Causes for slacking AFR jump to 234?

colman · 08-16-2020, 05:57 PM

My bank 1 AFR is lagging behind when letting of the throttle. This happens when just cruising around and on WOT pulls. My STFTs also don't follow well.

I have replaced 2/3 injectors on bank 1, about to do the third. Out of curiosity, could anything else cause this issue besides leaking injectors? They were all index 12 to begin with.

_N54 · 08-16-2020, 08:33 PM

Got a log? Curious to see it.

colman · 08-16-2020, 08:49 PM

Quote:

Originally Posted by ///S58

Got a log? Curious to see it.

Here's one:

https://datazap.me/u/criemersma1/sta...&data=3-23

I've taken a few more with the same results (still going after the boost leak).

Also, I have tried cranking the car with the injectors unplugged electrically and out of the engine which I've seen some do in videos to track down leaks. I didn't have any leaks in that test.

So I'm curious of that test's validity, or if something else like O2s could cause this issue. Obviously more will be known after replacing the 3rd injector.

JM98 · 08-16-2020, 08:57 PM

Leaky injector. You have an injector continuing to introduce fuel to that bank after the throttle is closed.

BM3Rrrr · 08-16-2020, 09:46 PM

I dont see anything wrong with the STFT's
JM98 is correct, the AFR lagging behind is a leaking injector.
Even index 12's can potentially leak, easiest way to test this is to let the car sit overnight and pull the spark plugs to check if they are wet/smell of fuel

Soden82 · 08-16-2020, 10:19 PM

Quote:

Originally Posted by colman

My bank 1 AFR is lagging behind when letting of the throttle. This happens when just cruising around and on WOT pulls. My STFTs also don't follow well.

I have replaced 2/3 injectors on bank 1, about to do the third. Out of curiosity, could anything else cause this issue besides leaking injectors? They were all index 12 to begin with.

My bank 2 does that. As stated could be a leaking injector, or possible a vacuum leak somewhere in the system.

Donutz · 08-17-2020, 01:55 PM

Subscribed. I have this on both banks when I lift off throttle.

dpaul · 08-20-2020, 06:57 PM

Quote:

Originally Posted by colman

My bank 1 AFR is lagging behind when letting of the throttle. This happens when just cruising around and on WOT pulls. My STFTs also don't follow well.

I have replaced 2/3 injectors on bank 1, about to do the third. Out of curiosity, could anything else cause this issue besides leaking injectors? They were all index 12 to begin with.

Yes, aging/dying pre-cat O2 sensors can present with that behavior. They get slow to respond. I'd agree with the other posters that the most common explanation is a leaky injector but since you've replaced 2 out of 3 on this bank without effect, the odds are improving for a different explanation than injectors.

colman · 08-20-2020, 09:48 PM

Quote:

Originally Posted by dpaul

Quote:

Originally Posted by colman

My bank 1 AFR is lagging behind when letting of the throttle. This happens when just cruising around and on WOT pulls. My STFTs also don't follow well.

I have replaced 2/3 injectors on bank 1, about to do the third. Out of curiosity, could anything else cause this issue besides leaking injectors? They were all index 12 to begin with.

Yes, aging/dying pre-cat O2 sensors can present with that behavior. They get slow to respond. I'd agree with the other posters that the most common explanation is a leaky injector but since you've replaced 2 out of 3 on this bank without effect, the odds are improving for a different explanation than injectors.

I think you are right! I just replaced the entire bank with no effect. I did run live O2 voltage through inpa and everything looked good, but that still wouldn't necessarily show an O2 that was slow to respond.

zomski101 · 08-21-2020, 12:09 AM

Leaking valve cover and/or gasket can cause this too. Did you have oil on the injectors?

colman · 08-21-2020, 09:42 AM

Quote:

Originally Posted by zomski101

Leaking valve cover and/or gasket can cause this too. Did you have oil on the injectors?

I did not, but I have replaced the VC in this process as well. I would have to lean toward O2 issues at this point. They are original and have close to 140k on them

RoughKnight · 08-21-2020, 12:56 PM

OMG this happens to me all the time since the DP's. I let off the throttle and they both read 234

stewbets · 08-21-2020, 01:21 PM

Quote:

Originally Posted by RoughKnight

OMG this happens to me all the time since the DP's. I let off the throttle and they both read 234

It's normal for both of them to go to 234 when you let off the throttle and coast. It's not normal for one of the banks to lag behind the other, but a sign that there's likely a fuel leak or sensor issue. They should mirror each other pretty closely.

stewbets · 08-21-2020, 01:23 PM

Quote:

Originally Posted by zomski101

Leaking valve cover and/or gasket can cause this too. Did you have oil on the injectors?

I haven't heard this before. Not saying you're wrong. I just don't understand the logic.

colman · 10-09-2020, 12:29 PM

Update: all 3 bank one injectors replaced, VC replaced, bank one pre-cat 02 replaced, adaptations reset.

Now the bank one AFR won't even get to 234.5 and just hangs out around 220.

Bmacc0 · 06-09-2023, 06:28 PM

Sorry to bring up this old post.. Im having the same issue in bank 1 all new injectors.. I see yours just hung around 220 after o2 replacement. Were you able to fix it? If so how might I ask.

Jerr135I · 07-04-2023, 01:49 PM

Same situation as OP, I would like to know what else can cause this.

Dav3 · 12-20-2023, 06:48 PM

Reviving ancient thread, but any reasons/fixes for this?

All my injectors are new and moving them between banks doesn’t change the rich afr on decel

Biggsie · 01-12-2024, 06:55 AM

Quote:

Originally Posted by Dav3

Reviving ancient thread, but any reasons/fixes for this?

All my injectors are new and moving them between banks doesn’t change the rich afr on decel

I would also like to know....

Dav3 · 01-18-2024, 07:02 AM

Quote:

Originally Posted by Biggsie

I would also like to know....

Based on my research of people with similar situations the culprits could be:

- Defective Injectors or bad seals/decouplers (new, didn’t fix it)
- Valve Cover and gasket (new, didn’t fix it)
- Bad O2 sensors
- Bad turbos

Doing hybrid turbos in the near future with new o2 sensors, so will report back if it fixes it

08-16-2020, 05:57 PM	#1
colman Enlisted Member 3 Rep 35 Posts Drives: E61 535xi MT, E92 335xi AT Join Date: Oct 2019 Location: Grand Rapids, MI iTrader: (0)	Causes for slacking AFR jump to 234? My bank 1 AFR is lagging behind when letting of the throttle. This happens when just cruising around and on WOT pulls. My STFTs also don't follow well. I have replaced 2/3 injectors on bank 1, about to do the third. Out of curiosity, could anything else cause this issue besides leaking injectors? They were all index 12 to begin with.
	Appreciate 0 Tweet Quote

08-16-2020, 08:33 PM	#2
_N54 Captain 300 Rep 884 Posts Drives: 335d Join Date: Mar 2020 Location: USA iTrader: (0)	Got a log? Curious to see it. __________________ 2013 335is - sold 2011 335d
	Appreciate 0 Quote

08-16-2020, 08:57 PM	#4
JM98 Lieutenant 391 Rep 532 Posts Drives: 2009 135i Join Date: May 2016 Location: SoCal iTrader: (0)	Leaky injector. You have an injector continuing to introduce fuel to that bank after the throttle is closed.
	Appreciate 0 Quote

08-16-2020, 09:46 PM	#5
BM3Rrrr Davy Jones, Giant Squid 271 Rep 913 Posts Drives: a Pirate Ship Join Date: Jun 2015 Location: The Isle of Tortuga iTrader: (0)	I dont see anything wrong with the STFT's JM98 is correct, the AFR lagging behind is a leaking injector. Even index 12's can potentially leak, easiest way to test this is to let the car sit overnight and pull the spark plugs to check if they are wet/smell of fuel __________________ 2010 e90 335i LCI - xHP - Mishimoto - BMS - CPe - Turbosmart - MHD - Eibach - Koni - VMR - LUX
	Appreciate 0 Quote

08-17-2020, 01:55 PM	#7
Donutz Lieutenant 140 Rep 476 Posts Drives: 335i Join Date: Sep 2015 Location: Toronto, eh iTrader: (2)	Subscribed. I have this on both banks when I lift off throttle.
	Appreciate 0 Quote

08-21-2020, 12:09 AM	#10
zomski101 Private First Class 55 Rep 147 Posts Drives: 2009 BMW 335i Join Date: May 2018 Location: Chicago, IL iTrader: (0)	Leaking valve cover and/or gasket can cause this too. Did you have oil on the injectors? __________________ 09 335i - MMP stage 3, fbo
	Appreciate 0 Quote

08-21-2020, 12:56 PM	#12
RoughKnight Private First Class 54 Rep 174 Posts Drives: BMW 335xi N54 Auto Join Date: Apr 2019 Location: Ottawa Ontario iTrader: (0)	OMG this happens to me all the time since the DP's. I let off the throttle and they both read 234 __________________ -------------------------------------------------------- ARM CP, DP, 7.5 FMIC, TiAl Q Bov MHD Stage2+/xHP/xDelete Road to 500hp daily on the way (ya right lol) --------------------------------------------------------
	Appreciate 0 Quote

10-09-2020, 12:29 PM	#15
colman Enlisted Member 3 Rep 35 Posts Drives: E61 535xi MT, E92 335xi AT Join Date: Oct 2019 Location: Grand Rapids, MI iTrader: (0)	Update: all 3 bank one injectors replaced, VC replaced, bank one pre-cat 02 replaced, adaptations reset. Now the bank one AFR won't even get to 234.5 and just hangs out around 220.
	Appreciate 0 Quote

06-09-2023, 06:28 PM	#16
Bmacc0 Registered 0 Rep 2 Posts Drives: Bmw 335 xdrive Join Date: Jun 2022 Location: Canada iTrader: (0)	Sorry to bring up this old post.. Im having the same issue in bank 1 all new injectors.. I see yours just hung around 220 after o2 replacement. Were you able to fix it? If so how might I ask.
	Appreciate 0 Quote

07-04-2023, 01:49 PM	#17
Jerr135I Registered 0 Rep 3 Posts Drives: 2009 135i Join Date: Apr 2023 Location: Toronto, Ontario iTrader: (0)	Same situation as OP, I would like to know what else can cause this.
	Appreciate 0 Quote

12-20-2023, 06:48 PM	#18
Dav3 Major 949 Rep 1,027 Posts Drives: G87 M2/E89 35is/F21 M140i/GT4 Join Date: Oct 2016 Location: Europe iTrader: (0)	Reviving ancient thread, but any reasons/fixes for this? All my injectors are new and moving them between banks doesn’t change the rich afr on decel
	Appreciate 0 Quote