Alternator going bad ?

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candymancan
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Alternator going bad ?

Post by candymancan »

Im suspecting its the alternator but basically. When the headligjts are on the dash lights. clock. overhead console all flicker.. If i tap on the gas ever so slightly the flickering goes away.. I suspect the alternator because it doesnt do this when the Jeep is off with the headlights on. Idle rpms are 700 according to my tach so im not sitting at low idle.

My ZJ did exactly this when the alternator was going bad. Its putting out voltage just fine but im suspecting its putting out some kind of ripple current in the system. Is there a way to check this ? What do you guys think ?

It wouldnt suprise me.. it is an advanced auto parts alternator.. I seem to go through those things like candy because they are junk. Its a 90a alternator
1998 Jeep Grand Cherokee 5.9L Limited 219k
1998 Jeep Grand Cherokee 4.0 I6 laredo 430k
1990 Jeep Grand Wagoneer 155k
1976 Jeep J10.. 85k(repaired)
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Stuka
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Re: Alternator going bad ?

Post by Stuka »

You can check for noisy power with a scope, but doubt you have one. As the vast majority of people don't.

If the headlights are off, everything is ok? Even if you say, turn on the wipers, radio, heater fan, etc? Because what you are describing could also be a ground issue with the headlights.
2017 JKU Rubicon
Pevious Jeeps: 1981 J10, 1975 Cherokee, 2008 JK, 2005 KJ, 1989 XJ

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candymancan
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Re: Alternator going bad ?

Post by candymancan »

When the headlights are off and i just turn on the side markers the interior dash and console lights flicker still.

Another thing i noticed is they will flicker to the radio as well.. Like everytime a song plays and i turn up the volume itll flicker to the beat of the song .. its weird

Ive already replaced or cleaned all the grounds. The ground by the grill undwr the overflow bottle i cleaned up. Has a new ground i added from the battery directly to the block mount and i also cleaned the oeiginal block to mount ground as well. has a new ground from the battery to fender as well.

Also have a huge brand new battery too. Got the biggest i could fit. Its got 850cca and 140min reserve capacity. I forgot the type off hand but its big. Would autozone or advanced be able to check for ripple in the alternator output with their little tester ?
1998 Jeep Grand Cherokee 5.9L Limited 219k
1998 Jeep Grand Cherokee 4.0 I6 laredo 430k
1990 Jeep Grand Wagoneer 155k
1976 Jeep J10.. 85k(repaired)

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candymancan
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Re: Alternator going bad ?

Post by candymancan »

well i bought a better multimeter to measure a.c voltage. The alternator is putting out only 0.03v for ac. So there is no ripple in the current. So the alternator must be good.. I wonder what is causing this then..

all the ground are new or replaced.. I wonder if its the dimmer switch.. Ima take it apart and clean it ect
1998 Jeep Grand Cherokee 5.9L Limited 219k
1998 Jeep Grand Cherokee 4.0 I6 laredo 430k
1990 Jeep Grand Wagoneer 155k
1976 Jeep J10.. 85k(repaired)
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Stuka
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Re: Alternator going bad ?

Post by Stuka »

As a curiosity, what happens if you brighten and dim the dash lights? I just recalled I had a switch go bad (although it was the older style switch) where the inside lights flickered. Turning it back and forth would change the flicker.
2017 JKU Rubicon
Pevious Jeeps: 1981 J10, 1975 Cherokee, 2008 JK, 2005 KJ, 1989 XJ

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candymancan
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Re: Alternator going bad ?

Post by candymancan »

If i flip the switch up and down it will go dimmer and brighter but the flickering gets worse as i do it. Like i can move it up slightly ir down slightly and itll flicker much worse and sometimes i can get to a sweet spot where the flicker kinda stops almost. Does this make sense ?

My headlight switch in the past has stopped working a few times as well.. Lile if its been on for awhile if i flip it off and come back 10 min later and turn it back on the lights wont come on unless i wiggle the switch a little by pushing it in more. I have a spare headlight switch ill swap em.. And the dimmer switch ill take apart and clean up the copper contacts and slides inside and add new dielectric grease to it.

Its just very strange.. I hate the electrical system on this Jeep.. You turn on every accesory and the dash will drop below 13v at idle yet the battery reads 14v still.. If i drive though at say 40mph itll be abive 13v.. I hate that about this damn Jeep

And as i said the grounds are all new. I even added a ground to the headlight ground below the overflow bottle i forgot to mention that. I ran a 12 or 10ga wire i cant remember from the headlight ground accross the radiator in the front tucked under the trim by the radiator and directly to the battery... New fender ground.. large 4ga ground from the battery to the engine mount frame side.. and new engine to engine mount ground.. Also have new positive cables too.. Nee battery as well..

Grr

I guess i should note the intrument cluster and overhead console lights i put in LED bulbs... But this doesnt explain why the clock and temperature display flickers as well. Maybe it is the dimmer switch
1998 Jeep Grand Cherokee 5.9L Limited 219k
1998 Jeep Grand Cherokee 4.0 I6 laredo 430k
1990 Jeep Grand Wagoneer 155k
1976 Jeep J10.. 85k(repaired)
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tgreese
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Re: Alternator going bad ?

Post by tgreese »

Are you using the same voltmeter for the battery and the "running" measurement? A dash-mounted voltmeter is way out on the end of the power delivery path. And the more load there is, the more voltage drop you will see from the resistance between the battery and the dash. V=IR.

If you worry about the alternator, there are two main electrical things that can go wrong. First the regulator in the alternator can break and no longer properly respond to the load. The higher the load, the more current the regulator sends to the alternator field and the higher the output. The regulator adjusts the current output by keeping the voltage constant. Note that Jeep picks up the voltage signal right at the alternator, and that is the large gauge wire directly to the battery. So the regulator is measuring the battery voltage, not the voltage at the dash.

Second common thing to go wrong is diode failure. The alternator is 3-phase, and one or even one-half of one of the phases can fail and reduce output. You'll only see this on a scope, or by measuring diode continuity, or maybe by guessing from the symptoms. I don't think this is relevant to you though. And modern diodes are reliable compared to those made in the 60s - the Motorola alternators had diode failure a lot.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.

Topic author
candymancan
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Re: Alternator going bad ?

Post by candymancan »

autozone tested it dioods were fine.

Yea the dash and if i measure with a dmm the wiring reports below 13v at idle with everything on this is when the blower motor slows down and the headlights will dim . but at the battery its 14.20v If i tap the gas lightly to raise engine rpms to say 800 or 1k then the headlights brighten up and blower blows faster and the dash gauge will go above 13v. But i dont like 1k rpm idle in gear if i were to adjist it to that, because in park itll make idle like 1500..

are there smaller pullys i could swap out on the alternator ? im using the duel belt pully that was on my older alternator i had to use an impact to knock it off and swap it as this one didnt come with a pully.. Im thinking a smaller pully will spin the alternator faster like me tapping the gas to raise engine rpms but eithout me having to raise the engine rpms.. because as you know alternators spin 2-3 times more then engines do give or take based on their pully

Is there no way to fix this ? Or is this jist common older BEEPY electrical systems.. My 5.9 doesnt do this at all.. the battery will read say 13.7v and im getting 13.7v in the vehicle or veey close to it.
1998 Jeep Grand Cherokee 5.9L Limited 219k
1998 Jeep Grand Cherokee 4.0 I6 laredo 430k
1990 Jeep Grand Wagoneer 155k
1976 Jeep J10.. 85k(repaired)
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Stuka
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Re: Alternator going bad ?

Post by Stuka »

The headlights being dimmer at idle is 100% normal and nothing to worry about.

If your voltage drops that much inside the cab, you may have a high resistance wire someplace. Which is not uncommon if its the original wiring.

Does the flickering go away if you are at 1000rpm?
2017 JKU Rubicon
Pevious Jeeps: 1981 J10, 1975 Cherokee, 2008 JK, 2005 KJ, 1989 XJ

Topic author
candymancan
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Re: Alternator going bad ?

Post by candymancan »

It goes away the moment i tap the gas just a tiny itty little bit.

Ill make a video gimme a bit for it to get dark out
1998 Jeep Grand Cherokee 5.9L Limited 219k
1998 Jeep Grand Cherokee 4.0 I6 laredo 430k
1990 Jeep Grand Wagoneer 155k
1976 Jeep J10.. 85k(repaired)
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tgreese
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Re: Alternator going bad ?

Post by tgreese »

It may be that the alternator is doing all it can to carry the load at idle. The output depends on both the field current and the engine speed. At higher speed, it takes less field current (less voltage across the field) to provide the requested output. Could be that the field is at full voltage and the load is regulating the battery voltage at idle.

Not familiar with the 1990 dash cluster, but I expect the voltmeter voltage comes from the cluster. Trace the cluster supply back to the where the battery voltage and supply wire are the same, then look for a bad connection between that point and the voltmeter.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.

letank
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Re: Alternator going bad ?

Post by letank »

a good time to clean all contacts points at the alternator, particularly the alt plug, make sure that it is tight and dirt/oxydation free
Michel
74 wag (349 Kmiles... parked, next step is a rust free body)
85 Gwag (229 Kmiles... the running test lab)

Topic author
candymancan
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Re: Alternator going bad ?

Post by candymancan »

alternator is fairly new and battery is new been doing this with a tiny 500cca battery and a 60 or 6x alternator i forgot exactly what size the old one was that orevious owner had on so its deff not connections.. but ill clean em up anyway.. its worth a try lol

What you said about the alternator struggling to put out amperage.voltage at idle is what i was saying.. i was wondering maybe there is a smaller pully (smaller mesns more output) ima look to see if there isa different pully i can get. The one thays on this 90a alternator is thr one i took off the 6x alternator since this 90 had no pully on it.

Also i ordered two new belts. ai looked at the belts i got on this thing.. they are for the non 85+ alternator. I do remember one didnt fit right. I doubt this will help as both belts are tight.. but hey its only 10$ and takes a few min to put on.

Starting to wonder if all this is normal.. Stuka mentioned the dimming headlights are normal at idle which leads me to believe well thats just the way these Jeeps are.. I put a bigger alternator on much bigger battery and nothing has changed.

If only we ould have one of these Jeeps brand new to test on lol.
1998 Jeep Grand Cherokee 5.9L Limited 219k
1998 Jeep Grand Cherokee 4.0 I6 laredo 430k
1990 Jeep Grand Wagoneer 155k
1976 Jeep J10.. 85k(repaired)

letank
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Re: Alternator going bad ?

Post by letank »

candymancan wrote: Starting to wonder if all this is normal.. Stuka mentioned the dimming headlights are normal at idle which leads me to believe well thats just the way these Jeeps are.. I put a bigger alternator on much bigger battery and nothing has changed.
I have a 70A alt, when the 80A failed the local store in Mojave did not have an 80A. So for the last 3 or 4 years, this is what I have, an no dimming at idle with headlights on, OK, my idle might be a tad higher than most, running manifold vacuum makes the idle a tad higher than 700rpm, may be 850ish...
After the last smog check 10 days ago, I did not bump the timing to 15deg, so my idle is lower, but the voltage is still above 14volts at idle.

in fact a larger alternator is going to put more drag on the engine, larger output, larger resistance, bigger drag
Michel
74 wag (349 Kmiles... parked, next step is a rust free body)
85 Gwag (229 Kmiles... the running test lab)
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tgreese
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Re: Alternator going bad ?

Post by tgreese »

Realize that, like flashlight batteries with a nominal voltage of 1.5V, a lead-acid car battery has a nominal voltage of 12.6V. Ideally a fully charged battery should read 12.6V with nothing attached to it. That's the electrochemical potential of lead and sulfuric acid - determined by the chemistry of the battery. So when your Jeep is running and you see 13V or 14V at the battery, that is above nominal voltage and the battery will be charging if there is any chemical capacity to be replaced. See here - http://www.siranah.de/html/sail080e.htm

The regulator limits the maximum charging voltage to about 14V, because the battery will charge faster at that voltage than at 12.6V. Much higher and the internal resistance of the battery makes too much heat, so 14V is about the limit. The alternator at idle has to overcome any load and provide enough voltage so that the battery isn't drained. The charging wire from tha alternator is connected directly to the battery on a '90, so the battery gets the least voltage drop of any possible current sink. The rest of the car is out beyond that, so the voltage should drop as you get further away (electrically) from the alternator. V=IR.

A larger alternator is going to put more mechanical load on the engine ... but it should only offer more mechanical load in proportion to the electrical load. In the case of Letank's alternator above, the higher voltage at idle represents a larger load, but that's being imposed by the regulator, not the battery. If the battery is above the 12.6V nominal level, it's fully charged and is simply passing along that higher voltage to the rest of the Jeep.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.
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