potential problem???

[Alastairm]

over the last couple of runs in the Cerbera i've noticed when it is idiling for a minute or so when warm that the revs tend to dip a little-like it's trying to cut out but does not. It's particularly apparent with the lights on, when i switch them off the revs rise-could this be a sign of the batter on the way out?? if so is it easy to switch batteries and is there anything that i need to look out for? Plus which battery do i need???

Thanks in Advance.

[madasahatter]

It could be that when you are sitting idle, the engine heats up, and then the two fans come on to cool the engine (if you have A/C). This would be quite a big drain on the power, and if the lights/back window deminst are on as well it might be the large current drain taking away from other parts of the engine....like the ignition system.

Mine does that too, so if others claim it is not a problem with them, then I am gonna need a battery before too long

[james]

When you put electrical load on the system, it doesn't take electrical power away from the ignition. It just puts more load on the alternator, which then puts more load on the engine. That then slows it down a little. You shouldn't really notice it though. I'd be inclined to get it checked out if I were you.

James

[5MUGHubby]

Reminds me of an old trick to test if your alternator is working; turn lights on at idle, rev engine above idle, if lights become slightly brighter the the alternator is ok (or will get you home)!

[johnmckenzie]

quote:
When you put electrical load on the system, it doesn't take electrical power away from the ignition. It just puts more load on the alternator, which then puts more load on the engine. That then slows it down a little. You shouldn't really notice it though. I'd be inclined to get it checked out if I were you.

James

This is not strictly true. At idle the alternator is putting out a comparatively low output. With a heavy load - say both fans running plus another ancilliary, the current drain will possibly exceed the output from the alternator - net result is a voltage drop in the circuits (basic physics and ohm's law)
However, it is very unlikely indeed that this is the source of the problem. I am given to understand that most electronic ignition units today are very happy running on a fairly wide tolerance of input voltages (anything between 9 and 15 volts). More likely is something like this - as the fans cut in this loads up the alternator to whatever output it can give at those revs. This requires power from the engine to drive it and in normal circumstances the attendant rev drop is compensated for by the idle control circuit in the ECU. Now I'm no expert in this field but it sounds like idle rev compensation isn't taking place satisfactorily. I would have thought it's unlikely to be the ECU itself. Over to Joolz who knows a bloody sight more than I do about how idle control is achieved.

Regards

John

[clarky5150]

When i had my air-con serviced this summer they faffed about with it at tickover, no other electricals on and after about 5 mins of this the tick over dropped and eventually stalled. With stereo, rear screen, lights this im sure would have been seconds as oppose to minutes (6 month old battery fitted with optimate so no fault there) A good run with no ancillaries on sorted it. Nothing since.