GreenXJ95

I had my altenator check by a local parts store and it came back good, the volts were right on. Battery is good the volts on that is right on. Every morning i wake up and start my jeep the battery gauge reads 14 or just below. As i drive and things start to warm up it drops in between 14 and the red. Now if i run my heat low setting does not draw much but on high i can see the tach move down. With all electric off while driving ill turn my fogs on which draws the tach to redline on the battery gauge. I cannot run my electric fan,fogs,and heat at the same time. Whats my problem??? i tried a brand new battery but still had the same effect. All help needed

5-90

Especially prior to 1996 (OBD-II,) the IP voltmeter is a notorious liar. It's even worse with RENIX (1987-1990) and earlier.

Any suspect IP Voltmeter readings should be verified indpendently with a DMM, before you take any other action.

I've had five RENIX XJ's to date, and four of the voltmeters were way off. After figuring out where the needle was in which states (the battery resting voltage was, say, 12.8VDC - but the IP voltmeter told me it was ~14VDC. It got worse from there...) I just drew new marks on the windows with a grease pencil, and used it for a relative state-of-charge indicator.

So, start with taking your voltage readings underhood with a DMM. Compare your readings by moving the positive probe between the battery + terminal, the alternator output terminal, and the PDC input studs (they should all be within 0.2-0.5VDC of each other, with the alternator output post on the back of the case being highest.)

troy fritz

Try tightening your belt. Mine was doing the same thing for a long time and a buddy told me to tighten the belt a month ago and its been fine since.

fantic238

True true..

5-90

For possible low output? True.

For possible high output? Not so much...

troy fritz

He said it drops not goes up.

5-90

Oh. Probably read it backwards, then.

The rest of the advice still stands. I've even noted wandering voltage readings at the IP with the DMM being rock steady, so I shall continue to say, "Any and all suspect readings at the IP must be verified with a 'known good' multimeter before proceeding with troubleshooting and diagnosis."

GreenXJ95

Yea its a 95 cherk but its wierd every morning its fine right up by 14 then drops as the day goes on but will not go into the red. my belt is tight i dont want to over tighten it. I would like to run my electric fan my massive fogs and well not soo much now but the heat at the same time without having to worry about the battery or the altenator taking a sloppy poop on my in the woods late at night

5-90

A serpentine belt needs more tension to function than you probably think...

"Quick and dirty" - Grip the longest free span of belt between your fingers, and try to spin it. You should just be able to get a quarter-turn out of it - if it's easy, it's not tight enough. If you can't make a quarter-turn, it's too tight (or you're too weak...)

"Proper" - go to NAPA and order a Cricket II Serpentine Belt Tension Gage. Follow instructions for use.

GreenXJ95

so you are saying my altenator could "possibly not turning"?

5-90

I'm saying there may not be enough tension on your drive belt. If that's true, there's going to be more than your alternator "not turning" when the belt slips, y'know?

fantic238

I knew the same trick by measuring the deflection that should be less than one inch between the idler pulley and the PS pump.

GreenXJ95

if my belt was loose wouldnt it make a noise?

Colinjohns

alternators require alot more to turn when under load..so when you pull it off the shelf you can turn it with your fingers but when it is under load (in use) in your car it is alot harder. And your belt wont necessarily squeal at first but maybe over time. Tighten it up and then put some conditioner on it...it is actually recommended to put some on every oil change. Good Luck!

Jerry Solomonson

My 2000 Cherokee was worked on at dealer. Spark plugs , fuel injector service . Now my voltage gauge sometimes works or doesnt work or registers very low. Any suggestions?