URGENT: 98 1.0 will only start off a jump when cold

[stevieg306]

car is a 98 1.0, since the cold weather it is very difficult to start the car off its own battery sometines taking anything upto 30 secs or more of cranking but still it may not start. it will start fine off a jump and will start again after the engine running for a few seconds. need some help quick as i am trying to sell the car

[dannicoll]

If you say it starts fine of a jump it's got to be the battery. Cold weather can affect old car batterys indicating needing replaceing.

[LesterPiglet1]

I agree. Try a different battery.

[stevieg306]

its not the battery, it has a new (6 month old) diesel van battery in at the moment

[dannicoll]

When starting does it sound sluggish or does it seem to turn ok?

[stevieg306]

spins over fine , hook it up to another car and it will spin over a tiny bit quicker

[LesterPiglet1]

Ok then, A lot of peeps have been having problems with crankshaft sensors. Although I say try a different battery.

[stevieg306]

it had a brand new crank sensor a few months ago.
the battery in it at the moment that came out of a mates van, the battery that was in the car starts the van up fine (2.2 common rail turbo diesel).
tested the alternator and it gives out almost 14v, i also tried a jump lead from the battery to the hoist point on the engine incase there was an earth issue.
when cranking off only the battery there is a relay (purple) that clicks irregularly, its to the left of the glovebox when glovebox removed, its on the same relay block as the fuel pump relay and 'lights on' warning buzzer, what is this relay for? i have tried hard wiring this relay on pins 33 and 87 as it would be on a normal relay and the car still wont fire.
sometimes it will fire out of time and stop the starter from turning then the starter will crank the engine again and after a few complete revs of the engine it will fire out of time again.

if you give me a list of things to check then that would help loads, i have already checked the throttle pot against what autodata says and it seems fine, need to finish off the rest of the items on the check list

[LesterPiglet1]

Sorry not an electrical person but if you suspect the relay borrow your mates.

[stevieg306]

its not the relay as i have tested it with my multimeter

[LesterPiglet1]

Sorry but i test like with like.

[stevieg306]

there was another purple relay next to it, swapped the 2 round and still the same, ill try and get a mate to let me try his relay when i see them next

[colly130]

it is the battery ....

[ManicGTI]

Ok, so it starts when jumped...but not normally, but it will crank over fine? So has to be a power issue surely?

As a side note, i'd check all the contacts/terminals on the live leads from batt to starter as well as the earth like already have.