Thoughts on erratic wheel speed signal

[Davidv]

Hey guys,

Just wondering if any ideas on this.

My wheel speed signal jumps around a bit, it will spike to a very high value momentarily then go back to normal.

I've examined the length of wires that run to the sensor for any exposed wire or breaks etc but it seems fine (although I guess it could still be an issue) and I suppose a faulty sensor could be a problem as well.

But it just seems weird that it only happens once in a while, just wondering if anyone's had the same thing before. It's a Toyota altezza 6 speed box with the speedo output wired directly to ECU, does not go through the dash etc.

I guess next thing to try is replace the speedo drive, then if not that replace the wiring if there are no ECU settings that I've selected wrong etc.

Here are the settings I'm using for it as a DI.

 

[JMP]

I'd be replacing the wiring first, potentially with a shielded run.  There's quite a few places around that sell the toyota/sumitomo terminals used in the speed sensor plug and AMP superseal pins so you don't need any solder joins in the loom.

[Rich RDE]

I have seen bits of metal and shavings floating around and just has some gum up around the sensor itself that was causing a similar issue one time. Double check that before digging deeper.

[Davidv]

Thanks guys. 

Last night I tried the different options for rising or falling active edge, and turning off the pullup resistor.

Seemed to improve when set to rising edge and no pull up. But it would still have issues, especially past 100kph.

Interestingly it seems to get worse with a rise in engine rpm, if I try hold the engine at 4000rpm the speedo signal throws its toys out of the cot. Even if at a lower vehicle speed. So perhaps that is indicative of needing shielded wire. 

I'll check the sensor first and then report back. It's a 3 wire type that has a 12v power supply to it, is there any chance that perhaps it's supposed to be 5v supply?

Edited July 13, 2016 by Davidv