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I need some help to create an own 180 km/h speed limit defencer. The question is simple:
In hondas how mach the period time of the VSS sensor signal at 180 km/h?
Have somebody measured this?
The Mitchell's Repair manual said:
VSS signal is generated by speed sensor, which produces 4 pulses per speedometer cable revolution.
What does it mean? How many pulses per wheel rotating?

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oh god...

if its a 88-91 ecu system a simple chip could defeat it
if its a 92-95 ecu system a simple chip will defeat it
if its a 96+ ecu system convert to 92-95 and read the second line...

I don't want to convert ECU. Anyway it is an OBDII P5P.
I've interested in only speed limit defence.

thnx

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"4 Pulses per cable revolution" dates back to cars that had a speedo cable. Your car, and most other hondas made after 92, have an electronic vehicle speed sensor that pulses 4 times / revolution of the wheels. (I believe)

If you wanted to build an electronic device to remove the speed limiter without touching the internals of your ECU or the code running it, you would need to limit the frequency of the pulses generated by the VSS module to less than the frequency of your VSS at the speed limiter.

What I would do:
-Get a multimeter with a frequency counter or a oscilloscope
-hook it up to the VSS signal being fed to your ECU.
-go for a drive. Record the frequency of the speedo at 100mph (safely below your speed limiter)
-build a device to limit the frequency to the 100mph freq maximum.

I'm going to add some of this info to the wiki.

http://www.nitroburn.com/pgmfiwiki/index.php/VehicleSpeedSensor

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Thank you for answer.
Yes I know this. I have made my own speed limit defencer device already with an Atmel microcontroller. The hardware works properly with the first assembly program. It only copy the VSS signal from input to output. The ECU works OK.
The second program was a simple divider algorythm, which by-passed only every second signal (the car moves 100 km/h, the ECU sense only 50 km/h.)
It isn't good because I have 4 speed automatic transmission.

The final algorythm is: measuring the period time between two VSS pulses and if the wehicle speed is above 170 km/h, thereafter the program send pulses according to 170 km/h. The TCM doesn't disturbed by this because the TCM switch to 4.th at 160 km/h

This is that I want to know the period time between two pulses.
Good Idea to measure the frequency, this is the only way I think (My multimeter has no freq measure, and I ask here the information)

Do anybody measure this for me???

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you might try this for a crazy idea:

http://crx.honda-perf.org/math/index.html

180kph in 4th gear (closest to 1:1 as I understand it) with a CRX w/ J1 transmission = 8025 RPM w/ 185/60/R14

8025 * 4 = 32100

32100 is pretty damn close to 32768 isn't it? odd coincidence or what?
I'd try limiting your pulse frequency to 32000 Hz. I bet it would work

I'd love to see your design/code when you get this working!

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by the way- thankyou for the service manuals! I grabbed a few from your website. very helpful!

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I am happy to help you and thanx for information.
Popularize my website please.

I will present my speed limit defencer when I finish it. It is a very cheap design with a simple software and very easy installing (only 4 wire)

32KHz? Hm I think I need to raise the frequency of the microcontroller because at 32 kHz the period time is aprox: 31 us. I am using 3.6468 Mhz quartz now.

Blundar: Are you sure, the RPM is equal the speedometer cable revolution?

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I have a JDM CRX SiR with speedo initially in Kph

the car has a simple electronic 5/8th divider, meaning my speedo now reads in MPH rather than KPH - so I now have a cool 180mph speedo and my mileage now counts in miles instead of km's

Positioning the divider is another matter - as close to the speedo as possible - after the pulse wiring split to ecu/speedo gives a correct MPH reading but doesnt delimit the vehicle.
Placing the converter before the wiring split means the limit is effectively raised to about 180mph, but also raises the vtec activation speed to the point that vtec doesnt occur in 1st gear!

my current setup is the first option - I have an accurate speedo and have removed the limiter in the Rom, thus retaining 1st gear vtec activation

AFAIK - The only way to effectively remove the limiter is to disable it in the Rom

HTH

Mark

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Mark, he isn't talking about a simple divider - he's using a micro to pass-through the VSS signal until a certain point, at which it gets "held" at a level pre-speedlimit.

Can anyone else here speak about 4th gear in a CRX SiR being close to 1 wheel revolution per engine revolution? Or better yet Mark, can you scope your VSS signal and find its period just before the revlimiter kicks in?

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I have bought a digital multimeter with frequency and duty cycle measuring. And I have measured the VSS signal. Here is the suprise result:

Duty Cycle : 50% at all speed
Frequency:
42Hz at 60 kph
70Hz at 100 kph
84 Hz at 120 kph
119 Hz at 170 kph

Honda Prelude with 4 speed Automatic transmisson and 205/55 R16 tires
(factory tyre is: 205/50 R16)

So I beleive the RPM is not equal "speedometer cable revolution".
I'll make a new program if I have Time. I will report...

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216 Turbo:

I beleive the Vtec Activation is depend on only the RPM and oil pressure not the Vehicle speed.

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Sorry hondainfo but 216 Turbo is right. You can tested in your car, disconect the vss terminal and go for a ride.

peluca: Well I dont know. If I disconnect the VSS terminal, the ECU goes into a backup safe mode. I will try It.

"The HKS Speed Limit defencer " said:

in JDM cars, cutting off the VSS signal to the engine ECU can lead to one of three conditions. One is the ECU will just ignore the absence of the VSS signal and continue operating as normal. In another, the engine simply won't start or will die when gear is engaged. The final condition is the ECU program, because it now cannot determine how fast the car is travelling, goes into a backup safe mode in which it runs the engine rich. This unnatural rich mode is undesirable and will actually lead to a slight loss in engine power as well as oil dilution (contamination of engine oil with petrol).

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Hondainfo

Try putting a 5/8 divider in the wrong place - and you will see exactly what I mean
What happens is the divider moves the min speed for Vtec activation to a point where it is almost unusable in 1st gear.

Dave - I understood the quest here - but I thought my own issues with the pulse generator / divider / speed limiter were maybe remotely relevant
Most of the technical work on this forum is way beyond me - and I freely admit to being lost when I look at code!
I can build cars, engines, gearboxes, I can use the software that the good people here provide, and I can tune on a dyno - and I can give limited feedback on here where I have real world experience. - even if its not entirely relevant

Mark

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