Voltmeter/Ampmeter whatever the gauge in the dash is, going nuts

[k20]

Ok ive noticed that if Im runnin along steady speed on highway, 65 or so for extended periods (noticed today cause had nice long drive to jobsite) that my voltmeter or ampmeter or whatever the stock dash gauge is called, would start falling over to low side (has an 8 13(12maybe) and 18 on the gauge, and it would fall to just above yellow area. However, if i adjusted speed, faster or slower it would go back up to normal, sometimes it would just pop back up on its own. Idling in traffic and all it was fine. What gives? ALternator going bad (rebuilt around a yr ago), bad gauge, what?

 

[pauly383]

Could be alternator going , or bad wiring to batt. Find out now, if its running on alternator and not charging battery, or if its running on battery , sooner or later it will drain enough to not crank the engine. Just have the battery and alternator checked, before you replace the gauge /forums/images/graemlins/k5.gif

 

[k20]

well i doubt its running on the batt, fuel injection, msd, fuel pumps... for 50 miles up interstate, 50 miles back, stop & go traffic included. Also how would i check that the alt is working prop if it just f's up every little bit? like i mean it might take 20mins b4 it does it again, at 65mph lol.

 

[pauly383]

Well you could run it for a while with a multimeter hooked up and see what you get, you obviously cant do it while driving , but measure the battery before you start and run it , and after it is running . perhaps let it run awhile and see if it does it on the gauge and doesn't on the multimeter . Also do it on the fusebox on an ign source /forums/images/graemlins/k5.gif

 

[84gmcjimmy]

I dont know what your problem is, but the oil pressure gauage in my Jimmy went wild last winter, it would spin around like it was a pysco

 

[rjfguitar]

Test the alt with a load tester, my guage is off for some reason and moves around a lot especially with the system going.

 

[dyeager535]

I just read a thread on another board where someones GM alternator was doing similar, except that it would start overcharging, then fall back to normal, randomly.

Turned out it was the voltage regulator, even though it tested good.

If it's a free replacement, turn it in and see I guess. Having it tested might work, but depending on how intermittent, they might not see the problem either. I hate that. If not, a rebuild kit with a new regulator is about $20, and easy to do.

 

[rjfguitar]

[ QUOTE ]
I just read a thread on another board where someones GM alternator was doing similar, except that it would start overcharging, then fall back to normal, randomly.

Turned out it was the voltage regulator, even though it tested good.



[/ QUOTE ]Mine did that exact thing when my voltage reg. went out a few weeks ago in my alt...easy diagnosis IMHO.

 

[k20]

ok update, tested it somewhat just a bit ago. Voltage at the batt was 12.6 with truck off, start it, 14.6volts. I let it warm up, still same, so shut it off, wait a min start it back, then its 13.6v. WTF. How does it drop a volt in that short bit, that add any clues to the mystery?