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MG MGB Technical - Starter problem ?

1972 MGB
I've had an intermitant problem starting the car. Sometimes she starts right up, but maybe once evey two weeks she acts like the battery is flat (the starter doesn't engage just makes a zzzz noise like its just the solenoid thats trying) So i charge her and sometimes after but five mins she'll fire up, other times it'll be an overnight charge.
Yesterday same problem, charged overnight, it never seems that the battery takes a hight charge, and this morning no better. Also some times when i tried to start it the ignition light didn't come on.
I cleaned the battery terminals, and the connections at the battery, still no better.
Tried a light tester and found that with the ignition on, no ignition light, i didn't read any power getting to the starter, but with it off i was able to detect current at the starter ?
Please help, is it the starter ?
Gerry Lodge

Sorry ment to say i cleaned the connections at the starter as well.
Gerry Lodge

Gerry. You should, always, have current present at the main terminal of the starter solenoid. It is a direct link to the battery and a test light, or volt meter, connected to the main terminal and a ground should show full system voltage.

First thing, remove the battery terminal clamps, clean the terminals, and take a voltage reading. A fully charged battery should show between 12.5 and 13.0 volts. If not, charge the battery, connecting directly to the terminals, not the clamps, and leave it charging until the battery charger shows it fully charged. Then, check again with your volt meter. If you do not show 12.5 volts, have the battery tested at a parts store or by your mechanic.

With a known good battery, install the battery terminal clamps, preferably after cleaning the inside surface, and check the voltage at the clamps. If the clamps are clean and making good contact, you should see the same voltage as at the battery terminals.

Then, check your voltage at the main terminal of the starter solenoid. You should, again, see full battery voltage. Anything less indicates a possible problem with the battery cable or its ends. If you do not have full voltage, replace the cable.

If you have full voltage at the starter solenoid, make up a jumper wire going from the main terminal of the starter solenoid to the cockpit of your car. Using your volt meter, test for full voltage (your base line), then, try to start the engine. The battery voltage should not drop below 11.5 volts and 12.0 or above is better. If you see a significant voltage drop, you have internal problems with the battery cable when it is under load. I have seen, with problems as you describe, readings as low as 4.0 volts when the starter is engaged. With that reading, the starter does not move, nor could I hear the solenoid engage. With a somewhat higher reading, the solenoid would engage and "flutter" or click. I have had to replace the battery to starter cable on three cars over the last ten years due to internal corrosion. The type of replacement battery terminal clamp having the two nuts which hold the bare end of the cable are a common problem if you find them in your system. They do not work as well as the molded on terminal as they get both dirty and corroded, causing the electrical contact between the cable and terminal to go bad over a period of time.

If you are getting good voltage to the starter, even under load (i.e. when the ignition switch is in the start position), and you know your battery is good, you have to have the starter tested for function.

The lack of an ignition light would indicate either the plug at the back of the alternator is not making good contact or that there is a charging system problem. But, you need to have the engine running to test it out. Check out the starting problem and, when you have it fixed, post again if you are still having a problem with the ignition warning light.

Les
Les Bengtson

Besides the battery clamps and terminals, check the the earth lead where it bolts to the car.
c cummins

The confusing symptom of sometimes having voltage and sometimes not will almost certainly be due to a bad connection in the heavy current circuit between battery and starter solenoid, and battery earth terminal and the body.

With the ignition *on* test the voltage right on the battery posts, if no voltage here then the battery is bad.

If that's OK test between one post and the other clamp and vice-versa, if one of these shows no voltage then it is the clamp that your meter is on that is faulty. If you have twin 6v batteries do this on both, and if everything shows 12v then finally test from the right-hand battery +ve (12v terminal) to the left-hand battery -ve (earth terminal).

If that shows 12v then test between the right-hand battery +ve and a good earth on the body somewhere. If that shows less than 12v then where the earth cable goes in the battery clamp, or the body lug, or the connection to the body itself is bad.

If that's OK then retest between a good body earth, and the starter solenoid stud with the thick cable on it. If that still shows no voltage then either the 12v cable in the battery clamp is bad, or where the battery cable and two/three brown wires bolt to the solenoid stud is bad.

Also check that you don't have a non-standard join in the main battery cable anywhere, if so the problem could be there.
PaulH Solihull

Could the zzzz sound be the starter spinning
without the pinion engaging the flywheel?
I'm not sure if that is possible with the pre-engaged starters though. The usual sound
of a weak battery or poor connection is a clicking sound of the solenoid.

Ralph
Ralph

As you say unlikely with pre-engaged as the motor isn't (supposed to be) powered until after the pinion has engaged. The other issues of no voltage must be fixed first, then if there are any other additional problems with the starter itself they will be revealed. It depends just how low the voltage with the bad connection is going as to precisely what audible symptom you get, anything from the solenoid chattering that you describe, to the starter relay buzzing, to nothing at all which seems to be the case now.
PaulH Solihull

Thanks for the help guys. I didn't infact have a battery tester, but a simple earth with a bulb at the other end. Anyway start at the beginning, i took the battery to a Parts store and the charged it overnight and then put a load on it next morning. It charged and took the load, so battery fine. I bought a new earth strap and positive terminal, and installed them tonight. Result, not the starter, not the end of Summer cruizing. Oh joy. In hind sight i could have done this before posting, but,i didn't think it was going to be that easy.
Thank you every body for your posts
Gerry Lodge

Gerry. Sometimes it is the simple things. Glad you got it sorted.

Les
Les Bengtson

*Always* start with the easy stuff.
PaulH Solihull

This thread was discussed between 15/08/2010 and 20/08/2010

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