Digital Dash down to 0

sounds like your dash power supply has gone out. are you seeing anything light up on the dash? also note that if it is only the speedometer not working and always showing zero, your speed sensor has gone out.
if your tach meter is showing zero then your boost sensor has gone out. all these things ended up going out on both of my cars haha. its very common.

so, your power supply which based on your description sounds like the culprit, is located under the dash next to the steering wheel, in the area above your right knee. just remove the lower trim panel (be sure to disconnect the footwell light) and look up and you will see the box. its held up by two bolts and a plug. little pain to get out, but why its in there you can check the connection by pressing down on the plug going into it. try this while your car is on and watch your digital dash and see if anything changes.

if you find that your box is bad, have it sent to the guy at xenonzcar. he does the repair for about 75 bucks. i sent him mine and it works great.
http://www.xenonzcar.com/z31/DigitalDashRepair.html for reference

Bon

Troubleshoot the speed sensor first. I'm assuming that you have a digital dash-- if so, the speed sensor is located on the firewall side of the passenger side strut tower., between the fender and the cruise control actuator. Things to check-- disconnect the cable going into the bottom of it and verify it's spinning when the wheels are turning. If it is, hook that back up. the next check is to ensure you are getting voltage and a pulse signal out of the units. There's 3 wires-- power (it's either 5v or 12v, I can't remember which), ground, and signal. Power to ground should net constant voltage with the ignition on. You should get a pulse signal to ground any time the unit is spinning.

Thanks for the information this is a diigital dash and I the dash itself is fine, I showing a zero on speed but everything else works just fine. I will check the cable, I have no way of seeing it spin sitting in my garage but I at least have an idea of what to tell my regular mechanic what to check. I lost the cruise, trip meters and instant gas mileage at the same time which I assume all run off the accurate speed. So it could be the cable or the unit, I will try to see what I can figure out.

Okay, sorry to double post, I found it seems like it is connected fine. I am going to buy a new cable and new unit and bring to my mechanic, z31partsforyou has a unit that is tested working (god I wish I could buy a new one). The way it cut out seems like the cable might have snapped, it was very sudden, do you think I should buy a new cable too?

don't go throwing parts at it. i wouldn't get a cable unless you know its faulty. most likely your sensor is bad. these do fail after years. mind did on my 87. i replaced it and the speedo worked again. mind you it was used from Steve at 300zxpartsforyou, so it wasn't new. but this is the reality. better to have a working used unit than a faulty non-working unit. there may be a way to troubleshoot it still… have you gone over the FSM and looked at the speed sensor unit system? read pages EL-70, 71, 72 in the online FSM at the website i mentioned earlier.

i'm not an expert on the speedo cable, cruise control, or trip meters; but i'd be willing to say those stopped working because the car lost its ability to sense the driving speed. think about it, among the other factors here, the cruise control system uses the vehicles speed to set, resume, and accellerate speed; the trip meters use speed to calculate distance traveled and so on. so, if your speed sensor fails, the car will have no way of determining the actual speed in order for these other systems to function and so logically if it goes out, then they go out too. if by chance you find that your speed sensor isn't bad, then go from there and check the cable.

and you don't even need a mechanic to replace your speed sensor. its very easy to access and you can swap it yourself.

Bon

Thanks Bon, appreciate the advise. I have an email into steve already for the parts, I am horrible at DIY so I will let the mechanic do it, I have to get a smog test anyways so easy to have him throw it in and hope that is the problem. Steve's website indicated he has a tested working unit. The cable is only $27 so I am going to order this as well just in case so I have it in hand but I think your right that this is just the sensor unit.

no problem. glad to help. I can vouch for SteveB. I've bought many of his parts and i never get let down. the speed sensor I got from him still works. you might want to replace your cat converter if you're having smog issues. Dave at certified muffler has them available. hell, get yourself a complete new exhaust system from him if you want.

Thanks dude really appreciate your help. I printed out the instructions on replacement for the sensor. I also had to do the cat for the 2nd time (not bad for 35 years of service) 2 years ago when I was due for smog. Is certified muffler a mail order?? I had to cut and weld in the new one two years ago as I couldn't find a bolt on one, do these bolt on?

I also did the exhaust many years ago still in great shape, aftermarket magnaflow I think but that was so long ago cannot remember.

I may actually get away without having to spend $500 this time smog test as I think I have replaced everything! I have bought from Steve before so I know his parts work, just fixed the compass (broken for 5 years) with the little brain and have bought plenty of other stuff from him, always in exactly the shape he describes and always work!

CM, has a website that you can order from. the system uses bolts, not clamps, from the turbo exaust going back, so it is direct fit. I ususally call Dave and tell him what I need. A few years ago he built me a 2.5" SS mandrel bent turbo-back exhaust system for my 87 2+2 with a straight pipe and muffler with seperate dual tips. but he also sells pieces individually.

now, I had to replace the cat on my 84 recently, so I got the part from CM and the shop I took it to told me it needed all these modifications to fit.... but honestly I think they just scammed me. but the cat is on there now and works fine (this is with the factory exhaust). your best bet is to pick the part you want, in this case the cat; remember to specify fed or california car, and then call and talk with Mr. Dave and tell him exactly what you need.
I loved the way the exhaust looked and sounded on the 87

and yeah I really like what Steve does. he's really one of the last used part Z specialsts around. I'm glad he's there. when i can't find it, he usually can.

Bon

Thanks, I think I am going to pass smog the Cat is only 2 years old so it better!!! I am going to the guy that installed it and fingers crossed it wil pass, I live in CA and they test your gas tank to make sure it is still tight, which always scares me, thankfully the gas tank still makes a nice sucking noise when I open to fill the tank. I also ordered the parts from steve and they are on the way! Thanks Bonfire!!

you're welcome dude. glad to help. CA.... i love california but your smog laws are insane. there is no way any of my Z cars would ever pass. if you still fail, check and make sure your EGR valve is installed and working. that may help.

Bon

Let us know if you passed smog!

Finger crossed that it will. I did EGR Valve several times now and Cat 2 years ago, I will let you know if I pass. I also have the speedo cable and speed sensor from Steve, hope that is fixed too.

She's passed smog in CA for 35 years.....the stupid law in CA was for 25 year old cars to be except and they changed that law so 1975 or older, bastards!