Tacho make me go nuts

[pressman]

hi,

i've been reading all the posts about how to fix a tachometer and my tacho still doesn't work any suggestions ANYTHING PLEASE i need my tach
Mike

[JP Noonan]

What do you mean it dosen't work? Like it is dead, it bounces, it stops at 1000 RPM? If it doesn't work try grounding the sender input wire (black/purple stripe )the tach should max out then drop to zero, if it drops then spikes then drops it has an internal problem but should still register. Next see if the black/purple is hooked up to the neg side of the coil (the same side as the points). If it still doesn't work hook a jumper wire (a 10' wire with two female termals on its ends) between the coil and the sender input on the back of the tach. Still nada, make sure the tach is getting +12V form the red/white wire, and that the brown ground wire is good. The blk/blue wires are for display lighting.

[pressman]

Thanks i'll try that tommrow at work when i'm figuring out the cars problems

The tacho is "dead" as in when i turn on the car the tach doesn't show idel the needle just sits there and doesn't move at all. any ideas on how this can be solved?

[JP Noonan]

Pop the gauge out first and make sure the red/wht, blk/pur, and brown wire are connected. Then make sure the blk/purple wire is hooked up to the coil. Then try the other things I suggested.

[John Rogers]

If you have a "test" type of tach, you can clip it to the wires in the dash after you pull out the stock tach. This would tell you if there was an open/short/etc in the wires from the coil to the dash. I tried to fix guages in the past, but since the well-being of our little 2.0L depends on the tach, especially in autocrosses or when Julia is zooming around, I had ours done by a repair shop. They guaranteed the repairs too.

[pressman]

Hi,

Thanks for all the advice but no luck so far i think it is just the tach that is broken what kind of test tach are you talking about?
I really need a tach cause i'm loosing power by not shifting it at the right RPM i'm shifting too early i think.

[Dave at Pelican Parts]

If you have to ask.... ;^)

You can do some troubleshooting without a spare tach of any kind, though.

Make sure that the silly thing is hooked up, first. And make sure that the tach wire on the coil (black w/purple stripe, purple is hard to see so it looks like the thinner of the two black wires) is hooked to the "-" terminal of the coil. That's the same terminal that the green wire from the points/condensor goes to.

If it's hooked up and you're still getting nothing, try the test JP suggested by grounding that black/purple wire while looking at the tach. If still nothing, then start checking the wires. Check for continuity between that BK/PU wire and the one on the back of the tach. Then check for +12V and ground on the appropriate terminals on the back of the tach. If your car's wires don't match what JP said (they *may* be different year to year, I don't really know) then check the Haynes wiring diagram for your year.

Another possibility is that the signal wire (the black and purple one) has a short to ground somewhere. To test that, disconnect both ends and tape one of them so that it is NOT touching a ground. Then check for continuity between the other end of the wire and a ground. There should be NONE. Of course, this test assumes that there is continuity between the two ends of the wire.

If you're getting +12V where you should, ground where you should, the signal wire (BK/PU) is good all the way through, and it's not shorted to ground, and your tach still doesn't work, then it's the part that is dead. Find a wrecker with a 914/4 and get the tach. See if you can find one that will let you swap for another tach if the one you get has problems. Many 914 tachs "bounce" quite a bit, but they don't have to. Try to find one that doesn't.

Used tachs are *much* cheaper than getting a tach repaired. Palo Alto Speedo (probably also their sister shop, N. Hollywood Speedo) will charge you $176 to fix it. Pelican charges quite a bit less, but used tachs can be found for $35.

Oh, and on the shifting too early: Find a good VW Bug shop or maybe even an ordinary FLAPS. Then talk to the parts guys about rev-limiting distributor rotors. You can get them set for various RPMs. (www.res-systems.com used to have a listing in their tech documents section, not sure if they still do.) The range goes from ridiculously low, like 3500 RPM, up to 8000 or so. Get one that is "about right" for where you want to shift, and then shift gears when your motor hits the limiter. It's an unmistakeable sound: rrrrraaaAAAAA-PA-PA-PA-PA-PA-PA!!! At a guess for a stock 1.7 or 2.0, I'd say about 4000-45000 would be a good limit to stay in the power. (I just wind mine up to the redline, though.)

Oh, don't "ride the limiter" too long--after about a second, you start getting enough unburned fuel in the exhaust to cause backfires. You lose style points for loud "BANG! POP! Ka-BLAMM!" noises, and the detonations aren't that good for your exhaust.

--DD

[This message has been edited by Dave_Darling.]

[JP Noonan]

I had a nice ($90) Equus multi test meter that did dwell angle, tach, cont, ohms, etc. well my "expert" friend borrowed it to use at work (alarm installer) and blew it up. So now I bought a $25 Sunpro by Actron at Discount Auto Parts in Miami. I compared it to a freinds Sears Engine Analyzer and it seems accurate. It has dwell, LO tach (0-1200 RPM), and HI tach (0-6000). It olny has two wires, two switches, and one gauge, so it is pretty simple to use. It would be nice if Pelican solds these (hint) maybe includes in a major tune up kit (hint hint) you know, wires, coil, plugs, points, cap...

[pressman]

Hi,

Thank you everybody for your replys and suggestions about how to fix this but in a few weeks the whole car is coming apart to go for painting so when it's coming apart i'm gonna buy a new tach for it.

[Wayne 962]

I just had a Taco from the Bell, that's making my stomache go nuts...

But anyways, we can rebuild tachs for $75 each. We'll also let you know if there is anything wrong with your tach too before we touch it.

Dave, (now that I remember, I've been trying to email you for several days, but your email keeps bouncing?)

I really wouldn't recommend using the rev limiter as a control on driving. It's mainly there as a safety control. Besides, you don't really want to always shift at the same moment, depending upon what you are doing. The rev limiter should be set to limit you from over-reving, and 99% of the time (especially with 914s) the power curve drops off before the red line.

Additionally, the rev-limiter causes the engine to literally misfire, which can place a lot of loads on the motor and the crankshaft. 914 Cranks are somewhat bullet-proof, but 356 and 912 owners are very aware of making sure that their cars fire well - otherwise excess vibration and loads can lead to a cracked crankshaft. Needless to say this is bad.

As an interim solution while there is no working tach, that sounds ok, but as a long term practice, I'd recommend against it...

Thanks,

Wayne