Weak battery and symptoms????

[sshaunus308]

Hi, is anyone able to help me out with this? On starting, my xj8 is a little lazy. Sometimes it’s hesitant and today, I had to try it a couple of times before the engine even turned over and started. When it does turn over, it starts fine but there is sometimes a delay before anything happens. Is this a result of a weak battery?
Next, IF this is a weak battery, would this affect the functioning of other electrics in the car ie. reverse sensors not working though all individual sensors are working, motorised mirrors working sometimes, like when setting them, but then not working a few days later (and after there were problems turning over engine on starting) and memory seat positions not being recalled even though they were set last time car was used. These little electrical things generally work but sometimes they won’t do stuff they’re suppose to do when programmed. Could this be connected to my intermittent starting problem???

NB the car runs and drives perfectly fine btw. Any help or suggestions would be appreciated

[BrianG]

If your car won't turn over sometimes it could be a dodgy starter solenoid. However it is more likely that the battery voltage is too low. I would get a "drop test" done on the battery. Have you measured the battery voltage? If the battery is older than 5 years then it's probably on the way out. A poor battery will definitely mess up just about anything electronic with stored settings on these cars. You say it's fine when running, but that may mean that once it runs its relying on the alternator to keep things going. This can damage electronic systems due to excess voltage from the alternator, (can go beyond 16V) because the battery is not drawing a normal charge current.

The reason for the delay in anything happening when it does turn over is because the V8 engine needs to know where the piston positions are in the cylinders in order to fire the plugs in the correct order (no distributor on these engines), it does this by looking at pulses from sensors on the camshafts to know where engine cycle is relative to No.1 cylinder, and until it has this worked out it won't fire. Low cranking speed and low battery volts for the engine management electronics all go to make this delay longer and may even prevent it from firing if it gets really bad. A secondary effect could be because low battery voltage may cause low fuel pressure at the injectors while cranking, so insufficient fuel to fire up.

[sshaunus308]

Hi
Thanks for you reply. I'm a bit relieved because I couldn't understand why the electrics were playing tricks on me. I've only had the car for a few months and I know that different cars and engine sizes react differently to low voltage. I think the battery is probably more than 5 years old though hardly used.

[sshaunus308]

Update...

New, more powerful battery and everything, as far as I'm aware, is working properly now. No starting issues. Engine turns over straight away with a growl before it starts its rumbling purr. Parking sensors working properly, electrics working fine.

Glad I checked battery before messing around with the electrics etc...

[Andy P]

Take care
Andy