speedo out twitchy, course resolution

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ashford
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speedo out twitchy, course resolution

Post by ashford »

i am wondering if ther is a better way to run my speedometer than what i am doing or if i have to live with it. the speedo start to get twichy, loose resoulution as the speed increases about 65 mph each increment is about 4-5 mph on the gauge.

my current setup is a 99 mustang that had a 3.8 t-5 i bought the car with a blown trans and poor running engine. just for the hell of it i wanted to see if a 302 would fit in, and low and behold my old 5.0/t-5 combo bolted right in with mismatched motor mounts, shifter and everything lined up im even using the v-6 exhaust, just had to shorten it about an inch. after a bit of head scratching and whatnot i ended up keeping the stock ecu to run the gauge cluster since it is based on ford 1850pwm datastream. i have the speedo run off of tacho out through a capacitor to turn it into an ac signal the computer can use.

for settings i have 8000ppm in and 30000ppm vss out. and it is really close. ts and the gauge match at lower speeds. i don't know how ms handles this internally, if i use different methods like time period and or tire size tooth count etc if it will change things or not. like ts is a front end to convert different metrics to the same thing going on in the background.

so i think one of several things i can try if they are worthwile

1. try using different measuring methods
2 half both ppm values( don't really care if ts is reading higher mph as long as the dash is correct)
3. buy a frequency multiplier and knock down the output number.(thinking jeans pwm frequency multiplier but i don't know how well that would work)
jsmcortina
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Re: speedo out twitchy, course resolution

Post by jsmcortina »

Please post an MSQ and video.

James
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ashford
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Re: speedo out twitchy, course resolution

Post by ashford »

heres a video https://www.youtube.com/watch?v=0jYSVX_ ... e=youtu.be

msq is in my laptop at work
ashford
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Re: speedo out twitchy, course resolution

Post by ashford »

i have the msq
ashford
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Re: speedo out twitchy, course resolution

Post by ashford »

bringing this back up, i have done another install where there is a high ppm to run factory dash/ cruise control, this really makes crusise control useless.
this is easy to do bench testing on, set vss out to whatever car uses(30000ppm) for my car loop to another input ans set vss2 to it and set same ppm.
with this settings @100mph vss2 jumps from 91ish to 100
the lower the ppm the more resoulution ie if i use 7500ppm i have about 1 mph resolution at 60mph.
i had started a thread earlier about using a pwm multiplier as a frequency multiplier and i am about to give this a shot.
jsmcortina
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Re: speedo out twitchy, course resolution

Post by jsmcortina »

The VSS out is using a software timer and will indeed become coarse at very high PPMs.

James
I can repair or upgrade Megasquirts in UK. http://www.jamesmurrayengineering.co.uk

My Success story: http://www.msextra.com/forums/viewtopic ... 04&t=34277
MSEXTRA documentation at: http://www.msextra.com/doc/index.html
New users, please read the "Forum Help Page".
dontz125
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Re: speedo out twitchy, course resolution

Post by dontz125 »

Any suggestion as to what the highest frequency that would give a reasonable granularity (say, 1mph) might be? Users needing a higher pulse rate could use a frequency multiplier.
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ashford
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Re: speedo out twitchy, course resolution

Post by ashford »

i tested with a pwm multiplier, it worked wonderfully. the mustang dash/computer wants 30,000 ppm, i did a *8 on the pwm multiplier and a 3750 on speedo out, then looped it back into vss2( set for 30,000 ppm) for testing. then hooked vss1 to a signal generator, at 200mph i had steps of about 2mph.
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