95 Lt1 in 86 T/A. My tach isn't working. I've swapped in another tach, nothing. Checked the wire from pin A13 of the LT1 PCM to the tach and it checked out fine. I'm getting 12V on the tach output with the key on and the engine on and off. When i rev the engine, the voltage drops a couple volts. Hardwired the tach just in case of a bad connection on the back on the guages, nothing. Programmed the PCM with new madz28.com tune, since i haven't done it yet, nothing. Used Freescan to check for codes, only code that came up was Code 11: SES light failure. Well the SES light and vats wiring are removed. Freescan also showed accurate RPM but still no tach working. My PCM is socketed/repaired, so the possiblity of a bad pcm exists. The car seems fine though, i'm guessing i drove it up to 40MPH on my one and only test drive so far.

No speedo output also but that could be how i programmed it for the 700R4. Haven't ran tests for the speedo not working yet, need a laptop and another test drive.

Any other ideas to make the tach work? Is it possible to get the tach to work by using the low res signal from pin B2? Or is not having the SES light and VATS wiring/modules there causing the tach not to work?

 

I tried a tach from a 305 car TPI car, one from a 305 TBI car and a tach from a 350 TPI car, the 8k tach was the only one I could get to work which was out of a 350 TPI car.

 

thanks klortho. I'll try that.

 

I had a similiar problem when I did my swap. I tried different clusters, checked wires, and still nothing. I ended up running the white tach wire from c100 to my coil. This was the only way I could get it to work. I guess the wire that goes fom the pcm to the tach must have been corrupted or possibly went through the 4th gen bcm in the original configuration.

 

Try out an 8k tach from a 350 tpi by chance? Just wondering. I got my 8k tach coming in mail hopefully soon. If it still doesn't fix it, i have an 8k tach instead of a 6k tach. So its all good. I'll wire it up to the coil if the 8k tach doesn't fix my problem. Getting the 140mph speedo too while i'm at it, cant beleive i was going to leave the 85mph in there.

 

When I talked to Dana at LT1350.com about the tach, he said as long as I had 12v coming to the tach wire inside the car with it running, and the voltage going down everything was good to that point but finally got it going with the 8k tach.

 

The 8k tach didn't fix it. So, should get the tach going by running a wire to the ignition coil next.

 

still not getting a working tach, which exact wire should i be going off of to get a signal from the coil?

 

The white one if I remember correctly

 

the white with black stripe wire made the tach work. Awesome!

 

You might wanna double check your tach accuracy once you get it going. I noticed when working with tunercat I had my rev limit at 6300 but my tach would almost go past 7k before cutting out.

 

yeah, i'll be watching for that, the factory tachs aren't the most accurate from what i have heard, hopefully i'll luck out and the tach wont be off by 700 rpm

 

Good. it seems to be progressive, reading very accurate at idle but getting mucked up near the end of the tach.By the way Ive been watching your speedo threads im trying to figure that one out myself

 

i have to figure out if my pcm is even outputing a signal for the speedo or if my calculations are way off. It wasn't outputing a tach signal. Right now the speedo puts out 0V with key on and according to the pcm pinouts on shbox.com its supposed to be like 6.5V or something like that. I'll get it figured out soon.