Ok, my car has had a "jumpy" tach for a little while now. It goes up and down as smooth as any of my other 1st gens, never sticks. But sometimes it jumps when I floor the car. I have mechanical secondaries, and if Im hovering around 3K-5K and just floor it, the tach jumps. Somtimes only 500 RPMs, sometimes to like 5K. Sometimes it stays there until I actually reach that RPM, sometimes (most of the time) it just drops back down to the correct RPM. Anyone have any ideas? At first I thought the ignitor might be going out, so I swapped it. No change. So I swapped it again. No change again. Anyone have any idea what else it could be? Thanks guys .

~T.J.

EDIT: Nevermind .

 

Well, I would guess you have a bad tach, probably sticks when it cold too huh.

Replace tach, or add a really tachometer like a Autometer.

John

 

because the stock rx7 tach's aint real ??

i'ld say its the tacho not the ignitor. the back of the tachs are oil filled and in colder weather can stick. maybe try pulling it out and giving everything a good clean?

 

As I said, it never sticks, no matter what the weather. The problem is far from it sticking. If it stuck, the RPMs would read lower when they in fact are higher because the needle is stuck, or the needle would stick in one place when the RPMs are coming down. My problem is the tach jumps higher when the RPMs are lower. Shall I make a video of this?

Basically, the tachs not sticking. Its just jumping around whenever I floor the car.

~T.J.

 

Ok, so heres a scenario:

Driving in 3rd gear at 3K RPMs (35 MPH). Deciding to accelerate, I floor it. Tach jumps from 3K to 5K, then drops to 3200 or whatever the engine has made it to in the time it took for the needle to jump up and come back down. Then tach operates normally. It moves a HELL of a lot faster than if the engine were revving up. It litterly jumps up there, and then falls down hella fast too. Ya know how fast the tach drops when you turn your car off? Thats how quick it moves up and back down.

~T.J.

EDIT: The tach works normally until I let off and floor it again, it will just jump all over again. Its just everytime I floor it.

 

Maybe it's all the hidden HP you didn't know about quickly breaking your tires loose, then they grab again? Lol... no... I'd say if anything that the Tach itself is going, as it is an electronic tach, it might be having some issues that way, which I couldn't explain. I guess I'm kinda the "replace to diagnose" person. I put new parts in, starting with the cheapest option, until something fixes the problem, haha. Maybe not such a good idea when it comes to something big, but, on my RX-7 everything's mechanical/carburated, so it doesn't matter.

 

Whenever I have had problems with a jumping tach, it has been because one of the fuseable links has eiter needed replacement or had come partially disconected, athough I tend to get the jumping on bumpy surfaces or when the electrical system is under heavy load. You could try making sure they are all pushed in properly.

 

When's the last time you changed the spark plug wires?

Jumpy tach is usually because of jumping spark.
Bad Ignitor= no tach.

 

Sounds like a typical case of demonic possession.
Maybe YZF can help with that.
"Heal, tach-o-meter of Satan!"
-WG

 

I need to change my spark plug wires...I do in fact know that my coils are still kinda arcing every now and then...Hence me asking for part numbers in the DLDFIS thread .

Oh please dont bring YZF into this .

~T.J.

 

Could your clutch be slipping? When my clutch went it did the same thing. Just a guess...

 

For one, it jumps WAY too fast to be the engine revving and then catching, and for two, its a new Centerforce Stage I .

~T.J.

 

Ok, Im bringing this back only to say that with new plugs, all was better even with the old wires . I started it up and drove it like that for a while, and I havent seen it since. Then I got some dielectric grease for all the connections again, just for good measure .

~T.J.