restoring83

I just picked up an 83 GS (I think it's a GS... Sunroof, A/C 5-spd, pwr mirrors, but no pwr locks, windows, etc.)
Anyway, my tachometer didn't work. It worked for like a day after I changed the plugs, wires, rotor, cap and filters, but stopped again.

Does anyone know where the sending unit is located and where the cabling goes? Or has anyone else had this problem? Any ideas on how to fix it?

Thanks!

I'm restoring this car to as close to original as I can.

riffraff

silly question, but did you remember to hook everything up the same on the coils.. the tac reads off of the trailing coil, so check those leads..

restoring83

I hooked up the wires the same as I found them...

ben79

Since the tach didn't work when you picked it up, you might wanna double check it against the haynes manual. My 79 had vacuum lines places where no vacuum should be, fuel valves backwards, and the wireing all messed up. Yet it still somehow ran just easy assurance

error402

or make sure the cables behind the tach didn't come loose. it's happened to me once.

MarkPerez

not knowing if you are new to the world of rotorys,
but there are leading (L) and trailing (T) coils,and plugs.
if the car has drum brakes on the back then your GS.
disc brakes would be GSL,the wires can sometimes
become brittle over the years, if you plan on keeping
the car,,a book will help,,and welcome to the forum.
there are some very nice and helpful people here.
restore that puppy,.,..,.

85RX7GS

iTrader: (1)

Those older tachs on the 83's are prone to acting up. I'm not sure at to how to fix them - maybe replace the connection or the cluster.

restoring83

Ok... so I replaced both the ignition coils cause I thought it was a bad connection, and the tach STILL isn't working. I am on to replace the igniters next since I have two that I can replace them with, but if one was bad, wouldn't the car have trouble starting? The engine is running very well right now. BTW, does anyone know which coil is supposed to be the trailing coil? Right now it is the one closer to the front of the car, and the leading coil is the one closer to the windshield. Does it matter? And just to make sure my spark wires are connected correctly, as you look at the spark plugs from the drivers' side, top left is T1, top right is T2, bottom left is L1, and bottom right is L2. Just want to make sure I have the wires going to the right places.

Now back to the tach... it was working intermittenly for a little while, and now hasn't worked at all for a few weeks. I think maybe it might be a loose electrical connection, but even after moving all the wires i could find in the engine compartment, I couldn't even get the tach to budge.

The long and short: If you have any suggestions, I am absolutely in need... Thanks!

Project84

Yes, it matters. At higher RPMs the trailing plugs will stop igniting when there are not enough combustable gases in your exhaust to keep the flame burning in the thermal reactor. I know that may sound like a bunch of B.S., but that is how the rotary works. Welcome to the 1st Gen club. As far as the tach problem, you will want to get a Haynes manual (Chiltons don't give you near as much info) and look up the instrument cluster. It has a picture of the back of the instrument cluster and show what all the plugs and pins are for on the printed circuit. Your problem may be in the printed circuit. If you plan on modding the car, you will definitely need the book; the RX-7 is a higher maintenance car compared to a regular stroker, and you should try to understand how the rotary works to truely appreciate it. And thats why we are here, to help you do that!

I scanned a picture out of the book but I can't get it to upload. If you want to check it out so you can see where the pin is for the tach (pin J) and see if it is tightly connected I can email it to you. The book tells you how to remove the circuit. Check a junk yard and see if you can get another circuit for a few bucks. After market tachs are nice, but expensive.

Welcome to the forum and keep the questions coming...

riffraff

project84.. it does not matter wich coil is the trailing and which the leading (both coils are the same).. all that matters is that you have everything correct going from the dist cap to the plugs.

Project84

huh, learn something ever day.

thanks

RotorMotorDriver

iTrader: (1)

Sounds right to me, good job . Also, as far as I know, the coil closest to the radiator is the trailing, and the one closest to the strut tower thingy is the leading. I think that the physical coils are the same (interchangable), but once hooked into the car properly, you cannot put the leading wire on the trailing coil and expect it to work, and vise-versa. Its because the distributor tells the coils when to fire, and if you have the leading plugs trying to fire when the trailing plugs are supposed to be firing, your gonna have problems . Basically, I think its more the distributor that defines which coil is which, rather than the physical coil itself. If that makes sense...Hell, I dunno, that could be all wrong...

~T.J.

riffraff

i thought that the wires going to the coils were just for power. (one ground, one power, and one tac). i figured that the coils are always firing, and it is the dist rotor and cap that decide when the coil actually connects to the plugs.

jeremy

iTrader: (1)

project84, the 79's are the only ones with thermal nuclear reactors. everyone else got cats, meow. the reason you are talking about is also why the 79's read rpms off of the leading coil.

jeremy

iTrader: (1)

the coils have "continual" juice being fed to them. basically big capacitors. they constantly feed the dizzy. as the dizzy passes one of the metal prongs in the cap, it arcs the power to the post, down the wire, and sparks across the plug. now the coil has just let the power go so it will automatically juice back up before the dizzy gets to the next post. as you can imagine this happens very quickly.

MyRxBad

Look at the wiring for the coils themselves (power to the coils) One coil should have an extra wire going to it (count them). That extra wire is the signal to the tach. Check and make sure it's connected and not corroded. If you have the same amount of wires (power wires) to the coils then you have a problem. If not my best guess would be the trailing ignitor.

Project84

I'll buy that.
But the haynes book, (blue cover 79-85 All models RX-7) don't say its for specific year or models. I think everyone should get headers, high flow mufflers, ditch the air pump, and get an electric water pump and electric fan. Thats what I plan to do.

79+80_rx-7

BZZZ WRONG.......... 80 has thermal reactors too.......

Project84

Ok, someone put up a questionaire asking who has the thermal nuclear reactor and who doesn't.

REVHED

Uhm, that's really not how an ignition system works mate.

Inside the coil there's a primary winding and a secondary winding. Current flows through the positive terminal, through the primary winding, out through the negative terminal and finally to ground via the the ignitor. This current flowing through the winding causes a strong magnetic field to build up inside the coil.

Now, when the lobe on the dizzy shaft passes the electronic pickup it triggers the ignitor into switching off the primary circuit. This causes the magnetic field inside the coil to colapse rapidly which then induces a voltage into the secondary winding. Because the secondary winding has a far greater number of turns the voltage induced is a lot higher.

The secondary voltage then makes its way out through the main post of the coil, through the dizzy cap to the spark plug and you know the rest.

Thank you for attending REVHED's ignition 101.

restoring83

Thanks all. It seems all the connections in the engine compartment are in order, and I even changed the igniters. (I guess they didn't need to be changed) My next step is to pull apart the gauge cluster and make sure that all the connections are properly connected. If that still doesn't work, I'll try a new gauge cluster, and if it still doesn't work , I suppose that means there is a disconnected wire somewhere in the main harness that will cost WAY too much money to search out. I would be better off buying another 7.