db9 starting issue

[ian448]

2005 db9 , when starting the car from cold the engine really cranks over with some vigour but then when warm and restarting it sounds really laboured when turning over / cranking.

I would have thought the opposite would be the case, is it normal or have I a possible issue ?

thanks in advance

[sidewaysste]

On other vehicles I've had similar issues - this has usually been due to a failing starter motor - they can swell and bind and the armature windings can break down with heat.

There may of course be a completely different DB9 specific issue that I'm not aware of.

[8Tech]

Sounds to me like the heat soak could be stressing the starter motor. Try doing a current draw test when starting the car from cold and again from hot. If the draw is around the same, then I would suspect the starter motor, if the current required to start it when hot increases, you have a serious issue if the engine is tightening up when hot.

[R129 300SL]

Hi

This is a common problem on a Porsche 911.

Is to do with the earth wire to starter motor connection. At hot temp I think resistance increases.

We had issue on a 996 and remedy is to replace the wire that connects starter motor to battery. Comes as a loom of sorts.

May be worth checking corrosion at connectors?

[belfry]

I had the same on a 911. It was a corroded earth strap. Once cleaned the starter motor worked fine again. Only happened on hot starts.

[ian448]

Thanks for the replies , would a new battery with a higher cca help do you think ?

[belfry]

No need to change the battery if it's a corroded earth strap. Try there first. It'll be much cheaper!

[AM4884]

+1 on corroded ground straps...

I will stretch out on the limb here and say that many of the electricity related gremlins folks chase are bad earths. I've had the loom out of my DB9 and every ground was marginal at best. Light cleaning, new nuts for all of them. I guess 15 years of pampered living is still 15 years!

[ian448]

I’m presuming the earth strap will be off the starter selonoid

[8Tech]

ian448 said:

Thanks for the replies , would a new battery with a higher cca help do you think ?

No, however much power the battery has, it still cant pass the current if the connection to the starter is poor.

[8Tech]

ian448 said:

I’m presuming the earth strap will be off the starter selonoid

Unlikely, there will only be a main 12v and a switched 12v to the starter, the earth is where its bolted to the engine, and then the engine will have an earth strap somewhere.

[AM4884]

DB9 Starter has two 12 leads - one switched (low current), one not switched (high current). The high current lead come down along the front chassis box beam and bolts to the chassis just behind where the front "k" frame mounts to the main tub. There are three ground strap points there as well.

The starter is grounded to the engine by being bolted to it, which is grounded by the torque tube by being bolted to it, which connects to the main tub down along the RHS near the power connection.