Afr goes lean after decel in gear

Tuning concepts, methods, tips etc.

Moderators: jsmcortina, muythaibxr

mk1rocc
Helpful MS/Extra'er
Posts: 71
Joined: Tue Feb 10, 2015 4:20 am

Afr goes lean after decel in gear

Post by mk1rocc »

Hi folks,
After finally getting my engine to rev past 2.5K, the VE map is pretty close after autotune, but I have this issue that I can't find an answer to.
If I accelerate to say 4K and then let off the throttle and decel in gear after I reapply throttle the afr oscillates badly going from very lean to rich.
I played with everything I could think of: overrun fuel cut,accel enrichment, EGO... Still can't solve the issue.
And the issue is a little random because sometimes if after I decelerate in gear and put it in neutral and let it get to idle the Afr is ok, but sometimes not, to solve it I have to restart the engine otherwise the afr stays wild!

I posted a datalog and you can see that after a hard pull in gear the afr goes nuts.
And also I have this issue where sometimes the engine dies after revving the engine and letting the rpm drop suddenly .
2015-08-20_07.53.51.msq
2015-08-18_13.12.48.msl
Matt Cramer
Super MS/Extra'er
Posts: 17499
Joined: Thu Apr 16, 2009 8:08 pm

Re: Afr goes lean after decel in gear

Post by Matt Cramer »

A lot of the oscillation looks like your O2 correction. Try cutting Controller Authority to zero and adjust the VE table to better hit your targets in this region.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
Yves
Super MS/Extra'er
Posts: 1505
Joined: Tue Jun 17, 2014 1:23 pm
Location: Belgium

Re: Afr goes lean after decel in gear

Post by Yves »

AE not right at small throttle openings.
mk1rocc
Helpful MS/Extra'er
Posts: 71
Joined: Tue Feb 10, 2015 4:20 am

Re: Afr goes lean after decel in gear

Post by mk1rocc »

Ok , EGO authority is set to zero, the AFR is ok during accel but the same thing happens on deceleration. IN the attached log you can see starting at 23438s I start to accelerate to 4.6k and then let off the throttle in gear to around 2.2K at that point I try to reapply throttle ut the afr is still lean and oscillating badly like during decel
Why is this ? I can't figure it out .....
2015-08-21_00.23.21.msl
Matt Cramer
Super MS/Extra'er
Posts: 17499
Joined: Thu Apr 16, 2009 8:08 pm

Re: Afr goes lean after decel in gear

Post by Matt Cramer »

Are you having any misfires at that point? They can show up as lean spikes.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
mk1rocc
Helpful MS/Extra'er
Posts: 71
Joined: Tue Feb 10, 2015 4:20 am

Re: Afr goes lean after decel in gear

Post by mk1rocc »

Matt Cramer wrote:Are you having any misfires at that point? They can show up as lean spikes.
I knew about this but ruled it out because I could not hear or feel any misfires. I will try to reduce the AE rate low enough to catch that lean spike before it happens.
but i don't think the issues are related , I mean why is the AFR so lean after deceleration in gear , It clearly is getting fuel but the PW and Duty is too low for that particular load .... Could there be a link with the AE or some other enrichment?
turbo conversion
Super MS/Extra'er
Posts: 1281
Joined: Thu Aug 19, 2010 6:22 pm
Location: White House, TN USA

Re: Afr goes lean after decel in gear

Post by turbo conversion »

What I am seeing in your second data log is lean spikes are caused by no or very little acceleration enrichment on TPS changes.

At counter 23489.219-23529.465-23547.219 there very short short AE"S but fade to quickly.

I think you need to work on your AE threshold and taper for the lean spikes when reapplying the throttle.

What I see on decell going lean is the numbers in your VE tabe, try raising these at 24 kpa and above.

Also what engine is this?

Hope this helps, David
1976 Datsun 280Z L28ET Garrett GT35R T3-T04E stage3 50 trim 63 A/R housing custom grind cam 2000-6000 rpm 440cc injectors intercooled 18 lbs. boost
3" exhaust turbo back LC-1 o2 sensor Hallman manual boost controller EDIS 6 ignition batch fire 60mm throttle body 5 spd T5 borg warner 3.54 lsd
mk1rocc
Helpful MS/Extra'er
Posts: 71
Joined: Tue Feb 10, 2015 4:20 am

Re: Afr goes lean after decel in gear

Post by mk1rocc »

This is an Audi 1.8t AEB engine, but the turbo is not providing any boost yet, I wanted to make sure the AFR was Ok before I add any boost.
About the lean spikes on reapplying the throttle , they are not actually spikes they seem that way because I do not stay on the throttle long enough because I do not want to melt any pistons . If I keep my foot down after a deccel to 2K the AFR never recovers! it stays lean and varies between 18 and 21! So I doubt this is and AE related issue, or could it?
The area in the log you mention is not reflective of the issue I am describing , there I agree with you the AE is not ok, but if you look at 23438-23463 you will see what I am talking about, You can see everything is ok during accel in gear and during deccel in gear but when I apply throttle at 23459 the AFR keeps climbing as if the ecu doesn*t care that the tps is reading 27 , and that is no spike , it lasts more than 2s .
Sometimes what ever I do the AFR does not get back to normal , meaning it will stay lean ALL THE TIME no matter the TPS or AE the only thing that cures it is if I turn the engine off and on again !So the ecu gets stuck in Deceleration mode somehow or at least thats how it seems to me...
grom_e30
Super MS/Extra'er
Posts: 4451
Joined: Thu Mar 08, 2012 12:44 pm
Location: UK

Re: Afr goes lean after decel in gear

Post by grom_e30 »

looks like you need to increase the ve numbers in the lower part of your ve table.
1990 bmw 320i daily driver with m20b25 ms3 sequential fuel, 380cc injectors, d585 coil near plug, home made cam sync, launch control, fan control, vss, homebrew egt logging what's next????
mk1rocc
Helpful MS/Extra'er
Posts: 71
Joined: Tue Feb 10, 2015 4:20 am

Re: Afr goes lean after decel in gear

Post by mk1rocc »

grom_e30 wrote:looks like you need to increase the ve numbers in the lower part of your ve table.
I used auto tune and it did a pretty good job , but I'll try to tune the low load mid range part of the VE manually maybe thats it...I'll give it a go, thanks
grom_e30
Super MS/Extra'er
Posts: 4451
Joined: Thu Mar 08, 2012 12:44 pm
Location: UK

Re: Afr goes lean after decel in gear

Post by grom_e30 »

i found its best to do the bottom of the table by hand my experience was that driving in the low load needs higher ve numbers than being in the same cells when decelerating.
1990 bmw 320i daily driver with m20b25 ms3 sequential fuel, 380cc injectors, d585 coil near plug, home made cam sync, launch control, fan control, vss, homebrew egt logging what's next????
mk1rocc
Helpful MS/Extra'er
Posts: 71
Joined: Tue Feb 10, 2015 4:20 am

Re: Afr goes lean after decel in gear

Post by mk1rocc »

OK I adjusted the VE manually and went for a drive , now after the engine is fully warm and only than after maybe 2secs of constant throttle or immediately when accelerating the engine starts to buck and bog so I've gone from bad to worse... and there is the same sound from the exhaust as before when it was going lean after deccel . So the problems are linked and it is getting worse...now the car is impossible to drive...
Here is a short log that I took , you can see it*s starting to do it at 615 in 2nd gear when the TP is starting to wave even though I am not moving my foot,I lift for a sec and when I reapply the throttle the same thing: TP is waving and the car is bucking like a wild bull .
I'm starting to think there might be something wrong with the TPS but why is it only happing when the engine is warm?....
2015-08-22_14.49.56.msl
jsmcortina
Site Admin
Posts: 39587
Joined: Mon May 03, 2004 1:34 am
Location: Birmingham, UK
Contact:

Re: Afr goes lean after decel in gear

Post by jsmcortina »

What part of the VE table did you adjust? grom was suggesting that you adjust the bottom rows (where the dot goes on decel) not the mid/upper rows where you'll be during normal driving or acceleration.

James
I can repair or upgrade Megasquirts in UK. http://www.jamesmurrayengineering.co.uk

My Success story: http://www.msextra.com/forums/viewtopic ... 04&t=34277
MSEXTRA documentation at: http://www.msextra.com/doc/index.html
New users, please read the "Forum Help Page".
grom_e30
Super MS/Extra'er
Posts: 4451
Joined: Thu Mar 08, 2012 12:44 pm
Location: UK

Re: Afr goes lean after decel in gear

Post by grom_e30 »

in the latest log where the bucking is happening it does appear that the ae is cycling in and out quite a lot and making a pig spike in the injector pw
1990 bmw 320i daily driver with m20b25 ms3 sequential fuel, 380cc injectors, d585 coil near plug, home made cam sync, launch control, fan control, vss, homebrew egt logging what's next????
mk1rocc
Helpful MS/Extra'er
Posts: 71
Joined: Tue Feb 10, 2015 4:20 am

Re: Afr goes lean after decel in gear

Post by mk1rocc »

jsmcortina wrote:What part of the VE table did you adjust? grom was suggesting that you adjust the bottom rows (where the dot goes on decel) not the mid/upper rows where you'll be during normal driving or acceleration.

James
Yes the bottom rows I got that.
mk1rocc
Helpful MS/Extra'er
Posts: 71
Joined: Tue Feb 10, 2015 4:20 am

Re: Afr goes lean after decel in gear

Post by mk1rocc »

grom_e30 wrote:in the latest log where the bucking is happening it does appear that the ae is cycling in and out quite a lot and making a pig spike in the injector pw

Yes that is what I thought too so I raised the AE treshhold allot higher and went for a drive.... same thing.. the car will not accelerate for more than a few seconds or stay at constant throttle . I doubt this has anything to do with the MSQ settings and might be a mechanical or electrical issue that is not showing in the logs¨... I was thinking maybe the coil... or the injectors.... I'm really struggling to figure this out ..and it's getting worse and worse,....
2015-08-22_15.32.33.msl
mk1rocc
Helpful MS/Extra'er
Posts: 71
Joined: Tue Feb 10, 2015 4:20 am

Re: Afr goes lean after decel in gear

Post by mk1rocc »

The problem is most definitely not related to the tune because I burned an older tune that worked before and I still have the same problem.
It's weird because it seems RPM depended... If the coil was the problem I would be getting misfires so I think I can rule them out right? So what is left is the fuel delivery...could plugged injectors be causing this? Any insight is welcomed.
Yves
Super MS/Extra'er
Posts: 1505
Joined: Tue Jun 17, 2014 1:23 pm
Location: Belgium

Re: Afr goes lean after decel in gear

Post by Yves »

try a 50/50 split map/TP ae and set the map so that it won't engage at idle. Use small pw's and see what the effect is. My .02$ because for me it worked and also did away with the exhaust farting.

PS : I have ITB's, which might be different from what you have, but trying won't hurt.
mk1rocc
Helpful MS/Extra'er
Posts: 71
Joined: Tue Feb 10, 2015 4:20 am

Re: Afr goes lean after decel in gear

Post by mk1rocc »

AE is not the problem, You can see in the log that at 3324s Ae kicks in and the afr goes a bit rich but comes back and everything is fine until 3328s and out of nowhere AFR goes lean 17.5 and if I keep my foot down it stays that way so it's not a spike from misfire.
From 3438s to 3446s "something" happens and the afr goes nuts and leans out even at constant throttle and MAP...
I checked the injectors, fuel pump,FPR and measured the coil pack resistance everything is fine, no vacuum leaks...
I do not understand what is going on, the PW and duty stay ok how can the afr go so lean out of the blue?What could cause this?
Please help it's driving me mad.
2015-08-26_13.16.00.msl
grom_e30
Super MS/Extra'er
Posts: 4451
Joined: Thu Mar 08, 2012 12:44 pm
Location: UK

Re: Afr goes lean after decel in gear

Post by grom_e30 »

have you checked the fuel pressure is not fluctuating?
1990 bmw 320i daily driver with m20b25 ms3 sequential fuel, 380cc injectors, d585 coil near plug, home made cam sync, launch control, fan control, vss, homebrew egt logging what's next????
Post Reply