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89 XJ voltage fluctuation ?

Kristjan

NAXJA Forum User
Location
Iceland !
Hope i'm welcome from Iceland...
I'we got this problem with my Jeep now. It starts up fine, and runs very good, But while running the volt meter starts to fluctuate from 14V-11/12V and while at it the dimmer starts to fade, but everything else works flawlessly. This fluctuation is sometimes for only 1 sec, but other times it stays at 12V for some period of time, My lights are Wagon Halogen and they are not working now, probably just ruined. Could that have something to do with the voltage fluctuations ?

Noticed my ground strap from Cyl head to Firewall was missing completely so today I did put together a new cable today and put it in. I did put it under the headstud nearest to the firewall, driver side. also did put the other 3/8" end under it's bolt. Still no improvement. Also my car seem's to idle way to fast in park sometimes. It doesn't matter if it's hot or cold, It just idles above 2000 rpm's for no reason, The idle slows down a bit when in gear.

best regards from Iceland.
Kristjan.
 
The last time it was the alternator, but now i got this problem again. The volt meter would carge little above 14V in normal driving but hitting WOT it would just go down to 9V but after letting it idle for a few moments it would go back to normal, sometimes it would go to 16V ! or so. Also i noticed that if I held down the power window switch UP (window already up) it would send the volt meter down. As soon as i released the button it would go to normal charge of 14V

This morning it's completely dead !
 
Assuming the alternator is good, the first thing I'd suspect here is belt tension. Don't count on it to squeal. It will sometimes slip silently.

However, you should also remember that the in dash voltmeter is not at all accurate, so when troubleshooting it's a good idea to check voltage at the battery terminals.
 
I gave it start today and took it for a spin, The headlights and dash lights fade when the voltage drop (WOT) or over 2500-3000 Rpm.
When i got home i parked it and it wouldn't start, did just click the relay.
My thoughts were also about loose belt, Will check that.

Best regards.
 
Kristjan--why don't you share with the rest of the class what you did about the alternator from 3 weeks ago?
 
1) If he's got a voltmeter, he doesn't have an alternator light. RENIX has one or the other - not both.

2) Check your grounds as well. In this case, pay particular attention to the cleanliness of the termination of the primary engine block ground - it's back near the dipstick tube, and retained using the same stud (if the stud backs out on you and won't go back in, get a 3/8"-16x3/4" screw and a few 3/8" flat washers, and put it back in that way. Problem solved.) If this ground is dirty, it will screw with your voltage output directly.

3) Also, check the ground from the cylinder head to the firewall - it will probably want replacing (use min. 8AWG wire for termination, you can re-route it to the rearmost mounting screw for the fuel rail for better access, if you want. That screw will accept a 5/16" ring, and the screw on the firewall is an M8 - which will also accept a 5/16" ring. Or just use 3/8" rings on either end.) If this ground is dirty, it can screw with your gage readings - it's the primary ground for the chassis (which also provides the ECU ground, so it can be causing other latent problems that will go away if/when you renew this ground.)

That's what I'd do first. RENIX uses the Delco CS-130 alternator, which is a pretty damned hearty unit and can go through an awful lot (I've seen some of them seriously abused while I was working as an industrial mechanic, and I've seen plenty of them used in marine environments as well.) Checking and cleaning the grounds is the least expensive to do, and even if it doesn't fix your alternator problem it will probably fix other problems you didn't know you were going to have yet...

As far as the alternator directly, there is also a drilled/tapped boss on the back of the CS-130 case. Use an M8-1.25x20m/m screw, and attach a ground cable (min 10AWG) between the alternator case and the battery negative post if you like - make it around twenty-four inches long, maybe a bit longer. I've offered one for helping steady the readings on very-high-output units, since the primary engine ground is so far from the alternator. It can help.

Even if you had to replace the alternator (which I won't eliminate as a possibility,) cleaning the grounds won't go amiss.
 
Thanks 5-90 !
I have recently replaced the main ground from firewall to cylinder head. it was missing completely when i got the Jeep.

Will go through these grounds on my Jeep again.

The last time the Alternator's rotor was toasted, I got one that was working from a friend. Maybe it's the fault this time also ?
But it's draining the system since it won't start after little drive.
Would that be symptom for bad alternator ?

Best regards.
 
Thanks 5-90 !
I have recently replaced the main ground from firewall to cylinder head. it was missing completely when i got the Jeep.

Will go through these grounds on my Jeep again.

The last time the Alternator's rotor was toasted, I got one that was working from a friend. Maybe it's the fault this time also ?
But it's draining the system since it won't start after little drive.
Would that be symptom for bad alternator ?

Best regards.

Could be shorted diodes.

A "diode," as you may or may not know, is a one-way valve for the flow of electric current (up to a certain point, of course. If you exceed the PIV - Peak Inverse Voltage - spec of a diode, it's either going to "short through" (and conduct in both directions) or "blow out" (and not conduct at all.))

Diodes can also be arranged in various configurations to achieve different results - in this case, a network of diodes is used to convert the AC voltage generated by the alternator to the DC voltage used by the rest of the vehicle.

The diodes can begin to "short through," - which can cause some "ripple" in the DC output voltage (remnants of the AC voltage passing unrectified,) but also allowing a reverse current flow when the vehicle is turned off. Therefore, your battery would be discharging through the alternator armature - causing the drain, causing the flat battery in the morning.

As I said before, don't rule your alternator out for this malfunction. But check the grounds as well anyhow - you'd be amazed at how often an automotive electrical problem can be traced back to shonky grounds...
 
Could my problems be related to dead/bad battery. I'we took it out of my Jeep and connected it to the battery charger and left it over night. When I got down this morning the charger was just clicking and the battery reads aprox 9V. dead.
The Optima red top battery in our dragster reads 12V. all the time when dead.

Best regards.
 
It's pretty clear that the battery is stuffed, and that's probably the first thing to address. A bad battery, especially if it has internal shorts, can do all sorts of things. But just in case, you should keep an eye on things for a while after you replace it, to make sure it wasn't a bad alternator that killed the battery in the first place.
 
Got it running today with the same old battery and alternator, and there's still fluctuation, especially when at WOT. But if i drove carefully it would stay at approx 15V. !
And when i turned it off it would start right up ! so i measured the voltage at the battery posts and it read 12.6V.

So this is confusing me a bit.

Best regards.
 
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