How can I test my alternator if the engine will not run?

[nickbw]

I suspect the answer is "you can not" My problem is, basically, my fuel filler to the fuel tank (petrol) is shot . I need to get the stealer to collect it and sort it ($1000 US) in the mean time I am doing those major maintenance items, pcv; cam belt etc; serpentine belt. Trouble is there are fumes left in the tank hence engine will not start and run (since pcv system) for more than seconds. In this time I saw a message " electrical system fault" or some such. There is nothing stored in message center and Vida/DiCE shows no codes stored. I must say getting the serpentine belt back on was the biggest hurdle in the whole process (there is no room, even for small hands). I have re-connected all the electrical connections and the B+ on the alternator/generator is tight and clean. I have the two sensors on the TCM inlet pipe connected and the TCV and vacuum lines are all good. The car is in a small garage at the foot of a steeply sloping drive. The nearest reputable stealer is 25miles away. If this was your baby what would you do next?

[hoonk]

The alternator recharges the battery and provides current for the car to run on once it has started. Some race cars running short sprint races don't even have alternators, they just run on the stored current in the battery. So if the battery is fully charged the alternator does not matter (until you use all the current in the battery) In other words if your engine spins over but does not catch you should not be questioning the alternator.

Answering your question - yes, you can test the alternator with the engine not running but you will have to remove it from the engine first and take it to someone with a tester. :rolleyes:

Did the engine start and run normally before you worked on it?

[pelagikos]

The behavior may differ model year to model year, but my '03 XC70 did not complain when the alternator died until battery voltage dropped below 11V or so, and only then got "Low Voltage" message.

My point being, if the battery is fully charged, and the alternator is out of commission, in my car case, one should not even notice unless one checks the voltages.

Newer model years have a more elaborate circuitry where excitation current is controlled from the car's main computer and not by the regulator itself. In fact in those cars, the regulator-like piece on the alternator is just the rectifier and the brushes, but the "regulating" is done by the computer.

[Willy]

Quite so.
If I am not mistaken, the alternator in our cars doesn't deliver any current while crancking.
This seems a logical thing to do, since an alternator delivering current is a "counterforce"
to the starter that is doing its best to spin the engine. Once the engine runs, current delivery
is ramped up to reaches normal capacity once a given RPM (1500?) is reached.

[swimNdrive]

you will have to remove it from the engine first and take it to someone with a tester. :rolleyes:

I took a alternator to both Pepboys and O'Reiley once for testing. The test results said the alternator was good, however, it just could not charge up the battery. With a new battery in place, I decided to get a new alternator from eBay regardless ($100 shipped), problem resolved.

[hoonk]

The smiley face is a joke, I think it would be silly to remove an alternator that takes so much time to take off to have tested. (unless you did not own a voltmeter) To test an alternator with the engine running you measure the voltage in the system. Engine hot, cold, under the maximum load you can give it, and after running for a while. (hot alternator) A fully charged battery is about 12.5 volts. Anything more than that (any higher voltage) with the engine running is coming from the alternator. Sure you can have a cool (expensive) tester than measures diodes, ripple, ac, current output, and all sorts of other stuff that usually does not matter or is a problem. Usually 13.2 volts or more at the battery when running above idle speed (with a fully charged battery) is good. Anything less - not so much.

[nickbw]

The alternator recharges the battery and provides current for the car to run on once it has started. Some race cars running short sprint races don't even have alternators, they just run on the stored current in the battery. So if the battery is fully charged the alternator does not matter (until you use all the current in the battery) In other words if your engine spins over but does not catch you should not be questioning the alternator.

Answering your question - yes, you can test the alternator with the engine not running but you will have to remove it from the engine first and take it to someone with a tester. :rolleyes:

Did the engine start and run normally before you worked on it?
Yes it did. It has been off vehicle for three weeks, and battery has been disconnected for same length of time (but on a standby charger) I have no reason to think either component has stopped working. The one major change is that I replaced the sparking plugs with new Volvo ones. The ones I removed were heavily fowled and Bosch multi electrode type - the kind my old Alfa used- I have never seen these in a Volvo before and decided to ditch them. So now with the pcv system totally refurbed and oil and plugs changed I go to start it expecting there is too little fuel to get line pressure and sure enough it takes a lot of prompting but eventually fires but cuts out after 20 seconds. I assume no fuel. In that very brief time I get a transient message in the display something like "electrical fault". Afterwards, when attempting to duplicate this no message is stored, and engine does not start. I am tempted to put a long neoprene tube down the filler into the tank with a funnel attached and try to get some fuel in - trouble is previous time I tried this, (filling tank) at filling station, within seconds fuel was spilling everywhere under the car. So I guess what I am really saying is "am I an idiot even contemplating doing this in a small garage integral to the house (which also houses the main electrics and a gas supply meter?" It's a no brainer really! Leave it to the stealer!

[guymon]

Note:
Unlike older cars a our Volvo can't really go very far on battery alone. Our cars have so many electronics, computers and those damn driving lights, that it wears down the battery very quickly. Once you get the low voltage alert, you better stop pretty quick, as when it does finally go it can be dangerous. When I tried to push it, the transmission went out then the accelerator, I had to pull over pretty quickly while on a highway. The car shut off shortly after that. These cars need that full 12v to work. Towed home, put a new alternator and battery and back on the road. Hardest part for me was figuring out how to pull the alternator out. Heres my notes,

http://www.volvoxc.com/forums/showthread.php?21457-Replaceing-Alternator&highlight=guymon+alternator