Page 1 of 2 12 LastLast
Results 1 to 20 of 31

Thread: leaning out on warm idle and off accelerator pedal

  1. #1
    crazydriver81's Avatar

    Offline
     
    Name
    Stefan
    Join Date
    Jan 2009
    Last Online
    30-01-2022
    Posts
    2,024
    Country
    Germany
    Location
    Leipzig area
    Car
    Legnum 25ST-R
     

    leaning out on warm idle and off accelerator pedal

    Hi to the Pro's on here,

    I Need your help.

    Now, that the winter is almost over and the Legnum is about to hit the roads again, I still have to deal with one issue which I did not fix last year. The car developed a leaning out issue. I also remember @foxdie assuming that I might have a small boost leak while he was mapping my car. However, what I am looking for is some advice, on which points to look at.

    The issue:
    - car leans out to 19ish AFR's when warm idling and during driving when lift off accelerator pedal completely
    - when pressing the accelerator pedal on idle (stationary) slightly, revs go up and AFR's go to 16ish before going back to 17ish to 19ish
    - while driving when AFRs are lean car seems to take a "second" before AFR's are getting back to normal values
    - when under boost and accelerating, car runs fine with stable 11.5 AFR's (as mapped by @foxdie)

    The car developed this issue on the way to the mapping Event (so before car was mapped!). The 600kms before after Manual gearbox swap it ran just fine.

    So, what to you think guys?
    - ICV to be cleaned and checked (plus install new base idle screw and seal)
    - boost leak test to be done
    - TPS Setting to be checked

    Anything else I need to check for? Thanks for your input.
    the one and only...Pearl White Legnum 25 ST-R...registered in Germany - now featuring a 6A13TT engine (unless you know otherwise)


  2. #2
    Confused's Avatar

    Offline
     
    Name
    Garry
    Join Date
    Apr 2005
    Last Online
    Today
    Membership ID
    714
    Posts
    3,536
    Country
    United Kingdom
    Location
    Notts
    Car
    Legnum VR-4
    My Garage
    Visit
     
    Right, lets tackle them one-by-one

    When you come off the throttle completely, the ECU should disable the injectors until the engine speed drops to around 800rpm. You should see the Injector Duty Cycle drop to 0% and the Injector Pulse Width drop to 0.000 too, if you're logging via EvoScan. This is perfectly normal, and on a long enough zero-throttle coast, the AFR should lean out as far as your wideband will read. Well, it *should* be doing this, but @foxdie did set the injectors to come back on at 2000rpm rather than 800rpm in his tuned ROMs - for pops/bangs on overrun - so this may affect what I said above (it certainly did on my Anglia!)

    At idle, it *should* be aiming for 14.7, and it should "hunt" either side of this very slightly (14.0-15.4ish, as I've seen on my Anglia)

    When you press the accelerator slightly, the engine ingests a sudden gulp of air - this causes the initial leaning out. When under no load, very little fuel is required to maintain that increased engine speed, so it is not surprising to see an AFR of 18.

    There is also the response speed of your wideband - some will "smooth" the output over a few samples rather than giving an instantaneous reading - don't forget too that there's the delay in your gauge too - a gauge with a digital readout will always respond quicker than a gauge which has an arm that has to move.

    Realistically - AFRs at high load high boost are most important - and 11.5 is absolutely spot on.


    Checking for boost leaks is always a very useful diagnostic test - and if you're unsure, perform a boost leak test ASAP!
    If the AFR isn't leaning right out on no-throttle coasting, then definitely do the TPS setup procedure to ensure that it's providing the Idle Position signal to the ECU (as a side note, I've never been able to get a value for the Idle Position Switch option in EvoScan, so make sure you use the feeler gauge/multimeter method to adjust it).

    The ICV/screw should only be played with if it hunts badly at idle or can't catch the revs dropping away from high RPM (ie if it drops to about 500rpm before recovering to about 670 - it should catch it before it drops below 650).

  3. #3
    crazydriver81's Avatar

    Offline
     
    Name
    Stefan
    Join Date
    Jan 2009
    Last Online
    30-01-2022
    Posts
    2,024
    Country
    Germany
    Location
    Leipzig area
    Car
    Legnum 25ST-R
     
    Quote Originally Posted by Confused View Post
    Right, lets tackle them one-by-one

    When you come off the throttle completely, the ECU should disable the injectors until the engine speed drops to around 800rpm. You should see the Injector Duty Cycle drop to 0% and the Injector Pulse Width drop to 0.000 too, if you're logging via EvoScan. This is perfectly normal, and on a long enough zero-throttle coast, the AFR should lean out as far as your wideband will read. Well, it *should* be doing this, but @foxdie did set the injectors to come back on at 2000rpm rather than 800rpm in his tuned ROMs - for pops/bangs on overrun - so this may affect what I said above (it certainly did on my Anglia!)

    At idle, it *should* be aiming for 14.7, and it should "hunt" either side of this very slightly (14.0-15.4ish, as I've seen on my Anglia)

    When you press the accelerator slightly, the engine ingests a sudden gulp of air - this causes the initial leaning out. When under no load, very little fuel is required to maintain that increased engine speed, so it is not surprising to see an AFR of 18.

    There is also the response speed of your wideband - some will "smooth" the output over a few samples rather than giving an instantaneous reading - don't forget too that there's the delay in your gauge too - a gauge with a digital readout will always respond quicker than a gauge which has an arm that has to move.

    Realistically - AFRs at high load high boost are most important - and 11.5 is absolutely spot on.


    Checking for boost leaks is always a very useful diagnostic test - and if you're unsure, perform a boost leak test ASAP!
    If the AFR isn't leaning right out on no-throttle coasting, then definitely do the TPS setup procedure to ensure that it's providing the Idle Position signal to the ECU (as a side note, I've never been able to get a value for the Idle Position Switch option in EvoScan, so make sure you use the feeler gauge/multimeter method to adjust it).

    The ICV/screw should only be played with if it hunts badly at idle or can't catch the revs dropping away from high RPM (ie if it drops to about 500rpm before recovering to about 670 - it should catch it before it drops below 650).
    Hi Garry,

    thanks for all the explanations. I have a PLX wideband kit, so the readings are rather quick and precise. I know about the fully leaning out on coast.

    We tried to setup pops-and-bangs on my car while mapping but it ended in massive overfuelling, so we disabled it.

    I suspect the TPS as a cause, because when on coast and pressing the accelerator pedal slightly (e.g. just to keep a certain speed) it will also lean out. And this is not normal. Also when rolling to traffic lights with the clutch disengaged, it leans out to 19ish AFRs and almost stalls. AFR's are fine, if A/C compressor engages.

    Anyhow, I just wanted to have some thoughts if I possibly miss something. So, I will work off the list above and Report back.

  4. #4
    Confused's Avatar

    Offline
     
    Name
    Garry
    Join Date
    Apr 2005
    Last Online
    Today
    Membership ID
    714
    Posts
    3,536
    Country
    United Kingdom
    Location
    Notts
    Car
    Legnum VR-4
    My Garage
    Visit
     
    If you don't have it already, get yourself a cheap VAG KKL cable (about £5 on eBay, the one with the translucent blue plastic case works well), modify it (if you can't find it, I'll dig out a link when I'm on a computer) and get a copy of EvoScan ($25, and you'll need 2.7 for the VAG cable, not 2.9).

    This will give you access to all the engine data, and has to be one of the cheapest and best diagnostic tools you can get!

  5. #5
    TAR's Avatar

    Offline
     
    Name
    Tim
    Join Date
    Apr 2006
    Last Online
    Yesterday
    Membership ID
    346
    Posts
    3,887
    Country
    United Kingdom
    Location
    Aylesbury
    Car
    '97 Legnum
    My Garage
    Visit
     
    I had an issue with car running lean a couple of years back. I have to admit I never got to the bottom of it. There is a lot of good info in it and worth a read.
    https://www.clubvr4.com/forum/showth...ttle-any-ideas

    Hope it helps.
    '97 Manual Legnum in silver with some subtle mods

    My first VR4 - '97 Legnum Dark Green & mean ...it was love at first sight - now sold

  6. #6
    Confused's Avatar

    Offline
     
    Name
    Garry
    Join Date
    Apr 2005
    Last Online
    Today
    Membership ID
    714
    Posts
    3,536
    Country
    United Kingdom
    Location
    Notts
    Car
    Legnum VR-4
    My Garage
    Visit
     
    To set the TPS correctly, put a 0.65mm feeler gauge between the stop and the spinny wheel part where the throttle cable attaches, then adjust the TPS so that pins 3&4 are just disconnected. They should then give continuity when you remove the feeler gauge.


    To use the cheap VAG-COM KKL cable, you need to connect pins 1 & 4 whilst it is plugged in - I opened up my cable and connected them internally - you could also connect them externally.

  7. #7
    foxdie's Avatar

    Offline
     
    Name
    Jason
    Join Date
    Jan 2008
    Last Online
    Yesterday
    Membership ID
    518
    Posts
    5,030
    Country
    United Kingdom
    Location
    Birmingham, UK
    Car
    Silver PFL VR4
    My Garage
    Visit
     
    Quote Originally Posted by Confused View Post
    When you press the accelerator slightly, the engine ingests a sudden gulp of air - this causes the initial leaning out.
    This can be addressed using the TPS delta tuning, it's a table for how quickly the throttle is pressed (distance between each "read" of the TPS, the delta) and enriches based on that
    Want your car tuning? Here's my pricing
    Have questions about performance upgrades and ECU tuning? Before PM'ing me, Check this thread first
    Please support CVR4 & become a Full member, you get a full years access to guides, games, chat & much more!

  8. #8
    foxdie's Avatar

    Offline
     
    Name
    Jason
    Join Date
    Jan 2008
    Last Online
    Yesterday
    Membership ID
    518
    Posts
    5,030
    Country
    United Kingdom
    Location
    Birmingham, UK
    Car
    Silver PFL VR4
    My Garage
    Visit
     
    Also hi Stefan, hope you're well
    @Confused has covered quite a lot here, I don't feel like I can add much more at this point, idling between 17-19 without any occasional swings towards 14.7 I would say sounds a lot like an old / faulty narrowband sensor, but as you have a PLX I'd expect better.

    Your PLX is emulating narrowband output for the ECU yeah? Could be worth slightly offsetting the output voltage for that to steer it closer to 14.7 ?

  9. #9
    Nick Mann's Avatar

    Offline
     
    Name
    Nick
    Join Date
    Sep 2003
    Last Online
    17-03-2024
    Membership ID
    17
    Posts
    24,895
    Country
    United Kingdom
    Location
    Redditch
    Car
    Legnum type-S
    My Garage
    Visit
     
    I'd check the voltage on the plx. If the narrow band emulation is swinging around 0.5v whilst the car is running 16afrs then you have found the culprit.
    I would be suprised if that is the case.
    Modifying the emulated narrow band output (assuming the output is correct) seems to be like putting a bandage round a leaking water pipe. It might work but it might just be disguising a bigger problem.

  10. #10
    crazydriver81's Avatar

    Offline
     
    Name
    Stefan
    Join Date
    Jan 2009
    Last Online
    30-01-2022
    Posts
    2,024
    Country
    Germany
    Location
    Leipzig area
    Car
    Legnum 25ST-R
     
    Again, thanks for all the input guys.

    I am not quiet sure if the PLX narrowband emulation can be tweaked. I just received the bung to test the IC pipework for leaks. I will work through all these points next week and will hopefully find the issue. Luckily I have access to the MUT-III tester and can check for correct base idle settings. I tend to believe that either the TPS is off or the ICV is faulty. But this will be discovered once I am in the workshop with the car.I'll also try to "calibrate" the PLX wideband which should be easy, now that the car stood in the garage over winter and exhaust is full of air.

    What really bugs me with that are two facts:
    - when coming to traffic lights with clutch disengaged, it will nearly stall and gets AFR's in the 19ish region (once engine is warm)
    - when on cruise and try to keep speed and use the accelerator pedal slightly, it leans out

    Anyhow, I'll report back. Keep the fingers crossed, I'll solve it.

  11. #11
    foxdie's Avatar

    Offline
     
    Name
    Jason
    Join Date
    Jan 2008
    Last Online
    Yesterday
    Membership ID
    518
    Posts
    5,030
    Country
    United Kingdom
    Location
    Birmingham, UK
    Car
    Silver PFL VR4
    My Garage
    Visit
     
    In both those situations you describe it's running in closed loop mode.

    Stefan, just out of curiousity, can you measure the voltage on the o2 pin on the ECU when this happens?

    Sent from my SM-G930F using Tapatalk

  12. #12
    Confused's Avatar

    Offline
     
    Name
    Garry
    Join Date
    Apr 2005
    Last Online
    Today
    Membership ID
    714
    Posts
    3,536
    Country
    United Kingdom
    Location
    Notts
    Car
    Legnum VR-4
    My Garage
    Visit
     
    @Davezj has found that his STFT (Short Term Fuel Trim) does not appear to kick into action properly until you give it a kick up the backside when idle.

  13. #13

    Offline
     
    Name
    Chris
    Join Date
    Apr 2012
    Last Online
    11-06-2018
    Posts
    1,294
    Country
    United Kingdom
    Location
    Luton
    Car
    Legnum VR4
     
    There could be few factors that cause it.
    Most of the VR4s here on the club are modified. Basic modifications are higher flow air filter, decat pipe or 3" exhaust.
    I suspect, that it helps engine to breathe easier and simply with the same throttle possition there is more air entering the engine.
    I may be wrong but that's what I suspect.
    Recently had chance to work on Nissan 350Z VQ35HR (convert to LPG) which had full custom exhaust system and 2 HKS panel filters.
    First quick inspection of fuel trims and turns out idle is towards leaner side, idle fuel trim was around +12 .. .. +17 with max +25.
    There was no air leaks (idle manifold intake pressure was correct) and no exhaust leaks.
    Mid load fuel trims were perfect around 0% but high load and high rpm were stupidly overfueled with AFR 10 or less.
    All these symptoms are similar to what most legnums suffer from.
    To make sure that there is no air leak I would try to meassure idle manifold intake pressure. It should be roughly 0.28bar of vacuum with no extra load on the engine (aircon off).

  14. #14
    Nick Mann's Avatar

    Offline
     
    Name
    Nick
    Join Date
    Sep 2003
    Last Online
    17-03-2024
    Membership ID
    17
    Posts
    24,895
    Country
    United Kingdom
    Location
    Redditch
    Car
    Legnum type-S
    My Garage
    Visit
     
    Back in the days of my hks boost controller my legnum used to idle at around 0.48 bar of vacuum. I don't monitor it so much now.

    Also, do you have evoscan? That will show what the o2 sensor is doing.

  15. #15

    Offline
     
    Name
    Chris
    Join Date
    Apr 2012
    Last Online
    11-06-2018
    Posts
    1,294
    Country
    United Kingdom
    Location
    Luton
    Car
    Legnum VR4
     
    0.48 bar of vacuum is way too much air for idle. That will definitely cause lean idle and fuel trims out of working range.

  16. #16
    Nick Mann's Avatar

    Offline
     
    Name
    Nick
    Join Date
    Sep 2003
    Last Online
    17-03-2024
    Membership ID
    17
    Posts
    24,895
    Country
    United Kingdom
    Location
    Redditch
    Car
    Legnum type-S
    My Garage
    Visit
     
    Sorry, it was 0.42 not 0.48. It would get to around 0.58 on over run. I am now wondering if I have remembered the units wrong! It was perfectly healthy.

    I will check my current vr4 at the next opportunity.

  17. #17
    Piers1989's Avatar

    Offline
     
    Name
    Piers
    Join Date
    Mar 2009
    Last Online
    04-10-2022
    Posts
    518
    Country
    United Kingdom
    Car
    VR-4 + BMW 335
     
    I just checked mine as we were discussing the lean idle in another thread.

    My gauge isn't aligned great but it looks to be around -0.6bar for my car!
    It does always run a little lean on idle (15.7-16.5), but when its been left to heat soak for half an hour can go to 19-20 and struggles to run. As soon as you drive it returns to normal tho.
    For reference this was the case before I had my AFR gauge (which does simulate the narrowband) also - the rough idling.

    Did we discuss what could cause this?

  18. #18

    Offline
     
    Name
    Chris
    Join Date
    Apr 2012
    Last Online
    11-06-2018
    Posts
    1,294
    Country
    United Kingdom
    Location
    Luton
    Car
    Legnum VR4
     
    Correct idle manifold pressure without load is max 0.3bar or -0.7bar of vacuum with the engine warm. Anything above that is suspicious and 0.42bar or equivalent -0.58bar of vacuum isn't definitely right.

    Sent from my SM-G901F using Tapatalk

  19. #19
    Davezj's Avatar

    Offline
     
    Name
    Dave
    Join Date
    Jan 2006
    Last Online
    09-01-2024
    Membership ID
    255
    Posts
    16,245
    Country
    England
    Location
    Manchester
    Car
    VR-4
    My Garage
    Visit
     
    vacuum is normally measured in millimeters of mercury (mmHg) well my gauge does and in the plenum at idle it normally reads 500 to 600

    This is the conversion i got from google

    500 millimeter mercury (0 C) = 0.666612 bar
    600 millimeter mercury (0 C) = 0.799934 bar

    both of my VR4 have always been this value.

    Bye for Now!

  20. #20
    Piers1989's Avatar

    Offline
     
    Name
    Piers
    Join Date
    Mar 2009
    Last Online
    04-10-2022
    Posts
    518
    Country
    United Kingdom
    Car
    VR-4 + BMW 335
     
    Quote Originally Posted by Davezj View Post
    vacuum is normally measured in millimeters of mercury (mmHg) well my gauge does and in the plenum at idle it normally reads 500 to 600

    This is the conversion i got from google

    500 millimeter mercury (0 C) = 0.666612 bar
    600 millimeter mercury (0 C) = 0.799934 bar

    Both of my VR4 have always been this value.
    I checked mine in more detail and its about -0.7 bar when i factor in the needle being misaligned. That sounds bang on what Dave's saying too.

Page 1 of 2 12 LastLast

Similar Threads

  1. Replies: 5
    Last Post: 19-03-2017, 11:27 PM
  2. Stuck accelerator???
    By JimDiGritz in forum General / Questions
    Replies: 14
    Last Post: 31-08-2013, 11:13 PM
  3. HKS F-Con V-pro Semi warm idle problem
    By gareth001 in forum ECUs / Mapping
    Replies: 8
    Last Post: 05-01-2012, 06:58 PM
  4. Rough idle and stalling when warm
    By foxdie in forum Engine
    Replies: 6
    Last Post: 25-11-2010, 02:30 PM
  5. Sticky Accelerator
    By colVR4 in forum Questions
    Replies: 10
    Last Post: 27-11-2003, 12:57 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •