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Old 05-16-2013, 03:51 PM   #1 (permalink)
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Wheel speed sensor and MPGuino issues

Car is a 2006 honda Insight, manual transmission (of course)

OK so the wheel speed sensor on the Insight is actually tapped in at the transmission, so i guess its more of a transmission speed sensor - but anyway...

So i got this sweet as MPGuino installed, and its a pretty simple little device, displays fuel consumption/mpg/speed etc. using the speed sensor, and the injector signal. calculate how long the injector is open (which is directly related to how much fuel is used), and related that to vehicle speed - and instantly calculate MPG numbers. Kinda like the stock Inisght FCD but better

So its all working great, EXCEPT that sometimes (often) the speed sensor is all over the map! i'll be going a steady 55mph (as displayed on the regular Insight gauges and again confrimed via stead RPM given by the Ultra Gauge), but the MPGuino displayed speed is jumping around: 52.04 mpg, then 56.5mph, etc etc. it jumps around a lot, but usually stays within about 5mph of what is the actual speed.

at higher speeds, and in lower gears (such as climbing a big hill at 50mph in 3rd gear), the reading is even more off. sometimes as much as 10 or 12mph above actual speed.

problem is that with inconsistent speed data, the MPGuino is unable to correctly calculate MPG!!! MPGuino reads i am going faster than i actually am, and hence spits out overly optomistic MPG numbers


why would the speed sensor be jumping around so much?
it seems to do it more in lower gears, possibly relating to RPM. but RPM is very low (less than 3000rpm) when i drive..
is this normal, and the stock speedo kinda 'averages' the imput from the speed sensor? (i doubt it)
maybe getting interference from another wire or system or something? i dunno


btw: the stock speedo on the insight does not jump around like this at all.

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Old 05-17-2013, 03:54 AM   #2 (permalink)
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Not my own experience, but;
My friend was having same kind of problem as you, but while doing own speedometer. He fixed the problem by adding around 0-100n capacitor between signal and ground(can't remember, just test different values).

And another had an interference from aftermarket cruise control, whick solved by adding an low-pass-filter on the speed signal, by cutting at around 400Hz.

So, you might want to take a multimeter and measure around..
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Old 05-19-2013, 03:41 PM   #3 (permalink)
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You can try to use shielded wire for VSS signal with ground on the shield. Capacitor can help as well. You can try to change VSS delay settins and see if that will help to stabilize VSS reading.

Anyway from experience I can tell that proper ground is a crucial thing for MPGuino.
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Old 05-20-2013, 11:07 AM   #4 (permalink)
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thanks for the suggestions!

car does have cruise control. i need to remove (and sell) that stupid thing. i'm gonna remove it, and report back. expect a few weeks tho. i'll also check my ground for the MPGuino, but i'm pretty confident that is totally fine.

it should be stated that when coasting down a hill in neutral, even at high speed, the MPGuino reads PERFECTLY. doesnt jump around at all. As soon as you put in in gear, it starts jumping around again. what do you guys think that piece of evidence means?


any other suggestions appreciated
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Old 05-21-2013, 03:03 AM   #5 (permalink)
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I think that has to be some kind of electrical noise. Try to connect capacitor and use shielded wire for VSS signal.

Have you checked if rpms are read correctly?
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Old 05-22-2013, 11:42 AM   #6 (permalink)
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odd...

drove to work today. speedo on the MPGuino was reading perfectly the whole time. no issues whatsoever, no matter what gear i was in, etc, just no problems at all .

havent worked on the car AT ALL since first reporting the issue. very weird.... if the issue comes back again, i'll for sure let u all know!
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Old 05-22-2013, 05:21 PM   #7 (permalink)
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Strange indeed... I presume the issue was based on some bad contact and it could disappear with different humidity, road bumps etc. Or it can be just noise from high voltage wires and that could disappear in dryer air, or again some road bumps.
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Gerhard Plattner: "The best attitude is to consider fuel saving a kind of sport. Everybody who has enough money for a strong car, can drive fast and hit the pedal. But saving fuel requires concentration, self-control and cleverness. It's a challenge with the nice effect of saving you money that you can use for other more important things."
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Old 08-28-2013, 12:53 AM   #8 (permalink)
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issue came back (surprise surprise)

so i did the right thing and removed the crappy red clip connector thingie that the previous owner installed to tap the VSS wire. then I soldered the VSS wire; havent had any issues since (its been a few weeks now). so i'm going to tentatively call this issue solved, and blame it on a bad connection. the true test will be thru the winter months, as its been a pretty consistent temperature here lately. if it can go all of winter without issues, then it was for SURE the crappy connection

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