A car knows!!!!

shane25 · 24th January 2011, 11:29

I've had an offer on my R75 2.0 v6 (selling due to running costs), so as you would expect i went out go give it the once over as its been standing for a couple of months, i've been going out every week or so to start it, apart from the battery being flat its been fine before, starts first turn of the key and everything works fine.

Today giving it the once over i started up by jumping it from the missus foci, started up fine, so i looked at the dash and nothing was working, i had the normal lights (oil, battery etc) on the first turn of the key, but soon as the car was started they all went out and the dash was blank, so i tried everything else in the cab to see what wasn't working:
all dials/displays
elec mirrors
a/c
fans
rear screen heater
fob only unlocks but the button in the cab to lock and unlock the doors work, tried putting the key in to lock and only the drivers door locks.

So far i have checked:
Fuses
plenums
loose earth/cables

If any has any ideas or suggestions please do feel free to speak up

mantianak · 24th January 2011, 16:01

Don't know too much about the electrics but I remember reading a while back that when jump starting the ground shouldn't be grounded to the battery as the power surge can damage the ECU. Grounding it elsewhere (like the alternator) was apparently the best place. Don't know how accurate that is but I hope that's not what's happened to yours.

Have you tried disconnecting the battery for 30mins and trying again?
Does the car still start or crank?
Does central locking work or any other electrics work?
Have you checked all the fuses bothing inside the car and under the bonnet?

James.uk · 24th January 2011, 16:05

Try fully charging the battery off the car..

75's do NOT like having a low charge in their battery..

...

kevin · 24th January 2011, 16:10

Quote:

Originally Posted by James.uk

Try fully charging the battery off the car..

75's do NOT like having a low charge in their battery..

...

shane25 · 24th January 2011, 16:32

Quote:

Originally Posted by James.uk

Try fully charging the battery off the car..

75's do NOT like having a low charge in their battery..

...

Cheers guys, i done that exact thing earlier and it fired up work as it should.

So all sorted

Shane

Jakg · 24th January 2011, 16:41

Quote:

Originally Posted by mantianak

Don't know too much about the electrics but I remember reading a while back that when jump starting the ground shouldn't be grounded to the battery as the power surge can damage the ECU. Grounding it elsewhere (like the alternator) was apparently the best place. Don't know how accurate that is but I hope that's not what's happened to yours.

Sorry to ruin it for you, but everything connects back to the battery by a short bit of cable anyway, won't make a difference.

mantianak · 24th January 2011, 17:13

Quote:

Originally Posted by Jakg

Sorry to ruin it for you, but everything connects back to the battery by a short bit of cable anyway, won't make a difference.

Yes I'm aware of that. But even the AA recomend not connecting the negative to the battery but to a grounding point elsewhere. Although they don't state why. Also they say wait 3 minutes turn the car off then start them both without the leads. I assume this is due to voltage spike from cranking which could damage the electical systems (although probably the donor car). I'm sure the cars can handle it but I would rather play it safe.

http://www.theaa.com/motoring_advice...jumpleads.html

Jakg · 24th January 2011, 17:25

Quote:

Originally Posted by mantianak

Yes I'm aware of that. But even the AA recomend not connecting the negative to the battery but to a grounding point elsewhere. Although they don't state why. Also they say wait 3 minutes turn the car off then start them both without the leads. I assume this is due to voltage spike from cranking which could damage the electical systems (although probably the donor car). I'm sure the cars can handle it but I would rather play it safe.

http://www.theaa.com/motoring_advice...jumpleads.html

The idea is that when you connect the final wire, you will probably get a spark. The idea is that if you connect this to the battery, you *may* ignore the vapors, which could cause an explosion.

For this reason, you are meant to connect the last one up away from the battery, which you can do by connecting it to the body...

The voltage etc will be the same as your still connecting to the battery.

raykay · 24th January 2011, 18:28

The reason for leaving the two batteries connected for a period of time is so that some power can flow from the charged battery to the flat battery so there is some power in it, which helps prevent a power spike.

That is how the leads you see that connect to the cigarette lighter work.
If you leave them too long though, you will get two half charged batteries instead of one charged and one flat!

COLVERT · 24th January 2011, 19:22

Quote:

Originally Posted by raykay

The reason for leaving the two batteries connected for a period of time is so that some power can flow from the charged battery to the flat battery so there is some power in it, which helps prevent a power spike.

That is how the leads you see that connect to the cigarette lighter work.
If you leave them too long though, you will get two half charged batteries instead of one charged and one flat!

That is absolutely not true !!!!
To understand it you must think in terms of water !!!!
If you have a tank one foot in diameter next to a tank ten feet in diameter and they are both full to the same level in water.
Then connect the tanks together with a pipe, say halfway down, the water from the large tank will NOT flow into the small tank.
The surface level of both will remain EXactly the same.
Obviously the large tank will hold much much more water than the small tank.
Now back to batteries.
The voltage in the two batteries, in good condition, will be twelve volts whether they are charged or discharged. ( ie. the height of the two tanks of water ) no flow between them.
The capacity of the batteries (ie. their ability to do work ) will be the volume of water in the respective tanks.
There will be no flow between the charged and discharged battery because their voltage is the same !! ( Height of water in the two
joined tanks. )
So, little tank ( Discharged battery, will not have enough capacity to start the car )
And big tank ( Charged battery, will start the car with power to spare. ) Even though both have twelve volts. ( Pressure of electricity. )
So you cannot charge one twelve volt battery to another by joining them together.

Colvert.

24th January 2011, 11:29	#1
shane25 Regular poster Rover 75 Saloon V6 2.0 Join Date: Nov 2008 Location: Beccles, Suffolk Posts: 45 Thanks: 0 Thanked 0 Times in 0 Posts	A car knows!!!! I've had an offer on my R75 2.0 v6 (selling due to running costs), so as you would expect i went out go give it the once over as its been standing for a couple of months, i've been going out every week or so to start it, apart from the battery being flat its been fine before, starts first turn of the key and everything works fine. Today giving it the once over i started up by jumping it from the missus foci, started up fine, so i looked at the dash and nothing was working, i had the normal lights (oil, battery etc) on the first turn of the key, but soon as the car was started they all went out and the dash was blank, so i tried everything else in the cab to see what wasn't working: all dials/displays elec mirrors a/c fans rear screen heater fob only unlocks but the button in the cab to lock and unlock the doors work, tried putting the key in to lock and only the drivers door locks. So far i have checked: Fuses plenums loose earth/cables If any has any ideas or suggestions please do feel free to speak up __________________ http://img.photobucket.com/albums/v3...verturbo-1.jpg

24th January 2011, 16:01	#2
mantianak I really should get out more....... ZT 190+ Saloon Join Date: Nov 2006 Location: Poole Posts: 2,413 Thanks: 6 Thanked 22 Times in 21 Posts	Don't know too much about the electrics but I remember reading a while back that when jump starting the ground shouldn't be grounded to the battery as the power surge can damage the ECU. Grounding it elsewhere (like the alternator) was apparently the best place. Don't know how accurate that is but I hope that's not what's happened to yours. Have you tried disconnecting the battery for 30mins and trying again? Does the car still start or crank? Does central locking work or any other electrics work? Have you checked all the fuses bothing inside the car and under the bonnet? __________________ http://i35.photobucket.com/albums/d1..._signature.png

24th January 2011, 16:05	#3
James.uk Passed Away 2002 Pale Blue. Rover 75 CDTi Connoisseur auto. 170K miles Join Date: Dec 2008 Location: Near the M67. Posts: 14,509 Thanks: 199 Thanked 585 Times in 397 Posts	Try fully charging the battery off the car.. 75's do NOT like having a low charge in their battery.. ...

24th January 2011, 18:28	#9
raykay I really should get out more....... Now Other Manufacturer Join Date: Nov 2006 Location: Co. Kerry Posts: 2,786 Thanks: 16 Thanked 310 Times in 283 Posts	The reason for leaving the two batteries connected for a period of time is so that some power can flow from the charged battery to the flat battery so there is some power in it, which helps prevent a power spike. That is how the leads you see that connect to the cigarette lighter work. If you leave them too long though, you will get two half charged batteries instead of one charged and one flat!