Well, I've searched and can't find anything that directly relates to what my car is doing. Car is in sig, for the last couple years whenever you accelerate hard,
the tach drops out, and just reads 0 rpm until you let off the gas. Then it will snap back up to whatever rpm the engine is at. It seems to be worse the warmer the car is, either ambient or engine. Recently it seems to be getting worse (more sensitive), and also seems to be affected by electrical loads. For example, the tach was pretty much not reading at all during hwy cruise the other night, I turned off the fog lights and it was ok (as long as i didn't accelerate hard). also turning down the cluster dimmer affected the twitchiness of the tach too.

None of the other gauges are acting up and the engine never misses a beat. The gauge cluster is clean front and back, all of the connections are free of dirt and corrosion. Any help here would be great.

 

well, still working on it, ran a bypass wire from the pcm to the back of the cluster, same result. Has anyone had problems with the Trans Am tachs going bad, or is this more likely to be a bad signal from the pcm? Could there be a signal strength issue, either too strong, or not strong enough and the tach simply cannot pick it up?

 

Id try a smaller resistor on the booster wire so more voltage reaches the tach

It could be a failing tach as well

 

Booster wire? Is that the signal wire from the pcm to the cluster. I have also wondered if it was the tach, but I don't really have any way to test it.

 

Booster wire is different from the tach signal wire from PCM to cluster. Birds have a very sensitive tach that almost always requires a booster wire to work

In a nut shell you tee into an IGN source, install an inline 680 ohm resistor and tee into the tach wire adding a few more volts to the signal. That usually clears it up

 

Sounds like a loose ground. Is it only on acceleration or can you provoke it by maintaining a steady speed and turning back and forth aggressively to violently? Perhaps it is getting pulled or pinched from engine movement.

 

Ok, thanks, I'll see if I can get something wired up. I just have to remember to go to Radio Shack now

It is mostly on accel, can sometimes happen on sudden decel too. It has always been heat sensitive though. I haven't tried watching while going side to side, if the booster wire doesn't work, I'll check this out too.

 

Did you ever figure this out? I'm having the same issue..

 

Actually yes, I did. Basically was just giving it a couple Weeks of shake down before I updated this. Exactly as pocket said, splice in an 'IGN on' wire to the tach signal wire (with the resistor inline before that) and it's been great. I've been able to take it up to 6k no problem, solid as a rock. Now gotta decide if I want to clean up the harness or just run it as is since it's fairly well tucked in there on my car.

Hope this helps

 

I have been searching for a fix for this issue for years... I will try it today and hope it fixes the problem.. Thanks for the post guys!