Tach erratic problem resolved, but now raises new question

Hi folks,

Well, the jumping tachometer problem I've been having (tach would work intermittently, only under acceleration) is resolved, just bolted down the trailing coil (had it loose for cluster master cylinder bleeding).. I guess it grounds at the front two studs.

Now my sequential shiftlight works, and the in dash tach works great. However, now hooking up the autometer 5" ultralite tach, and setting it for 4 cylinder, I read 500rpm low from ~3K on up.. Below 3K, the interval seems smaller (200-400)

so.. Is my stock tach a piece of crap that I just can't trust, or is my autometer doing something fun-ky? All with regard to an ITS 88 RX-7.

PaulC

Do you have everything hooked up/tapped into one wire? That could be your problem. You might need a tach output booster if you run too much off the coil's tach wire. Also you are running of the leading or trailing coil pack?

Oh and as a side note, on my 85 GSLSE when I hooked up just a shift light, I noticed it was about 200 rpm off so it could be just your stock tach. I am still working on my rx7 so if I ever get around to installing a tach I'll let you know!

BTW, did you ever fix your idling problem? Sure would like to know what you did.

Interesting.. Ok, I'll move the line to the actual bullet connector on the trailing coil instead of hijacking the line feeding the stock guage.

Kinda sorta fixed the idle problem. Removing the thermowax and fast idle cam left the primary throttle plates fully shut. Compared TBs with a junkyard one (complete with thermowax and plates), and the bottom plate still had a significant gap in it, even with the thermo fully disengaged. I bumped the throttle stop up, and now it idles at 1500. Hunts at that RPM though, still suspect a vacuum leak. It's on the trailer to head over to the alignment shop, but this weekend I'll have time to dig into it.

PaulC