Rev counter going crazy!
 

My Rev counter goes crazy when I switch the ignition on. Bounces around all over the place. Sometimes it moves normally but I don't think it's reading th right rpm. Rest of the dials seem fine to my knowledge. That said oil pressure sits on 0 most of the time. I know it's OK as I have a mechanical garage in the bay so don't panic like I did first time I happened! I haven't driven it yet and can't so don't know if the speedo works. Fuel and water temp seem to though. Can anyone let me know what the issue is so I can fix it please!

Thanks
Lee

Some people with more experience can probably jump in, but I've also had my tach and oil pressure gauge go bad. It's not a huge issue for me since I have a PFC commander to check on that stuff.

As far as the tach goes, some people have had luck repairing it by fixing the grounds and/or replacing the solder joints and capacitors. Initially my tach was bouncing around a lot and so I followed the procedure in the pdf I attached (please note this isn't my work, just something I found with some google searching), it worked for a few days and then went completely dead (sits at zero), so the grounding points are next on my list to try. There's also some more info in this thread, but as you can see it's not necessarily predictable which fix will solve the problem you're having.

As far as the oil pressure gauge, this thread is pretty representative of my experience - gauge sits at zero except under throttle, but I guess there isn't much advice there except to replace it if you want a working one. Maybe someone else has had success fixing them.

This is a very common problem with FDs. Your only choice is to rebuild the tachometer (redo the soldering and replace certain components as needed) or replace it, which involves replacing the entire meter panel (to my knowledge, they don't sell individual gauges).

You can find information on how to rebuild the tachometer in the forum.

Thanks Guys'
I was hoping to avoid swapping the instrument cluster completely. but will do if I have do.
Will check into the repairs suggested and much appreciate the info.

Regarding the oil pressure gauge am I right to think this will be the sender rather than the gauge if it starts to show pressure at higher rpm? is the sender a RX7 specific part or can it be replaced with something more readily available?

Thanks
Lee

Got my counter all out and ready to go and capacitors to replace even though all the components look fine to the naked eye? I have read a round a few threads on the subject and all of them say my counter reads about 500-1000 out intermittently.. mine bounces around all over the place to red line from the moment you put the ignition on and power to the dials.. sometimes it stops for a bit and then sort of reads okay when the engine is on. Then it will go mad again?! Do you think this is still the same problem or while I have it out should I be looking for something else as well such as a wire shorting out? if so what wire/plug should I be checking and in what way?

Thank you
Lee

Need some help here guys! Re-solder and replaced the capacitors on my rev counter ad no different. Plug it in and put the ignition on and the needle starts going mental and then eventually sticks around at red line? All the other gauges appear to work ok other than I cannot test the speedo as I cannot drive the car. Is it a shorted wire somewhere maybe? Can anyone give me any tips on what to check or look for please?!

Thank you
Lee

The problem is there are so many things it can be. I cant answer your question. I am battling a non working Tach myself. Have checked a million and 1 things. I even bought a new cluster and swapped in a known good tach so it isnt the tach in my case. I wouldn't be surprised if that is your case as well. My tach did what yours did before it died completely. It would bounce around at idle then shoot to redline and back, get stuck at 9k etc. I'll let you know what I find, well if I find something...

you need a new tachometer. it's happened to many of us.

i'm sorry to deliver the bad news.

But your man here says he tried a new Tach and no cigar? Or is there something else in the cluster gone. Sure it cannot be a shorted wire? Will be gutted if I have to swap clocks out as I have white mazdaspeed ones. Unless I can just swap a tach in and change the face if the rpm range is the same?
if I find anything else I will also reply. I think next step if no other pointers here on what to look at in wiring is borrow another clock set to test it.

Anyone ever tried changing the main chip on the circuit board and seeing if that fixes it? Not sure if it is an off the shelf swap in item or needs programming or anything? just a thought.

I'm under the impression the cluster board itself is to blame in some cases. You'll need to jump the wires from the harness directly to the tach. Here's a DIY thread on how to do it. Read over it and give it a go.
https://www.rx7club.com/interior-ext...epair-1055763/

I've seen some poor quality harnesses with insufficient or non-existing shielding cause this issue as well.

I think I will get a spare working tach and try first and go from there, then maybe change the chip if possible and look at option of jumping wires or changing tape that connects to that bit of the board.

Cheers
Lee

Just to update this in case anyone searches! I fixed it.. For now at least!!
Using the PDF attached a couple of posts up I had the capacitors replaced. That did not fix it. And a few joints were resoldered at the same time. I was told the rest looked fine. Having found a post on a different car forum for the same issue it suggested the main chip soldering to be the issue. So I took it out again and had the main chip and any remaining solder joints reworked and voila it works!
It was reading about 500rpm too high when I put it back in so I fixed this by turning the blue potentiometer counterclockwise about 30degs. RPM now reads in the right ball park and no more bouncing around!
:lol:

Oil pressure sender
 

This is likely too late, but the oil-pressure sender can often be restored to proper function by removing and squirting carb-cleaner into the hole in the sender fitting. When I did that, after a couple of flushes, crud stopped coming out, and when re-installed it worked correctly.

I have a spare to try now. But will give that a go.. It's a tiny feed hole on the main sender. Is there some kind of filter I can mount it with to try and prevent it keep happening?

I just cleaned mine and it's worked for 2-3 years now. I think the oil just "cokes-up" in the sender and eventually blocks the orifice. I don't think that's something you can filter out.

I've never heard of anyone using a filter for that.