ever moving amp gauge

[natedogco2007]

this one should rack some heads. i have a 91 explorer and i am driving along and all of a sudden the needle on the dash starts moving back and forth. so i think that my amp has fried another alternator so i exchange it at a my local advance and put the new one on and drive off. well, later that night it starts over charging. so the next day head on into the parts store again thinking that maybe i got a bad one. put it on and drive off everything is fine. that night it gets reallly cold (for SC that's about 30 degrees). And then the needle starts doing the same thing and like last time the lights keep fluctuating with the needle. I have checked the battery, the cables, the grounds, the belt is new (past summer) , and every time i drive more than 10 miles it starts doing this? what could it possibly be? the only thing that i can figure is that it has something to do with the temp and possibly a ground, but everything works fine just sometimes the acc's start seeing peaks and valleys in their operation. PLEASE HELP !!


nate

 

[bitchinexplorer]

mine has been doing the same for a very long time. replaced damn near everything. it still does it. i have no idea what it is though.....

 

[agzaretzka]

You could connect an aftermarket gauge to verify the stock one isn't the problem.

 

[bitchinexplorer]

i thought about that, but my lights and everything flicker when the gauge moves.

 

[Opera House]

Time to check things again unless you got glowing lights hovering overhead. If the individual parts are good, the system will work. I don't know how you checked your grounds, but very few people have the equipment to do a test like that. I suggest you run a seperate wire from the engine block to a clean ground on the body. The alternator references its voltage to the engine and the gauge is referenced to the body.

 

[Eneurb]

Are your electrical accessories by chance drawing too much current for the alt. to handle???

 

[natedogco2007]

i think that opera is right it might just be the body ground. but my lights do flicker along with the gauge when it's moving. and i sure as heck hope that it ain't the cables cause FORD wants "uuuummmm...... about 250 for parts and labor..." ~ el jerko. lol . the only thing that i am ever running when it does it is my amp. and it isn't that big nor has it caused a problem for the past three years. this is why i am so confused.

 

[natedogco2007]

any body come up with anything? i still can't figure it out.

 

[Opera House]

Replacement battery cable ends are only $1 and a decent DVM is only $10. Untill you measure the battery voltage directly on the battery while you drive, there is nothing to make an assessment on. Also measure from the body to a 12V distribution point. This is an easy problem, but the answer isn't going to drop out of the sky. Unlike many other engine problems, everything here can be measured.

 

[adale]

VERY LONG POST...sorry! IF YOU ARE NOT COMFORTABLE PLAYING WITH THE ELECTRONICS OR THE ELECTRICAL SYSTEM OF YOUR X...TAKE IT TO A PRO.

Ok...here is an easy method to check the grounds, which is what I think is the problem. It involves a voltmeter and a long, heavy gauge, like 12ga, wire with alligator clips at both ends. First start the X and after the systems have settled down, check the voltage at the battery posts. The amount is not important, but the value is. Next attach the positive meter lead on the positive post or have somebody hold it on there and hook up the long wire to the voltmeter negative lead and then to the battery. Make note of that voltage also. Leave the positive lead where it is and remove the negative lead wire from the battery and touch the negative wire to the alternator houseing, be careful of the moving belts, etc. Note the reading. If the difference between the battery reading and this reading is drastically differnt (after your subtract the difference between the straight battery reading the negative wire reading) then you have a flaky ground from the battery to the alternator. Lets put some numbers in this so it makes sense. Your direct battery reading is 13.75 volts at idle. With the long negative wire attached it is 13.74 volts meaning the wire is droping .01 volts. The voltage when you touch the alternator housing is 13.24 volts, which means there is a difference of .5 volts between the battery ground and the alternator ground. That is the problem. I have seen the voltage difference anywhere for a couple of hundredths of a volt to 2-3 volts. If your X is over 5 years old or has a 100K miles on it, I will bet you negative and possibly your positive battery cables are very resistive. It's nothing you've done wrong, it is just the nature of the beast. Don't try a save a couple of bucks and put a new battery end on it, they add more problems then they get rid of. Go out and buy a new cable. I just replaced my negative cable since my alternator was output low voltage at idle when hot, found the main negative cable was the problem using this method. BTW, you can't simple check the resistance in the cables as the amount of resistance you are trying to measure is less than 1 ohm and any volt/ohm meter that costs less than $200 isn't that accurate at those low readings. You can also check anyother ground in the vehicle by simply touching the negative wire to that point and seeing the voltage difference.
Hope this helps!
ad

 

[natedogco2007]

i like working on the electronics on my x. i am also a parts pro at an advance auto. i put a volt meter on the battery when the gauge inside was messing up and the voltmeter confirmed the gauge inside the x was working properly and i put new ends on and ran wires to the alternator and then to the body and still i get this jumping gauge. i have no idea what the heck is going on. i have had everyone at the store confused as crap. it doesn't matter what acc. i have on or what speed i am driving at. the gauge will do it at idle as well as while i am driving down the road. i think that it may be the voltage regulator. but this is the second alt. that i have put on and they both do it. i tried changing the belt. i also changed the end on the alternator. i am really stumped. i am wondering if a bearing on the idler pulley could cause it. it isn't making any noise though so i doubt that it is going bad. i will change it this weekend and see but i don't think that it is it. i am really confused.

 

[adale]

So I take it that the voltmeter is acting the same as the gauge in your X. If so then I would look at either the battery has some type of internal short or something, test this by hooking the voltmeter to the battery and then with the X not running turn on your lights and watch the battery voltage. If the battery voltage starts to go down without any jumping around then you battery is probably good. Don't discharge it too far. Also have you ever discharged your battery to the point that you had to put a charger on it? If you battery checks ok then it is either the wires going to from the battey to the alternator (including the starter relay) or the alternator voltage regulator is having problems. There has been discussed on this forum that the stock alternator in X's is weak at best and if you have weakened your battery then that could cause your alternator to start having problems. And remember just because you have changed out the alternator does not rule it out. Hope this helps.

 

[natedogco2007]

thanks man. i haven't tried to discharge the battery with the lights. i did run it a lil down when the alternator went out but before i put the new one on i charged up the battery. about now i am thinking of just running off the battery. lol j/k when the alternator starts acting up it just doesn't feel right in some way. no that it loses power or anything or surges, just feels wierd in the car. i think that it's just a mind over matter thing. watching that gauge moving like that drives me crazy. thanks again. nate