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Help - starter motor problem


700newtons

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We are just at the end of a 125 Roadsport build and trying to turn he engine over for the first time. The solenoid seems to engage and disengage rapidly (rapid on and off sequence) without turning the starter motor. Grateful for any wisdom.....

 

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Ah no, at rest the car is at 11.5v and drops to 4v once the ignition is engaged and the solenoid is oscillating on and off. To me, this implies current is passing through the starter motor (but we have got something wrong). Any more ideas ( thanks for your help by the way).

 

Edited by - 700newtons on 24 Jun 2014 16:45:52

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Quoting 700newtons: 
Quoting Jonathan Kay: 

Battery voltage at rest and when you try to start?

 

It drops to 4v...

 

My new battery drops to just over 11v when starting, so try with another battery. Also, measure the voltage drop between ignition off and ignition on, without starting. Then turn the lights on and measure it again. It shouldn't drop my much. If it does, the battery is duff.

 

Just because the battery reads over 12v unloaded, doesn't mean the battery is good. I had 2 bad ones that both read 12.4v unloaded.

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Ok tried a different fully charged battery. When ignition turned we had a large spark near the starter motor. No fuses were blown, no relays damaged. However, solenoid no longer clicks. Dammit.
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Check the engine to chassis earth connection. If it arced then its likely it just needs tightening as the arc has made the poor connection go open circuit. You may have to scrape off a bit of paint, either on the block or the chassis.

If you haven't already you should check the connections to the starter motor as well.

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Ah ha,

 

We took the starter motor out, tested it, put it back. Then success...

 

 

Your earth comments might have been correct or maybe the starter motor was just stuck.

 

 

 

Edited by - 700newtons on 24 Jun 2014 23:40:42

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What kind of fuel pump problems?

 

A classic build issue used to be (probably still is) to accidentally connect the fog lamp to the fuel pump connector and vice versa. When you turn your ignition on, your fog lamp lights briefly and the goes out - and your fuel pump never triggers. 😬

 

I've done it *redface*

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Quoting Myles: 
What kind of fuel pump problems?

 

A classic build issue used to be (probably still is) to accidentally connect the fog lamp to the fuel pump connector and vice versa.

 

No not that... It was just a blown fuse.

 

We have ignition! *cool*

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