Would you buy a speedometer "corrector"?

[Ground Loop]

I don't actually have one to sell (yet), but I'm curious to know how much interest there would be in a small digital circuit to remove the 8% error from the Elise Speedometer.

The assumption here is that it is entirely plug-in.. snaps into the Diag port under the dash, fixes the speedometer and does nothing else. Remove at any time to revert to stock behavior.

[Greg]

I don't think it would be so easy (for a digital solution).

The best hope you have is if there is a speedo cable in the transmission. If so, you just need to resize the small gear in the cable. I know it's possible, because people swap these out when they change drive ratios w/ diff swaps, to make the spedo and odo work correctly. Bombproof solution, but probably not worth it.

A few searches on the web found an electonic adaptor for $150 for mopar, perhaps something like this is what you are after:

http://www.transmissioncenter.net/sp...n_______va.htm

'Greg

[iRod]

Originally Posted by Greg

I don't think it would be so easy (for a digital solution).

Someone on this board (rob13572468) already digitally corrected the speedo.

[ChrisH]

Originally Posted by iRod

Someone on this board (rob13572468) already digitally corrected the speedo.

I think the problem with Rob's solution is that it affects the odometer. But, I would prefer Rob to step in and say something about that.

For info, see
http://www.elisetalk.com/forums/show...ht=speedometer
and this issue has been rehashed many times. Also see
http://www.elisetalk.com/forums/show...ht=speedometer

and for a correction device (that may affect the odometer), see
Speedo Corrector

[Evl]

I'd be interested if it put out the speed pulse to the radio too. In fact I've got a gschem window open on my desktop machine with the start of the circuit described in the other thread. I was thinking of converting the gas guage into a g-meter as well, just as an interesting excersize.

[Highlander]

Modifry over on s2ki has designed a cheaper yellow box -- Modifry's Yellow Jacket

Assuming there is a suitable speed sensor wire to the ECU, it should work just as well on an Elise as it does on the S2000...

[andykeck]

Originally Posted by Highlander

Modifry over on s2ki has designed a cheaper yellow box -- Modifry's Yellow Jacket

Assuming there is a suitable speed sensor wire to the ECU, it should work just as well on an Elise as it does on the S2000...

But it sounds like the Yellow Jacket would screw up our odo to get the speed correct. Not a good trade off for me.

[Greg]

Originally Posted by andykeck

But it sounds like the Yellow Jacket would screw up our odo to get the speed correct. Not a good trade off for me.

If the speedometer is off, so is the odometer. There's only 1 rpm sensor coming from the trans. If it doesn't match up with the final drive ratio, tires, and wheel sizes, then it's all off.

'Greg

[TimMullen]

Originally Posted by Greg

The best hope you have is if there is a speedo cable in the transmission.

Nope. In fact the service manual mentions that you can remove the plug that would normally be for the speedometer sensor and use it to fill the transmission oil...

They must be pulling the speed info from the ABS sensors on the wheels...

Hey, that's how to correct the speedometer... Install larger diameter tires...

[TimMullen]

Originally Posted by Greg

If the speedometer is off, so is the odometer. There's only 1 rpm sensor coming from the trans. If it doesn't match up with the final drive ratio, tires, and wheel sizes, then it's all off.

I believe it's been determined that the signal from the ECU to the instrument cluster is accurate (it's a CANbus signal). The odometer correctly displays the correct values, but the speedometer, by design, indicates a higher value. Again, it has to do with European laws that require that the speedometer never reads low, even with larger diameters tires installed - so, by European regulations, the speedometer has to read high. Unfortunately for us in the US, we get the same speedometer.

If something is done to the CANbus signal before it gets to the instrument cluster, then the odometer would read low (I believe that violates a few of our Federal regulations). The proper fix would be to change the logic in the instrument cluster to not artificially increase the speedometer reading.

Or we can just get used to it...

[andykeck]

Originally Posted by Greg

If the speedometer is off, so is the odometer.

Nope. Like others here, my odo is right on while the speedo is 8% high.

[pinmagic]

Originally Posted by TimMullen

Or we can just get used to it...

Around here? Get used to it??? You must be kidding!

[Ground Loop]

Our system is unusual indeed.. here's the system as far as I can tell so far..

First, there are wheel rotation sensors on all four wheels, of course. These are shielded wires that run to the ABS controller.

The ABS controller converts these to a stronger signal and sends them, via four discrete wires, to the ECU in back.

So, the ECU knows all four wheels speeds, and not the tranny speed.

From these (and maybe others?) it derives the speed of the car and sends that to the gauge pod via CANBus, along with some of the other dash readouts.

The dash pod is the guilty party. You could say that either the servo-needle controller is fudging, or even that the silkscreen on the dials is inaccurate, but the effect is the same -- needle reads high.

However, the odometer is dead accurate, as far as I can tell. I've measured long drives against the GPS, and while the speedometer reads ~8% high, the odometer is very close to true.

But here's the kicker.. dorking the speedometer via CANBus DOES NOT seem to impact the rate at which the odometer is racking up miles. Rob12349734 confirmed this some time ago when he had his very cool 160mph stationary experience while accumulating no miles.

So, if it all holds true, then it should be possible to 'adjust' the speed from the ECU to the dash to read 8% lower, get an accurate needle on the speedometer, and still have correct odometer operation. Of course, I'm not comfortable with all that until I know how the odometer is getting its mileage. Nobody wants to have to check the "odometer tells lies" checkbox on the pink slip, right?

A speed-pulse output from the same circuit would be doable.

[TECK]

To me the character of the Elise is "exagerated" overall so the optimistic speedo seems to fit, so it does not bother me.

If my BMW's speedometer was off the same amount it would drive me crazy and I would fix it.
I have different standards for different cars. This may or may not make sense but how I "see" it.

[Keeper]

Originally Posted by TECK

To me the character of the Elise is "exagerated" overall so the optimistic speedo seems to fit, so it does not bother me.

If my BMW's speedometer was off the same amount it would drive me crazy and I would fix it.
I have different standards for different cars. This may or may not make sense but how I "see" it.

From what I understand, BMW speedos tend to be off (higher) by a greater amount than most manufacturers.

[ChrisH]

I like the speedometer to read accurately.

However, it is more impressive to passengers if the speedo reads high.

[clrodrick]

I voted to pay up to $50. This is one of those issues that bugs me a little bit, but I know I can live with. So if this ends up being an expensive fix, I'll just make due with an optimistic speedo. It's interested reading these threads though and learning more about how various parts/circuits in the Elise work.

[inetd]

Rather than correct the function of the speedometer, why not reprint gauge marking on a replacement backing for the dial? This is assuming that the 8% inaccuracy was consistent with all of the cars and that the 8% difference increases linearly with acceleration. Otherwise predicting the hash marks would create new inaccuracies.

It would seem that this theoretical part would cost <$50. Although, I would be willing to pay more.

[Ground Loop]

Originally Posted by inetd

Rather than correct the function of the speedometer, why not reprint gauge marking on a replacement backing for the dial?

Mostly because it's much harder to get to than the diag port. And less flexible. A digital solution lets you dial in any correction you like, and may have other side benefits.

This is assuming that the 8% inaccuracy was consistent with all of the cars and that the 8% difference increases linearly with acceleration. Otherwise predicting the hash marks would create new inaccuracies.

True, but it does seem to be consistant accross (at least) US Elises. Everyone's reporting about the same speedometer error, and it does appear linear.

It would seem that this theoretical part would cost <$50. Although, I would be willing to pay more.

The CANBus microcontroller ($10 PIC18), J1962 connector, and assembly are the expensive bits. The rest is support parts and software. And time. And probably a lawsuit or two.

[reganfin]

Just curious if you are working on this or if it is just another idea that has been filed away.