Problem starting engine - electrical-related

[fragmented]

Hi all

I have had a problem that has got progressively worse over time.  If my starter battery is freshly charged it will start. After driving for a few hours I pull into a petrol station to fill up.  When I try to start again the van does not start sometimes leaving me a bit stranded. It's usually OK on a sunny day as I can use solar maintainer to add the extra charge needed to start the engine again but at night I generally cannot risk stopping and turning off the engine was I know it will not have enough charge start the van.

I have been investigating the problem with a voltmeter to see what is going on:
Generally the starter battery holds a charge of 12.9V.  This should be enough to start the van (was in the past) but now it is not. I have an immobiliser/alarm fitted but the alarm does not seem to work any more so don't bother to arm it. However, the immobiliser needs disarming when you turn the ignition on before the van can be cranked obviously.  So the problem is this: If I have a reading of 13.1V on the starter battery (when the solar maintainer has been connected and the weather is sunny) then the van WILL start. But if I start from the night-time/dull weather starting point of 12.9V the van stubbornly fails to start.

On further investigation I found the following:
Voltage on starter battery before starting ignition: 13.1V
Voltage on starter battery after immobiliser disabled by key fob: 12.5V
Van starts - so 12.5V enough to start the engine.

But this DOES show that on disarming the immobiliser there is an immediate voltage drop of 0.6 V.

My main question is what could be causing that drop in voltage - could it be the faulty immobiliser or is it something that is connected to the ignition circuit that is drawing current?  Has anyone else had this problem in the past that could shed some light please? Any advice about the best way to troubleshoot this would be greatly appreciated.

Van is 1983 T25 1.9 Petrol DG engine WBX

[mrhutch]

have you measured the voltage drop when cranking??  a dropped cell in a battery can show 12v+ when no load but drop to under 9 when under cranking load

[fragmented]

I’ll try that this morning but the battery was new in August as I bought one in France when we were stranded in a car park!

[RogerT]

When you say not starting, what kind of not starting?

1/ cranking and coughing
2/ cranking and no cough
3/ slow cranking
4/ click
5/ dead silent

[ZsZ]

As RogerT said, we need input on the symptom.

No crank no click could mean bad ignition switch or oxidation in trigger wire.
No crank but click - bad starter (eg oxidized wire from solenoid to motor).
Crank but no start - bad ground for ECU (if fuel injected petrol)

And it is two person job, but check voltages also at the starter.

[fragmented]

Thanks guys.  No crank, no click.  Will check ignition switch/trigger wire.

[cotswoldstony]

Hi, testing a battery using a voltmeter will not tell you the condition of a battery it will only show the surface voltage of the combined cells.  This could show good voltage but is not how you test a battery, you need battery testing equipment that can show the cranking amps  the battery has to compare to the battery manufacturer's data normally a CCA (cold cranking amps) number or ETN/DIN number.
I hope this helps.