Speedometer Mod

[bendychicken]

OK, here's da plan. Put a resister in between the speed sensor on the transmission and the ecu. This will fake the ecu out into thinking the car is going slower than it really is so that it doesn't cut out at 120mph. Then put a transformer on between the ECU and the speedometer so that the speedo reads the actual speed.

Lets just say that the speed sensor put out 15 volts at 150mph for the sake of simplicity. You put in a resister so that at 150mph the voltage reacing the ecu is 10V so the ecu thinks your only doing 100mph when your actually doing 150mph. It then sends 10volts out the the gauge. You put in a transformer betwwen the ecu and the gauge to step the voltage back up to 15volts so the gauge will still read normal(even though it doesn't go that high you still want it to be accurate at lower speeds so that you don't get a ticket when driving on the street.)

This would be really cheap, prolly under $20 to do. Thats cheap when you consider the cost of an ecu upgrade to do the same thing.

sooooooooooo, does anyone have some wirering diagrams. If you hook me up i'll try it on my car and if it works I'll write a detailed "how to" with high res pics. any takers? comments?

[cory2081]

Good idea, could also use this to correct your speedo when using different size tires. *bump* Anyone have schematic for the VSS??

[bendychicken]

C'mon people. I know someone's got a wire diagram, or a sciamatic or somthing.

[NisMoSilEiGhTy]

check either advance auto parts or autozone's websites i know one of them has the wiring diargram in printable and viewable form. i need it to wire up my 240's halo headlights i got

[RalphCare]

OK, here's da plan. Put a resister in between the speed sensor on the transmission and the ecu. This will fake the ecu out into thinking the car is going slower than it really is so that it doesn't cut out at 120mph. Then put a transformer on between the ECU and the speedometer so that the speedo reads the actual speed.

Lets just say that the speed sensor put out 15 volts at 150mph for the sake of simplicity. You put in a resister so that at 150mph the voltage reacing the ecu is 10V so the ecu thinks your only doing 100mph when your actually doing 150mph. It then sends 10volts out the the gauge. You put in a transformer betwwen the ecu and the gauge to step the voltage back up to 15volts so the gauge will still read normal(even though it doesn't go that high you still want it to be accurate at lower speeds so that you don't get a ticket when driving on the street.)

This would be really cheap, prolly under $20 to do. Thats cheap when you consider the cost of an ecu upgrade to do the same thing.

sooooooooooo, does anyone have some wirering diagrams. If you hook me up i'll try it on my car and if it works I'll write a detailed "how to" with high res pics. any takers? comments?

20 dollars? ha.. more like 5...canadian.

[nismofan14]

Let me save you some time. Just cut the speedo wire at the ecu and unplug the 5th gear sensor on the transmission.

That was a good idea you had but the wiring for the speedo is like this..... transmission>speedo>then ecu. by cutting the wire at the ecu, you still have a functional speedometer but he ecu has no signal. By unplugging the 5th gear sensor on the transmission, you eliminate the signal to the ecu that tells it the car is in 5th at a certain speed, which signals another limiter.

You could still use you idea to modify the signal to compensate for different tire sizes.

[spec-u-later]

If you want to kill the cust out just cut the yellow wire with a grey stripe that goes to your ecu and unplug the 4th and 5th gear rev limiter on your transmission. Total cost = 10 minutes.

[HaveBlue]

the speed signal does not depend on a particular voltage. it is a series of pulses, the speed of which determine the reading on the speedo. resistor idea will not work for this.

[USDMSTALKER]

Anyone have the schematic for the actual circuitry in the gauges. Because i need to keep the speedo and make a switch for having two odomotors to keep under 5000 miles a year. I get an exempt on emisions if i can do thisI need two odometers to keep track of miles for oil change.Will be putting in sr soon don"t need to fail emisions

and also to fool your computer you can build a divider circuit for the pulses they can divided by what ever number you want as long as the pulses are digital

[bendychicken]

Spec-u-later what yellow wire with a grey stripe?there's all kinds of yellow wires on the ecu, red stripe, blue stripe, black stripe, green stripe etc....

but no grey? it's a 93 5speed, ka

[WAbernethy]

It's actually a green and yellow wire. Check this http://www.240sx.org/faq/articles/spdgov.htm

[Toms240420]

i heard some where that there is a 1st gear limiter. is that true?

[RalphCare]

i heard some where that there is a 1st gear limiter. is that true?

theres a rev limiter in every gear. but not a speed limiter.

if you download the rom editor on your computer, you can see

[p00t]

the speed signal does not depend on a particular voltage. it is a series of pulses, the speed of which determine the reading on the speedo. resistor idea will not work for this.

yessir, for bendys idea to work you would need a little unit that would limit the pulses. so above lets say 110mph+ it would only put out that max limited number of pulses (speedo would stop at 110 and just sit there).... hmm business venture methinks.... haveblue ill split the revinue with you since you seem to have to concept down too how bout it?

[bendychicken]

OK, it works now.I unplugged all of the sensors from the transmission except for the speedometer wire.Then I cut the 8th wire down on the ecu which is yellow with a green stripe. Fired up the engine(the car is on stands) put it in fifth gear and revved it out to 6000rpmthe speedo hit the bottom of the gauge cluster with no cut out:batman

[HaveBlue]

I have the concept down but failed my Computer Engineering class. This would take a small micro processor to accomplish. it would have to listen to the pulses, pass them along untill a certain point (110mph) and then start passing on 'fake' ones instead. not much work for someone who knows what they are doing but stilly when you can just remove some wires and accomplish the same thing.JWT removes the limiter on the ECU.

[spec-u-later]

BendychickenYeah maby the stripe was green. It was a little dark when I did mine and the wire may have been faded a little but it looks like you got it.

[bendychicken]

ok, so here's the next question: will this work on my 91 automatic? if you cut the speed signal going to the computer, how will the ecu know when to shift?

[HaveBlue]

ive discovered my 1990 automatic doesnt have a speed cut. Ive buried the speedo deep in the black and it keeps going. go figure.

besides i think the ecu doesnt decide when to shift. there is a separate ecu for the automatic transmission that shifts based on engine rpm and throttle position. Im not sure about that though.

[lenso]

just confirming haveblue's reply that autos dont have speed limiters. i was well into 125 (keeping up with a friend).

[bendychicken]

I did some math and the tope speed of my car(93 coupe 5 speed) should be about 157mph at 7000RPMs (not factoring in aerodynamic drag)Has any one topped out a stock s13 yet? What did it top out at? I tested mine on ramps. I can't test it because there's no bumper or fenders on it.

[HaveBlue]

the gearbox is your limiter. aside from power. it is in the 160mph range. the auto gearbox tops out at about 145. you can look the EXACT numbers up, these are off the top of my head.different rear end ratio and tiresize will alter this.

[SilviaS14KA24DE]

how about for an S14? anyone have any ideas how to remove it?

[SHIEF]

Or you could just plug in an auto ecu in your S13, if it's a 5 speed. That'll get rid of rev-limiter and speed limiter.

[veilside180sx]

confirming that putting a auto ecu into a manual doesn't affect anything, but does rid you of that pesky speed governer. I just unplugged mine and swapped it ten minutes ago. Then quickly ran out and did a run up to 130.=) How nice. I hated that dumb thing.

[veilside180sx]

by the way mine was a '90 sohc s13, i swapped it with a '90 sohc ecu from the auto. as long as you stay same year or sohc or dohc it should work ok

[HaveBlue]

ive heard of cold start issues with an auto ecu in a 5spd. ymmv.

[veilside180sx]

mine already had cold start issues, i need to replace my iac. Although i think it starts easier since i swapped it. I guess i'll find out tonight when it 's cold and hasn't been run all day. (at work). I'll make sure and report afterwards. Up till now i have yet to see shortcomings.

[WAbernethy]

I tried the trick with the transmission plugs and the wire at the ecu and it didn't work. I left the 4th and 5th gear sensors unplugged when I re-installed my motor a couple of weeks ago and I cut the yelllow and green wire at the ecu and things got worse. I got limited in third at high rpm and 4th and 5th before I could get over 90. That sucked. I'd like to try the ecu swap thing, anyone else verify that this works? 1/4 mile trap speeds and speed limiters don't get along too well.