tach needle problem

[hughesracing9]

My tach, now has an erratic pointer.
At idle, the pointer will be at 1200ish and then jump for a split second to 1700-1900

When i hold the throttle at, lets say, 3000 rpm, the recall will read 3200-3400

This is a accutech stepper tach with the memory playback. Didnt change anything since last used, and didnt have that problem before.

What Ive done so far: tach has its own switch and ground, nothing shared. Good connections.
separated wires under dash, wrapped tach wires to eliminate noise
new clip in HEI, solid connection

What else should/can I check??

Also, I am running a rev limiter that plugs in to the distributor. I set a 3k chip in it and revved it up, cylinders dropped but the recall still said 3200, so im not thinking its anything on the distributor side

I dont really use the tach as I have a rev limiter and know which gears to run, but if its not acting right it needs to either get fixed or removed, ya know?

[Lizardracing]

Just an idea but you might check for cross firing in the cap or carbon tracking across the towers. Might try a different coil too if there something funny with the saturation/collapse of the mag field.

[Racer96m]

The engine is running smooth and only the tach is jumpy right? If you took off the ground and cleaned the lug, then its got to be internal to the tach. You got it wet washing the car didnt you? It happens. Somebody has to have one you could jumper in and see if that works correctly.

Dave

[hughesracing9]

engine runs smooth, just a confused tach lol
what i did today, swapped distributors, but not caps as i only had one- results were the same

knocked all the powdercoat off the ground connection and checked it, same results

dabbed some dielectric grease on the connections for battery and tach under the cap, same results

the tach hasnt gotten wet as the car only had races on it, all the same weekend on a slick track, just wiped it down and had it covered in the shop.

Ive been reading about rotor phasing, i remember i got lazy and instead of better adjusting the dist. gear, i popped off all the plugs wires and moved them over one mark, maybe the rotor is off a tic?
had to put the car on hold, work is calling.

but my main question, im racing this weekend, if Im not worried about rpms, will my rev limiter still hold true to the chip i plug in?

[ep33510]

hughesracing9

It sounds like you have the dreaded carbon button material causing scatter inside the cap. If you go to your favorite auto parts store and pick up a can of Starter/ Alternator cleaner( NOT Brake Cleaner!!!!). Spray out the inside of the Dist Cap and let it dry out before reattaching. The issue is very common out there, the High energy ignitions will cause carbon particles to blow off the carbon button on the inside of the Dist cap. The carbon will float around until attaching themselves to the inside of the Dist cap. When enough are present the ignition arc will try to jump to the carbon particles then to ground. The tell tale sign is a bouncing tach at idle which will over time get worse and start to cause engine missing. We recommend this cleaning process to our customers as part of their race prep. Yes, it may seem like a little over kill but it keeps the ignition hit to the sparkplugs consistent. Hope this helps!!!! :)

[roundboy]

Thats a great tip ep!!! Ill be doing that to my cap before going to the track!!

[hughesracing9]

Thanks everyone, feel better about this weekend
I cleaned the cap and still had issues
I called longacre and turns out I have an earlier model tach that had problems with an hei
It must have been on a shelf because the newer style came out in September

Exchanging this next week