Need help; Wont start, erratic tach...

[Juan]

New to the Forum, Spent a lot of time reading first post... Be gentle.
I have searched around and could not find a solution to my problem so here it goes;

have a 90 yj, "nuttered" last spring due to crapped out electronic carb etc. have had no problem with it for 18 months or so, driven regularly almost dailywent to go for a rip one morning this week would not start, looks like the battery was drained, even though it was just parked over night. So the oddities are that when the ignition is in the run position (Jeep not running) the tachometer jumps around... which made me thing ignition module or coil short???  but I can roll start her and once the engine chugs several times and the alternator starts to register a charge she starts right up and runs like a top! Tach works properly, drove around for 15-20 min under load not a hint of a problem, it will not hold a charge though.

 Not being to Electrically inclined I am wondering what may be shorted out (as that is my suspicions) that would cause the tach to jump around when the vehicle is not running, but apparently allow it to run fine once it gets going?
Any help would be appreciated
Cheers,

[esi]

Check your battery terminals, may be unhook and clean. Also check your negative where it grounds to the frame, possibble remove and clean. Or your battery is humped, Some places(maybe crappt tire or wally world) will do a free load test on your battery.

[hps4evr]

ive seen alternaters crap out on the inside and drain the battery. not common but its happened more then once.

[Gearhead]

ive seen alternaters crap out on the inside and drain the battery. not common but its happened more then once.

X 2     This can happen on those old Delco alternators if the diodes fail.  Diodes only allow current flow in one direction , a failed diode can go open  or  allow current flow in both directions (shorted).

Have the alternator tested.

Lot's of wierd 80's  engineering on those old carbed 258's , too much vacuum operated junk , pulse air , relays , manifold heaters , stepper motors ,fusible links and resistor wire buried  within the wiring harness and an abundance of other crap , all of it   far more complicated than necessary and a sonovabitch to diagnose.


A whole lot  of info here , somewhat intimidating to the untrained or electrically challenged but worth a look .

http://home.sprynet.com/~dale02/list.htm

[Jrama]

I had the exact same deal with the tac "dancing" when my cars battery went last year, the batttery died overnight too. I just changed the battery and it was fine.

[apex]

I just lived through all this over the course of a couple years. I thought it was a bad ground shorting out somewhere in the harness.

At first I thought it was just a battery problem. Upgraded to a red top optima and swapped to new posts/terminal leads, that helped for half a year.

Rebuilt the alternator through the electrical guys and that helped for a couple months but then it started dying again overnight.

Last thing left was the starter.  Replaced that and now I'm solid. No problems for a month now. JUst wish I did the starter a year ago.

Electrical problems are the worst IMHO. I'd look at your Alternator first, then double check your main grounds and positives for oxidation. Good luck!

[Juan]

Update;
Took the battery in for testing, it was 80% charged and 100% life... I have started Tracing connections and cleaning them up, Starter, battery post etc.
Will look into the starter for sure, as it does run, just won't start! 
I must agree, Electrical problems make my head hurt the most as well.

[Juan]

Thanks as well for the input so far 

[Juan]

Been out of town for a while, all is good again.

Bad power connection to battery, caused intermittent "electrical Surges" tach picked it up like it would a firing plug but all messed up. once it was running and the battery was out of the loop all was good. cleaned up the electrical connections and the problem is solved... until the next.
Thanks for the support.

[FiEND]

cool, glad it's worked out.  i experienced this for the first time not too long ago.  dead battery made the fuel gauge go crazy.