porscheEH!

My tach only runs every once and a while, it's extremly annoying lol also somtimes the fuel flow will work but not the Tach side. I've cleaned the lead at the coil and cleaned the plug at the Gauge, every so often when I tap the dash the needle jumps up and immediately goes back to 0

Any suggestions?

It's an erly style dash 1983 944

UncleMaz

I have never tried this with a tach, but the way to test almost any gauge is to ground the lead. The gauge should pin if working properly. Once that is eliminated (good or bad), you can go from there.

porscheEH!

Yea one problem though, the plug in the back of the tach has like 10 wires going into it!!

UncleMaz

At the sender. Is the coil the sender? Then ground it there.

porscheEH!

hmmm, it doesn't pin the tach gauge, how would i check the coil to make sure it's sending a signal to the post?? and if that does work, is there anything between the coil and the tach to check??? fuses etc?

UncleMaz

I have not done this one before. Let me do some research. I would hate to steer a lister wrong. Anyone? If not sooner, I will be around a 944 electrical guru on Friday and I will ask him.

UncleMaz

If I had to guess, it is one or the other (coil or tach). More specifically, I would say tach. The easiest way to check is always with a known good version (of each). I may have a spare around if you give me a little bit to check.

porscheEH!

yea that would be appreciated!

jpk

The tach doesn't work the same way as say a fuel guage or temp guage work. For most guages, a set voltage is supplied to the guage and the sender acts as a ground. The sender is designed to vary resistance based on what you're measuring (oil pressure, water temp, etc...) The varying resistance changes the voltage in the circuit and the gauge reads that. The guage is, in effect, just a volt meter.

The tach, on the other hand, is a pulse counter. It requires a significantly more complicated circuit. The main "sender" is the terminal 1 connection on the coil. This is directly fed by the DME (pin 1). The tach senses and counts these pulses. There really isn't anything that can go wrong with the "sender" for the tach - if the DME isn't firing the plugs, the car won't run.

The connection for this on the back of the tach is pin 6. The ground for the signal is pin 4. If the connection is clean, the problem is internal; likely a old, dried out electrolytic capacitor. If you're handy with a soldering gun, you can try taking the tach apart and replacing the electrolytic caps inside (that's a good fix for the early clock that doesn't keep time as well)

I used to have that problem with my early car, but not all the time - usually just after starting the car, especially if it sat for a while. After a few seconds, it would start working.

porscheEH!

thanks alot for the reply!! that helps me out ALOT

UncleMaz

Thanks John. I never tested a tach before. That was helpful. PorscheEH, I will still look for that spare tach over the next few days (probably after the weekend will be best).

porscheEH!

The car has sat for 8 monthes and i havn't gone on a good drive yet, Is it possible it could start working fine after i get the car woken back up?

ekeeton

It's been my experience that these cars do need to be driven. Take it for a long drive, what have you got to lose?

porscheEH!

it's not saftied yet lol Yea like you said, it needs to be driven, it's crazy the shape these cars can get into by sitting, I bought the car 2 monthes ago and i've never driven it for more than 10km, you think the car will be different or sound different after a long run? also i just put a flowmaster muffler on it so i am expecting it to brake in and sound a little different than right now.