Mira,

Here is a really good PowerPoint presentation (runs right in IE) about sensors. You have to scroll through a bunch of slides about the educational facility first, but the info is excellent once you get to it.

https://facultyfiles.deanza.edu/gems/...john/sense.ppt

Hmmm. Engine off, it's a flat line. Maybe I will need some more hunting. Should the TPS signal come directly off somewhere near the throttle?

Thanks! That was interesting. I hope that I will be able to tell the difference between the MAP sensor and the TPS.

Just to clarify, engine off, or engine stalled with the key at "run"?

Normally, yes. If I'm not mistaken, the TPS is a simple potentiometer, eg.:

https://www.sdsefi.com/pictures/tps.jpg

Well, I spent most of last night building a digital tachometer, from a kit. It was rather fun, actually. What was more amazing is that when I tested it, it worked straight away. When I hooked it to the wire marked "IG", the meter went up as the rpms climbed. Since I didn't have a stable 12V power supply at home, only in the car, I couldn't really calibrate it properly yet. But it's rough enough. I do have the oscilloscope to check frequency, however. And that told me that my car idles at around 1000rpm (25Hz).

I needed to change the timer. Although the catalogue states that it only works for 4-6 and 8 cylinder cars, it also works for 3 cylinder cars.

It supplies the following resistors for the different cars:
8 - 47k
6 - 56k
4 - 82k

There is a 50k pot to adjust, so I just soldered the 47k to the 82k to make a 130k resistor. Good enough. Calibrated the tachometer so that it idled at around 1000rpm, which is good enough.


I also had a bit more of a look with the other oscilloscope, which appears to have a better trigger. That #10 is definitely an injector signal, which means I'm in business for constructing an instantaneous FE meter.

And I'm pretty sure that the other thing is the MAF sensor, as it changes as the rpm changes.

Well, I finished the RPM meter, calibrated it properly and gave it a test run in my car. It has yet to find a proper home, that is the next step. But we are almost there.

Here it is:
https://img84.imageshack.us/img84/1/pic001rs2.jpg
https://img84.imageshack.us/img84/4936/pic002hp5.jpg
https://img84.imageshack.us/img84/1792/pic003aq8.jpg

So... now I know that my Mira idles at around 1000rpm, and hits 4200rpm in fifth gear at 100kph! That's not exactly "just ticking over". I wonder what the redline is? The speed goes up to 140kph on the speedo, but the engine starts to sound ugly at around 5000rpm (119kph).

It's going to be ripe for taller gearing/larger wheels. With the addition of aero mods so that the engine is not struggling at cruise, there should be lots of potential here.

What type of gearing modifications can you do transmission wise? How much did you spend on the digital tach, I need one for more precise stuff every so often and it'd be cute to make one, you know.

4200 is ridic, do you have any stats on the tranny?

Hmmm. It's a fwd, do they even have differentials? I'm really not sure what my options are here. I agree that 4200rpm is ridiculous. I will certainly find a way to tall out the gearing, just not sure how or what my options are. Any advice welcome.

I certainly won't be modifying it until my aero mods are done though, but it should give me some time to do some investigation.
Roughly $30 USD. Link here. I suggest you'd search under google via "digital tachometer kit" for something a bit closer. I estimate I probably spent 5 hours soldering it.

BTW accuracy is only two significant figures. The last two digits are wired zero.
No clue. 4200 seems reasonable, as the only reason the engine doesn't sound high is because the road noise covers the engine at 100+kph. It does sound noisy at the same revs and lower speed. And the fact that it idles around 1000rpm, which seems reasonable.

I'd love to know what the redline of the vehicle is. I figure at least 5000rpm, but no idea above that. Tell you what though, having an instantaneous fuel economy figure is going to make it SO much easier to drive slower. I tend to get impatient and drive faster because I get bored. If I had a meter that would help me to optimize my driving habits for saving money, it would help so much. I want a reward for travelling at 90kph, damnit!

FWD cars have the diff built in to the transmission. Where the axles come out, that's the diff.

Your options are: taller tires and/or wheels & tires, or a different transmission.

Redline: to give you a ballpark - my 993 cc Suzuki 3-cyl (6 valves) rev limiter is 7K RPM, the Honda Beat 660 cc engine has a 7200 RPM cutoff, or a 9k RPM cutoff, depending on the model.

Ahah! So even though the engine sounds like it's going to explode any minute, there is actually no problem! Cool...

I'd still like to get it down to something at 3k or below for cruising.

As for the tyres, probably best to assess things as a wheel/transmission system. Since we may need to change both, and the options probably don't lie along a continuum, best to see what will give best combination of both rolling resistance and gearing.

Thanks for the help!

Well, I just found the throttle positioning sensor (TPS), although I have not yet been able to track it back to the ECU. I basically just followed the throttle wire to the engine, where conveniently it sits somewhere along the intake line.

I opened the housing, and saw that the bottom two wires (a white and a yellow with green stripe) connect when the throttle is pressed. This obviously sends the idle signal, something I found on the ECU, marked "IDL".

The other wire must give the position. It is yellow and red.

Edit: Hmmm. Maybe it isn't a potentiometer.

I had another look. It seems that the upper is permanently on +5 Volts, the lower is permanently on ground, and the middle is at 0V at idle and +5 Volts at WOT.

That's pretty damn lame, if I am correct. It means that I can't get a look at where the throttle is without grafting on some sort of aftermarket TPS. Damnit. I wonder why the engine doesn't need to know where exactly the throttle is?

google gave me this.

So basically, looks like if I want TPS I'd better attach my own aftermarket one.

That saved me a lot of work trying to find a TPS that wasn't there. In the meantime, I should be able to build myself a little FE meter or a coastdown tester.

Injector waveform:

https://i7.tinypic.com/211jbd3.jpg

This $20 1960s vintage scope is easily the best investment in test equipment I have ever made. Here it is sitting in my car plugged in from the inverter.

Hmm, smack on a honda tps, same upper/lower limits but with a continual blah blah.Do you have a MAF sensor?

That is one phat ****ing oscilloscope.

Thank you. I knew another EE would appreciate it, especially one who actually was interested in that sort of stuff prior to getting into college. I wouldn't worry about getting a job post college... it's always the guys who actually do this stuff for fun who always end up readily employed.

It's funny, this is the first non-software EE stuff I've done since college, and I'm enjoying it. All 10Mhz of bandwidth, too! Should be fine for an automotive application.

I wish I had a pic of the banana plug to BNC connector I soldered up. Unfortunately this is the only photo I took with most of the scope in the picture.

The scope cost something like $21 AUD and I had to spend a couple bucks for the connectors and $30 for a new probe. I tried adjusting the probe, but I think it just has some residual waveforms showing through from the inverter in the car. Anyway, it's close enough for what I want to do. Ebay rocks.

To put it in perspective, I would have paid $128 for a new 10Mhz scope with about a third the visual area. Of course, this does take 3 minutes to warm up, but them's the breaks. But it does have excellent triggering, the other scope I bought from the same guy is 20Mhz, dual trace, but does not have as good a triggering. Maybe it's just my incompetence though. (I got the 20Mhz dual trace for $50 AUD.)

https://i7.tinypic.com/212uwzo.jpg

Pretty sure I do. I have a sensor that looks almost like the throttle, but after the rpm catches up with the throttle, the line backs down. Why?
Cool! I'll have to have a look. I am not really sure where I would get one from, any ideas? Should I expect it to just bolt on?

I have no idea about it bolting on, I'd have to see a comparison. Matt has some, I'm sure.

Anyway, the MAF would prolly explain the crappy tps, since the MAF will know well how much air is coming into the engine, so*shrug*

Hmmm. Does MAF * RPM = TPS? If so, I could simulate a TPS signal.

The MAF should operate outside of any other crap. I think it really exists only to replace the IAT.

It basically just measure the amount of air entering the engine by weight. So I could see how the ECU would sense idle/wot as seperate things and for the rest use MAF and RPM to calculate fuel trim. But mehbe that's all BS.

Newbie-Wheel size change &c on L200
 

Hi all, glad to have found this group!
Being short on cash this Xmas, I chose to drive my 1992 Mira L200 from Alice Springs to Adelaide, (Usually around 1600 km).
Temperatures were (low for here) but around 37-39 degrees. So I pulled out the air-con radiator before leaving (otherwise the car would have overheated). I split the trip over 2 mornings, leaving at 4 am daily. I left with 2 full jerrycans to avoid the exhorbitant fuel costs mid-way.
I travelled while outside temperatures were between 23-34 degrees, spraying myself with water from a bottle to keep cool, keeping windows closed but interior fan on. I was pretty comfortable, other than a paralysed foot on the accelerator to keep a steady 110 Kph.
Well, I can say that the average consumption was 5.1 l/100. The only time it was lower was between 3:30 and 5:30 am, when it was dark and I drove at 70-80 to avoid kangaroos: then I did a refill and had managed 4.6l/100.

Now the trip is over, I have already put larger tyres on my Mira:
replacing the 145/70R12s with 155/80R12s gives an 8.5% increase in radius.

I bought second-hand tryres, testing them in case the tyres scrubbed or the vehicle mis-handled. Fine all round; even better feel to the car. (I will possibly have to add larger shocks to cope with the extra 1 kg/wheel unsprung weight).
The change to gearing is dramatic; I no longer shift to 5th gear in city traffic at 60Kph as was intended for a shopping-car Mira(?). I can now do as low as 70 kph in 5th, as long as there's no hint at an uphill drive.

I'm now preparing my trip back. I've fitted a Uniden GPS301 (picked up for $100) just so I get a correct speedo reading. I've got a cruise control ready to squeeze under the bonnet for the next 1600 kms of straight road. (There is a real risk of deep vein thrombosis when you cannot move your feet around for 10 hours at at stretch.
I am watching these posts intently for advice on sensible modifications.

kind regards,

Steve Peters

Well, I've found the time to post the photos of all the modifications. The next post will have a discussion. Here goes:

https://img253.imageshack.us/img253/3...x480nh9.th.jpg

https://img402.imageshack.us/img402/7...x480pv9.th.jpg

https://img402.imageshack.us/img402/6...x480rd6.th.jpg

https://img402.imageshack.us/img402/6...x480hj1.th.jpg

https://img253.imageshack.us/img253/7...x480fe4.th.jpg

https://img402.imageshack.us/img402/6...x480cz9.th.jpg

https://img402.imageshack.us/img402/7...x480eg6.th.jpg

https://img210.imageshack.us/img210/3...x480bw7.th.jpg

https://img402.imageshack.us/img402/9...x480qy9.th.jpg

https://img253.imageshack.us/img253/9...x480bq3.th.jpg

Ok, so in total the current modifications are as follows:
grille blocking (with approx 200mm * 40mm hole for radiator)
- everyone wonders about that. The fan goes on sometimes when traffic is stopped on really hot days. It never overheats. The thing to realize is that the resistance of a typical radiator is very high. Imagine a cluster of tiny straws, for example. Note that they will not flow as well as a single pipe with the same cross sectional area as the sum of all those little straws. The same applies here. Although if I really had a problem, I'd make sure to completely duct the little airhole so that all air had to pass through the radiator.

Air holes on the front of car are primarily for the benefit of the lay public, who appreciate the stylistic aspects of lots of air holes.

front air deflector
The first picture shows this. Basically just a rectangle of aluminium (0.6mm from memory) bent around, so that from the front it sits just in front of the wheel. Took less than an hour (but more than that to test, because I originally made them too long and they scraped).

partial boattail
-it's about as long as you can go and still pass Australian regulations for rear license plate visibility, which must have 45 degrees to the vertical unobstructed.
-I used some sort of aluminium from the local hardware store for the frame, some bolts to bolt it together, and pvc film (0.3mm from memory) taped around with industrial strength clear tape. It flaps a bit in the breeze. You can't secure via drilling for this thickness, you must use tape. But it works. The first time I used thicker stuff, and thought it looked marginally uglier (also aerodynamically uglier), because I used 3 sheets, one for top and two for sides. The heavier 0.9mm stuff I used the first time hung down because it was heavy, meaning I had too sharp an angle between the top of the car and the boattail.

In total, took the better part of a day.

full 0.6mm aluminium undertray
-this took about 4 hours work, and someone helping for about 2 hours of it. Needed jack stands, and rested all four wheels on the corner of a wooden pallet.
Rattles a bit like an airplane at idle (sometimes), next time I take it off I'm putting flame proof insulation to damp the vibrations down. It stretches from the front to the back, just cut out where the suspension is. The reason I used aluminium and not corflute is because my exhaust system zigzags all under the car and it was a false economy to cut it out and patch it with aluminium over the heat sensitive end - far, far, far too much work. As it is, it's two sheets screwed together. I've screwed it into the chassis in a couple places as well as under both sides. I've duct taped the two sides together (for smoothing reasons, not structural of course). If it leaks oil, I might remove some of the duct tape.

rear fender skirts
-These are a single piece of aluminium, screwed using small galvanized sheet metal screws. Note they attach to the mudguard at the rear, flare out quickly and take a slow angle back (much like a typical airfoil). No bracing other than the natural stiffness of the aluminium.

rear deflectors
-self explanatory. Held on by two screws.

removed left side external mirror
-In Australia, if you have an internal mirror you only need a right external mirror, automobile manufacturers stick the other one on for symmetry. So I removed it and fashioned something in it's place with some rubber, some aluminium and some bolts.

faux racing rims
These are the cheapest 12 inch wheel covers I could find. The same pvc film is screwed all around, then heat-gunned a bit as an attempt to shrink it. In hindsight, should have used the tape I used for the boattail. May do if I can be bothered.

In future, I plan to cover up the gaps in the front under the bonnet with expanding foam, and do the front wheel skirts. Front wheel skirts I plan to make with aluminium and fish pond rubber (very similar to inner tube material, but flat). Basically the aluminium strip will extend virtually to the front of the bumper, flare out a little, and also around the back. Probably about 100mm long in total, if that. Hardly enroaching into the wheel well.

I figure if I make the flexible material as big as possible (i.e. roughly the shape and size of the wheel well) then it will bend easily and not rub excessively or ride up.

Ok, so how does it go? I've noticed vastly improved ability to coast. Take a relatively shallow hill, and I can go in neutral down it and maintain a speed of about 80kph. Steeper hills get closer to 90kph.

And that's pretty good, for a fairly light boxy car. The wake in the rain is also vastly reduced.

The pvc boattail flaps a bit at speed, but I can't hear it. My only concern is as to whether the aerodynamics are messed up at all. I might restretch it a bit more and retape it, but I can't really be bothered.

When I'm travelling at 100kph, my subjective feel is that the engine is only working to do the excessive 4000rpm (or whatever it is) required of it, the load of actually working against the wind is fairly minimal. I can of course put larger tyres on it as the desert mira has done. I think that would be a good option.

The other option is pulse and glide. It's funny, I don't think I was all there when I bought the car. The idea was that with a tiny EFI motor of 660cc, roughly half the size of the civic, that it should be more efficient at partial loads such as when I modified it. I didn't realize it didn't bump start too well though - in the manual it warns not to, something to do with the catalytic converter. It seems to take some effort to bump start, and I don't like using up the vacuum in braking without thinking, so that I get the heart stopping no brakes feeling with another car looming up ahead of me.

The other idea was that it was very light (600 something kg) and also had a small cross sectional area, so that was a good starting point.

Anyway, pulse and glide. Now I realize that having a small engine WILL be an advantage, and I might not even need to get bigger wheels. A car in idle should expend a roughly proportional amount of fuel with respect to engine size, so a small engine should get very good results from a neutral, engine-on glide. It might also be an idea to adjust the idle to the minimal value such that it won't conk out. So, if I'm pulsing and gliding, the engine will be in a relatively efficient range when working, and when not working, the bigger tyres won't be helping anyway.

Anyway, couple a car that coasts very well, an engine that doesn't use much fuel in idle at all, and since I haven't been pulsing and gliding, I think I've got some better fuel figures to post. Especially considering that an engine forced to overcome friction at 4000rpm should be much more efficient at 700rpm or so.

All in all, it has been an interesting experiment. With a bit of paint, the car would look a little less science projectish. I'll probably get that done after I make the front skirts. And it is a good learning experience on a very cheap car, before I get something like a prius and give it the full aero treatment.

I'd like to thank basjoos for providing a bunch of inspiration, and a commute that made this all necessary. Thanks also those who have been logging bike miles such as svoboy, I've probably clocked up about 10km trips to local stores so far that would have been done in the car previously.

One thing I would warn, when working with pvc film, start in the middle, pull to the other side, move a bit down, pulling as you go. In this way you don't tend to get ripples. The best way to get ripples is to secure the corners first and then do the middle - it will either be too loose or have ripples that way.

One other thing I had planned was to do subtractive testing rather than additive testing. i.e. Do everything I know should work, then do A-B-A testing by removing the modification, leaving all other modifications on.

Doing this I'd expect to see more of a difference, reducing the error. That's because you are comparing Cd to (Cd + x). The smaller the Cd value is, the larger [(Cd + x)/Cd - 1] should be.

If aussie regulations regarding licence plate visibility is your only concern, then why don't you build a boattail onto your hatch that would cover the entire back of the car and would flip up with the hatch when you open it. Just mount your license and rear lights into the back of the boattail. Design it right and you could also considerably increase your interior storage space.

That's what I would do if license plate visibility were my only concerns. Remember, I live in the city and my commute is at least half city (it's quite impressive that I'm achieving better than Australia's version of EPA rating for highway as well as city, for city I'm bettering it by about 40%.).

Other concerns are
-ability to park it easily in the city - one advantage of a kei car I've come to really appreciate.
-time/money calculation - the investment could easily be a week's worth of work.
-worries about lift generated by such a boattail. It's a light car, and the torque generated might be significant.
-crosswinds removing a lot of the benefit. As it is now, there is minimal area on the sides for a crosswind to affect
-I want to have things, once painted, eventually look, if not factory, at least competent aftermarket manufacturer-like.

My car is less an experiment in what can be achieved in fuel economy with no expense spared, than a synthesis of the practical and low hanging fruit in terms of payback periods and consumer acceptance. It is also a way to learn how to do this sort of things, hands on, in a car that is virtually a throwaway item. Considering the car cost about $4000k AUD, that's a year's depreciation with most other cars.

If I eventually decide on an experiment that is more "balls to the wall", I will probably be picking a car that is either already mostly optimized for drag such as the insight or the prius, having the bonus of safe, easy and zero fuel used in EOC. That way I can just do grille blocking, mirror removal, undertray, and front skirts. The only problem is that these cars already have the very tip of the rear facing horizontal, so it's not easy to extend via a boattail. In fact, to make it look professional would be a multiple of the price of any fuel saved.

Or: I will be picking a ute/convertible/something etc, that has the combination of overall low height, that height very close to the front and the back exceptionally low, in order to minimize total length. Think ford capri.

So thinking on this a bit more, I'd like to go further than I have in order to approach ultra low fuel consumption. But...
1. It must be similar in practicality to the parent vehicle.
2. It should conceivably be an investment with a fairly low payback period, 3 years at most.
3. Aesthetically, it should look somewhat professional.

One thing that must be investigated is if similar results to a boattail can be had by increasing the rear angle (shortening the boattail) and tripping the boundary layer into turbulence. If so, that might enlarge the range of vehicles that could be modified.

Practically, that means two things.

1. The vehicle must be modified to have as small a drag figure as possible.

2. The engine must have miniscule idle consumption at worst, or so-called mild hybrid capability for everything except stop start driving. Of course, regenerative braking is great with city driving, but a lot of that can be minimized with enough attention on stop lights.

The choice, as I see it, comes down to:
1. Accept the rear end of an insight or prius as given, seeing as modifying the rear as I would like is in the too hard basket, and just modify the things I can.
2. Go nuts with a capri, using a mild P&G with the relatively small engine it has.
3. Enlarge the circle of cars I'd be willing to look at a bit, and nut out all the hairy details of an aftermarket mild-hybrid conversion. Frankly, that looks difficult and expensive to get it to even the stage where it switches on and off and doesn't harm the engine when the throttle is below a certain point.

I suppose if I can start a trend or make it fashionable to have all the things that are currently considered stylistically ugly or unecessary (such as fender skirts, grille blocking, LHS mirror missing, etc), then maybe the auto makers will make something more extreme in terms of what the rear end suction is doing than the prius or insight.

Or maybe someone like JanGeo could help me out with option 3. Frankly, I need to measure my own car's idle fuel burn and evaluate the maths of P&G before I even seriously consider things.