Fuel relays with/without diode and possible battery drain

[TimJM]

You may recall last week (or maybe the week before) my Griff let me down for the first time due to the fuel pump relay dying. It wasn't too bad a breakdown as I guessed it could be the relay (fuel pump not priming but car fires then dies) and the RAC chap had one in his van that worked and got me home.

I ordered a new one from eurocarparts once they found the right part (the part number has changed from 0332014112 to 450220610) as they have a special offer on them currently. Here is the correct relay with the diode - I advise you to buy a couple as the ECU is the same one whilst they are on offer:
http://www.eurocarparts.com/search/450220610/p/hom...

I didn't drive my car while I was waiting the 6 days for the new relay to arrive because the RAC guy did mention it had been in his van for many years rattling around and he couldn't guarantee how long it would last. Also, the RAC relay doesn't have the diode like the correct BOSCH one does.

When the new relay arrived I went out to the car to swap it over but it didn't unlock. In fact it didn't do anything. I got into the car and put a multimeter on the battery and it showed 0.00 volts. Totally dead.

I thought this was really odd as I have always been amazed at how long the battery lasts in my Griff compared to the Cerbera I used to have. I have posted about it before on here as I have left my car in the past nearly six weeks uncharged and it has started fine. This was 6 days and the battery is totally drained; 0 volts.

I am not sure it it is possible but the the only difference made to the car is the RAC relay without the diode was plugged in. I have recharged the battery (hopefully it will not be knackered) and plugged the new relay with diode back in tonight.

So it could just be coincidence and it may not even be technically possible but would the fuel pump relay without the diode cause a battery drain?

[Loubaruch]

No highly unlikely that these relays have anything to do with battery drain as with the ignition off they are not energised.

More likely are the internal lights relay, immobiliser etc. See info under other threads on here:

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

[spend]

Loubaruch said:

No highly unlikely that these relays have anything to do with battery drain as with the ignition off they are not energised.

Unfortunately the ECU and one of the relays are live with the ignition off in most of the cars I have seen.

One of the things to watch out for when installing alternate ECUs and ensure they only become live with the ignition.

[blitzracing]

The diode is just whats called a flywheel diode, it stops voltage spikes affecting the ECU electronics when the relay is switched off. It has no current draw. The ECU draws current as the internal memory always has power to retain its fuel trim values, but it should not flatten the battery noticeably.

[TimJM]

blitzracing said:

The diode is just whats called a flywheel diode, it stops voltage spikes affecting the ECU electronics when the relay is switched off. It has no current draw. The ECU draws current as the internal memory always has power to retain its fuel trim values, but it should not flatten the battery noticeably.

In that case something else must have gone wrong causing the current draw. I can't see how a battery that has previously after nearly 6 weeks standing stayed over 11v could go from full (12v+) down to 0v in 6 days. Unless the battery is on the way out.

I won't be driving the car again until tomorrow so will check how much it lost today later. I can always put the multimeter on it to see if any significant drain has appeared that wasn't present before.

[Mr Jenks]

Have a good look at the relay the RAC fitted, not just the diode but terminals as well. If its a normal 5 pin changeover type it will give a current drain because the permanent supply will be connected to one of the output terminals with the ignition off. iirc this will feed the o2 sensors and flatten the battery in a couple of days

[rigga]

This is what you want .....

[Mr Jenks]

What you don`t want


|http://thumbsnap.com/QGJCLBzy[/url]

[TimJM]

Mr Jenks said:

Have a good look at the relay the RAC fitted, not just the diode but terminals as well. If its a normal 5 pin changeover type it will give a current drain because the permanent supply will be connected to one of the output terminals with the ignition off. iirc this will feed the o2 sensors and flatten the battery in a couple of days

I think this could be it.

The relay looks pretty old and in fairness it did get me home but it must of caused the battery drain. After putting the new correct BOSCH relay in I left the car for 48 hours and tested the battery and it was at 12.5 volts (from 12.6) so no real drain at all.

The relay is the only thing to change and although some people have said this isn't possible my findings are:

• Before RAC temp relay fitted battery would be fine for up to 6 weeks without running or charging.
• After RAC temp relay put in car was 0.00 volts in 6 days standing.
• After putting new correct relay in car lost under 0.1 volts in 2 days.

If it isn't relay related then it is a massive coincidence.