Ok...
My tach has some problems. It bounces..or jumps (sometimes as much as 1000 rpms) usually at light throttle/cruise. Its just the tach, not the engine surging, the engine runs fine.

If I see it while crusing(1200-2000 rpm) and put the tranny in N it (usually) goes away (even if I keep the rpms up), if I put it back in drive it reappears.

It seems to happen more when the car is warmed up.

I have read from posts on here that its the coil in the distributor. Thing is I have brand new Accel wires and a new distributor (its remanu one from advance auto parts), new cap. It seems to have showed up after the wires/distributor install...(checked, rechecked all connections, move wires farther apart etc).

Alt/Battery voltage is rock solid.

So my question is how can I test the distributor coil to make sure its good without pulling the dist?

Could it be this OEM/Reman dist is going bad?

Any tips would be appreciated.

 

Hmm..looking at the ALDL data it seems my battery voltage is varying a bit...13.2 - 14.4 with some spots looking jumpy. Older data shows only like .2 - .3 variation...could this be the problem?

In the moates software does battery voltage refer to the battery or alternator (ie. which one is bad).

 

Had the same problem with my 91 Z28. Turned out to be the white wire from the coil to the tach. I replaced the wire from the firewall connector to the coil and problem is solved. Might want to look into it

 

Yeah, had the same problem. Make sure the white wire going to the coil has a good connection. That was my problem.

 

The voltage is your problem, do you have underdrive pulleys?

If your volts dip below 13.5 your tach will go nuts. Back and forth, up and down, etc...

The alternator doesnt acheive max output at idle or cruise in OD. I am willing to bet this is where you see your probs.

Ask me how I know this, LOL!

This occured on my 87 Formula until I ditched the underdrive setup.

If you dont have underdrive pulleys it very well could be the reman alternator. I was in to swap my reman out on the lifetime warranty and the one they gave me was "dead" out of the box, barely put out 13 volts on the test bench, so they had to grab another off the shelf. Take it to be tested, it should put out 14-15 volts on the bench, if it doesnt get another one.

 

Nope, no underdrive pulleys.

Yep it happens at cruise, and seems to happen more when the accessories (lights stereo etc) are on. It seems to have stablized...for now..drove it all day Friday (with the Computer hooked up) and it did once....ironically just as I was pulling into the driveway. Probably time to get the alt checked....by the time I am done the whole thing is gonna be new..

Thanks

 

Yep, have that alt bench tested.