Voltage drop - car not starting

[Rawhide]

My car is a third car and due to these problems seeing even less use. I had a problem where occasionally the starter would not fire. It was sporadic but very annoying. Sometime I would be stranded waiting for AA then the car would just start.

I had battery replaced by AA for a new unit. The car also had a new engine fitted by Dan at SJM who did not report anything wrong.

The faults kept happening but the car seemed OK if constantly on CTEK overnight. The alternator is good. I get 14v whilst running and fully charged.

I paid an auto electrician an hour who diagnosed starter motor failure. However after he left the car just started so he came back and diagnosed one of the pink relays was dodgy. He said all other wiring looked OK.

I replaced the pink relay with one from eBay and the car ran fine again. However the battery won't keep charge still. I had AA replace it again under warranty but the fault is still there. I'm now down three batteries and don't want to swap another.

I have a multimeter but have never really used it. I am not really sure where to start and the fault finding procedure.

The electrician said the fault was between the relay and the starter motor but I can't see how that would cause a voltage drain? The two pink relays both work when swapped but one had embossed font and the other does not.

I not wanting to take it to a garage if it's something I could fix myself.

Any ideas or video links to help learning welcome please!

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[Rawhide]

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[bashracing]

Start by cleaning the earth points,
Also check the voltage drop over 24hrs then try removing the power and exciter wire off the alternator and check the voltage drop again over 24 he period

 

[GrahamS]

When you say voltage drop that is usually a wire which drops voltage when current passes through. The starter motor earth is the strap from the gearbox to the chassis rail, clean up all contacts on that.

Voltage drop can be tested at each point of the circuit. You test the circuit with no load and then with load. If the voltage changes dramatically then you have voltage drop and it's likely the wire/connector is faulty. You're not looking for continuity because a cable causing voltage drop will likely still have continuity.

As an example this was in the fuel pump circuit of a car I had, it had continuity and 12v until you connected the fuel pump on the wire and it started to draw current. This wire was actually just under all the relays you're looking at as it's a common place for the insulation breaking and water getting in.

This is a very good video and has helped me test parts in the past.

 

[Rawhide]

Thanks for the replys so far guys. Really appreciated. I cleaned up the earth from the battery already but will look for the starter earth next.

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[bloke]

This is a very good video and has helped me test parts in the past.

think i've sent that one to a couple of people, is it the one where he explains it like a hose pipe?

 

[DanSej6]

Battery drain would be the correct way to describe it. Voltage drop is a resistance issue.
You can trace a drain via measuring microvoltages across fuses or using the ammeter setting on your multimeter.

 

[GrahamS]

think i've sent that one to a couple of people, is it the one where he explains it like a hose pipe?

yeah certainly is. Really helped identify the wire I found corroded.

 

[Rawhide]

I've had my father in law round and with the multimeter we've identified there is a draw of 2.6amp. We've disconnected the alternator and also the starter connection from the battery positive.
All doors are closed and the 5amp interior fuse is removed also. We're unsure on where to go from here.

Any ideas really welcome..

 

[Rawhide]

I've had my father in law round and with the multimeter we've identified there is a draw of 2.6amp. We've disconnected the alternator and also the starter connection from the battery positive.
All doors are closed and the 5amp interior fuse is removed also. We're unsure on where to go from here.

Any ideas really welcome..

EDIT - the draw is 0.4amp (400ma)

 

[DanSej6]

As said earlier, micro voltage measurement across the fuses. Or pull fuses until the ampage drops away.
You may need to leave everything for half hour or so for all the control units to be fully switched off so you don't get a false reading.

 

[Rawhide]

I had my car on CLIP today and checked over. They can find no fault and advise the draw is about right.

We now think me leaving my car unlocked is causing the problem. I had no idea that would cause a higher drain.

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