MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - car hesitating and cutting out

I have just been to a local car show car ran as it normaly does on way there, but comming home the engine kept cutting out and backfired a couple of times ,kept restarting with a rolling start and only once at trafic lights stalled and started first time and would run ok for a bit then do it again after a while ran ok the rest of the way home, checked all connectons on coil which was slightly warm, all ok checked coil resistance 2.5 ohms and 10.79k ohms 12 volt coil no balast . Left for a while to cool down and tried again and it is doing the same again its got electronic ignition in dizzy .
1500 engine,
britpart ignition,
12 v lucas sports ciol,
rev counter all over the place when its playing up.Anoyther thing that has started happening dont know if related radio keeps cutting out but not when the engine is playing up.Not sure if its a coil problem or an ignition switch problem.
any ideas would be appreciated .
mark heyworth

Quick thoughts -

Rotor arm type?, recently fitted?

Ignition switch or any of the connections from battery forwards (depends how your radio is wired for radio), fuse box, any earth from battery forwards.

Electronic ignition wires are delicate, easily,scuffed or caught inside dissy or outside dissy, any earths to dissy.
Nigel Atkins

Was going to say Red rotor arm until you mentioned the rev counter and radio issues which has me flumuxed too.
Dodgy battery?
Others who know about the dark art of electrics will no doubt point you in the right direction.
Jeremy MkIII

Yes, how's your battery, Mark?
Yet it keeps starting OK, so that would be a mystery.
Nick and Cherry Scoop

Quick up date came to put it back in the garage and just the dreaded clunk no starter checked battery (10months old)12,45 volts 8.4 underload staring to suspect it for both faults . Put on charge and after an hour showing 13.34 volts which drops quite quickly to below 13 volts will leave it overnight and see.Just a thought if it was not charging correctly I wonder if the voltage has been dropping below a certain point and that is why the radio has been going off intermitently, same for the coil and ignition.
mark heyworth

Faulty car batteries are very rare so if it is it's more likely something has caused it like lack of charging or a drain or poor intermittent connections somewhere.

I'd have thought, don't know, if the battery got that low it'd fade the car to a stop and probably wouldn't have enough to power to get the starter turning the engine over.

You need to leave the battery on a long and low charge, perhaps 24 hours or more, off the car. If you have a battery conditioner it might take longer.

It doesn't at the moment sound like it's the battery in itself that is a problem.


Nigel Atkins

Have you checked both earth straps, Mark?
When several things go mad at once, it's often the battery at fault.

(Not knowledge, just bitter experience)
Nick and Cherry Scoop

has a few earth straps one to the starter and a seperate one to engine , starter appers to be stuck now somethig is conspiring against me , had a battery fail while faily new before on my modern car ,cant help thinking all these are connected to much of a coincidence not to be .
mark heyworth

"charge and after an hour showing 13.34 volts which drops quite quickly to below 13 volts "

This is quite normal after charging, Mark. It will for a while show the higher voltage that the charger has been providing, and then drop down to give a true voltage of the battery which would be around 12.6v. This however doesn't proove the battery is good as what you would need to do is measure the voltage after several sessions on the starter so as to simulate a heavy drain. A poor battery will drop to below 10v or less. There is a proper procedure for doing this test. (Ask Bill Mohan, if he drops by)

But you say that the REV COUNTER JIGGLES VIOLENTLY. This narrows down the fault to the low tension side of the ignition circuit.(unless there is more than one fault) So forget about the high tension stuff like plugs, leads and iffy rotor arms. Forget about fuelling problems. The fault will be with the low tension wiring or connections of the ignition system.

So: lead from battery or starter solenoid to ignition switch/ switch/ lead to rev counter/ rev counter/ lead to coil/ coil/ lead to distributor/ contact breakers - or in your case the electronic ignition module.

Check for loose connections. Check for "floppy" wires which can indicate a wire that has fractured inside the insulation so that when cool the broken wire ends connect, but when warmed up the insulation softens, sags and opens up the broken wire inside. It gives exactly the mysterious symptom of an electrical fault that magically cures itself after the car has sat for 10 minutes! Of all of this, if the connections are tight, then the igntion switch is the likely culprit, I would think.

If you had points I would say check the points gap!
GuyW

Check connections to ignition switch. Ironically I have been to a show I help run today and mine suddenly started playing up as I was about to come home. Turned out to be the topmost spade connector had come off and was laying on the terminal hence intermittent connection. Not immediately obvious when looking from underneath dash. Spade needed nipping up a bit and suspect it had come off due to a few speed humps at the location.

Trev
T Mason

Faulty batteries exist but are rare on the type we use in our classics, it's much more likely that a faulty starter will pull the battery down than the other
way round.

As Guy has put the only real test is a drain down test usually with the starter - but of course even a 10 month old battery could eventually be critically weakened by such as a faulty starter and other problems.

See if you can freely move the square nut on the starter now the battery is out of the car or put it in gear and push it forward a bit to see if the starter releases.

Even allowing for the twitchy tacho needle rotor and/or dissy cap problems can throw up unusual issues.

I always think it's worth starting from the battery forwards when looking for electrical issues, once you've made all wires and connections, including all earths, clean, secure and protected following subsequent checks can be quite speedy but shouldn't be overlooked.

I've had fuses, bulbs, spade connectors, etc., etc. that look fine visually but when tested, sometimes by just feeling if they're loose, they have failed.

Nigel Atkins

update battery charged and holding staedy, starter motor removed and freed had some damaged teeth that appeared to be the problem with it jamming took it to get new pinnon fitted.I think next I will refit starter and and check alternator charging,then take the ignition out of the curcuit and see if fault that should narrow it down to which side of the curcuit it is.Maybe I should start beleiving in coincidences
mark heyworth

Does your ignition warning light behave as it should now?
GuyW

wont know till i get starter back but taken ignition switch off and eratic resistance beteween contacts taken it apart and a part of it is broken allowing the plate inside to move, so looking for a new switch hopefully thats the problem.
mark heyworth

update refitted starter and engine runs ok alternator charging, waiting for a new ignition switch to arrivest checking all contacts on ignition switch not 100% happy so cripped new spades on all of them will see tommorow if it has cured the fault.
mark heyworth

update
fingers crossed changing the ignition switch seems to have cured it just been out and it ran fine covered 4 miles going out tommorow so see if its ok .
mark heyworth

been on a long run and it did it a couple of times again ,rev counter all over the place ,am i right in thinking
a,if the rev counter is erratic then dead until it restarts its unklikly to be rotor arm.as its the signal from ignition it counts not sparks.
b,its now either electronic ignition or coil.
so try points and see if it repeats itself.
mark heyworth

forgot to add ignition light does not come on untill engine stops rotating.
mark heyworth

Simlilar issue on my 79 MGB a few years back. Check coil lead. Mine worked its way loose just enough to backfire and break up (over 3k RPM) as the tach bounced wildly.

The other issue later on was the car would just drop dead and then come back alive. That was the ignition switch failure.

Check the rotor arm also. They are among the "usual suspects" as well.

Cheers

Gary
79 MGB
gary hansen

Just trying to clear something in my mind would the rev counter not still show a reading if the engine is still tuning and the points/electric ignition are sending the trigger signal to the coil if so rev counter failing should equal bad electric ignition unit ? but i might be wrong in my thinking.
mark heyworth

I had a similar issue with a 1500 recently which slowly got worse over several weeks, the engine's occasional splutter got worse and worse until the rev counter started acting erratically and the car spluttered to a halt.

Thankfully the fault was pretty obvious as the electronic ignition live wire had worn away after wrapping round the distributor cam below the rotor arm and had kept earthing presumably causing the splutter until over a long period of time the wire eventually snapped and that was that.

Maybe nothing similar but mines was the electronic ignition, rejoined new cable soldered it and it was like a new car.

Tim

Tim Lynam

Tim
which ignition have you got fitted
mark heyworth

Mark,

Accuspark, its been fitted about 20 months
Tim Lynam

quick update new accuspark ignition fitted replacing britpart unit so will see how it goes just incase i have fitted a temporary light from the live side of the coil so if it happens again i can see if its a coil supply problem.
mark heyworth

Mark, good luck on a successful conclusion.

FYI, I had problems with the Accuspark after first fitting also on a1500 but after several days of no success was advised by Accuspark that it had to be wired direct to the live side of the fuse box, after disconnecting from coil and wiring direct to fuse box its worked well ever since. Not sure if others have theirs wired up same way but it worked well for me.
Tim Lynam

I ran a new cable in on its own fuse when i built car, just for coil supply and stowed the balast cable .
mark heyworth

This thread was discussed between 02/09/2018 and 12/09/2018

MG Midget and Sprite Technical index

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