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MG MGA - Slow On The Starter

Unusually for me the car was a sod to start this morning, very slow on turnover as if the battery was almost flat (temperature -4 centigrade). Flicked the second battery in and away she went. I normally run 2 x 12v batteries in parallel with one always isolated. I rotate the in-use battery every day or so to keep them charged.

At the end of the morning I tried to start her again on the other battery and still very sluggish. Is this possibly a sign that the starter switch is on the way out (high internal resistance)? Any checks I can do on the starter switch?

Please don't give me advice on the other parts of the starter circuit - all terminals tight and very clean, batteries less than 3 years old, starter motor barely 2 years old etc. It's not an ignition problem, just starter rotation speed. Makes no difference to rotation speed if ignition key turned off. Oil is 10-40.

Yes, it's cold outside, but not that cold. Lovely drive to work. Hurray winter is here. Time for real MGA driving - hood down and flat hat!

Steve
Steve Gyles

No, a bad starter switch alone would probably not cause those symptoms. Adding a second battery in parallel would not overcome the effects (high resistance) of a bad starter switch. A bad switch would become very hot after a little while of slow cranking.

The likely causes are the ones you said you didn't want advice about, the battery, starter and connections. Ruling out parts of the starting circuit just because they are only a few years old is a sure way to frustrate yourself. Parts can and do fail at any time.

Jeff Schultz

Often overlooked is the heavy jumper cable at the right engine mount that grounds the engine to the body.
J Heisenfeldt

I don't know you personally and this is not a judgement of you but: as a profesional mechanic and owner of a repair shop for over 26 years. When ever a customer tells you what it is not. The answer is always on his list. This phenominom is not only limited to car owners. Prior repair shops have sent cars over with the same type list. I once saw a mechanic replace 3 perfectlly good starters in a row because he had eliminated the battery terminals from the list, they did look perfectly clean from the outside. I call it a form of tunnel vision.
Jeff is right any connection that is limiting current will get hot. A ammeter and a volt meter used properly will always answer this question.
R J Brown

Steve, you could follow Barry to Oz - we don't have cold weather problems here!
Mike
Mike Ellsmore

Jeff & RJ

Whilst I agree with what you are saying, the reason I stated what was not the problem was that I took all the connections apart yesterday afternoon and thoroughly cleaned them, but with no improvement. Also, individually selecting each battery made absolutely no difference to the starter rotation speed, so the chances of both batteries failing at exactly the same time was unlikely. That left the internal contacts of the starter switch as a possibility and also perhaps the internal workings of the starter motor. The starter is only 2 years old and had been working fine up to yesterday morning. Therefore, I was biased towards the internal contacts in the starter switch. I did not replace the switch during my rebuild 11 years ago and before that it had sat unused in a Californian field for 22 years.

Mike. Oz is tempting but your 7 year drought could leave you short of Yellow Tail Chiraz. Staying put for a while.

Steve
Steve Gyles

Steve
What difference does bridging the contacts of the switch make (use something heavy duty like a jumper lead.

If the motor then spins fine, it's the switch, and you are right.

If it makes no difference, then the others are right.

You did check the earthing strap too, didn't you?
dominic clancy

Thanks Dominic. Obvious way of checking the switch now you mention it. Will do that tomorrow. Earthing strap is ok as far as I know. I did break, clean and remake all connections.

Steve
Steve Gyles

Steve,
If bridging the starter switch makes no difference. There is a possibility the cable from the batteries to the switch has deteriated internally from a nick or cut of the insulation.
To test..Pull the battery out of the car (if needed)
and jump the battery to the started side of the starter switch. Careful of the polarity.

Ray
Ray Ammeter

If you connect the battery directly to the starter side of the switch why would you have to use the correct polarity? Doesn't the starter motor turn in the correct direction with the polarity connected either way?

I would not remove the battery to connect to the starter motor side of the switch because if the starter switch is then not in use there would be no power to the coil and the generator would not output to the ignition coil at cranking speed.

Use a separate battery on the starter cable and turn the ignition on so that the fitted battery powers the ignition coil.

Mick
Mick Anderson

Trying to diagnose an electrical problem without a meter is like shooting in the dark. You may guess the direction and eventually hit what you want but will surely waste a lot of time. With the low prices of the cheap meters from China, anyone who does anything DIY should have one. Even at Maplin you can get them for £5.99 and there are probably cheaper places. http://www.maplin.co.uk/Module.aspx?ModuleNo=37279&&source=14&doy=25m11

Jeff Schultz

Jeff

Yes I have a meter. I am quite comfortable checking basic circuits, probably less so knowing what sort of reading to look for in a potentially high resistance junction. And that was the basis of my original post. I went through every terminal at the back end of the car again this morning and it's not made any difference. I did not get round to the switch terminals nor the starter terminal as I was collared for shopping! Will have a look tomorrow with Dominic's check.

Steve
Steve Gyles

Since you have a meter, 5 or 10 minutes of testing will point you to exactly what is wrong without guessing. The first thing to do is to connect it between the input terminal of the starter switch and some metal part on the engine block. If it is less than 12 volts without the switch activated, then you have a battery or charging problem. If it is 12 volts or above, then pull the starter and read the voltage while cranking. If it drops way down(~8 volts or less) then you have either a bad battery or bad connection or a shorted or jammed starter. If it doesn't drop much at the input terminal when cranking, then connect between the output terminal of the starter switch and the engine block. If the cranking voltage is much less there than on the input terminal, then you have a bad switch. If the cranking voltage is 10 volts or more at the output of the switch, then measure the cranking voltage right at the starter. If it is still 10 volts or more right at the starter then the starter is bad.

Jeff Schultz

Simply based on the mechanics of things, I would suspect the starter more than the starter switch. You may have bad bushings or a dirty commutator, either of which would give you starting trouble. Take some jumper cables directly to the starter and you will know everything you need to.
mike parker

Since we are all making wild guesses, my wild guess is that there is a problem in the charging circuit and the batteries are not getting fully charged. Any problem with high resistance(ie bad switch, bad connection, dirty commutator, etc) will cause a voltage drop. Connecting one good fully charged battery in parallel with another good fully charged battery will not raise the voltage, so would not overcome the voltage drop caused by a high resistance connection.

Again, 5 minutes with a meter will point to the problem.
Jeff Schultz

Thanks Jeff

I have 12 volts, dropping down to 9 volts cranking a cold engine. Other side of the switch is also 9 volts. Should I be looking at the starter?

Steve
Steve Gyles

Nine volts is kind of marginal and could cause slow cranking, so I still wouldn't suspect the starter. The next thing to do is to measure the voltage right at the battery terminals when cranking. If it doesn't drop significantly at the battery terminals when cranking, then you have a bad connection somewhere between the battery and the starter switch. You can move the meter to each connection to see where the voltage is being dropped. If the battery terminal voltage drops down to 9 volts when cranking, then either the batteries are going bad or they are not fully charged, or else the starter is drawing excessive current. You would need a high current ammeter to determine if the starter is drawing excessive current(ie shorted). A fully charged 12 volt battery is actually about 12.6 volts with no load.
Jeff Schultz

Since I am suspecting the battery, here is a page about testing a battery using a digital voltmeter. It tells how to check the state of charge, and how to compensate the voltage readings for low temperature. It also tells how to use the digital voltmeter to load test just by cranking with the ignition off for 15 seconds.
http://www.pacificpowerbatteries.com/aboutbatts/Car%20Battery%20FAQ/carfaq4.html
you may need to copy and paste the link as this bb didn't used to like the % in a link.
Jeff Schultz

Thanks Jeff. All very good info, much appreciated. I am finding it hard to believe it is the battery but am keeping an open mind. I have 2 x 12 volts in the cradles, wired in parallel, with an isolator on each. I have just found the invoices for them. Both have 5 year warranties so I can get them changed if they are not up to spec. One battery is 3 years old, the other is 2 years old. I am presuming they are fully charged but will put one on charge overnight to see if it makes any difference. I run an alternator (year old). Ignition light operates correctly, so up to now, have not had any suspicions about the charging circuit.

Steve

Steve
Steve Gyles

Are the batteries sealed? If not, how is the water/acid level in each?
Steven B

Steven

Yes, sealed. Car started great this morning, spun over like a dream. I am puzzled.

Steve
Steve Gyles

Steve,
We have had one or two frosty mornings in this part of the world. Couldn't be just colder and hence denser oil that was /is the problem ?
As a point of interest my present A is very sluggish even with new batteries (2 x 6Volts)whereas my previous one spun like mad with 2 x 6 volts. How soft and flexible should the main lead be from the battery to the starter switch? I fitted a new jumper lead between the batteries last year and was surprised how soft and flexible it was compared to the old one and also the main lead, and I wonder if the whole main lead is cooked on mine giving a sluggish turn over ?
David
D C GRAHAME

David,

The original battery cables were made with thick copper wires and were/are very stiff. They are also practically indestructable. The only area that could cause concern (apart from damaged isulation causing a short)is the connection between the cable and end clamps.

It is those connections (between cable and clamp and between clamp and terminal/bolt) that become corroded or broken.

Most of the newer cables are made with (more) thinner wires inside and are therefore more flexible. As long as the old cable is long enough and the insulation is OK you can always fit new ends (or refit the old ones if they're OK).

Neil
Neil McGurk

Neil,
Thanks for that.Job for tomorrow checking the terminals I think !!
David
D C GRAHAME

Glad battery worked OK - What was the temperature this morning Steve? - I'll bet it was a lot warmer than -4C , lead/acid cells' efficiency does plummet with falling temperatures. By the way Steve - did you see the South African Lightning (fighter plane) on BBC2 programme on the earth's atmosphere this evening? cheers Cam
Cam Cunningham

Hi Cam.

Yes, bit warmer today, plus 8. Only car on the block with the hood still down! No, missed the programme. Watched my team get beaten in Spain.

Steve
Steve Gyles

Steve - I wouldn't let on that you are an Ar*enal fan too loudly round your way - the Mancs will not take it lightly!! Sounds as though it is a temperature related battery fault - cheers Cam
Cam Cunningham

Cam

Very wet this afternoon. Got absolutely soaked coming home. Car started okay though!

Steve
Steve Gyles

This thread was discussed between 23/11/2007 and 28/11/2007

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