Car battery drain

[Sumer321]

Serious power drain on battery on Audi 80 1992.30 mins after turning engine off no battery power won't start.ALL main components seem fine.After turning engine off a humming noise comes from back of engine ?this stops if I disconnect negative terminal on battery.Could this be causing power drain.?.if I disconnect negative terminal after turning off it starts fine when reconnected.Any help would be appreciated.thanks.

 

[telectrix]

after switching off get a d.c clamp meter on one of the battery leads. this will tell you what current is being drawn. then investigate, starting with whatever is humming.

 

[rapparee]

You obviously have a parasitic drain.

Is there a light in the glove box or boot staying on?

 

[telectrix]

think it's more than a courtesy light if draining battery in half an hour.

 

[Gary latto]

Clamp meter then whilst showing it's draining start taking out fuses until it stop then will know where to start looking and the noise from rear may be fuel pump

 

[Lucien Nunes]

I think you have two problems, one of which is that the battery is not holding anything like a normal charge. For a normal battery to discharge in 30 minutes to the point where it will not start the engine, the load would need to be 50-100+ amps, which is more than any individual item in the car and will hardly go unnoticed as it will kick out a lot of heat, whatever it is. I suspect that you have a modest parasitic load and a battery of very limited capacity (or that is nor being properly charged).

 

[Sumer321]

Could some fault with fuel pump cause such a quick battery drain.?if so which part ?thanks.

 

[telectrix]

first issue would be a battery check. get it discharge tested. and a test of the charging system. then if battery is OK, look for the drain. as Lucian says, have to be a serious fault to drain a good battery in 30 mins.

 

[Sumer321]

How do you change a relay on a fuel pump?thsnks

 

[plugsandsparks]

Find it, order exactly the same part from bosch or whoever and replace. fuel pump should not be running when you switch off so if it is, the relay is stuck or have wiring fault