aftermarket Tach

I haven't looked yet, mainly because I'm lazy and tied up with my '68 project right now, but I do want to put an aftermarket Tach in this 91 OCC since the factory one is way off. That being said, do these cars have a terminal on the distributer to hook one right up or where does one need to go to...

The white wire on the coil is the tach lead.

Fred Kiehl wrote:

The white wire on the coil is the tach lead.

thanks! makes it easy on me.

Same on the 96 Roadmaster ?

96 RM does not have a tach, so I do not know.

I have a 96 RMW and for a tach, and other information, I just put in an OBDII Scangauge.

Simple installation, good information although no transmission temp, and the tach is right there with the other information.

The Opti makes regular tachs not work well, it appears, from all I could find out.

I'm not positive but i thought there is a green wire that comes from pcm for tach, for lt1 cars. if i get a chance i will check the factory service manual

The roadmasters actually output a tach signal from the PCM to the climate control, iirc. I wanna say it's pin 13 but let me double check my notes on my laptop. I ran the wire to an aftermarket tach for a while then moved it to the tach in my camaro gauge cluster when I swapped it in

https://www.impalassforum.com/threads/tach-wire-install-on-pcm-pics-included.1043681/

Here is a thread on the other forum that is pretty in-depth. If your car doesn't already have the climate control signal from pin a13 and you don't want to run new wire, grab the pink wire in the blue harness 16 PCM spot (oil change light) remove the pin from the harness, and plug it into a13 in the red harness. Then remove or cut the pink wire from your oil change light behind your gauge cluster and run it to your tach. Otherwise just plug a new wired pin into the a13 harness and route the wire to your tach so your oil light stays functional (assuming it still works- many don't.) This should output a good tach signal in all 94-96 B-bodies except some of the Impalas, which for some reason cut the frequency in half so you have to wire your tach in 4 cylinder configuration.

Thanks, BUT I bought a hood tach repro of 71 GS hood tach. I need to connect under the hood. I'm thinking probably one of the wires plugged into the coil, but don't want to tap the wrong one.

This may be the info you want then. The PCM harness and coil in the Camaro are essentially the same in '96, but the actual wire to the tach from the ignition control module probably isn't there since your car didn't come with a tach. But again, using the A13 pin from the pcm is the same signal, easy to locate, the PCM is under the hood (below your airbox) and there's no chance of accidentally splicing into the wrong coil wire if you aren't sure. Just run a wire from the A13 pin (they are labeled on the harness connector itself) to your tach trigger input and you are golden. I even have an extra wire with the connector pin already attached I can mail to you if you don't wanna source one

https://www.camaroz28.com/forums/lt1-based-engine-tech-9/tach-wiring-question-444176/

One other note - if adding a tach to the LT1 cars, definitely do NOT tap into the white coil wire. The PCM checks resistance on this wire and will set codes if it is too high or too low. I'm currently driving a '95 Caprice wagon the previous owner installed a Z28 gauge cluster in and it was constantly throwing a code 42. I moved the tach wire to A13 and the problem went away.

OK, I test wired the hood tach with no results. Seller recommends a pull up resistor. I bought one from summit. instructions say LS tach outputs 2 pulse per revolution, so set the tach for a 4 cylinder engine. Sounds logical, but there are no adjustments on this tach. Does anyone know if the LT1 puts out on or two pulses per revolution? I plan to try some time this weekend anyway.

Thanks,

Tom

Sorry for some reason my phone logs out of the forum whenever it updates and I don't get notifications until I remember to log back in. My 94 lt1 only puts out 1 per rev, so my Auto Meter tach is set to 8cyl. Did you test the wire after adding the pin to the connector to make sure you are getting a signal? Are you using an aftermarket ignition box, or have any non original wiring at the coil or opti harness? If you aren't getting a tach signal from engine to the ECM it should throw a code, so I would start by testing continuity from the harness ( remove from the ecm so you can get your multimeter lead on the correct pin out) to the tach end of the wire. If you do, then I would reconnect the ECM and make sure you are getting an output signal at the end of the wire with the engine running

I have the pull up resistor, but have not had time to test wire it up. Hope to take a swing at it this weekend.

Sleeperwagon: thanks for your response, hope to see results Sunday.

Isurf wrote:

I have the pull up resistor, but have not had time to test wire it up. Hope to take a swing at it this weekend.

Sleeperwagon: thanks for your response, hope to see results Sunday.

there is a tach pin on the PCM. I bought a Z28 cluster and the instructions told me which pin.
Unfortunately the cluster fell into the black hole of my garage and I'm not sure where it is now (was going in the T56 wagon that got totalled) since I 'stored' it about 4.5 years ago.

Higher priorities have delayed this project. Had a radio catch fire in the dash while driving. Kitchen remodel also consuming much time.