Battery question

[PranK]

Is it possible for a diesel passat to not start because of an old battery even if the engine turns over ok?

Our passat for months has been a bastard to start some days. Leave it for 10 mins and its fine.

On the weekend it totally refused to start, despite turning over fine so today it was towed to mechanics and with a new battery it was fine.

Maybe the glow plugs arnt warming enough?

Thanks in advance.

EDIT: I should add that we usually get some error or fault on the MFI when it fails to start (such as oil pressure fault) but the error disappears when it does start (and is not in the faults.) Over the weekend we had a funny one 'depress clutch' - funny because its a DSG and the clutch depressing was out of my hands.

[booba]

That is very strange. I guess that it is feasible that with the faulty battery that certain computers etc weren't getting enough power and could have been malfunctioning.

[PranK]

That is very strange. I guess that it is feasible that with the faulty battery that certain computers etc weren't getting enough power and could have been malfunctioning.

Yeah thats what I was thinking. What if there was ample power until the engine started cranking and then one or two computers lost power momentarily.

[DonJuan]

The battery will still tend to start your car after you've left it for 10mins even if the cold crank amps are down on what is specified for your car. Cold morning starts after the battery has day around all night is another thing.

You are probably hearing your starter motor turn over, that is normal when it is in good working order, the muscle in the battery may be down compared to new.

It is hard to tell if its the battery from here. Have you hot a multimeter? A flat battery reads 11.9 volts or less. If it is just flat you may have a parasitic draw on your battery which means it will go flat over night. Your alternator should be working ok given that it starts again after leaving it for 10 mins.

Take it to Battery World where they will test your battery for free.

Any other questions, let me know.

[vdubmotorworx]

if its taking that long to start and its turning over at a good speed i would suspect you have a cam/crank sensor fault... if it keeps happening get it code checked...weak batteries on diesel vws do cause poor starting as the crank speed needs to be over 280 rpm for the sensors to trigger but if you are cranking for over 10 mins of trying then sounds like you battery must be good anyway...VDUB..

[Transporter]

Is it possible for a diesel passat to not start because of an old battery even if the engine turns over ok?

Our passat for months has been a bastard to start some days. Leave it for 10 mins and its fine.

On the weekend it totally refused to start, despite turning over fine so today it was towed to mechanics and with a new battery it was fine.

Maybe the glow plugs arnt warming enough?

Thanks in advance.

EDIT: I should add that we usually get some error or fault on the MFI when it fails to start (such as oil pressure fault) but the error disappears when it does start (and is not in the faults.) Over the weekend we had a funny one 'depress clutch' - funny because its a DSG and the clutch depressing was out of my hands.

What's your mechanic saying? Get it looked professionally, don't rely on the internet diagnosis.

[PranK]

Well, the mechanic put a new battery in and has started it 20+ times with runs around the block. Zero issues.

They said the battery was dead as disco, which I knew because we killed it over the weekend trying to start the bastard.

My concern is that this is not a new problem, the weekend was the worst as its never taken more than a 10 - 15 min break for it to start. So, I'm concerned that the problem is not fixed and I'm trying to ascertain whether a slowly dying battery could cause these intermittent problems over a few months before it finally gave up the ghost?

[PranK]

if its taking that long to start and its turning over at a good speed i would suspect you have a cam/crank sensor fault... if it keeps happening get it code checked...weak batteries on diesel vws do cause poor starting as the crank speed needs to be over 280 rpm for the sensors to trigger but if you are cranking for over 10 mins of trying then sounds like you battery must be good anyway...VDUB..

Nono, we'd try two or three times, realise she wouldn't start and then come back after 10 mins. We def wouldn't keep trying for 10 mins solid.

Over the weekend we tried it half a dozen times, waiting the usual 10 mins did nothing.

If the engine needs 280rpm before the sensors even come on, then it would likely sound no different at 250rpm to me and this gives more clout to my theory that as the battery slowly got worse, it was still turning over enough that we wouldn't notice a difference but there wasn't enough power to actually get it running.

maybe ...

[wai]

Well, the mechanic put a new battery in and has started it 20+ times with runs around the block. Zero issues.

They said the battery was dead as disco, which I knew because we killed it over the weekend trying to start the bastard.

Might also want to check out the charging circuit.

[PranK]

Got the car back and while its impossible to tell if the problem still exists, one thing is for certain; I have to hold the key in (start) for half the time I used to. Its almost instantaneous, even when cold. It was never like that before.