MtnRacer

So I finally hooked up the speed sensor on my AVC-R, tapped the ABS harness, grn/red, and I've got the dreaded +/- 20kph problem. Not so much at lower speeds, but upwards of around 100 kph, it's downright unreadable. What causes this? Searching turns up the problem, but no theorizing on the solution. Only that some people got it, and some don't. I'm kind of thinking it maybe an age thing. If your speedo cable is old and slipping, it cause these kinds of fluctuations that wouldn't register on the tach because of the built in dampener. What do you guys think? Did anybody ever actually solve this problem? Looking forward to your thoughts/experiences fellas.

Steve

Icemark

is this a speedo input for the AVC-R??? and it is not reading correctly??

Crusader_9x

Mine does the same thing. I hooked into the same wire and i get the same result. I havent found a fix yet either. I do however have a brand new speedo cable and it still does it so i think the problem is elsewhere. Maybe interference with some of the other nearby wires?

MtnRacer

Yup Mark, you got it. It reads close to what the dash speedo says, but gets increasingly off as speed rises. When the dash speedo ready 110, the avcr is reading around 95, but it's up-and-down-and-up-and-down, like 85,113,95,80,97,115,etc,etc,etc.

Thanks Crusader, at least I can save myself the trouble of replacing the speedo cable. Damn, that sounded like a good theory too.

This is a fairly common problem, there's got to be an explanation for it.

Steve

RETed

ABS?
Why haven't you connected it to the cruise control signal?

Possible reasons why the ABS sensor input is not reliable...
ABS sensor is bad.
ABS sensor is dirty - ever looked at the mag sensors? They are usually covered with iron flecks.


-Ted

MtnRacer

This car has no ABS, it's a GTUs. I'm just using the ABS harness which, if I'm not mistaken, should be getting the EXACT same signal as the cruise control.

Steve

uRizen

iTrader: (2)

If I'm not mistaking, doesn't the cruise control computer recieve it's signal off the ECU? I thought the ABS system was all on it's own and had it's own sensors (the mag sensors that are integrated into the hub) that were seperate from the cruise control system.

Crusader_9x

I forgot which harness it is that i hooked mine into but i do rememeber its up above the clutch somewhere in that mess.

MtnRacer

As I understand it, the ABS, cruise control, and the power steering all get their speed signal from the same place, the dash cluster. The ecu never sees the speed signal.

Steve

uRizen

iTrader: (2)

Yeah, it looks like you're right. I checked the shop manual and it says it pulls of the cluster for both sections.

I'm assuming the magnetic sensors in the wheel are just there to tell the ABS computer when a wheel locks then, right?

Could you maybe stick an analog voltimeter in the connector while driving and see if it does a smooth sweep and isn't fluctating there? It might rule out if it's the signal or how the AVC-R is handling it. I don't know if that will work for sure because it might be putting out a pulsed signal rather then just increasing voltage w/ speed. The diagnostics page off the book doesn't say.

RETed

Uh, no.

The ABS gets its input from the wheel sensors in each corner.
There is a gear trigger + mag sensor in each corner - this allows the ABS computer to monitor each individual wheel speed.

The cruise control gets it's signal off the transmission.
This signal is a lot cleaner, and not as flaky as the ABS signal(s).
We've managed to o-scope the two, and the ABS sensors have a lot of "noise" sometimes.

I've used the cruise control signal wire (driver's side kickpanel) with great success with both the A'PEXi S-AFC and the AVC-R.


-Ted

MtnRacer

I have it spliced in on the ABS harness in the same location, which one is the cruise control harness?

Steve

P.S. And if the ABS harness uses the wheel sensors, then why am I still getting a fairly accurate speed signal with no ABS ever installed?

NZConvertible

The speed sensor wire is indeed green/red, but it does not go to the ABS system. I just looked at the ABS electrical schematics (which you should've done... ) and I can't see any green/red wire anywhere, so I have no idea what you're connected to...

I suggest you relocate your connection to speed sensor wire at either the instrument cluster, AAS control unit, cruise control unit or power steering control unit.

MtnRacer

Ok, my bad. It was the cruise control harness I tapped. Somebody told me that it was the ABS harness, but I just checked the pin connector against the FSM and it's cruise control.

So I've tapped in the same location as Ted's, but I'm still getting the sloppy signal. What gives?

Steve

RETed

Speed sensor on the transmission bad?


-Ted

uRizen

iTrader: (2)

How well does your cruise control work? Does it hold a steady speed? I'd also backprobe the connector while ripping down the road and see if the meter fluctuates alot. Maybe the wiring to your AVC-R or the AVC-R itself just doesn't like the car?

Wankel7

The device that converts teh mechanical movement of the speedocable into an electrical signal is inside the gauge cluster.

So, if there is a problem...it is in the gauge cluster.

Swap gauge clusters and see what happens?

James

NZConvertible

You mean speed sensor in the instrument cluster...

MtnRacer

No cruise control, it's a GTUs. I have a good cluster with 54k on the clock that came from a pristine car, so it should be in excellent condition. I guess I'll try swapping that in next. Unfortunately it's in Sacramento, so it'll be a while before I can grab it. I'll let you guys know what happened when I install it.

Steve