ECU stuck in open loop while idling??? NA6

[Fatty]

i had a bit of a mishap when disconnecting the battery yesterday, i was undoing the - terminal and my spanner touched the + terminal and put on an impromtu fireworks display for me.

so i don't know if it's related, but now the car is not going into closed loop when it's idling. it's also running very rich at idle. i have only discovered these 2 symptoms as i have an AFR metre in my car. it's going into closed loop when cruising, so the o2 sensor is working , at least while cruising.

so i am a bit worried i may have fried some of the electronic doodads, ecu, sensors (most likely the o2 sensor as i know it is rather sensitive) etc when i short circuited the battery.

also, after 30 seconds or so of idling normally (apart from the fact that it's pig rich and in open loop) , it sometimes suddenly starts doing the idle down / idle up that we all know and love. it's doing it rather badly too.

anyone got any thoughts on this? seeing as it's just developed really suddenly and chronically i'm not sure it's the normal idle problem that others often talk about.

[Matty]

Hard to draw a conclusion as it's not like the short should have damaged anything except maybe the battery. You may not be in closed-loop at idle if the O2 sensor has not heated up first (and it will cool down after a while of not driving also). That can be accentuated if the O2 sensor is starting to die. Could possibly be tied into a bad tank of fuel, or any number of other issues.

[AJ]

realistically, the system should be protected against that kind of thing, should blow a fuse or relay before it fries anything............but you're running a piggyback ECU Fatty???.......if so, that may not have the same protection as the factory stuff, you might have to get someone to run a diagnostic on it..............OR, check your fuel map, it may have reset to default with the spike...........................just some suggestions

[Fatty]

matty , that's an interesting point about bad fuel. i had not thought of that. as it happens, i was almost empty yesterday so i topped up at a servo i do not usually go to, and they didn't have any 98. i only got about 12 litres... just enough to get me to and from work today. i will fill up tomorow with vortex 98 from my usual servo and see if that improves things.

as for the o2 sensor not being heated up, i'd thought of that too but nope even after 20 minutes of driving the problem is still there. it should be well and truly warmed up by then.

AJ , yep i run a piggyback fuel ecu but the stock ecu is still in charge of the open / closed loop stuff. the piggyback sits on the AFM wire, in front of the stock ecu. altho yeah, it could be telling the stock ecu to pump in too much petrol i suppose, thus it doesn't go into closed loop.... hmmm. but i don't see any issues other than at idle . it seems to be running just fine everywhere else.

thanks for your thoughts guys.

some other info - the o2 sensor is only about 2 years old, the leads are about a year old, and the plugs are 6 months old. so everything should be sweet

keep the ideas coming!

[mekros]

disconnect the battery, go have a cup of coffee, reconnect it and see how that goes

If anything got scrambled by the fireworks, you would have blanked out the short term memory of the ECU (don't know about the piggyback) and it will relearn everything again.

[Fatty]

ah yes, the old "unplug the battery and clear the fault codes from the ecu" trick. good suggestion, why didn't i think of that?! *slaps forehead?*

so i topped up the fuel with some 98 today and then went on an extended drive home. after about half an hour or so, she suddenly started acting properly and went into closed loop at idle. so it's all good, everything back to normal.

so it was either bad fuel , or fault codes stored in the ecu, that have cleared after xxkm. i think that's how it works , a fault is logged and then it disappears if the fault does not reoccur ??

but anyway, the main thing is that it's all back to normal. thanks for the input guys.

[Sean]

I'd suggest checking TPS is reading as closed when you're at idle.