My tach is possesed

[1988starter]

OK here is the deal when my engine tachs up the tach has a tendancy to jump up instead of climb. This is a recent devolpement. I don't have custom gauges and have never removed the gauge faces or needles. I want to know what is happning I have currently an MSD 6AL and an accel coil with IHE highflow cat NGK plugs .056 crane cam firewires. can someone give me some advice.

[rallyeNate]

your cennection for the tach could be loose, or look for arcing and cross talk between wires

[1988starter]

yea I have all the wires together with a split hose could that be it.

[CoAsTeR]

well that tach takes a signal coming off the blue wire from the coil, just seperate it from the rest of the wires... if anything check to see if its shorting somewhere.....

also the blue wire goes to your fuel cutoff relay if you're carb'd

[keruhas184]

My tach jumps too, but the engine power stays the same...

Most of the time the needle gets stuck at 3500-3700 max, but I can hear it rev higher if I keep flooring. When it's stuck like that, I shift at about 3700.

Then I would be driving around 50-85, and as the engine is stressed the tach would suddenly jump to 5500! But - nothing actually changes, engine is going at the same speed. When it becomes unstuck, I would shift at about 5500, which corresponds to the earlier 3700 reading.

So my tach lies, and I don't know the real rpms. Oh, and sometimes she likes to start with insanely large rpms, which drop down after some driving...

On the side note, which should be a different issue (or maybe not), I'm about to resolder/replace my main relay, cause she likes to die in some very inconvinient places. I'll put in a new coil too, and will make sure I get the connections right.... Speaking of which, does anyone know what that small black thingy (relay?) is, the one connected to the stock coil?

Another Q: 87lx has an ECU right? You guys say it's under the driver's seat... how do you get to it again? (I haven't tried yet)

Thanks a bunch

[dXsquared]

i dunno what tach is wrong, but my new aftermarket tach is a bit off.. its higher by 100-200 rpms... i dunno which one is accurate.. oh ya... i wored the tach without even runnin a single new wire or switch... theres a clump of 4 screws on the back of the gauge cluster that has all the conections needed.. i even have the illumination fader with my tach !

Travis

[eightyfivelude]

if you ran the tach lead off of the -side of the coil then you could get some problems. IF you have it runnin off the coil, the MSD has a tach output on the side that you are supposed to use. Switch it over if you don't have it running off the box already.

Matt