Speed sensor ques

[cheese9988]

I don't know if anybody will know this....will the ecu throw a code if it thinks you are going lets say 50mph all the time, even when you are at idle or driving around at any other speed?

 

[posol]

lol umm...

the speed sensor is mecahnical. theres a notch on a spindle thinggee which gets turned by the tranny.

so, unless your sitting there spinning it, or the insides of your tranny are moving, its not possible

 

[radnulb]

the VSS is simply pulsed to ground 4 times per revolution of the wheels. Someone on PGMFI actually made a really simple device that removed the revlimiter by sending a bogus speed signal to the ECU above 100mph. Sending a fixed frequency pulse is probably not the best idea, especially considering how easy it is to simply pass through low frequency signals and cap their frequency to control maximum speed.

 

[posol]

Originally posted by radnulb@Aug 20 2004, 04:51 PM
the VSS is simply pulsed to ground 4 times per revolution of the wheels.

[post=379806]Quoted post[/post]​

well, yeah. the thing i described above spins, and hits some kind of contact point or something inside, which then gets translated into electronic pulses to the ecu.

there are two main types of sensors-

pulse and voltage

 

[cheese9988]

the speed sensor is mecahnical. theres a notch on a spindle thinggee which gets turned by the tranny

I know that, I was thinking that I could trick the computer into thinking I was going say 50mph all the time with a simple 555 timer or something. I'd just put the scope on the output from the speed sensor and see what the pulse was. I just wasn't sure if it would make the computer act wierd if it was constant. I could build it to go up and down at a fake rate, but that would be more work.

 

[radnulb]

or you could use the design to pass through the signal until it is too high and use the design that is already done instead of reinventing the wheel...

 

[cheese9988]

Eh, 555 sounds just as easy, I'll just plug the scope into a power inverter and see what the pulse looks like when I drive around.

 

[radnulb]

it varies in speed. you'll run into a few minor issues in terms of fuel economy stuff and idle if you disable it.
You also won't be able to use a VSS-based 2step limiter.

 

[cheese9988]

But it won't affect driving preformance that much do you think. You probably know more about the ecu's than I do.