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alternator testing procedure and questions
Hi Everyone,
1985 911 Carrera lost power and after a brief rest it restarted and was able to go another 5 miles before losing the ability to crank the starter. Battery voltage was 11.6V when I had time to check. Noticed that the alternator lamp was lighting briefly at idle but goes out when the revs increased My question is where is the location of the relay board mentioned in the tech article by JimT for troubleshooting the charging system? Also how many shims total should there be for the fan belt? 6? I detect a fan wobble noise and suspect the previous owners of messing up the belt replacement by putting the incorrect number of shims in the wrong side and damaging the alternator shaft. |
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09-07-2002, 04:02 AM
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Senior Member
Join Date: Jun 2000
Location: N. Phoenix AZ USA
Posts: 28,943
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Charge the battery overnight with a good slow charger. Measure it and it should be 12 or so volts using a digital volt meter.
Start the car, measure the volts again, should be 12.7-13 or so. Have someone rev the car up to 2000 rpms and check it again. Would like to see 13.5-14.7 volts. Turn on the fans, ele window heat and headlights and would like to see it not below 13 volts. Anything less, especially with it loaded up, means its time to pull it out and overhaul it. Usually either the diodes in the alternator or the brushes have gone south. Mine went at 70k or so and thats about average for the 3.2 alternator. Get it overhauled locally for around $75 or so. If your pully is moving more than it should then it may have damaged the bearings, which should be replaced during any overhaul. Do a search on "fan belt shims" here and you will find more info on this area. Joe
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2013 Jag XF, 2002 Dodge Ram 2500 Cummins (the workhorse), 1992 Jaguar XJ S-3 V-12 VDP (one of only 100 examples made), 1969 Jaguar XJ (been in the family since new), 1985 911 Targa backdated to 1973 RS specs with a 3.6 shoehorned in the back, 1959 Austin Healey Sprite (former SCCA H-Prod), 1995 BMW R1100RSL, 1971 & '72 BMW R75/5 "Toaster," Ural Tourist w/sidecar, 1949 Aeronca Sedan / QB Last edited by Joeaksa; 09-07-2002 at 05:45 AM.. |
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09-07-2002, 05:41 AM
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Registered
Join Date: Dec 1999
Location: TX USA
Posts: 9,804
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ts,
The relay board is in the engine compartment ... bolted to left inner fender panel. Your coil is mounted on it, and a 3-position fuse block, rear defrost relay ... not much else. The fuse block is a good place to test alternator output while the engine is running. Your Voltage regulator is of the internal type, not mounted on the relay panel!
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Warren Hall, Jr. 1973 911S Targa ... 'Annie' 1968 340S Barracuda ... 'Rolling Thunder' |
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09-07-2002, 08:23 AM
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Thanks guys for the helpful replies.
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09-07-2002, 02:40 PM
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Senior Member
Join Date: Jun 2000
Location: N. Phoenix AZ USA
Posts: 28,943
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Let us know how it turns out.
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2013 Jag XF, 2002 Dodge Ram 2500 Cummins (the workhorse), 1992 Jaguar XJ S-3 V-12 VDP (one of only 100 examples made), 1969 Jaguar XJ (been in the family since new), 1985 911 Targa backdated to 1973 RS specs with a 3.6 shoehorned in the back, 1959 Austin Healey Sprite (former SCCA H-Prod), 1995 BMW R1100RSL, 1971 & '72 BMW R75/5 "Toaster," Ural Tourist w/sidecar, 1949 Aeronca Sedan / QB |
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09-08-2002, 06:59 AM
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Hi Everyone,
Checked the voltage after (trickle charging the battery) and revving up engine, all using the three fused terminal in the engine area under the triangluar cover with the wing nut. The voltage remained at 12.5 and never rose to 13.5-14.7 indicating the alternator is not putting out. Took it out and had it rebuilt with new bearings, etc. and new regulator was installed. Will put it into the car tonight and all should be well. With regards to the number of shims found when I took off the fan belt (it was 5 shims total, 2 before the pulley, 3 under the washer). Looks like there is a difference of opinion with the total number of shims (should be 6 but lot's of people have only 5). Tried the nearest dealer (useless waste of time!!! since they don't seem to even bother to stock anything small for owners or small independent repairers.)  Like most people I'll have to try running with 5 shims total until I get the last one from somewhere. |
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09-09-2002, 10:52 AM
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Senior Member
Join Date: Jun 2000
Location: N. Phoenix AZ USA
Posts: 28,943
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TS,
Glad to hear you found the problem. How much was the overhaul cost? Wish I could help on the shims but I do not count them, just mix them up until the tension feels right and then check it after driving the car a bit. Joe
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2013 Jag XF, 2002 Dodge Ram 2500 Cummins (the workhorse), 1992 Jaguar XJ S-3 V-12 VDP (one of only 100 examples made), 1969 Jaguar XJ (been in the family since new), 1985 911 Targa backdated to 1973 RS specs with a 3.6 shoehorned in the back, 1959 Austin Healey Sprite (former SCCA H-Prod), 1995 BMW R1100RSL, 1971 & '72 BMW R75/5 "Toaster," Ural Tourist w/sidecar, 1949 Aeronca Sedan / QB |
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09-09-2002, 10:59 AM
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Joe,
The car is up and running and the voltage at idle was measured at 14.2 V so it was a successful repair. The overhaul cost $145 total and I was told it included new bearings, brushes, and whatever is not right. I also believe the regulator was replaced included in the price. We'll see how long this unit will last. The car has 123,800 miles now and didn't need anything else besides new CV loints (4) all around and a little silicone sealer (to stop a minor oil return tube leak). I decided to retain the original oil return tubes since I didn't want to remove the exhaust system to replace the old tubes with the expandable ones when a little cleaning and sealing up the area where the original seals go did the trick. Also I don't have worries that the expandable ones will collapse at the worst of times leading to engine failure! Sure beats handing >$600 to the dealer to fix my alternator problem. 
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09-10-2002, 09:41 AM
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