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MG MGB Technical - Click no start
|Hi guys |
Got a bit of a problem with my dear old B...
She's been sat in dry store for quite a while now. I've been doing bit of work. Carb cleaning, new exhuast manifold that sort of thing.
I'm actually in position to start her up again now and that where my problem has arisen. I can't.
I was trying to start her and she was cranking for ages but not actually firing. thinking i'd maybe put plugs in the wrong order i went away to find out what the correct order was. Found out put them all back in (they were correct any way).
I then decided the spare battery i was using maybe wasnt up to snuff. So took the battery out of the jag, she's a 5.3 - this battery is huge, fully charged and could start an power station in the middle of an ice age so an MG should be small fry.
But i get something really strange happening. When i turn the key to on position i hear the fuel pump clicking and get a red ignition light, but so as i turn the key to cranking position i get one pretty loud click from the engine bay and then nothing. Even the ignition light goes out. I've checked around the engine bay and the alt loses power, the coil loses power everything seems dead. Tried a few different things but nothing happened. Then about 20 mins later the interior light came back on, the ignition light came back on. 12v at the alt and the coil, tried the key again. Same click and everything back off.
Took the battery back drop it in the jag and she started straight up so i'm pretty sure its not that.
I'm convinced there can't be too many things that would give these symtoms sadly i can't think of any. Thought about searching archive but didn't think "click" would really do it and i've got no idea where to start.
Any help greatly appreciated...
UK 1973 MG B/Gt
I had a similar sounding problem about a year ago. It turned out to be a poor ground between the battery and the chassis.
Hope this helps
|I'd check for a loose or jiggly brown lead wire at the |
Check to see whether if the spark plugs are
actually "sparking". If not, I'd try swapping in a new distributor cap & rotor to see if that'll resurrect your engine from it's slumber.
Agreed, you have a poor connection somewhere 'in the brown wires' (including the battery to starter motor cable) or a ground strap.
|Are you hearing a click from the starter relay near the fusebox? Or a clonk from the solenoid on the starter? |
If the solenoid is clonking but no cranking, is the ignition warning light dimming right down or barely at all?
If dimming then either the solenoid is applying power to the starter motor but something is preventing the motor from turning, or possibly there is a bad connection between the battery and the solenoid so there isn't enough voltage at the motor to turn it. However in this 2nd scenario there is usually not enough voltage to hold in the solenoid either, so it chatters.
If not dimming then power isn't getting as far as the motor windings, either because the solenoid contacts are bad, the motor brushes or commutator are bad, bad connections between the two, or there is a dead segment on the motor.
If it is the relay you can hear but not the solenoid then check that the is extending 12v from its brown wire onto its brown/white wire and this is getting onto the solenoid spade. If so the solenoid is open-circuit.
|Paul Hunt 2|
|Steve et all,|
I think its a clonk at the starter motor - although i'm not great with these things.
The problem is its not really a "dimming" of the igniton light its a complete abscence of voltage at any device.
A dodgy ground would do this but i can see why the ground cuts out when the starter is engaged. Its literally turn the key -> all power gone. (even the interior light from the door goes out).
Then all of sudden it all comes back - usually after a bit of jiggling turn the key its straight off again. Would the charge passing through the circuit cause the ground cable at the battery to be repelled in some way thus breaking the circuit ? Thats the only way i can reconcile it in my head - but this really isnt my field at all.
I can't see it being the brown wire to starter, becuase why would that cause the interior light, alt etc lose power ? I can see that stopping the starter working but i can't see how would it effect the rest of the electrics - surely the whole system doesn't go through the starter ? Am i missing something ?
Again any help greatly appreciated, assume nothing I wouldn't know if i've missed something basic.
Suppose you have a poor connection between the battery and the starter motor (including the earth return circuit). The current drawn by the other circuits (ignition light, etc) is not enough to cause a significant voltage drop across the poor connection, so things appear to work normally.
When you attempt to crank the engine, the starter motor takes a very high current and subsequently LOTS of voltage is dropped across the poor connection, so there isn't even enough voltage to illuminate the ign light.
Have a read up on ' OHM'S LAW ' if you would like to learn more.
The puzzling thing is that the ignition light doesn't come back on when you stop attempting to crank the engine.
Do the starter motor or solenoid get hot ?.
Having said all of that, it was cranking ok on the original battery, which only really leaves the battery post connections.
|Simon. I have had this problem before. It was always either a bad battery, bad connection to the battery, bad cable or bad connection to the starter or ground. Yes, the ignition warning light would come on, the key would be turned to the start position and the system would go dead. Then, after a wait, the key could be turned on again and, when it the run position, would give the ignition warning light and dash gauges.|
The first thing to do is either recruit an assistant or make up a long jumper wire to allow you to test various parts of the system with a volt meter while the ignition switch is manipulated. Check the voltage reading at the large terminal of the starter (68 onwards cars) or the starter solenoid with the ignition switch in the run position. Then, turn/have turned the ignition switch to the start position. If you are still seeing 12.0 to 12.5V, the battery, connections to the battery and cables are good. If you are not, there is a problem and you need to check it out.
Check the voltage of the battery at its terminals--should be something over 12V. Then, check the voltage at the terminals when the ignition switch is in the start position. If the voltage drops significantly, say less than 11.5V, look at the battery. If the voltage does not drop, perform the same test using the outside of the battery terminal clamps as your test point. If the voltage does not drop at the terminals, but does drop at the clamps, there is a problem between the terminals and clamps. Clean throughly and replace, then, recheck.
If you have good voltage at the battery clamps and low voltage at the starter, it is either the cable to the starter, the connection at the starter, the ground cable or the connection for the ground cable of the battery. Disconnect the battery ground terminal clamp, attach a jumper cable to the terminal, then to a good ground point on the battery box or on the engine. Check again. If the car starts, bad ground connection/cable. If not, connect the other jumper cable clamp to the starter solenoid terminal and the non-ground terminal of the battery. Try to start the car again. Somewhere in this process, you should find where the fault is, then take steps to correct it.
|There's always the old shade tree method of finding the heat. I think it's one of your big wires, check all of the ends for heat after you give it a crank. Find a hot one? That's the poor connection.|
That said, I had a starter with intermittent grounding of the fields to the case. It would kill a battery's charge almost instantly. Then sometimes it would work. Frustrating, but that was the problem 2 or 3 years ago, battery is still cranking, amazingly. So if all else fails, try a known good starter.
|I've had the same problem of ignition warning light, a single click, then no electrics at all and it was a bad connection at the solenoid. It can be caused by either of the battery connectors or the grounding of the battery ground strap, but it wouldn't be the engine ground strap. Problems here affect actual cranking but not warning lights etc. Ironically mine happened while undergoing its annual test at a garage operated by the AA (Automobile Association - roadside assistance and repair!) and they could not suss out what was wrong. I went down there and with a voltmeter showed than that some connectors on the battery stud on the solenoid showed 12v while others didn't. With the car already up on the ramp took about five minutes to remove and clean them all. People always forget the connectors, assuming that because things are physically connected together they must be electrically connected together. It just isn't so, they don't even have to be loose to be disconnected.|
|Paul Hunt 2|
This thread was discussed between 21/01/2006 and 24/01/2006
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