How to adjust alternator belt tension 1996 Jaguar 4.0 L

Sounds like the alternator may be failing.
The battery light on means the alternator is not charging the battery enough to turn the light off.

Basically first check battery voltage under load with headlights, fan etc on and give about 2500 rpm and check battery voltage with digital meter and expect to see about 12 volt range if Alternator faulty. If ok would be 14 volts approx.
Assuming battery voltage low. First remove negative battery terminal and proceed to take of drive belt by taking strain of belt by slackening tensioner on belt then remove and check belt for cracks etc on inside once removed. if damaged replace. Proceed and remove cowls, bolts etc as required to remove alternator. Before removing disconnect wires on Alternator. Assemble in reverse to above. Just a basic outline of how to do it.

Check the idle rpm (efi around 900 rpm ) carby around 750-800rpm. Very few alternators charge under 750 rpm as it requires 14 volts to charge the battery and at low revs the alternator will be producing around 11.5-12 volts. Check tension and condition of drive belt.

Take to an auto store and have them check the alternator, usually free, but sounds like alternator is on it last legs,

Check belt tensioner adjustment. Spray WD 40 on belts and pulleys and start. If no fix .it is most likely the rear bearings on the alt. before you buy a new one shoot some WD in the rear of the alt through the slits to the shaft. No fix take it to your local chain parts store and they will check it for free.

Mike

Sounds like you have an alternator belt that is slipping. Check belt for glazing and cracks. If either is evident, replace the belt

How to Replace an Alternator (DIY Time: 2.5 hours)
Complexity: Moderate

Parts:
1. Alternator - $151.95

Tools:
1. Combination Wrench Set
2. Screwdriver
3. Multimeter
4. Serpentine Belt Tool
5. 3/8 in. Drive Ratchet
6. Socket Set

Steps:
Step 1 Open the hood and locate your vehicle’s alternator.
o Tip: Safety Tip:Always wear safety glasses when working on your vehicle. Wear other personal protective equipment (PPE) when necessary, for example latex gloves or safety shoes.
o Tip: Always make sure the struts on the hood can fully support the weight of the hood so that it does not close on you while working. The use of a hood prop can securely hold it in place.

Step 2 Using your digital multi-meter, check the battery voltage. A dead battery will usually have less than 9 volts. This would not be enough power to start most vehicles.

Step 3 To verify that your alternator is bad, make sure your battery is fully charged and can pass a load test.

Step 4 With the good battery installed, connect your digital multi-meter across the battery terminals with the engine turned off. A good battery should read between 12-13 volts.

Step 5 Start your engine and read the digital multi-meter’s output. The voltage should rise near 13.5-14.5 volts.

Step 6 Using an open end wrench, disconnect the battery’s negative cable.
o Tip: When disconnecting battery cables, be sure to always disconnect the negative cable first and do not allow it to come in contact with the negative terminal post while working on the vehicle.
o Tip: Wrap the battery cable with a shop towel and pull it away from the battery terminal.

Step 7 Disconnect the power and ground wires on the back of the alternator paying close attention to where each wire connects. Disconnect the wiring harness connector.
o Tip: Check for a loose wiring harness connector, cracked wire insulation, and corroded terminals. Replacing the wiring harness may be necessary.

Step 8 Loosen the alternator bracket bolts, and alternator adjusting bolts or alternator belt tensioner so that you can remove the alternator drive belt.

Step 9 Using the proper size socket and ratchet, remove the alternator mounting bolts, spacer (if equipped), adjusting bolt, lower pivot bolt (if equipped), and the alternator.

Step 10 Install new alternator.

Step 11 Using the proper size socket and ratchet, loosely install the alternator mounting bolts, spacer (if equipped), adjusting bolt and lower pivot bolt (if equipped).

Step 12 Install the alternator belt.
o Tip: When installing the alternator belt, make sure the alternator belt is fully seated in the groove of the pulleys.

Step 13 Pull the alternator until the alternator belt is tight.

Step 14 Tighten the alternator mounting bolts while gently moving the alternator unit to achieve proper alternator belt tension.

Step 15 Reinstall the power and ground wires to alternator. Install the wiring harness connector.

Step 16 Push down in the middle of the alternator belt to check belt tension. If the alternator belt moves more than a half an inch, it is too loose, adjust the alternator belt to proper tension before proceeding to next step.

Step 17 Now that the alternator belt has been installed and adjusted, reconnect the negative battery cable. Start the engine and check the battery voltage to verify proper alternator charging.

Step 18 Turn off the engine and recheck the alternator belt tension. Readjust the alternator belt tension if needed.


Good luck (remember comment and rated this).

First thing to do is check the belts for proper tension. Then check the charging system completely. This includes under a load and when warmed up. It sounds as if you have a worn belt and/or a charging system problem.

if you have a multi meter,
check voltage at battery with car running,should be at least 13-14 volts,
now turn on fan motor to high,flashers on,radio on, and check voltage at battery,regulator should have adjusted voltage to handle the load,should still be 13-14 volts,
now turn all that stuff off,and turn on headlights and recheck battery voltage,if below 13-14 volts replace regulator,if voltage is spiking higher than 14volts replace regulator.you do not need other belts.

Have your battery load tested to make sure it's OK...14volts is the high limit for charging...If reading dash gauge, it's better to use a volt meter directly connected to the battery to get more accurate readings. What is the voltage with headlights and heater turned on (should be no less than 13 volts) I suspect that your battery may be at the end of it's service life but accurate testing is necessary to verify this!!