Severe battery drain after cleaning ECU plug

Vagabondrobb · Apr 3, 2022

Hi guys,

Did random Red ecu plug check and noticed small amount of oil, so sprayed with contact cleaner. Plugged back in, turned the key and starter limped over - no start.

Got the jump leads out and she fires up straight away. Took for a little spin and then checked voltage while still running (14.21 v), and then switched off, believing all fine.

Few hours later battery drained again. Jump start again and left running to recharge a little. Switch off and watched the voltage on the battery steadily decrease on the multimeter (0.1 V every second or so). Disconnect battery and drain stops.

Just for the heck of it I put spare battery in, same thing.

Almost certainly this began after cleaning the ECU plug - been very cold here last week and she has sat for days and started immediately. I had taken her for a drive before cleaning the ECU, so battery should have been pretty full before unplugging.

Anyone had anything similar happen to them? I guess next step is check voltage the fuse plugs, but it does seem so strange that it's all happened after cleaning the red plug!

sierrafery · Apr 3, 2022

Hi. Did you disconnect the battery before you unplugged the ECU? if not it can be a problem cos the ECU might suffer from that, hook a multimeter set on amps in serial with the positive lead(or use a clamp a-meter if you have) to see the drain and according to the result we'll speak again

Vagabondrobb · Apr 3, 2022

sierrafery said:
Hi. Did you disconnect the battery before you unplugged the ECU? if not it can be a problem cos the ECU might suffer from that, if you disconnected the battery then hook a multimeter set on amps in serial with the positive lead or use a clamp a-meter if you have to see the drain and according to the result we'll speak again

I can't remember for sure, but I usually would disconnect at the negative terminal as force of habit, so no reason to think I didn't this time.

By the time I have the engine off and have pulled the leads from the battery the draw in amps is all over the place for the first 15 seconds or so - between 1 and 3 amps! After about 30 secs it settles at about 0.40 and gradually goes down to about 0.05 where it seems to stop, all of which happens over a period of about 3 minutes or so...

sierrafery · Apr 3, 2022

That's quite normal behaviour and at 50mA drain which should drop more after 1 and a half hour when the SLABS goes to sleep there's no reason to kill a powerfull battery in a day, not even in a week

Vagabondrobb · Apr 3, 2022

sierrafery said:
That's quite normal behaviour and at 50mA drain whih should drop more after 1 and a half hour when the SLABS goes to sleep there's no reason to kill a powerfull battery in a day, not even in a week

Thanks for clarifying. With jump leads she fires up immediately and everything is completely normal. I charged battery up at 12.8 V but she wont start on her own.

Think I'm going to check the terminals first think in the morning... Dodgy contact could make sense here (I hope).

Cheers

sierrafery · Apr 3, 2022

Just measure the voltage on your battery while cranking and if it drops below 10.5V that battery is weak no matter how much is charged and it will not start on it, you need a strong and at least 110AH 900CCA battery, the stronger the better

Vagabondrobb · Apr 3, 2022

sierrafery said:
Just measure the voltage on your battery while cranking and if it drops below 10.5V that battery is weak no matter how much is charged and it will not start on it, you need a strong and at least 110AH 900CCA battery, the stronger the better

Will do, thanks!

Vagabondrobb · Apr 5, 2022

sierrafery said:
Just measure the voltage on your battery while cranking and if it drops below 10.5V that battery is weak no matter how much is charged and it will not start on it, you need a strong and at least 110AH 900CCA battery, the stronger the better

Both old and spare batteries were dropping well below the 10.5 v mark, and a new battery solved it - thanks for sharing the wisdom!

Ratae · Apr 5, 2022

Flat batteries need to be fully charged using a battery charger.
Jump starting & taking the vehicle for a quick spin will achieve very little.
www.optimabatteries.com/experience/blog/fact-alternators-are-not-designed-to-charge-dead-batteries (Ignore the redtop/yellowtop/bluetop ad at the bottom.)

If you have spare batteries then these need to be stored off cold floors & need to be regularly put on charge.

sierrafery · Apr 5, 2022

Vagabondrobb said:
Both old and spare batteries were dropping well below the 10.5 v mark, and a new battery solved it - thanks for sharing the wisdom!

Welcome, i'm glad it was just that... now make sure that the charging system is OK to not kill the new battery

JUKE179r · Apr 8, 2022

Keep in mind a battery can show average voltage but have low amps.

sierrafery · Apr 8, 2022

JUKE179r said:
Keep in mind a battery can show average voltage but have low amps.

... and the clear sign of that is that the voltage drops hard under load

Severe battery drain after cleaning ECU plug

Vagabondrobb

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sierrafery

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Vagabondrobb

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sierrafery

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Vagabondrobb

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sierrafery

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Vagabondrobb

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Vagabondrobb

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Ratae

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sierrafery

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JUKE179r

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sierrafery

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