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Question on car batterys
jacko - 14/1/14 at 05:11 PM

Hi All the boss has a corsa b 1000cc the engine had started to run a bit rough and the engine management light keeps coming on
If i sit and rev it the light goes out and the roughness goes away
I have just put a battery charger on and the charger is showing the battery too be flat
Could this be why the engine is running rough ?

Thank's jacko

John P - 14/1/14 at 05:28 PM

Not sure how relevant this is but I had very similar problems with my Mazda 6 after the battery was removed for replacement.

Straight afterwards the engine ran very rough and it kept stalling when pulling up at junctions but at speed ran fine.

Having searched various forums I found that by disconnecting the battery the ECU had lost the idling strategy and it had to be re-learned by leaving the car running at tickover for 10 minutes with everything turned off then turning on the air-con to provide some load and again leaving it to tickover for another 10 minutes.

Worked fine and afterwards the engine ran as it had before fitting the new battery.

John.

garyo - 14/1/14 at 05:29 PM

Same thing happened to me with a K series engine. Rough idling, had me going round in circles. A new battery was like having a new engine.... so it's definitely possible.

Jenko - 14/1/14 at 05:41 PM

Check voltage when the engine is on...you should get a good 13v plus across the terminals.....less than this could also mean the alternator is not doing it's job......

deezee - 14/1/14 at 06:13 PM

quote:
Originally posted by John P
the ECU had lost the idling strategy and it had to be re-learned


Kinda. It will loose its trim values for sensors. It isn't learning though, just adjusting and saving the trim values. An ECU doesn't need 10 minutes to adjust, it just needs full sensor range. So engine cold and engine hot. Air con on and Air con off. Lights on, Lights off, Rich mixture and Lean mixture. It has values for all these, but an engine just reads sensors and relates it to its model or map. Like when you pop in higher octane petrol, the knock sensor reports less knock, so it advances the ignition. Its not learning and writing a map though, it knows what to do with each sensor value, its just saving all these values so it doesn't do it every time you turn the key.

But to answer the original question. Battery sounds goosed. If it won't hold a charge, just swap it. It will only get worse until the car won't start.

bi22le - 14/1/14 at 06:19 PM

I would expect the battery light to be on if the alturnater is giving no or low charge.

perksy - 14/1/14 at 06:22 PM

If memory serves me right most Engine management systems need 10volts to function correctly and if the battery is on the way out you'll get all sorts of problems

jacko - 14/1/14 at 06:27 PM

It's NOT the battery light
it's the engine management light the one with a picture of a engine on
thats why i didn't think it was the alternator

MikeRJ - 14/1/14 at 06:50 PM

quote:
Originally posted by deezee

Kinda. It will loose its trim values for sensors. It isn't learning though, just adjusting and saving the trim values. An ECU doesn't need 10 minutes to adjust, it just needs full sensor range.


It needs a LOT longer than 10 minutes to restore the long term fuel trim tables.

coyoteboy - 14/1/14 at 07:02 PM

quote:

Like when you pop in higher octane petrol, the knock sensor reports less knock, so it advances the ignition. Its not learning and writing a map though, it knows what to do with each sensor value, its just saving all these values so it doesn't do it every time you turn the key.


TBH the knock sensor works as negative feedback - the tables are set for best performance, adding high octane fuel just reduces knock and lets the ECU run up to the max advance levels where normally it would be retarded by knock events.

It is learning, it's learning its sensor limits and adjusting trims to suit. I know where you're coming from, it's not learning the best control strategy, but it is learning sensor values and how they relate to AFRs on THIS hardware. short term fuel trims are in the order of seconds, long term take hours of driving across the board.

The simple answer is yes a low battery can cause issues (loss of trims etc) and yes a low battery can take you into the realms of "questionable" voltage correction levels for both spark and fuel control (they never expected to have to deal with 9v and running normally, so if you have a damaged battery you could see this state and it not be well catered for).

Batteries are cheap. Generally. But you should see ~13.6+v while running, even at idle, if the alt is working. If it is, and it's still running rough after a 30 minute drive it's less likely to be that.

deezee - 14/1/14 at 07:24 PM

quote:
Originally posted by MikeRJ

It needs a LOT longer than 10 minutes to restore the long term fuel trim tables.


I dunno, anywhere from 10 seconds to 1 minute to update the LTFT. 1 minute is A LOT of time for an engine revving away! What ECU have you used that takes more than 10 minutes to update the LTFT tables?

gremlin1234 - 14/1/14 at 08:11 PM

I guess its just a car used round town?
often a long (and fast if possible!) run helps clear 'the cobwebs'

and yes failing batteries manifest themselves in many ways

jacko - 14/1/14 at 08:49 PM

quote:
Originally posted by gremlin1234
I guess its just a car used round town?
often a long (and fast if possible!) run helps clear 'the cobwebs'

and yes failing batteries manifest themselves in many ways


You guess right its a town 6 miles a day car
I do thrash the guts out of it if i use it but this is not just cobwebs
I will see how it goes tomorrow after a good battery charge tonight
Thanks
Jacko

MikeRJ - 5/2/14 at 04:55 PM

quote:
Originally posted by deezee
quote:
Originally posted by MikeRJ

It needs a LOT longer than 10 minutes to restore the long term fuel trim tables.


I dunno, anywhere from 10 seconds to 1 minute to update the LTFT. 1 minute is A LOT of time for an engine revving away! What ECU have you used that takes more than 10 minutes to update the LTFT tables? [/quote

Delayed reply I know, but the answer is: All of them. The LTFT at a specific load and rpm will be updated pretty quickly with the engine running at steady state, but to fill the entire LTFT table requires the engine to spend sufficient time at all useful operating loads and RPMs and that simply doesn't happen in 10 minutes on a road.