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MG MGB Technical - Alternator or not?

Hi. Finally got moved to Southern California from Northern Calif. and as usual with MG's, Murphy's Law hit. My 1977 MGB was sitting in a garage for over a month while I was house hunting, moving etc and when I finally went to get it it would not start. We jumped it and it ran for about 2 blocks then it stutterd and died and would not start. Pushed it back to the house and took the battery to get rechagered.
Recharging worked, car started and ran for about 2 blocks and died again and would not start, again.
1. I think my 4 month old Alternator is now dead. Figure the battery had enough too start it and run for a bit and the car used the gas in the line and when that fuel was used the car died (since the fuel pump wouldn't work without thew alternator producing power.) Ideas?
2. How can I check voltage to the alternator if I can't start the car?(not a big electrical guy)
3. If not the alternator, what else could it be?

Thanks,
Joe
joe fabian

Try driving around thge block with your gas cap off --- it may not be venting.
Dan

How old an what condition is battery?

Have you cleaned ALL battery, ground, charging system contacts?

Is there any electrical circut made -- like the trunk light or other similar -- that's drawing from the battery as the car sits?

On the surface -- as described -- it seems like a simple problem -- just a matter of basic trouble shooting.

Also, check the tension of the fan belt to insure the alternator pulley is not slipping.

good luck -- glg
glg

A fully charged battery in good condition should allow you to drive for more than a couple of blocks without the alternator. Do as glg suggests and check all connections. Also check the battery voltage at the battery. You can get an inexpensive multimeter for under $20. Set it for DC Volts and touch the red lead to + and the black to - (just like connecting your battery charger) your battery should show more than 12 volts. If it's freshly charged put the meter on and watch it for a while. If you see the voltage dropping, you either have a bad battery or a circuit in the car drawing current. If that happens, disconnect the battery cables and measure the voltage. If it's stable now then the car is draining the battery. If it's still dropping the battery is shot. If the battery voltage does not drop after charging, start the car and measure it while the engine is running. If the voltage drops now check the charging circuit. If it stays up above 12V while running then your problem is probably elsewhere.
Bill Boorse

If the battery got a full charge when you took it out to recharge (and is in good shape), you should be able to run a lot longer than 2 blocks without the alternator; the power draw for running (as opposed to starting) is quite small, even on a 77. A fully charged battery should let you drive for hours (somewhat less if using headlights).

I would start by looking for a bad cable connection. Check both ends of each battery cable, and also make sure that you have a ground strap with good connection from the engine/transmission to the chassis (looks like a braided wire strap, probably back by transmission mounts on a 77).

Your battery could be failing; sometimes one of the cells goes bad or shorts out. You can get one of the little battery cell charge testers (little glass tube and rubber bulb thing) and check the charge state of each of the cells in the battery; shouldn't cost more than 2 or 3 dollars. You can also find volt/ohm meters pretty cheap - a normal good battery should show close to 13 volts between the terminals, when the alternator is charging it, you should see more like 15 volts.

One unfortunate aspect of lucas alternators is that they don't seem to like charging flat batteries; doing a push start with a nearly dead battery puts a lot of load on the alternator to recharge, you are better off using jumper cables and letting the other car charge your battery through them for a few minutes before starting and disconnecting.



Tom G

Joe. As the others have noted, the car will run quite some time on the battery, if the battery is in good condition. So, you have a "beyond the basic" problem which is not going to be as simple as "replace the battery" or "replace the alternator".

Let us start at the beginning, which is the battery. Get a battery charger and charge the battery over night. Do this with the battery cable terminals disconnected and the battery terminals cleaned. Let the battery charge about 24 hours, or until the charger meter is registering about 1-2 amp charge rate. At that point, your battery should be fully charged. Measure the battery voltage with a DC voltmeter. It should read 12.0-12.5 volts. If not, there is a battery problem.

Then, connect the battery cable terminals to the battery terminals. Turn the ignition switch to the run position. You should see the red ignition warning light glowing. If not, there is a problem with that circuit and you need to find and correct it before moving on.

If the light is glowing, start the car and turn the idle adjust screw up so the tachometer is showing at least 1200 rpm. The alternator should be carrying the full load of running the engine at about 1000 rpm, so this guarantees the alternator is doing the work--if it is working properly. Measure the voltage at the battery cable terminals. You should see about 13.5-14.5 volts on the terminals. Batteries are always charged at slightly more than system voltage. If you are showing the correct figures, your alternator is putting out the correct voltage. To test the amp output requires the services of a mechanic having the proper meter to do the test. Most hobbyists, including myself, do not have this more expensive piece of equipment. However, if you have a problem of insufficient amp output, your car would be running, but draining the battery under high load conditions. This is not the problem you describe. If, however, you show good alternator voltage and the ignition warning light is glowing slightly, it is worth having this test performed. If not, assume the battery and alternator are working correctly.

That would leave a problem in the ignition circuit. The white wire circuit comes off the ignition switch and powers the igntion circuit and fuel pump. This circuit died on my daughter's 77 one night when I was driving it. The indicator was that the car would begin to run with the switch in the starter position (12V input from the starter), but would die when the key was returned to the run position.

Right now, the first thing you need to do is verify the battery and the alternator. If they are good, the problem lies elsewhere. We can deal with that when we know the status of the battery and the alternator. While you are checking, do check to make sure the main terminal of the starter is tight. If not, that would give you the problem you describe, even with a good battery and alternator. Les
Les Bengtson

You should be able to test both the battery and the alternator off the car. Take the alternator to your local parts house that advertizes a free test. They have a machine sufficient to say if it is good or bad. Take the battery to either a battery dealer or and auto electrical shop and they should have a load type instrument to load and test your battery.

If nothing else, this bit of running around will at least give you some concrete answers to the condition of these two elements of your electrical system. All the other things that the folks above have mentioned should be checked as well. I put my money on a broken (internal) or shorted battery.
Bob Muenchausen

Welcome to sunny So Cal. :)
Steve Simmons

This thread was discussed between 19/11/2003 and 20/11/2003

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