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Gtir Motorsport club » Tech room » Help and Advice » AFR starts to lean when engine is warm

AFR starts to lean when engine is warm

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1 AFR starts to lean when engine is warm on 26th November 2014, 1:21 pm

nibbz9999


Hi folks,

I have idle problem with the gtir engine. From cold start. the afr shows fine. around 14-15 afr.. rpm is around 1000k.. but when start to warm up after 10 mins. the afr start to get lean like around 17 to 19.. the rpm is around 900rpm.. what is the possible cause on it?

2 Re: AFR starts to lean when engine is warm on 26th November 2014, 3:05 pm

Whytie

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I wouldn't worry about afr on idle, if the engine sounds fine at idle then it's fine. If the afr is fine driving and on wot that's all that matters.

Back in the days of carbs that's how you set the idle by the sound of the engine ticking over

3 Re: AFR starts to lean when engine is warm on 26th November 2014, 3:59 pm

nibbz9999


okay. however.. the when the engine is warm it starting to have some misfires. in coldstart it's not.. then sometimes the idle is erratic. but when i turn on the AC it its become stable.

4 Re: AFR starts to lean when engine is warm on 26th November 2014, 4:04 pm

Whytie

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If you have misfires then there's an issue.

Will need to go through everything, plugs,maf, fuel pump, fuel filter, leads, vac leak

Where are you

5 Re: AFR starts to lean when engine is warm on 26th November 2014, 4:17 pm

Gaz GTiR

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Mines running at 10.7 on idle Shocked but it ok on part throttle & @WOT on full boost

6 Re: AFR starts to lean when engine is warm on 26th November 2014, 6:19 pm

nibbz9999


actually i was wondering if this could be the aac valve issue? as i read somewhere that if the aac fail then it's starting to get lean.. I have no problem on WOT as it reads 11ish AFR..

7 Re: AFR starts to lean when engine is warm on 26th November 2014, 10:01 pm

nomad

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Fuel pump .... o2 sensor ....?????


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8 Re: AFR starts to lean when engine is warm on 26th November 2014, 11:57 pm

GTI-R US

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As above
The misfire could be caused by dodgy plugs, leads or dizzy cap
Afr's are fine as cold start will be on when cold and as engine warms it will slowly shut off which means leaner running and 17s are all that's really needed at idle
If anything on the sensor side I would check your ecu temp sensor to make sure that's functioning correctly, also a dodgy lambda sensor could also give you issues at idle speeds


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9 Re: AFR starts to lean when engine is warm on 27th November 2014, 1:30 am

Gaz GTiR

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Ahh this may shed some light on my running rich issue then... As cold start idle is 10.7 & stays at 10.7 when hot

10 Re: AFR starts to lean when engine is warm on 27th November 2014, 4:23 pm

nibbz9999


so running on 17 to 19 at idle around 900rpm is fine then? i have no problem when cruising as I can run on 14ish.. as for misfire i have change the plugs and it fine now. but wondering why my idle start to drop when warm up like around 600rpm..

11 Re: AFR starts to lean when engine is warm on 27th November 2014, 4:33 pm

GTI-R US

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yes 17s is not unusual and most widebands are slightly out of calibration so you need to take that into consideration.
as long as when you start to come on boost it richens in line with the boost your running and throttle position to WOT that's what matters, you require very little fuel at idle, partial light throttle or lift off so why waste it when not needed


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12 Re: AFR starts to lean when engine is warm on 27th November 2014, 6:16 pm

Gaz GTiR

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I get 3 --- lines on lift off which means its leaning out, is that right? Its only on lift off tho

Its a AEM eugo wideband

13 Re: AFR starts to lean when engine is warm on 27th November 2014, 6:18 pm

nibbz9999


well i'm jut bit concern as i read the plugs it's a bit greyesh maybe because since I usually i drive on cruise it most often but so far on WOT the afr is fine.

14 Re: AFR starts to lean when engine is warm on 28th November 2014, 12:42 pm

GTI-R US

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@Gaz GTiR wrote:I get 3 --- lines on lift off which means its leaning out, is that right? Its only on lift off tho

Its a AEM eugo wideband

yeah that's quite normal, however with yours gaz as it has the pops n bangs put in to map you need to find out if its going off scale (3 lines you see) by being too rich or lean.
if too lean then not a problem but if its chucking crap loads of fuel in and overly richening on lift off then that could result in problems over time with bore wash which is why I don't hardly ever use that map on my gtr as Ian at Litchfield told me to only use it very occasionally (basically to show off) due to reasons ive just stated.

Nibbz..............that sounds all good to me with regard to your plugs, think you may well be overly worrying about something here.
as long as it all drives ok and not detting or holding back and with afr's as you've mentioned above I personally do not think you have a problem Wink


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15 Re: AFR starts to lean when engine is warm on 28th November 2014, 1:04 pm

Gaz GTiR

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Yeh the pops & bangs only work if you lightly tap the throttle on overrun... If throttle is closed completely then it dousnt work & Wideband reads --- lean.

But as for being rich on idle... Cold start is 10.7 & stays at 10.7 when hot... You can hear the choke cut off after 5 mins of it being started from cold... As it drops from 1400rpm to 1000rpm, so that's normal.
Would the ECU temp senser keep choke on if its telling ECU its cold all the time?

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