Aftermarket Electronic Speedometer on a 1998?

[Root Moose]

How would I go about hooking up an aftermarket electric speedometer to a 1998 XJ?

Is it a simple matter of intercepting the VSS wires at the transfer case and calibrating the speedometer or is it more involved?

Thanks!

 

[kastein]

depends on the electric speedo. You will want to leave the signal lines from the VSS to the ECU intact and simply tap into them otherwise it will run like crap iirc.

 

[Root Moose]

So, just splicing in is fine?

 

[kastein]

Should be, unless the aftermarket speedo is badly designed and causes problems. What speedo and what kind of signal is it expecting?

Depending on the speedo you use and the kind of signal it is expecting you may have to build a circuit to convert signal types and/or use a different speedo gear on the VSS.

 

[Root Moose]

I'm swapping a MY98 XJ 4.0/AW4/NV231 drivetrain into a MY87 YJ.

I'm going to replace the OEM gauges with something like Autometer Cobalt or similar (still researching the specific gauges). I don't know what signal it wants yet.

 

[kastein]

If it will fit I would just put the speedo drive line takeoff from the 87 YJ into the NV231. If it won't... you could easily just grab the speedo gauge out of a 91-96 XJ and wire it up, since those speedos are prebuilt to take the same signal that a 91-96 (and probably 97-01, I forget but I think it's the same) XJ VSS will produce.

Heck of a lot cheaper than an aftermarket gauge, as well.

 

[Root Moose]

I'm not worried about the cost (within reason). This is a project vehicle to be built the way I want it. How I want it may change at a moments notice.

The 87 mechanical drive will work but then the 98 PCM does not get its VSS signal.

Supposedly I could use a MY91 YJ speedo drive as it has both mechanical and VSS but that is not what I'm after (old gauge). I'm not certain if the signals are the same either.

 

[kastein]

yeah... the 91 YJ speedo drive is probably a reed switch type on the side of the cable under the dash, if it is anything like the old RENIX style XJ ones. It's only used for cruise control on those models iirc.

Good point on the 98 PCM not getting the VSS signal, I thought for some reason you were using the YJ's engine management system.

 

[Root Moose]

I thought for some reason you were using the YJ's engine management system.

Nope, I hate carbureted EMS.

 

[kastein]

:cheers: that makes two of us. Give me MPFI any day of the week...

People will give me crap for saying that, but MPFI works with the engine at any angle, so long as the engine oil stays where it's supposed to :moon:

I'll have to see if I can dig up some info on the signal the OBD type VSS units output, but my SWAG is that it's going to be a 5 volt pulse train of some sort, probably generated by a Hall effect type sensor. Not sure how many pulses per revolution, but I seem to recall it working out to (with the proper speedo gear and tire size) something around 112.xHz @ 65mph.

 

[DanMan2k06]

So does direct injection

 

[kastein]

yup, I have nothing against direct injection / compression ignition engines either.

I just can't stand all those fiddly floats and bowls and needles and jets and crap.

 

[DanMan2k06]

Agreed. Reminds me of the plumbing in my toilet.

... No wait, I have direct injection there too