dillonforbes

My zj lately has been having power issues. It isnt receving the proper 14 volts, when i start the car it turns over revs high then falls then goes almost to a stop wher i think it could die, stays very low idol. So far to try and fix the problem i bought a new battery and new altinator the probem is still here.No matter how high i rev the motor it wont go over 13.3 volts, it sounds like im being picky but it really dosent run right. What do i do?!

Thanks,
dillon

5-90

1) Verify any suspect readings at the IP using a "known good" multimeter before proceeding with troubleshooting! Sounds like you do have a problem, but there's no harm in confirming its presence or severity...

Meanwhile, here's a little writeup I've done for troubleshooting your primary electrical system (battery, starter motor, alternator,) that won't damage anything that is still good:

----- SNIP -----

ALTERNATOR/STARTER/BATTERY TEST

You'll need:
- A multimeter
- A notepad
- A pen
- A helper (very useful, but not necessary. You'll need longer DMM leads if you don't have a helper)
- A hydrometer (if your battery has removable caps)
- Some distilled or R/O filtered water (ditto.)

NOTES:
- If you are doing this because of suspect voltage readings at your Instrument Panel (IP,) VERIFY WITH DMM. The IP voltmeter is a notorious liar, particularly on earlier (1990-back) models!
- If the battery itself is suspect, check the electrolyte level (topping off with distilled/RO water PRN.) Put on a slow charge overnight (<5A charge rate.) Do this BEFORE YOU DO ANY OTHER TESTS
- If the alternator is suspect, charge your battery for at least TWO FULL HOURS at a medium charge rate (2-15A) before doing any other tests. Also, check the electrolyte level as above (if the alternator is undercharging, the battery will simply be discharged. If the alternator is overcharging, it's possible that water has boiled off in the battery, and the electrolyte will be low.)
- If the starter motor is suspect, check: the mounting screws (it grounds through them,) the stud nuts for the electrical contacts (loose connections increase resistance,) and that where the starter motor contacts the engine/trasnmission assembly is clean (screws with the ground.) Also, charge the battery - min. 1 hour at min. 10A.

(Yep - all of thes involve topping off the battery charge. And for good reason. If the battery is partially discharged, it WILL fail test!)

Now that you've got the basic checks out of the way:

1) If the battery caps are removable, pop them off (WATCH YOUR EYES! I'll usually put whatever I'm prying with in the notch under the cap, put my hand flat over the cap, and then turn away while I'm prying the cap off - and I wear spectacles! You can't be TOO careful with your eyes...)

2) Look into the holes - use a flashlight if you have to. The electrolyte level, ideally, will be even with the bottom of the hole. However, it MUST cover the plates entirely! Top off with distilled/RO water PRN.

2a) If you had to top off, put the caps back on and rock the vehicle at the bumper - you're trying to mix the water in so you don't get a "false discharge" reading.

3) Remove the caps again (see (1), above,) and get out your hydrometer. Draw a sample up into the tube, read the float, and note the reading. Squeeze the bulb and put the sample back in the cell. Repeat for the other five.

4) There are two things that should be checked with the hydrometer (Specific Gravity, or "s.g." readings. This measures the concentration of the acid in the cell, and therefore the state-of-charge of the cell.)
- If you have any values that are "obviously out of line," stop. You've got a cell going out on you. If not, take an average of all six values and then compare the individual values to the average. Individual values should not vary by more than +/- 0.025 from the average.
- Absolute readings - any cell that is OVER 1.225 s.g. is sufficiently charged. Anything 1.224 s.g. AND LOWER is not. Observe the following values (should be corrected for temperature to 72*F, but not all hydrometers do that. The variation is nominal

5) If the battery is fully charged, or after you have charged it, note the "resting voltage" (battery installed, engine OFF, key OFF, doing nothing.) Use a DMM at the battery terminals.

6) Verify that battery voltage exists at the large terminal on your starter motor (should not be more than 0.5VDC below battery voltage at the terminals) and at the large cable on the back of your alternator (likewise.) The primary distribution point may also be tested, but variation there will be less due to lead length (figure it should not be more than 0.25VDC below.) Examine, clean, and/or service any conductor showing excessive loss. If you don't get ANY voltage reading at any of those three points, FIND OUT WHY.

7) Disable your ignition.

8) Have a helper crank the starter motor while you monitor battery voltage. It will drop sharply then recover - it should recover to something above 9.60VDC (more is better.) DO NOT HOLD THE KEY IN THE START POSITION FOR MORE THAN FIFTEEN SECONDS, and ALLOW AT LEAST TEN MINUTES BETWEEN REPEATS IF YOU DECIDE TO REPEAT THIS TEST (don't do it too much tho - or you'll drain your battery.) Note the voltage you read for later.

9) Reconect your ignition. Recheck and note your resting voltage after one full minute - it will probably be lower.

10) Start your engine. Check voltage at the battery terminals. It should be higher than the resting voltage - if it is not, check for output at the back of the alternator. If you have higher voltage at the alternator output post, you have a failure in the conductor in between (they're fused from the factory - check the fuse link or fuses in the distribution box.) If you do not, you may have a failed alternator or a failed regulator.

11) Have your helper run the engine up to 1200-1300rpm and hold it there. Voltage should increase a bit more, especially if it was a bit low.

12) While at 1200-1300rpm at the crankshaft, begin turning on electrical accessories while monitoring system voltage. You should see a slight drop with each new accessory, but the alternator should recover. Unless you've gotten silly with add-ons, and you don't turn your winch on (which will ALWAYS have a draw in excess of your alternator's rated output!) you should see the system voltage stay above the battery resting voltage.

13) Turn all of your accessories off, and let your engine idle for 10-15 minutes. This will do two things - 1) it will charge your battery up from any remaining discharge from starting (typicaly starter motor draw runs 130-250A; depending on displacement, compression, and engine condition.) 2) It will heat up your alternator and regulator circuit.

14) With the alternator warmed up, repeat the tests and make sure you don't lose voltage above what you got "cold" (many automotive electrical/electronic failures are heat-related...) Losing a little with heat is normal - but all values should still be above the values in the chart below.

15) Shut down. Check battery voltage - should stay above the "full charge" value.

16) Check battery voltage again in one hour - it should still be about the value given in (15). If it is not, the battery is self-discharging (because a cell isn't dead yet - you'd have caught that earlier, but it's going...) and you should keep an eye on it.

VOLTAGE READINGS:

12.60VDC Battery, Fully Charged (min.)
09.60VDC Battery, Cranking Starter Motor (min.)
13.20VDC Battery, Engine RUNNING, Alternator CHARGING (min.)
15.00VDC Battery, Engine RUNNING, Alternator CHARGING (max.)

HYDROMETER READINGS:

-- 1.265 FULL CHARGE
-- 1.225 75% Charge
-- 1.190 50% Charge
-- 1.155 25% Charge
-- 1.120 DISCHARGED (1.120 is a max value - may be rather lower. Compare to computed average to determine if you have a dead cell or not.)

A battery should not be load-tested if the s.g. of the electrolyte is below 1.225 - charge first.

trucker

To my understanding the alt should "put out" 13.5 under normal operation with max to 14V. If more that 14V then voltage regulator is not working properly.

5-90

14VDC is the "normal max" - but I've run across some that were adjusted higher, and sometimes you can have all accessories off and the voltage will crawl up.

14.4VDC is the most you should see, but if you see a steady 15.0VDC with everything off but the engine, it's not a huge issue. It's also highly unlikely, but it should be mentioned.

TrollHammer

I'm having a high voltage issue. I still need to check with a DMM to see if it's correct, but it's gradually crept higher and higher over the last year, is also highest after a cold start and drops slightly after the car is warmed up. If I check with a DMM and find it is actually high, what is the culprit? the regulator? If so, is the regulator intergal to the alternator or is it seperately replacable?

5-90

My bet would be regulator, but don't neglect a potential wiring fault (which can cause all sorts of trouble!) Start with the grounds.

Where is the regulator? 1984-1990 used a Delco internally-regulated alternator. 1991-2001 used a Nippondenso externally-regulated alternator, and the regulator circuit was in the PCM.

TrollHammer

So the alternator is the same for a like year ZJ and XJ? With as much trouble as Ive had with my XJ alternators and the comment above that ZJs have rare high voltage issues I thought they were different.

greengoblin

my 97xj batt with everything off is 12.99. at an idol its 14.38 when i turn on lights,heater on high,radio one it drops to 14.29. does this sound correct to you or should i be looking for a bad ground. or to buy a pcm

5-90

Essentially the same. They may have a higher output rating, and some of the very latest WKs used Bosch instead of Nippondenso, but the theory is the same.

TrollHammer

Sounds pretty close to good to me. A standard healthy lead/acid battery, fully charged with no load sits just above 13 volts (like 13.3 or so) It's considered a 12 volt battery as it has 6 2volt cells, but without a load it rides a shade higher.

The charging system (alternator) puts out a volt or so higher so that current will flow into the battery, so modern charging systems will usually sit between 14v and 14.4 in my experience. Of course, turning anything on will drop the voltage as current is used. As long as the voltage isn't hitting like 15v or more I think you should be ok. (I had a regulator that was trying to hit 20V once, but the alternator wasn't working, so it didn't end up hurting anything) I'm sure there's mechanics on here that know exactly what voltages are proper, but I'd not be too concerned with a 14V reading, personally. I have to look at my wife's jeep, the dash gage is showing liek 15-16v...

As to what your numbers are telling me, they sound just fine. Expect slight drops in voltage as you turn on higher power items (headlights especially). It doesnt' sound like a bad ground to me, I'd expect to see much larger drops if there was a bad connection somewhere. Of course, this is all assuming you're using a meter to check and not the dash guage.

Thanks for the info! Perhaps I'll look into putting a Grand Cherokee alternator into my off road XJ next time I have to replace it!

greengoblin

[QUOTE=TrollHammer;820813]Sounds pretty close to good to me. A standard healthy lead/acid battery, fully charged with no load sits just above 13 volts (like 13.3 or so) It's considered a 12 volt battery as it has 6 2volt cells, but without a load it rides a shade higher.

The charging system (alternator) puts out a volt or so higher so that current will flow into the battery, so modern charging systems will usually sit between 14v and 14.4 in my experience. Of course, turning anything on will drop the voltage as current is used. As long as the voltage isn't hitting like 15v or more I think you should be ok. (I had a regulator that was trying to hit 20V once, but the alternator wasn't working, so it didn't end up hurting anything) I'm sure there's mechanics on here that know exactly what voltages are proper, but I'd not be too concerned with a 14V reading, personally. I have to look at my wife's jeep, the dash gage is showing liek 15-16v...

As to what your numbers are telling me, they sound just fine. Expect slight drops in voltage as you turn on higher power items (headlights especially). It doesnt' sound like a bad ground to me, I'd expect to see much larger drops if there was a bad connection somewhere. Of course, this is all assuming you're using a meter to check and not the dash guage.



Thanks for the info! Perhaps I'll look into putting a Grand Cherokee alternator into my off road XJ next time I have to replace it![/QUOTE





yes i am checking it with a multimeter

DaJudgw

Just where is the PCM located in a 91 Cherokee?

DaJudgw

Good response. Could a bosch alternator be used to replace the nippondenso on a 91 cherokee with the 4.0 ltr engine?