View Full Version : alternator

08-03-2010, 11:18 AM
Hi ,of late my alternator seems to be playing up , one time its putting out 14.2 volts then next time its about 12.6 . when doing about 60kmh seems to charge ok , but as soon as i use the brakes etc it drops alarmingly ! , at idle its only about 12.7 so if u then use the air-con or heater and brakes it drops even lower ,the battery flatened a couple days ago but has been ok since ? ive changed batteries checked belt tension and all seem ok , anybody got any ideas ? , ta......

08-03-2010, 11:28 AM
Just tested at 2000rpm 13.9 v , but seems to take a little while to get there , maybe just worn out ?...............

08-03-2010, 04:27 PM
Is it possible that maybe it's not the alternator at all, but a short in the system somewhere placing a massive drain on the battery?

08-03-2010, 06:39 PM
Thanks for reply , yes i have thought about a voltage leak/loss , cant remember how to test out wiring voltage versus voltage across terminals , anybody able to jolt my memory ? , thanks......

08-03-2010, 07:08 PM
Just finished checking voltage loss , rear alt output to + battery post .2 volt , alt chassis to - bat post .02 volt , cant see much of a problem there ...

08-03-2010, 08:10 PM
Could check relays under water resovoir, check the search engine for functions of particular relays, could even be that alt o/p is ok from the inbuilt regulator but the alt up for a new set of brushes soon, perhaps give a blast of wd40 in the guts to to see if any improvement, could even try hydrometer on the replacement battery, cheers

08-03-2010, 08:45 PM
I've heard of alternators playing up when they are near the end. Check the relays as falconxh said, but you COULD also be up for a reco.

08-03-2010, 11:48 PM
Sounds like the alternators regulator more likely as the regulator senses voltage drain from the alternators field coils to the electrical system during current draw devices running like lights and other accessories.

During this scenario if things are working properly, the regulator then increases the "excite" voltage to the alternator's wound rotor via slip rings and carbon brushes which then produces more magnetic flux to the field coils and hence more amperage and at a lesser extent more voltage to the electrical system. An alternator always works harder and requires more effort to turn at the necessary speed under load conditions such as a flat battery and heavy load devices running like heater fans on full blast and demisters running together with all of your headlights and wipers running too of course in such a situation.

Hope I haven't confused anyone here with this but I did an automotive electricians apprenticeship when I was younger and did learn the basics of alternator servicing and reconditioning. Check the regulator assembly which is internal on the Mitsubishi alternators and integral with the diode pack as well.

May be worth your while to have it tested by an auto sparky and replaced with a reco unit as it will be just as expensive with either option you take of having it repaired or replaced.


09-03-2010, 09:26 AM
Thanks for all your suggestions , might pop down the wreckers today !

10-03-2010, 12:56 PM
Hi went looking for a replacement alt , the one i got happens to be a mitsi unit ,none availiable locally ! , been told that plug must be changed to use the bosch unit ( anybody know how ?), someone reckons that a latter unit from ef/el will fit and has same plug , hope its true !...

10-03-2010, 05:36 PM
Hi went looking for a replacement alt , the one i got happens to be a mitsi unit ,none availiable locally ! , been told that plug must be changed to use the bosch unit ( anybody know how ?), someone reckons that a latter unit from ef/el will fit and has same plug , hope its true !...

An auto electrician can change the Mitsubishi suited plug to the Bosch one. I'm not sure of the actual procedure involved with doing this but it would be best done by a specialist. The wires from the plug must also be correctly polarised with the existing vehicle alternator wiring and I think that the Bosch units are wired differently at the plug. The EF and EL alternators are also different too I assume, don't quote me on this however.


11-03-2010, 04:10 AM
Hi, don't quote me on this either but the eb and el alts seem different, being in size and the pulleys for fanbelt/serpentine belt, the plug socket and the mounts.
You could find the correct plug to fit for your mitsubishi alt on an old wreck somewhere around the place that has the appropriate plug to save opening up the alt to fit a plug; chop the other plug connecter off and plug it into your alt then splice it into the correct cloured, yellow red and black etc wires on your car's wiring loom.
Do you have good battery terminals? Good contacts on all the little bolts and wires hanging off the terminals and all contacts clean? Earth straps to motor and body tight and clean? No grease or crud on the pulleys or belt? Good contacts to, and on, relays and circuit breakers under the coolant resovoir tank, and, care to try some wd40 and emery to clean up the relay pins, contacts etc?

11-03-2010, 04:48 AM
Pull the alternator out and check the stator has no major wear where the brushes from the regulator touch. Also check that none of the windings are burnt out. If all looks good and there is no slop in the shaft rotation, just change over the regulator and problem should be solved.
Maybe even check that alternator electrical connector is free of dust and oil and that the main lead is making a good tight contact.
If it all gets too hard and the wiring leading to the alternator checks out fine ( refer to manual tests), replace alternator.
If you need further explanation, just PM me. Hope this helps.

11-03-2010, 11:25 AM
EBII/ED Falcons came with either Bosch or Mitsubishi alternators(early type). The EF/EL alternator wont fit as it has a different mounting system and pulley. If you have a Bosch already, you can pull it apart and replace both bearings (the rear is the most important (experiences the most wear due to its smaller size). Withdraw your Bosch 14V4 regulator and inspect the brushes. New 14V4 regulator (includes new brushes)cost about $30 from Bursons. Two new bearings will set you back about another $20. Inspect your slip rings for excessive wear (can be skimmed on a lathe) if you have excessive ridges worn into the copper.

With the rear bearing in the Bosch rear housing, it may resist coming out of the rear housing. The stator/diode pack should stay with the rear housing. Levering carefully between the front housing/outside of the laminated iron stator usually allows the rotor and rear bearing to come away. Make sure the regulator/brush assembly is out first. The rear bearing should come out with the rotor. I have manufactured a short length of galvanised pipe with 2 notchs 180 degrees opposed filed on one end. This then sits over the 2 wires from the slip rings (rotor assembly)and allows 2 large screwdrivers to lever the rear bearing from the shaft.

To replace the front bearing, pulley must be removed and rotor pressed from the front housing. Undo 3 screw holding bearing retainer and then remove old bearing.

As already mentioned, inspect your stator windings to ensure the varnish coating (insulation)hasn't started to break away from the copper wire.

If you don't want all the hassle of rebuilding your alternator, then the local auto electrician should do an exchange unit with everything already replaced/tested.

As a few people have already mentioned, make sure you don't have a bad wire/connection in the system before assuming it is the alternator. Best thing to do is get a multimeter and turn everything on (start engine, lights, high beam, aircon etc). Then check for voltage drops across wires. If a wire/connection is good, it should have a tiny voltage drop (<300mV) at max load. I had an NA Fairlane I fixed recently with 0.6V across the wire from the back of the alternator to the positive battery terminal. It turned out to be a bad pair of black fusible link wires from the battery. I replaced them and all was good. Also don't forget about the negative side of the system. Check between neg battery terminal and engine block, neg battery term and chassis etc. All checks must be done using a multimeter set to DC volts with eng running and all loads on.

Do not and I repeat do not use a multimeter on ohms to check these circuits. They break down under load (high current flow). A multimeter at best uses a 9V battery and a couple of milliamps to test resistance. Absolutely usless for this type of testing.

11-03-2010, 04:17 PM
Thanks for replies , thought it would be easy just to swap from wreckers , ford alt 35$ , mitsy , cant find one ! , electrition wants 35$ to change plug , thats o'k' , does he change the plug on alt or the wire going to it ? , ta........

11-03-2010, 11:51 PM
will change the vehicle wiring (plug) and not the alternator.

12-03-2010, 09:11 AM
Might be abit difficult doing this , driving home to fit new alt after leccy puts plug on cable , is it hard ? anybody got any diagrahms ? ta..........

13-03-2010, 04:24 AM
If you're replacing alternator with same mounting points, you should be o k and just have to put it back the way you took it off and connect plug ( disconnect -ve side of battery before you start work)
If the mounting points are different, you may need to get the correct brackets and change your alternator belt to suit as it may be a differnt size/type. Good luck all the same. :)