 litre resolution per quarter of a tank. Considering how small the gauge is how wide the needle is and how vauge the scale is i thought this might be ok being as the gauge should be a lot more linear and predictable after the unit is fitted anyway.

any thoughts

[mesobitchy]

how big is the vr4 tank?!
i know the v6 is 64liters thats from bone dry to brim....
but the vr4 cant be that big as well..... can it?
cos look what else runs to the back of the car, the diff, propshaft.. surly this will decrease the size of the tank on the vr4?

[AlanDITD]

Garry great results

No idea what mine does pretty simaler. Then i dont care either.

[Davezj]

VR4 is 60L tank. it kind of saddle bags the prop shaft

but you can fit more in than that due to the length of the filler pipe. you can probably get a couple of liters in there as well.

[Dom B]

One problem which is a great feature on the cars is that the gauge reads even when the ignition is off. So i am guessing that the gauge is some sort of stepper motor instead of a normal coil gauge. This might be ok though as the driving of the motor is probably done in the dash panel itself and i should be able to just feed it a voltage like the original sender wire does.

[Turbo_Steve]

Dom, I don't think it's a stepper motor: old fords used to just keep power to the gauge all the time....lord knows why: i would guess because the gauge was deliberately damped to hide variations in the float as the fuel bobbled about.

I was thinking that given the rate the VR4 munches fuel, 16 points across the whole gauge would be sufficient TBH! That's better than most digital gauges offer.

[phosty]

Dom, I'm interested in you PIC project. I was thinking along similar lines but using inline flow meters for the fuel supply and return lines so you can calculate the instantaneous fuel consumption and then display the mpg. You'd need a feed from the speed sensor too.

I was thinking of using the arduino board for simple prototyping which includes some ready made i/o and a free IDE ... but it hasn't got any further than thinking about it so far.

[Dom B]

You may as well just do some static testing on the injectors, rail pressure flow rate and dwell times when you have finalised these figures you can use the injector pulses to know very accurately the fuel consumption at any point. I am surprised some the the piggy back ecu's don't do this already.

You would never find flow meters accurate enough to measure the fuel out minus fuel returned to the tank.

The way we used to measure instant fuel consumption at uni when we used the CADET test cell system is we had a fuel container that held 150ml. There were two float switches 100ml apart and we the computer filled the system every time the bottom float was tripped and stop about a second after it reached the top float switch. It then waits the second of two till the first float trips this time when the fuel leves drops past it and a timer starts and is stopped by the bottom float. From the known volume and temperature of the fuel and the time the fuel flow use could be instantly read on screen. We had one with a load cell on the bottom too to make corrections as the temp one was not always great. I am not sure how well this would work on a moving road car as opposed to a lab but ia might work with some averaging.

The electronic injection pulse measurement is probably the most feasible for in car though.

One thing mystifies me. How do the 2 halfs of the tank balance. I can't see a balance pipe anywhere? Surely it can't be just cornering splash. Can it!

PS i have my prototype fuel corrector on a board and the code seems top work. i just need to take the sender out of the tank to figure out which are the signal wires and the voltage rails. I assume the sender would be wired as a potentiometer? I have been waiting till i had anbother car on the road in case it is a overnight fiddle.

[peter thomson]

There is another pump on the other side of the tank which I assume would help to balance it

[phosty]

The electronic injection pulse measurement is probably the most feasible for in car though.

So is that how modern cars do it then? I assumed (incorrectly I guess) they used flowmeters. I thought I could get them from a breakers yard - but not if they don't use em!

[ritch_w]

on the latest gen mitsis you no longer get a traditional fuel or temp guage. on the 9g Galant (CY0 lancer) and outlander etc you get a wee info centre between the speedo and revs which tells you;
Fuel level
miles left
mpg
temp
odo
trip a
trip b
service info

in context of the thread - the fuel gauge indication does seem reasonably accurate. I tend to get approx 550 miles between fill ups and avg 46mpg from the info center which is backed up by the stats from my fuel card.

BTW thats mixed town / commute / and sheer hooligan driving (its the car - honest!).

[miller]

im lucky to see 150 miles out of a tank!

[apeman69]

On saturday, after a one-click fill-up, I did a journey from South Wales to Hertfordshire and I (intentionally) did not once see positive boost, generally travelling at between mach 7 & mach 8. (Try this type of driving in a VR-4: it's no fun.)

We travelled 170 miles on 23.54L of fuel. This works out at 32.78 MPG.

I dunno how many MPG it did on the return journey (now that my MAP2 and boost solenoid are sorted) but the gauge, after another one-click fill-up prior to departure, was reading a LOT lower than when I got there and the journey was 40 minutes shorter!
I guess I'll be back in the low 20s from now on.

[miller]

ha ha your right its no fun! thats what eurobox diesels are for!

[Dom B]

On saturday, after a one-click fill-up, I did a journey from South Wales to Hertfordshire and I (intentionally) did not once see positive boost, generally travelling at between mach 7 & mach 8. (Try this type of driving in a VR-4: it's no fun.)

We travelled 170 miles on 23.54L of fuel. This works out at 32.78 MPG.

I dunno how many MPG it did on the return journey (now that my MAP2 and boost solenoid are sorted) but the gauge, after another one-click fill-up prior to departure, was reading a LOT lower than when I got there and the journey was 40 minutes shorter!
I guess I'll be back in the low 20s from now on.

That mileage is incredible. I have new plugs, new air and oil filters, new oil, great cylinder compression pressure. I try all sorts of driving week to week. Some weeks i leave the car in 5th through towns etc and others i change down to keep the car in it's most efficient area just below 3000rpm, i do motorway mixed, gentle driving trying everything. Depending on how many people i am forced to overtake i either get 23 -24mpg no matter how carefully i drive. I have seen close to 26 once fairly recently but there is literally nothing else to ration.

[Dom B]

So is that how modern cars do it then? I assumed (incorrectly I guess) they used flowmeters. I thought I could get them from a breakers yard - but not if they don't use em!

yeah pretty much all cars use injection dwell and duration against known flow rates of the injector at the set rail pressure to calculate mpg. Diesels use pulse timing too but in a slightly different way. The secret to its accuracy is averaging. A flow meter is measuring real time flow and on a car even a vr4 the flow is almost too small to accurately measure. When they calibrate injector flow they pump an injector for hours counting the pulses of it on and off. they do this for all pulse widths. Whatever volume of fuel is collected is divided by the astronomical number of injector pulses in that time period and they end up with a very accurate figure for the fuel flow per injection pulse including the dwell times which are worked out but the difference between flow rates at different pulse widths etc.

Your ecu has this figure inside it and it simply counts the pulses and the pulse widths to make a pretty good guess at the mpg. Modern cars are quite good at it. Range is usually a bit more hit and miss though as they still rely on the gauge readings to calculate.

Out of interest does anyone know the system operation of the vr4 fuel tank with the second pump? Does it just constantly try to refill the right half of the tank with a low pressure lift pump? Is this why our gauge readings are so random.

[VR457]

I have found the boost controller (i use an MBC) can be a factor. dial it slightly different and the mpg often changes drastically. So far no known method of working this out scientifically. You end up going for max performance and cry lots about the fuel vanishing.

[Dom B]

To be honest, it's not just a case about saying power power power and forget the economy. I believe in making a better car all round. A car that is more powerful but doesn't needlessly drink fuel when it isn't creating that power. Hence i am not changing cam timing etc with my mods. After all modern cars manage to create a lot more power than a vr4 with far better economy, it's called technological advancement.

The more fuel you save when cruising then the more you have to thrash about with when you want to play.
I don't want to drive around with my wallet aching when i am just going to the shops but i do want performance and i believe there is a very capable solution to this compromise.

We can all build a road rocket that is uncomfortable to be in and has huge horsepower...thats easy. What isn't as easy is to have that power and handling in a comfortable reliable car that is efficient when going up the motorway.

If a car did that terrible mpg we would in all likelyhood leave it at home 99% of the time no matter how much power it had and drive some s#1tbox saxo into work. well that's the point in having a great really enjoyable car if you don't drive it.

I believe 45mpg is possible on a 400bhp car, it's a technical challenge as valid as any other. This forum isn't called 'lets make the most power.com' ,(to be honest the mine's bigger than yours big egos get so boring) instead it is a place to discuss all forms of challenges weather that be power, economy, modifications etc.

To be honest i despise all forms of ICE and the big speaker in the boot brigade, but there are plenty of people on here who love that and do some really interesting writeups about them. I would never soil any car i owned with thick audio cabling and ear splitting boot filling speakers, but i really enjoy seeing other people on here having a go at the mods and enjoying what they are doing, it is still very interesting, weather it is my cup of tea or not.

Lets face it anyone who is looking for performance, the first thing you need to do is throw all that junk in the bin. But that's not what personalising cars to achieve that persons goals, is all about.

I wonder what economy the vr4 would do with boost set to only 1psi on the motorway. Do the turbos help with removing manifold vacuum on part throttle cruise making it more efficient or not? Would be very interesting to find out.