Tachometer question

[Hedgehog]

I've been running a DUI Dist. Does the dist. chip have anything to do with the tachometer signal? Why do I ask? While attempting to get my CJ to pass emissions my tack suddenly decided to stop working. It does respond to shutting the CJ off, but it seems to be stuck at 1200 rpms. I've fiddled with the wiring with absolutely no change. This is a high quality Autometer unit that has worked flawlessly. Could the chip be compromised?

 

[Hedgehog]

Maybe there is no real answer to this question and my Tach simply took this time to take a trip to la-la land.

 

[gr8dain]

It has to, right? I mean on my HEI, the wire from the tach goes directly to the blade on the distributor.

I assume that when you take that off, the needle drops. Have you read the signal at that point at idle and at different revs? Any difference in the readings on a multimeter?

 

[Lumpy Grits]

Is there an adjustment for the number of cylinders on this tack?
If you replace it-Consider this brand.
In-Dash Tachometer. 60s Muscle - 1969 Camaro Style Tachometer

LG

 

[Hedgehog]

It is an old but NOS 4" Autometer tachometer when I installed it a couple years ago. It has worked perfectly until now. The number of cylinders is a hard wired affair, choose the right wires and hook them up or cut'em. Since a V8 is the default cylinder number you just hook the wires up, go to the distributor and plug it in. On Monday I was resetting my advance timing and some time during the reset the tack decided to go bad. It says the thing is stuck on 1600 RPM. On the way to work it did move some but made no logical sense at all. I did pull the Dist. plugs and reset them with no change. I fear the old girl is shot.

A new Speedhut gauge is on the way. My replacement gauges are all Speedhut units so I stuck with them. These gauges are made to order right here in the US. The type of lens, the needle, the color of the background graphics, text and other things are all made to order for your gauge. You can even customize the RPM range. Since the AMC engine would be in bits and pieces at anything much above 5,000 RPM's they are making the range 0-5,000. Surprisingly enough they are not crazy expensive. On par with the gauge Lumpy suggested.

I can't help but think the problem has something to do with adjusting the timing, Coincidences like adjusting the timing and a tack going out at the same time generally are no coincidence at all. Replacing the Tack was okay though. This is a steering column mounted gauge. When building the roll cage the cage was dropped on the gauge denting the bezel ring making an unsightly mess of it. Other than the look of it the gauge was unaffected by my being clumsy.

gr8dain - I really do need to test the terminal. What kind of reading should I expect? Distributors sort of scare me a little. There is so much electricity flying around in there right next to the chip there is a fear that badness could easily happen..

 

[Lumpy Grits]

HH-How is the tach grounded?
Is this the tach you ordered?
http://www.speedhut.com/gauges/Tachometers/?catid=f9|f292
Sure looks good.
LG

 

[Hedgehog]

Close:

3-3/8" Tachometer 5K RPM. Auto Without Shift-light From Speedhut.

It shows as white after customization:
Black face
White tick marks, with additional intermediate marks
Bigger font, AMC 150 %
Red Pointer
Dome face, tempered glass
Range 0-5,000 RPM's

The gauge will be externally mounted on the dash. Probably would look neater in the dash, but I life the versatility of being able to place it anywhere I want.

Honestly I don't remember how it's grounded, I believe its in the wiring harness but can't swear on it. The gauge has always worked flawlessly, never a problem.

 

[gr8dain]

Not sure what the exact readings should be but I would imagine that you should see variations when reving the engine and if you see a constant output that would explain the needle sticking to 1600 rpms.

 

[Lumpy Grits]

Nice! :drool:

Just for 'grins'-Run a temp GND lead and see if that makes any difference.
CK the connections near the dizzy as you were moving that to play with the timing.

LG

 

[Hedgehog]

Not sure what the exact readings should be but I would imagine that you should see variations when reving the engine and if you see a constant output that would explain the needle sticking to 1600 rpms.

I don't know how a Tach works. I imagine it would receive a pulse of some sort, possibly an increase in wattage. If it were a pulse it would be impossible for it to be on 1600. The gauge does reset to 0 with the key off which is not normal. It has always stopped dead where the needle is when the ignition is shut off. It would reset to 0 when the ignition was switch back on with the engine not running.

 

[Hedgehog]

Lumpy, already checked the connections at the dist. This is where an assistant would be handy, they could watch the gauge while I fiddled with the wiring. A jump in the gauge would indicate being close to the problem.

 

[Lumpy Grits]

Do you have a mirror you could put in front of the tach, and watch for needle bounce ?
LG

 

[Hedgehog]

Probably could, would be kind of acquired, but doable. I need to pull the cap and inspect the wiring. While fine tuning the timing I tapped on the side of the Dist. with a hammer to turn it ever so slightly. The dist was loose and the tapping was small, but you never know how finicky those raskley electricals are. They simply have a mind of their own sometimes.

 

[gr8dain]

Tackometer question

The fact that your tach does not fall to zero when off is different to me. Mine always falls to zero once turned off.

Good luck with the diagnosis.

I understand that the tach wire sends a pulse between 0 and 12v. Maybe use a test light and see if the frequency of the pulses increases with revs. Not sure if it will be noticeable or not.

 

[Lumpy Grits]

Missed the deal about not returning to '0'.
Something is up for sure. :dunno:
Wonder what happens when the + supply lead is removed from the tach??
LG

 

[Hedgehog]

At first not returning to "0" concerned me, come to find out that is the way this Tach is supposed to work. Kill the power and the needle freezes right where it is. If you are running at 2000 rpm, shut off the switch and it stays at the 2000 rpm mark. Stop and turn the switch on and it returns to "0" until the engine starts. This is a competition tach., not the most fancy type with shift lights and other goodies. Maybe that is part of being that type of tach.

Rascally electrons. A tech adjusted the carb to pass emissions and whammo, the tach. works once again. I have absolutely no idea why.

Doesn't matter the new tach will be a nice addition to the gauge package I'm getting ready to install.

Now to make it through emissions. So far it's failed 3 times. We are narrowing down the problem. Tonight we found a vacuum leak I didn't know I had. It's upsetting because I thought it was fixed last year.

 

[gr8dain]

Weird. But glad that is resolved. Good luck on the emissions stuff. Glad that is one I don't have to worry about anymore