Alto RS-X speed limiter

[Almost a Mini]

My '87 Alto RS-X has (like all Kei cars) an electronically limited top speed (120km/h). It also has a horrifically annoying chime that cuts in at about 90km/h.
Now, seeing as I'm planning to do a few circuit sprints, hillclimbs and stuff in this car, the limiter has to go. On my Cappuccino, this was as easy as chopping the speed sensor wire to the ECU. . .(lights up the engine check light - but chopping a wire is cheaper than buying an electronic speed delimiter).
Does anyone know *how* exactly the speed is sensed so that the ECU knows that the limit has been reached? The Alto's EFI system is an earlier 'generation' than the Cappu (no self dignostics etc) so I wont even have the check light problems!

Thanks for your help,
Pete in Perth

[evilgidget]

Contact Chiptorque or someone similar - cutting the speed sense in most cars is a bad idea as if you floor the throttle, the ECU detects RPM, engine load, and no speed, hence figures there's a problem & shuts the power down into 'limp home' mode, generally causing more headaches than it's worth. Having the limiter wiped or raised to 250kmh in the ECU's software is generally a lot better.

[Almost a Mini]

Aaahh, yes! I guess there is the potential for this type of problem. . .although it hasn't been apparent with the Cappuccino. . .
The ECU certainly uses both load (via the MAP sensor) and rpm (via the dissy) as part of it's fuel metering and ignition - but are you sure they use road speed?
Regardless, I'd like to have a bit of a 'play' myself (that's at least half the reason I bought the car) and I *am* monitoring fuel mixtures etc constantly to make sure I'm not causing lean mixtures and cooked pistons with any of my mods.
So, does anyone know how road speed is measured?

Thanks,
Pete in Perth

[evilgidget]

They usually use either an electrical pickup off the gearbox to the speedo via the ECU, or use a mechanical cable & have a sensor on the back of the speedo. Road speed is measured & used by the ecu to indicate the chime & speed cut (ignition/fuel cut), but i think you've already figured that...

[Almost a Mini]

Aaahh. . .that's what I was looking for!
There aren't any electrical connections from the gearbox (apart from the reversing light switch) so I imagine there's something on the back of the instrument panel. The 90km/h chime thing is back there somewhere as well, so I should be able to find it and trace the wiring to the speedo and back to the ECU. . .
Guess I could also test this by just unplugging the speedo cable and seeing if the limiter disappears. . .
Thanks!
Pete in Perth

[n2o_spark]

i know i'm grave digging. but can you tell us if you found that right wire to cut and did it work out?
i'll post some pics of the behind of my dash if that helps.
i too will be doing some track racing.. next weekend infact, and the though of a 2 minute lap due to speed limiter when i may be able to get a 1:20 if not a happy thought

thanks

[Almost a Mini]

OK, no problem.
I think I've seen from your other posts that you've got a '87 F5A RSR?
If that's right then your car *should* have the same wiring as mine. . .if it's a later (F5B powered) car then the wiring is certainly different.
On the back of the instrument pod, you'll notice that there are two connector plugs - each of the wires are numbered (the numbers are on the green printed circuit). The wire you want is number 10 - it should be a pale blue/grey colour with brown dots down it's length. I actually disconnected it from the ECU end (up behind the LHS of the dash) but there shouldn't be any problems disconnecting it at the instrument end.
Just for interest, wire 11 (a lilac coloured wire) is the rev limiter. I've left it connected myself because I figured that the factory 9,500rpm cut is well and truly enough. . .but the engine does seem pretty happy to spin well past that with the lilac wire disconnected. . .dunno how long it would last, though.
Oh, and if you still have that *bloody* annoying 90km/h chime thing connected and want to get rid of it, it's actually screwed to the back of the instrument pod, just to the right of the speedo cable connector - two screws and it's gone. . .
Getting rid of the speed cut, the chime (and the rev limiter if you want to) hasn't seemed to have hurt anything and it doesn't light engine check lights (cos there isn't one ) or hurt air/fuel ratios. . .so cut away!!

Keep us informed as to how the racing goes - I'd be interested to hear!
I haven't got all that far with the racing thing with mine. . .I'm trying to make the bottom end of the engine bomb-proof at the moment. . .sourcing forged pistons, machining up teflon buttons to get rid of the gudgeon circlips, having the rods cryo-treated, chopping some weight out of the flywheel etc. . .trouble is this is only one of many (too many) projects at the moment, so progress is a bit slow. . . .

Hope this helps,
Pete in Perth

[n2o_spark]

thanks for that.. i pulled the chime out and didn't know which wire to cut for the speed limited. i think i'll leave the rev limiter there but its nice to know.

Oh and i was wondering if there was supposed to be a waring light and my car was just odd. and it seems that they musn't have them full stop.

thanks

good luck with the projects

[Almost a Mini]

Oh and i was wondering if there was supposed to be a waring light and my car was just odd. and it seems that they musn't have them full stop.

The engine management setup in the CA72V Altos (CC72V for 4WDs?) is basic to say the least. No closed loop running (no ox sensor in exhaust), only a two step TPS (idle or run) and certainly no self diagnostics. Still, it simplifies things, I guess - until something goes wrong and you have to hunt down the dud component by yourself without any help from the computer.
Have fun,
Pete in Perth

[n2o_spark]

ok i've had the chance to check things out now... and all my wires are different colours. :S

and on the plug on the ecu i dont know which one is number 10. so here is a dodgey representation of theplug

|i|i| <- 10 ???
|i|i|
|i|i|
|i|i|
|i| |D
|i|i|
|i|i|
|i|i|
|i|i|

the "D" represents the clip on the plug. the arrow pointing to the "i" closest to it is what i thuoght may have been 10 but when i cut that wire.. the engine wouldn't start. and the fuel pump would not engage.

thanks

n2o_spark

[Almost a Mini]

ok i've had the chance to check things out now... and all my wires are different colours. :S
and on the plug on the ecu i dont know which one is number 10. so here is a dodgey representation of theplug
|i|i| <- 10 ???
|i|i|
|i|i|
|i|i|
|i| |D
|i|i|
|i|i|
|i|i|
|i|i|
the "D" represents the clip on the plug. the arrow pointing to the "i" closest to it is what i thuoght may have been 10 but when i cut that wire.. the engine wouldn't start. and the fuel pump would not engage.
thanks
n2o_spark

I disconnected the wire at the ECU end, but the numbers I was talking about are on the instrument end. If you take the instrument pod out, you'll see two wiring connectors. On the printed circuit of the instrument pod itself, you'll see one wiring socket numbered 1 to 12 and the other 13 to, I think, 24. It's number 10 that you want - if RS-Rs and RS-Xs are the same it should be a pale blue/grey wire with brown dots.
Cant remember off hand which number this wire is at the ECU end (should still be the same colour, though)

Hope this helps,
Pete in Perth

[truder44]

n2o_spark

On your diagram I ould expect pin 10 to be on the other side behind to the D and where you have the 10 to be pin 17.

This is NOT definite. Just working on the way plugs are often wired up odd one side and even the other.

[n2o_spark]

ok then thanks very much