Need Help-Still No Tach

[ad53030]

Installed the 680 ohm, .5 watt resistor exactly as described in the thread. T into tach lead, then resistor, then 12v + keyed start & run. Would it matter which way the resistor was facing? Tried both anyways and nothing. Tried All pulse settings on Tach - NOTHING. Man I hope someone can see something I'm not doing right. This is FUKT.

84 C10 w/ 07 5.3/4L60, current performance wiring modified factory harness & tune.

[ryanvv355]

I am not assuming you did not do any of this, but things to look into:

Is the tach pin correct coming out of the ECM?

Good power and ground to the Tach?

Try adding 5-6 volts with the pull up circuit and see if that works. The 680 ohm drops voltage to about 4v to the tach.

Resistors do not have polarity, you can install it either direction.

[ad53030]

Ok so I'm not familiar w/ the "pull up" circuit - no idea. Grounds & power r good, correct pin out. I have not checked voltage going into the tach after the resistor. I had a test light only earlier and I got no power after the resistor. Would 4v not light up the test light? Also, which setting should the tach be set to? Should it still be set to 4cyl w/ the resistor installed (Autometer Electronic Tach) ? The only life I've seen is the needle jumps a little bit while cranking. Nothing more...

[ryanvv355]

The tach should be in 4 cylinder mode, unless the tach output has been changed in the computer by the tuner. You can set the tach resolution to output a 8 cylinder signal, however, it is done when the computer is programed. I would check with your tuner or simply setup the tach for 8 cylinder output and check. However, if it was in 4 cylinder mode and getting an 8 cylinder input it would still move, just incorrectly.

The test light should illuminate but faintly. Ideally you should use a multimeter to check your output from the resistor.

How did you insert the resistor in the circuit? If the leads on the component are exposed and they touched a ground it could have shorted you circuit.

When my tach did not work it did not move at all, not even during startup.

[ad53030]

Resistor was soldered in and covered in shrink wrap. Def did not seem to have any light after the resistor. I will check it w/ a multimeter.

[Jaysz28]

pulled this up in a search

Trying to verify what I should be seeing on my multi-meter as a signal.

99 ls1 into a 91 firebird. I'm trying to make sure the correct wire is routed to my c100 connector. The tach does not flinch at all when you rev the motor.

I verified I have a wire in the right spot on the PCM, and in the c100. If I put a multi meter on the wire at the c100, I get 5.5v or so. Revving it doesn't make it change much.

Suppossedly the tach signal was 'stepped up' when I did the mail order tune so I could get it running.

Before I make a stepup circuit (+12v ign thru a 10k resistor), I want to verify that I have a good base to work from

thanks

-jason

[Jaysz28]

Well I got the tach to work with a +12v ign running through a 680 ohm resistor

Just in case someone else is having this issue later on

-jason