98 C1500 Tach Dont work?

[klug99]

I just fired the engine for the first time and all my gauges work great except my factory tach. Any ideas? I plugged in my Tech 2 and the only codes that showed up were P0650 (because Im not using a check engine light) and P0654 Engine speed output Circuit.

[kewljay223]

was the pcm tuned for it?

[LS2Goat]

I had to solder in a 680 ohm resistor to get mine to work.

12v+
|
680 ohm resistor
|
|
|----------------------------------->pin10 from pcm
|----------------------------------->tach

[farmtruc]

if his definition of doesn't work means no movement, then it's not the pcm and pcm's aren't tuned for it.
however, the pcm can be tuned for needle adjustment.

no movement is probably wiring or in very rare cases, a faulty pcm.

[klug99]

if his definition of doesn't work means no movement, then it's not the pcm and pcm's aren't tuned for it.
however, the pcm can be tuned for needle adjustment.

no movement is probably wiring or in very rare cases, a faulty pcm.

It doesnt move at all.. When I get home today I am going to check my wiring again.

[LS2Goat]

if his definition of doesn't work means no movement, then it's not the pcm and pcm's aren't tuned for it.
however, the pcm can be tuned for needle adjustment.

no movement is probably wiring or in very rare cases, a faulty pcm.

Before I added the 12V+ to mine, it didn't move at all either

[kewljay223]

i may be wrong but the reason i mentioned the pcm is because i thought the tach gets its signal from the pcm on pin 10. and on the newer pcms, you need a 680 ohm resistor as LS2Goat pointed out. i used this diagram http://lt1swap.com/lsx_tach.htm as most guys on here also do to hook mine up. durring one of my conversations with brandon IIRCC, he said the pcm can be set for however many cylinders you are running.... maybe i misunderstood and thats NOT how it works???? if not then what is the pcm doing?

i agree with LS2Goat, check the resistor thing as that may be your problem. what year pcm do you have?

[klug99]

It is a 04 Blue and Green connectors. I figured I would get a little movement from it.

[klug99]

I had to solder in a 680 ohm resistor to get mine to work.

12v+
|
680 ohm resistor
|
|
|----------------------------------->pin10 from pcm
|----------------------------------->tach

Took care of it! Thanks alot!!

[dimebagged]

I had to solder in a 680 ohm resistor to get mine to work.

12v+
|
680 ohm resistor
|
|
|----------------------------------->pin10 from pcm
|----------------------------------->tach

Would this be the same on a 95? I get no movement from the under hood white wire, but i did get some from the white wire behind the glovebox.