Engine dying with lights on

kilk

I took my friend's hymer for a few days recently. I discovered the engine tended to lose power and I feared would come to a halt when I switched on the lights whilst driving. I stopped on the side of a road and found that I could switch on the lights while engine was idle with no loss of power. I then could continue driving with the lights on. Any ideas on why this is?

petrol or diesel?

crabbypaddy

Id be thinking earth but its odd it doesn't happen at idle, inrush current for headlamps is up to 5 times the steady state current so can drop the voltage significantly. Maybe vibration of dodgy earth strap is dropping it more.

If there's aftermarket hids installed they can spew interference also.

If its one of the new fangled can bus stalks then all bets are off. Need more info year model engine etc.

crabbypaddy

crabbypaddy wrote: »

inrush current for headlamps is up to 5 times the steady state current so can drop the voltage significantly.

Closer double P.

crabbypaddy

Sir Liamalot wrote: »

Closer double P.

Its only a couple of milliseconds but you know what the electrickery is like nowadays.

kilk

Sir Liamalot wrote: »

petrol or diesel?

Diesel.

kilk

crabbypaddy wrote: »

Id be thinking earth but its odd it doesn't happen at idle, inrush current for headlamps is up to 5 times the steady state current so can drop the voltage significantly. Maybe vibration of dodgy earth strap is dropping it more.

If there's aftermarket hids installed they can spew interference also.

If its one of the new fangled can bus stalks then all bets are off. Need more info year model engine etc.

Just to clarify, it also loses power when parking lights are switched on when driving.
It's a '05 model with 2.8 fiat engine, I don't think there is any aftermarket stuff installed. The leisure battery was replaced just before I took it out. The old one was unchargeable.

crabbypaddy

crabbypaddy wrote: »

you know what the electrickery is like nowadays.

For intents and porpoises it's just under double from the point of view of the fuse, alternator compensation and my clamp meter set to inrush.

Kilk, if you could monitor the voltage drop when it happens and report back that would help.

I suspect a mechanical issue eg. alternator bearing shot, slipping belt.
Any belt squeak? Is the serpentine belt running true?
Any resistance on the alternator pulley with the belt off?
Could be an oddball electrical short or super krusty ground strap too I suppose.

Strange one....

kilk

Sir Liamalot wrote: »

For intents and porpoises it's just under double from the point of view of the fuse, alternator compensation and my clamp meter set to inrush.

Kilk, if you could monitor the voltage drop when it happens and report back that would help.

I suspect a mechanical issue eg. alternator bearing shot, slipping belt.
Any belt squeak? Is the serpentine belt running true?
Any resistance on the alternator pulley with the belt off?
Could be an oddball electrical short or super krusty ground strap too I suppose.

Strange one....

I'm not very mechanically minded... what is the serpentine belt? I just notice the loss of power when driving and I switch on the lights. I only discovered by fluke that I could switch on the lights when engine is idling.:)

It's what used to be a fan belt before electronic fans. Runs the accesories like alternator, water pump, power steering pump etc. from the engine crank pulley.

crabbypaddy

If the parking lights are enough to do it then its not likely to be belt related. Does it have cruise control? A cheap elm diagnostic cable plus multiecuscan will allow you to monitor whats happening on the ecu end. One thing that may account for it is if the ecu thinks the brake pedal is pressed due to stray voltage. Such as by bad earth, water ingress / corrosion in the fuse box, or in the cab to chassis junction box for the rear lights or possibly in the rear clusters themselves. Measure the voltage on the taillights when the sidelights are on, check the earth to chassis resistance at the rear clusters, check for voltage on the brake, indicator circuits when the sidelights are turned on.

kilk

crabbypaddy wrote: »

If the parking lights are enough to do it then its not likely to be belt related. Does it have cruise control? A cheap elm diagnostic cable plus multiecuscan will allow you to monitor whats happening on the ecu end. One thing that may account for it is if the ecu thinks the brake pedal is pressed due to stray voltage. Such as by bad earth, water ingress / corrosion in the fuse box, or in the cab to chassis junction box for the rear lights or possibly in the rear clusters themselves. Measure the voltage on the taillights when the sidelights are on, check the earth to chassis resistance at the rear clusters, check for voltage on the brake, indicator circuits when the sidelights are turned on.

It doesn't have cruise control. Thanks for your advice and help.