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.