97 Aftermarket Tachometer

[supspt454]

Have not seen much info on 96-98 Vortec trucks with aftermarket tach. Working on tach, water temp, oil pressure, and wideband install. Reading different things on the web about tapping into the tach signal wire, but also some people having issues with truck not running right and trans not shifting right after install. Does the pcm see rpm from the crank or the cam? Does the factory tach get signal from one of those or from the coil? And what color wire? I would like to kill the factory tach in the dash as it does not read correctly compared to VCM Scanner and it drives me crazy lol. Its about 300 rpm off. Thanks in advance.

 

[supspt454]

Have not seen much info on 96-98 Vortec trucks with aftermarket tach. Working on tach, water temp, oil pressure, and wideband install. Reading different things on the web about tapping into the tach signal wire, but also some people having issues with truck not running right and trans not shifting right after install. Does the pcm see rpm from the crank or the cam? Does the factory tach get signal from one of those or from the coil? And what color wire? I would like to kill the factory tach in the dash as it does not read correctly compared to VCM Scanner and it drives me crazy lol. Its about 300 rpm off. Thanks in advance.

The factory oil pressure and temp do not read correct either. Changed oil pressure sender and both temp senders when the engine was built a few months ago. I am not a fan of factory gauges because of this issue. And besides, I like aftermarket gauges because they look cooler lol.

 

[GoToGuy]

That info should be in the OE service manual. Have you checked ?

 

[supspt454]

I just found this. Circuit 1847 "D" wht/blk Tach Sig from ignition module to coil. Wonder if that is it.

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[supspt454]

Just don't know if it will screw anything up with the rest of the truck.

 

[supspt454]

Update on the tach. I tapped into the white wire on the coil and tach works, but jumps around above 2500. I have a signal filter on order and will be here Thursday and will report back. Side note: On the water temp gauge, I tried to use the factory gauge sending unit with the aftermarket gauge and that did not work. Truck would barley run and the gauge read real high. Was just hoping that it would work. So now I will use the supplied sending unit, as well as the oil pressure. I was just wishful thinking.

 

[smdk2500]

Update on the tach. I tapped into the white wire on the coil and tach works, but jumps around above 2500. I have a signal filter on order and will be here Thursday and will report back. Side note: On the water temp gauge, I tried to use the factory gauge sending unit with the aftermarket gauge and that did not work. Truck would barley run and the gauge read real high. Was just hoping that it would work. So now I will use the supplied sending unit, as well as the oil pressure. I was just wishful thinking.

Did you use the one in the drivers side head or on the intake. If you used the one on the intake that would probably be the reason for the truck running poorly. The ECM uses that one for its own purposes.

 

[supspt454]

Did you use the one in the drivers side head or on the intake. If you used the one on the intake that would probably be the reason for the truck running poorly. The ECM uses that one for its own purposes.

Tried to use the one wire sensor in the driver side head that feeds the factory gauge. Kind of weird. I can un hook that sensor and the factory gauge falls to 0 and truck runs normal. When I connect that sensor to the aftermarket gauge, the truck struggles to idle. Makes zero sense. And the aftermarket gauge shows about 25 degrees off.

 

[smdk2500]

Tried to use the one wire sensor in the driver side head that feeds the factory gauge. Kind of weird. I can un hook that sensor and the factory gauge falls to 0 and truck runs normal. When I connect that sensor to the aftermarket gauge, the truck struggles to idle. Makes zero sense. And the aftermarket gauge shows about 25 degrees off.

The falling to 0 is normal. The running poorly doesn't make sense with an aftermarket gauge hooked up. All that one does is feeds the dash gauge.

 

[L31MaxExpress]

The factory oil pressure and temp do not read correct either. Changed oil pressure sender and both temp senders when the engine was built a few months ago. I am not a fan of factory gauges because of this issue. And besides, I like aftermarket gauges because they look cooler lol.

My OE gauges are dead nuts on.