g14novak

iTrader: (1)

I have a 1989 GTU converted to carb. All of the cluster works just fine except the tach. It will come one maybe once or 2 times a week and work until I shut the car off. I've rerun the yellow w/ blue stripe wire with another that goes to the negative on the coils. Still does the same thing.

I even pulled the cluster out, took it apart and redid all the solder joints. I seriously re soldered everything on the bottom of the PCB for the tach, all the wires that connected to the back side of the tach and I've re-ran the wire that goes to the negative on the coils. I don't understand why the tach works intermittently. And the only thing that makes it work more often is driving in the rain.

Is their a separate wire that powers the tach but not the rest of the cluster? I noticed that in the wiring for the tach their was 3 side by side pins then the rest of the connector. I'm guessing these are the power, ground, and sensor for the tach?

I HATE wiring problems...

Thanks for the help in advance!

danegerous

iTrader: (10)

I'm having the same problem man...I have a faggy 5'' autometer tach wired in for now but I'm hopin for the day I can have my stock tach back

knivesm

the t1 and t2 act as a ground for the tach. i had a problem with that too. i found that cause i didnt have my ground right.

HAILERS

There's a yellow/blue (Y/L) wire in a black bullet connector at the Trail coil assy. That is the output signal from the trail ignitor that goes to the tach.

Get a spare piece of wire. Bare both ends. Put one end in the black bullet connector at the LEAD coil assy and the other end in the black bullet connector at the Trail coil assy.

Then pull both white plugs off the trail coil assy. Then start the engine. The tach should work. If it does not then the tach is bad if the wiring b/t the tach and the Y/L wire in the bullet connector is good.

g14novak

iTrader: (1)

Ok, I'll give this a try.

Right now I have a complete seperate wire run for the yellow/blue wire from the negative on my coils. I spliced it into the same wire thats giving my ebay tach signal and it reads fine when I start the car (the ebay tach, not the stock one). Unfortunately, the cars wiring was a hackjob when I got it. Another poster said something about t1 and t2 being grounds. Are t1 and t2 the other 2 pins on the outside of the tach pin on the connector?

HAILERS

I don't know the colors on the pigtail harness on the trail coil assy. I know the wire colors of the plug that attaches to the trail coil assy.

The yellow/blue is the tach signal and if it reads approx .76vdc at a 750 rpm idle then the output signal from the trail coil assy is good. The problem then would be with the tach itself or the wire b/t the trail coil assy and tach.

There is a black bullet connector near the trail coil assy and it is also yellow/blue and will read the same value.

The blue/yellow wire goes to the ECU pin 1X and should also read approx .78vdc at idle.

Random jpgs attached.

g14novak

iTrader: (1)

I've run a completely separate wire that comes from the negative on the trailing coil to the back of my cluster spliced into the same pin that my stock tach should be on. I wanted to eliminate as many problems as possible and changing it to a wire I KNOW is getting good signal seemed like the best way.

I guess I should be more detailed on the setup of my car as I don't have the original ignition system.

My car has been converted to carb. So I don't have any of the FI system anymore. I have 1st gen coils drawing power from the ignition wire inside the car. All proper wires are run from the coils to the distributor. Their is 1 last negative wire that runs inside my car for my ebay tach signal.

I've spliced into that wire and hooked it to the wire for my stock tach. I get very intermittent run times with the stock tach, however I never have any issues with the aftermarket one. Like I said, it works about once a week and will stop working if I shut the car off. Even if its for a few seconds and start it back up.

My theory is that their is a ground dangling somewhere that will hit bare metal while I'm driving causing the tach to work and stop when I shut it off.

HAILERS

Oh. I see. Carb with first gen distributor and coils. Read this thread from the first gen forum. It more or less states where the tach signal originates on a first gen: https://www.rx7club.com/1st-generation-specific-1979-1985-18/tach-not-working-1985-gs-826572/


You might take into consideration what one guy said about removing the TRAIL ignitor on the distributor and making sure it has a clean bond with where it mates with the distributor.

Next time the tach works, and then stops working, leave the engine running and pull the wire out of the trail coil to see if it's actually firing. Or pull a trail sparkplug wire off and see if its firing or not. Looking for clues is what it's called.

Make sure if you take both ignitors off the distributor, that you put them back as you found them. They are the same item, but say the trail has a fault where it works just part time. IF you put that ignitor in place of the lead ignitor, then when that ignitor goes south intermittently, the engine will almost not run at all. Failure of the Trail ignitor will be barely if at all noticable other than the tach not working.

I had a first gen that all of a sudden out of nowhere, ran crummy. I sort of figured it out and swapped the two ignitors and it ran like a champ once I did that. Bad lead ignitor was the problem. Lead plugs/coil wasn't working until I put the Trail ignitor in its place. Bought another.

HAILERS

Sorry, I forgot your aftermarket tach works fine. So it can't be the ignitor.

danegerous

iTrader: (10)

I'm not sure what it could be but I was rattling around in the engine bay , fired up the car and the tach worked all of a sudden...killed the car and restarted, no tach. If it works half the time it's got to be something simple we're overlooking

g14novak

iTrader: (1)

I had actually already had a problem like that. I had a bad ignitor AND coil. I noticed this when I first installed my aftermarket tach. It was when I first swapped in the new motor, it took forever to start, it ran but the ignition broke up over 4k under load and my (at the time) brand new tach didn't work. I thought it was a broken ebay unit. Ended up being a bad coil and ignitor. Replaced both of them and my aftermarket started working.

I think my stock unit is just busted. I was on my way to work today and it started working again but was WAY off. My aftermarket read 4k when the stock still said below 1. I took the car to redline and it only peaked at like 1200 rpm.

HAILERS

It's be helpful if someone else who has gone to carb could say how or if his stock tach works/does not work.

As an example go read the last post on this thread https://www.rx7club.com/2nd-generation-specific-1986-1992-17/crank-position-sensor-836085/

That fellow who made the last post on that thread says he has a carb RX. Maybe PM him and ask him if/how his stock tach works.

g14novak

iTrader: (1)

Must be a little bit early over there in Fort Worth. The post you linked me to is mine.

Well the signal coming from the negative on the coils should be the same regardless if its carb or EFI I would think. All my other gauges work without a problem (with exception to the speedo gauge, but I already know i'm missing the gear inside the transmission). I'm just going to try and put in another unit and see what happens.


Yeah, something like that happened to me also. The only time my tach has worked good was a little under a year ago. I was driving home during a hurricane (/facepalm) and the stock tach started working and reading correctly. From that day on, it got worse and worse and was dead again in a week.

HAILERS

Oppps. That was a big goof up by me.

HAILERS

I know the tach does not work of varying voltage, but freq, but seeing as how the stock cars tach sees something like 0.72vdc at idle and something like maybe 2.5vdc at high revs, then that could be part of the *problem*.

Because if you put your meter on the neg side of the trail coil(s) you'll see alternator output. Like I see 14.5vdc on my trail coils.

14.5vdc is a far cry from the 0.72vdc the tach output signal of the yellow/blue wire. I have a idea the stock tach just won't work with first gen coils/ignitor.

But I put up a thread on the Natural aspiration forum on this site . You might want to monitor it in case someone actually answers it.

g14novak

iTrader: (1)

Ok, I'll keep a eye on it.

This is driving me nuts, I may just end up drilling a hole in the middle of my cluster and dropping the ebay tach in it if I can't figure something out soon...