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MG Midget and Sprite Technical - Electrical deficiency on starting

In recvent months I have found that my car has become difficult to start. It would churn over and over without firing. I then realised that it only fired as I released the key!
What I think may be happening is the starter is dropping the voltage to such an extent that there is not enough power left for the spark. In the instant I release the key, power to the starter motor stops and while the engine is still spinning, the newly powered spark does the job.
I have checked the earths and battery terminals and all look ok. It is a new battery and when turning the motor it seems to do it with some enthusiasm.
If my conclusion is correct, I wonder if the starter motor is taking too much power? Does anyone know whether just checking the resistance would be an adequate measurement and if so, what that should be?
Someone has suggested getting inside the starter motor as he had experience of the braided internal connection partially failing.
Or any other suggestions?
G Williams

Hi Graeme,
Sounds like you may have a 1500 using a ballast coil? If so, check that the wiring connections at the solenoid are all making good contact.
Guy W

Is this a 1500 with a ballast coil?

If yes, I suspect the ignition switch or the ballast bypass wiring.

Try running 12v to the coil +ve direct from the battery (but only for a short test), if it starts the fault is in the ignition circuit.


Best of...
MGmike
M McAndrew

Hi,


First thing to do is check you have power on the white wire at the coil +/sw terminal when cranking.



Could be a faulty ignition switch, not uncommon on old well used Lucas switches. Often the power to the coil is momentarily restored as you release the key back to run.



Worth a look.


Regards Steve


SR Smith 1

if its the starter, its probably just dirty

These starters like to be super clean to funtion, they DO not like to be greased or oiled before installed and they defiatly dont like lubes while installed... super clean with brake cleaner or gasoline and installed dry

Prop
Prop and the Blackhole Midget

Graeme,

Read this, by way of an explanation of why I said earlier that it sounds like you may have a ballast coil system:

""Originally, all ignition systems did not have a ballast fitted which meant that the ignition system used a 12v coil with a 12v feed from the battery via the ignition switch. Such a system works fine when an engine is running, but problems can occur when starting the engine. The starter motor draws a huge current from the battery leaving less energy to create a spark across the spark plugs. The result is a weaker than normal spark which is not ideal for starting an engine. This problem is worsened by colder temperatures and/or a worn starter motor which will draw even more energy for starting and leave even less energy for sparking. To overcome such a problem, ignition systems were changed to run a lower voltage coil (usually 9v), and these coils could still give the same output as the original 12v coils. In order to run such a coil, the 12v ignition feed runs through a ballast, reducing it to 9v at the coil. To assist starting, a 12v feed (usually from the starter) bypasses the 9v ignition feed, giving the 9v coil a 12v feed. The result is a better than normal spark which is ideal for starting, particularly on cold damp mornings. As soon as the engine has started, the 12v feed is cut and the coil will run on the 9v ignition feed.""

Guy W

Description begins ---- :

"In recvent months I have found that my car has become difficult to start."

That suggests that the problem is with a fault that has gradually developed, rather than having incorrect wiring to the coil -- unless the wiring was previously altered or a ballast coil system fitted.

So my guess too, is the ignition switch faulty or the wiring altered, as Steve from Kent has suggested.

Has the wiring on the rear of the ignition switch been disturbed at some point prior to you having this fault?
Lawrence Slater

For the same reason, I suggested a poor (intermittent, deteriorating) connection on the back of the solenoid. It is this wire that by-passes the ballast resistor on the 1500 and without a reliable connection then the coil only operates at the lowered running voltage input, giving a poor start-up spark.
Guy W

Hi everyone

Missing fact: no ballast coil. It's a 71 Mk4 Sprite.

I had wondered whether a fault could have developed in the ignition switch. No wiring changes to explain it though.

Just thought: when the car is warm it starts ok. That must be significant and presumably rules out ignition switch issues.
G Williams

It could be that the ballast wire is no longer attached to the starter solenoid. If things have gradually got worse, that could be because of colder weather. (Pretty much what Guy says)


(I know nothing about Spridgets but it happened on my MGB.
Geoff_MGB

In that case, Mr Williams, then Prop got it. Poor starter is drawing too much current, especially when cold/damp. Probably needs new brushes though, rather than it being a problem with wrong use of lubricant on the Bendix drive gear.
Guy W

©¿©

Prop
Prop and the Blackhole Midget

closed down ign point gap acts a bit like that
A fresh set of points, correctly adjusted and a new set of plugs would most likely fix your problem
willy
William Revit

Hi again,


I'd still do the cranking check at the coil as I described.


It deffo isn't a ballast fault as a 71 car isn't fitted with a ballasted cold start system!



Might be worth checking the engine earth lead as well, or temp connecting a jump lead between the block and the battery earth terminal and see if that improves the cold starting.
SR Smith 1

It seems to me, that if the starter motor was on the way out, it would be evident by not turning the engine as well as described. And if it was drawing so much current, as to starve the coil, again it would be evident. You'd likely smell it I reckon, and the cable would get warm as well as the s/motor. If the brushes were toast, you would likley not get ENOUGH current flowing in the s/motor.

PS, this is EXACTLY where an AMMETER can be useful. You can see the current drain rather than just guess at it.

Has your car got a finger press solenoid? My '73 rwa has. Have you tried turning on the ignition at the switch, and then activating the solenoid manually?

My first step would be to run a lead from the battery +ve, to the +ve(switch side) of the coil. Then manually activate the solenoid. If you don't have a button press, use a screwdriver blade to short the terminals. Make the contact 'quickly' and you'll get hardly any arcing.

Lawrence Slater

On the selinoid,

I just unplug the white red wire hook a spaded jumper wire in its place then just strok the back side of the selinoid at the battry connections in order to turn the starter over, if I want to start the car, injust put the key in the ignition and turn the key to the on postion ... neutral gear and e brake on of course


And great call on the earth strap pointed out by SR...thats a 1st. look

Prop

Prop and the Blackhole Midget

Prop, I was suggesting a lead direct from the batt to the coil, to eliminate the ignition switch from the investigation.
Lawrence Slater

Not had the chance to follow this up yet. I will post again if/when I've sorted it.
Graeme Williams

Sorry lawerance,

Yes... thats also a great idea, and it has my full blessing

Hahaha

©¿~

Prop
Prop and the Blackhole Midget

I recall having this problem on a RWA midget years ago. It was 3 years old and my daily driver. Turns out it was the battery. Funnily enough the same problem arose on my modern diesel recently, it cranked over as normal but wouldn't fire. I called out the roadside repair thinking it was the glowplugs but after a lot of testing concluded the battery was tired and a jump start got it going. A new battery solved the problem in both cases.
Bob Beaumont

The battery is about 18 months old Bob. If it was getting on a bit I would have come to the same conclusion. Mind you it may have been a cr*p battery!
Graeme Williams

I had a 8 month old one fail got it replaced under guarantee has it had a 4 year one on it showed 12.5v but dropped to 9v under load and would not charge, also it would not jump start with it connected.
mark 1500 on the road Preston Lancs

I bought a new Bosch battery a couple of years ago which failed after a year. Changed under guarantee and its replacement is still going strong. May be worth a test just to eliminate the problem?
Bob Beaumont

What's the best way to test the battery?
Graeme Williams

have a look at the (more recent) John Twist video on the car battery and the cranking drop test

as Mr Twist says the car battery is one of the most over sold car part, I'd check the electrolyte level of each cell and top up if required then check/clean battery posts and battery lead clamps then fully recharge the battery out of the car using a long trickle charge (then I check/top-up/maintain with a battery conditioner - my neighbour bought a charger that is also a conditioner so fully charges the battery then automatic switches to conditioner mode it works very well)

I don't bother to charge or condition my battery as the (uprated) alternator takes care of the battery, on Sunday the car started first time after not being used for at least 5 weeks standing outside (I've had an operation so can't drive at the moment)

now you have an alternator you'll find the battery is able to work better and should last longer
Nigel Atkins

There's really only one way to test a battery and that's under load.

Basically, apply a very low resistance load which draws a high current for a short amount of time during which the voltage should not drop below 9V.

Search for battery load testers on the auction sites or check this out...

https://www.youtube.com/watch?v=3QiKyjWWiRo
He waffles a bit but does get the info right

or this if you have a min/max multimeter
https://www.youtube.com/watch?v=tsJUuLu1cw0

Best of..
MGmike
M McAndrew

Unless the engine is turning over very slowly, and with a struggle, when trying to start the engine, then the battery is a red herring. And since Graeme said it turns over OK, I can't see the battery being the problem.

BUT, the easiest way to elliminate the battery, is with a 2nd known good battery, or a set of jump leads.

How much current do you think it takes to charge a coil? Hardly any is the answer.

Where does the current that flows across the plugs gaps come from? NOT from the battery is the answer. It's there by virtue of the magnetic field collapsing in the secondary windings of the coil. As the field rapidly collapses and cuts across the windings, it induces the high voltage that causes the current to flow across the gap.

As long you as have the right mixture compressed above the pistons, at the right time, it will fire. But that needs the engine to turn quickly enough in the first place. If it is turning quickly enough, then it's not the battery. imo. :).

Does it start 'at all' now Graeme?
Lawrence Slater

Lawrence: it starts on releasing the key. If it's warm it starts normally but when cold it will not start until I let go of the key and the spring return takes it off the "starter" position.

I must say the thread is running faster than my time to investigate the problem. I haven't really checked anything out so was intially looking for pointers. Now of course the responses are based on potential results from checking things out, which I have yet to do. Need to get my finger out on this one!
Graeme Williams

" -- it starts on releasing the key -- ". So it must be spinning fast enough to turn the engine, AND charge the coil. Hence the battery doesn't spound like the culpret.

Now since you mention that the responses are running ahead of the investigation, I've got a great idea.

Look out in the general section, for a brand new thread. ;).
Lawrence Slater


" -- it starts on releasing the key -- "




Still sounds like a faulty or incorrectly wired ignition switch to me.
SR Smith 1

The ign. points, don't forget the points
William Revit

No points, William. Electronic
Graeme Williams

"Electronic"

Aha. That puts a different complection on it. Must have missed that in the earlier posts somewhere.

What is it, and how is it wired?

Even more reason to isolate the ignition switch -- and thereby elliminate it -- by running a direct feed and using the starter solenoid to start the car from cold. If it starts ok, you can start working backwards.
Lawrence Slater

Simon BBC. Wired as it has always been - correctly :-)

Don't forget the most significant fact here in all this lot: cold I have a probelm; warm I do not!
Graeme Williams

The parameters of electronic components change when warm/hot. Could be a failure in the bbc, only revealing itself when cold, but odd that the ignition switch postion seems to be involved.
Lawrence Slater

Still check the battery!
Bob Beaumont

(Sorry havent read whole thread)

I had a starting issue early this year. Even changed battery. Swore blind I'd checked everything. Was putting it down to higher compression 1380 (but knowing really something wasn't right).

In the end it was the gearbox/body earth strap. Looked bright and shiny and good nick. Only when I took it off did I find that one end literally fell off. Blow-torch and solder to reconnect end to braid and it instantly span perfectly.

Dont just look. dont just tug lightly. Give every connection a proper tug and wiggle. Something might be loose.
Dean Smith ('73 RWA)

Just got back in from cold, having done some more basic poking about.

For anyone starting in the middle:

1275
non-ballast coil
electronic ignition
new-ish battery

When cold the engine turns over strongly but only starts as I release the key. When warm no obvious issue.

-----

Today:

Inserted the spark-indicator devices between the plugs and the plug caps. Tried to start.
No spark when the starter motor was running but as soon as the key was released, spark and start!
The over-run from the starter had sufficient momentum to allow the engine to fire and run as the key is relaeased from the spring-start position.

Disconnected solenoid and held key against the spring (ie simulating a start but without power going to the starter motor.) 12.5 volts measured at coil.

Connected back up and put lamp between + on coil (power IN side) and earth.
Bright with ignition on, dim (but on) during start.

Measured voltage on coil:
12.5 with ingition on
7.5 during start.

That seems a big drop. Is it sufficient to fire the coil?
Graeme Williams

No Graeme it looks as if it IS the battery at fault

I did a sequence of tests based on my ex-employer's standard battey test

I was an AA patrolman and we used a test based on battery voltages under starting loads

I'll just pop the pictures I did on here then a quick run through afterwards

first: minimum battery voltage must be 12.2v, you rbattery passes that one


bill l

Then we test the battery voltage during the start process, the minimum should be 10v




bill l

the cranking should take place for something like 15 seconds and you should watch the meter reading

An acceptable volt drop is 0.3v during the crank session


bill l

If the drop is 0.4v or more there is a fault in the battery

7.5v seems like a hell of a volt drop, often caused by a single faulty cell failing to pass voltage under stress

If yours is new or has some guarantee left I would get it checked cold, as you drive the car the battery is receiving power from the generator and the engine warms up enough not to give the batterry any starting stress as it does when cold

I would advise you to get a check from a roadside breakdown organisation who can perform these tests and arrange for a new battery if necessary

Not good news sorry :(
bill l

I neglected to say that you need to disconnect the ignition feed from the coil to do the test

Just this one time

We do NOT want the engine to start

bill l

Graeme,
it will do no harm only good to fully recharge the battery out of the car on a long, slow trickle charge (see my previous post for details)

whatever problems you have with starting they will be easier to resolve with a fully charged battery as when the battery drains it takes more to start the car and might hide the cause of the problem - or as *might* be the case here, a drained battery is the problem
Nigel Atkins

damned computers!

edit - >or as *might* be the case here, a drained battery is the problem<

should have read -
or as *might* be the case here, a drained battery is part of the problem if not the problem

plus -
check each cell for electrolyte level and condition of plates

and check all connections and leads are clean, secure and protected - old cables and connections can go bad under the insulation so not be seen
Nigel Atkins

Thanks everyone.

Nigel: I think the battery is fully charged and it is usually connected to a conditioning unit.

Bill: thanks for that detailed explanation. I have checked the battery paperwork and it is May 2013 but has a three year warranty. I can see the biggest issue is going to be pursuading Europarts that their battery is faulty and not "It's your charging circuit mate!"
Graeme Williams

Tell them it failed a AA test, but the charging system passed.

Never know, it might work. :)

Sadly I can't post the test page from my old manual though it might be out there somewhere to prove the method.

Good luck with it
bill l

I've just been in touch with Eurocarparts and they tell me they can test the battery.
Graeme Williams

Hiya,


You've just said the magic words "Eurocarparts" and "battery", about the cheapest, nastiest batteries on the market, especially the ones badged "Lion".
SR Smith 1

there's a few inconsistencies I'm struggling to come to terms with here;
1, "When cold the engine turns over strongly" and
2, "Measured voltage on coil: .... 7.5 during start"

I don't think any battery which drops to 7.5v is going to turn the engine over strongly or be sufficient to keep the solenoid closed.

I agree 7.5v may not be enough to power up the electronics unit and hence no spark and when at rest ie no current flowing, you could/will measure 12v at the coil.

To help clear my confusion could you please measure the voltage during a start at the solenoid post where the starter motor connects?

Best of....
MGmike
M McAndrew

Mike:
I'll do that tomorrow. I need the help of my glamorous assistant who currently is in the shower.
Graeme Williams

Part of the AA's test is the time the cranking carries on for

15 seconds tests the endurance of cranking

most bad 'uns falter half way though that test
bill l

"...could you please measure the voltage during a start at the solenoid post..."

Better still, measure it at the battery posts.
Dave O'Neill 2

'I don't think any battery which drops to 7.5v is going to turn the engine over strongly ----- "

That's my thinking too.

" 7.5v may not be enough to power up the electronics unit -- "

And that.

Do you have the spec for the bbc? Does it say what minimum voltage is needed at it's input?

Ditto Dave Oneill.

But I'd still run a live direct to the bbc from the batt to elliminate the switch and other connections.

Thanks for the heads up on Eurocarparts batts. I need a batt and might have bought one from them too.
Lawrence Slater

Graeme,

>Nigel: I think the battery is fully charged and it is usually connected to a conditioning unit.<

if they conditioner has some means of showing the battery is fully charged then it probably is

but
>I think< - you know what thought can do - "I thought I'd farted but I'd shat myself"

another English saying for our American friends :)
Nigel Atkins

Graeme,

I assume you have a Powerspark right? It needs a switched live feed to the module and the coil.

Once you're satisfied the battery isn't/is responsible, why not put the the question to SimonBBC themselves.

They have forum for questions here.

http://blog.simonbbc.com/electronic-ignition-pages/powerspark-vs-accuspark-ignition-kits/

One bloke has the opposite problem to you. Starts cold, won't start hot. Might not be anything to do with the BBC of course.

Do you happen to have a spare distributor complete with points that you could chuck back in as a test?

Lawrence Slater

Have you measured the voltage between the battery earth post and the engine block - or better still the dissy body, when you are attempting to start it (and the problem is occuring)?
Jim
J Smith

THe votage across the battery drops to 9.5v on starting.
Without any drain it's 12.5
Graeme Williams

Graeme, I'm also suggesting you measure the volts drop on the earth side - between the battery earth and the engine block. this will give an indication of how good your earth straps are.

Jim
J Smith

Here's my knackered battery cranking over my 1275 Midget. 8.5 Volts across the battery post connections. It cranks over very slowly compared to how it should. BUT it starts from cold.

The difference is, I have points ignition.

With an electronic ignition module, you not only have to put current through the primary winding of the coil, you also have to provide the minimum voltage level to the electronic module, in order to trigger the electronics to switch the current on and off to the primary of the coil.

It looks like it needs a higher voltage than it's getting on Graeme's, when it's cold and turning the engine via the s/motor.

So as you say Graeme, when you switch the key back to ignition from the s/motor position, the volt drop is less, and the V across the bbc module rises sufficiently to trigger the switching of current to the primary of the coil.

This from the BBC website.

Battery voltage to coil:
" ---- Some vehicles have a resistor wire running from the ignition switch to the coil +ve terminal. This resistor wire drops the voltage below 9 volts so you may need to run a non-resistor wire from the ignition switch to the coil + terminal or run a +12V wire directly from the ignition switch to the red wire of the Simonbbc ignition module."

You don't have a resistor wire, but in effect you are simulating one when you crank the engine.

So not only might you have a knackered battery, you have a more sensitive ignition by virtue of having an electronic ignition.

Seems a VERY good reason to stick to points and condensor to me. ;).


Lawrence Slater

I repeat teat the battery!
Bob Beaumont

I would have thought that if the battery or ignition circuit was in question wiring a spare battery directly to the coil live side and block ground would provide a good 12V feed to the ignition and the result of the test should give some good indication of where the problem is.
David Billington

Tomorrow, with the aid of my lovely assistant, I shall repeat all the tests. Sorry it's taking so long but my lovely assistant feels the cold... and complains!

Unfortunately my other battery has different terminals so I can't just swap them over although I guess, when push comes to shove, I could swap the leads too. At least that would prove whether it is the battery.
Graeme Williams

Jump leads. No need to remove the other battery, just connect the 2nd good one in parallel. If it starts cold with the s/motor still engaged, you've got a knackered batt in the car.
Lawrence Slater

my last knackered battery had a bad cell showed 12v but underload droped to 8v, would not statr even with jump leads connected bad cell draged it down to 8v started first time with new battery.
mark 1500 on the road Preston Lancs

Mark. Are you saying that even with jump leads to a good battery, you couldn't spin your enigne over fast enough to start it? What kind of ignition do you have? Points or electronic?
Lawrence Slater

I agree with Lawrence that cold starting on a less than good battery is much, much better with points and a condenser; it should be almost instant, indeed my old Minor would start easily on a hand crank with a low battery. I have electronic ignition on my 1500 project (still doing bodywork so not yet used)and I bought a brand new battery to go with it. If you're having problems starting any car with a good battery then you really need to check everything again. If the ignition system checks out, consider servicing the starter motor. After many years they simply can wear as the insulating coatings on the windings degrade and/or carbon brushes wear out.
Nick Nakorn

Greame said: "The votage across the battery drops to 9.5v on starting.
Without any drain it's 12.5"

9.5v suggests the battery is marginal. 9.7v is commonly accepted as a minimum when cranking (as bill notes above).

However that doesn't explain the 7.5 at the coil (which appears to be too low for the ignition module).

Please confirm where the ignition module power lead is connected (usually red and on the +ve side of the coil)? If it is on the +ve side of the coil, remove it and run a wire directly from a point that holds 9.5v during cranking (battery, solenoid etc). My guess is the ignition unit will need at least 8v on it's supply to work.

If it then starts you'll need to find out where the missing 2v are lost.

Best of....
MGmike
M McAndrew

Lawrence
thats right the faulty cell stopped it turning it fast, i disconnected the battery and used the jump leads on the car battery connectionswithout the battery and it started first time i had never come across this before and found it odd .it must have been a high resistance in the faulty cell?
mark 1500 on the road Preston Lancs

In effect that faulty cell becomes a hole in the power supply and power falls though into hades

As Mike suggests the supply at the coil is the key to getting good starting

Try the often suggested (have you tried it) jumper lead from battery to coil ignition side when you crank the engine

This means the coil willl get all the available spare oomph from the battery except that which the starter drags away

There may well be naff connections that you haven't noticed, doing the jumper cable wheeze may take any such bad one out of the line
bill l

Hi Mark. Then that's your answer, But it's not so clear on Graeme's, since he says his spins fast enough.

His problem isn't even the low V at the coil I don't reckon.

It's the low V at the BBC Module. It's THAT that needs a min V, to trigger the internal switching, that allows the coil to charge and discharge, thereby inducing V in the secondary that causes the spark at the plug.

If he's not getting the min V at the module, it won't start.

Yep maybe a new batt, with a consistantly high V (Over 11v) will fix it.

But that also implies, that an otherwise good/ok-ish batt', is toast because of electronic ignition.
Lawrence Slater

pertronix Ignitor note 8 volts min.

Another Pertronix specialist suggests checking the ground from the dizzy module fixing plate direct to the battery negative pole - it should not they say be higher than 0.2 ohms as this is often were voltage is lost due to bad connections (internal dizzy grounding lead,distributor clamp to block, block earthing strap etc).

Must check mine sometime !

R.
richard boobier

THanks for everyone's continued interest. I am conscious that I am not getting back to the car sufficiently regualrly to report back but unfortunately my assistant is needed to turn the key while I'm under the bonnet measuring things. Assistant not available today but hopefully tomorrow......

I will report my findings and not leave it in the air (unless of course i have just left a wire off somewhere or connected something the wrong way round or done something else equally embarrasing!)

I can report that I have had the battery on charge but nowt went in so I assume it's properly full of electrons. The conditioning module is also showing all is well.
Graeme Williams

Hi Graeme,


In order to save the glamorous assistant getting chilly, it is easy to crank the engine.


Just pull off the white/red at the starter solenoid and make up a temp lead fixed that term long enough to touch the battery live lead at the big term.


You can then crank the engine by touching the lead to live whilst testing.
SR Smith 1

Ah yes... I can see that. I temp removed that one when I wanted to be able to fully turn the ignition switch to check all the contacts were making.

Hopefully tomorrow although I've just discovered the drain from the loo is blocked! THat may be the over-riding consideration!
Graeme Williams

Your car has a Loo? That's impressive. Mine has hot and cold running water but an on-board toilet - that must be one of the later models.
Guy W

Well Guy, you know how these old cars get customised.
It is a loo from the late 50's however with high level flush and that very rough toilet paper. Or torn up newspaper if we are going to a Show. I even use photocopies of the Daily Express for 1959.
Graeme Williams

See. It's those little hidden snippets of information that have led all astray. First it was the revelation that it has e-ignition not points.

Now we find out, the current is being drained off down the onboard loo, which given how low Spridgets are, will need a macerator, which is obviously what's blocked.

What next I wonder? ;)

Edit.
Oh I see. High level flush. That must look a sight to see going down the road. :).
Lawrence Slater

Some might say this suits my car very well. lol.


Lawrence Slater

But the flush seems to be wired in to the mains. And telephone too by the look of it. A loo with internet isn't a period feature.
Graeme Williams

LOL Graeme. I hadn't noticed that. I had to check on my original picture, to see if you'd altered it.

Anyway, period or not, it gives a whole new meaning to the word, "carsey". Don't you think?
Lawrence Slater

This thread was discussed between 09/12/2014 and 22/12/2014

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.