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Thread: AFR lean on hot idle

  1. #41
    crazydriver81's Avatar

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    Quote Originally Posted by Nick Mann View Post
    I run a PLX with narrowband emulation and don't have a problem. I'm not saying your PLX is good, just that it is not a normal issue if it is the PLX.
    Next chapter, chaps...

    Today we made the twin O2 sensor setup. I put another O2 bung into the PS Iida downpipes. There is a brand new narrowband one and next to it the PLX. Obviously there is no narrowband emulation from the PLX to the ECU anymore. Instead the narrowband sensor is connected directly. However, it did not change the situation, still too lean on hot idle (between 16ish and 17ish AFR's

    So what I can say is - the PLX narrowband emulation does not cause this abnormal engine behavior!

    We then began to check other sensors and values, such as engine coolant temp, ISC valve and base idle. We laso performed a full setup for the TB (inc. fixed SAS, TPS and IPS). Checked for air leajs - nothing. No change of Situation whatsoever.

    What we found:
    - base idle barely at 650 rpm [acc. to workshop manual] but ISC has 0 steps and base idle screw fully closed -> not correct
    - no leaks in exhaust or intake piping, no hissing sound etc.
    - even though the IPS/TPS is setup correctly the ECU does not sem to get the IPS signal - it always displays IPS = off.
    - the injector time is slightly going up from 1.8ms to 2.0ms seconds

    We then disconnected the FPR from the solenoid driven pressure source and connected a manual vacuum/pressure pump. Neither with 0.5 bar vacuum nor with 0.9 bar pressure the AFR changed. So now we are kind of clueless. I tend to believe that the ECU tries to get this "lean conition to be rectified but it cannot reduce air more (because ISCV is at 0 steps already = fully closed) and even with longer injector opening times it does not get more fuel.

    Does that mean, the FPR is the culprit? Why is it working spot on under WOT or hard accelerating then? When cruising the car perfectly fine swings around 14.7 AFR. When on WOT it gets 11.5 without issues.
    What does the IPS signal trigger inside the ECU? Is the factory FPR capable to handle a 255lph Walbro on constant 12V (e.g. if I am going to bypass the resistor pack in engine bay?

    In fact the situation does bug me. It's kind of "luxury" problem I am chasing, as it's only happening during idle but I know it's not correct and it will be an issue for next year's MOT/emmission test. So any ideas are very welcome....IMG_1139.JPGIMG_1140.JPG
    Last edited by crazydriver81; 25-07-2017 at 06:56 PM.
    the one and only...Pearl White Legnum 25 ST-R...registered in Germany - now featuring a 6A13TT engine (unless you know otherwise)


  2. #42
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    I've never had the engine ECU return a result other than OFF for the Idle Position Switch - but the AYC ECU does give the expected result. It's also used by the pre-facelift auto ECU (metal cased), but not plastic cased ones.

  3. #43
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    Stefan @crazydriver81 did you "park" ISCV by MUT or Evoscan according to workshop manual? From your description it is not parked properly. If you need more abot procedure, search for the same with Evo (easy Google).
    Ex: Galant VR4
    Running 268 HP ATW and 443 Nm torque at 0.9 bar
    Now: Lancer Evolution 8 FQ-300
    Running 325 HP ATW and 510 Nm torque at 1.6 bar

  4. #44
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    As i said before, i have exactly same problem as yours, the lean problem only happened when idle, and the problem last for 5 4-5years, until i solved it last month. I can confirm that it is not related to AFM, because i changed back using the old one for a month already and still no more problem.

    As you can see my change list in post #30, the AFM is fine, and no problem. How about this, may be you can also change new spark plugs, and make sure it is 0.8mm gapped, not just 1.1mm. I don't why, but I used 1.1mm plugs before. I don't know it affects lean idle or not, because i cannot change plugs with 1.1mm to test.

    Another you can try is clean the injectors. Although the Evoscan shows the injector timing, it is the time ECU requests injector to do, but imagine, if there is a little bit clogging, the actual fuel volume is less than a clean injector with the same 2ms timing.

    One more thing is, there is a common problem on throttle body, there is air leaks on the throttle plate shaft end, and also leaks on the SAS screw, that's why there is a cap to cover the screw. More info can be find from OZ forum. Last year, Mine had air leak on the throttle plate shaft end, then i changed an used throttle body, and tested no leak, but still lean idle, so throttle plate shaft end leaking may be not so serious.

    I guess you can clean injector and change plugs first, if really either of these two causes the lean idle, then you can fix that soon. Hope all these can help.




    Quote Originally Posted by crazydriver81 View Post
    Next chapter, chaps...

    Today we made the twin O2 sensor setup. I put another O2 bung into the PS Iida downpipes. There is a brand new narrowband one and next to it the PLX. Obviously there is no narrowband emulation from the PLX to the ECU anymore. Instead the narrowband sensor is connected directly. However, it did not change the situation, still too lean on hot idle (between 16ish and 17ish AFR's

    So what I can say is - the PLX narrowband emulation does not cause this abnormal engine behavior!

    We then began to check other sensors and values, such as engine coolant temp, ISC valve and base idle. We laso performed a full setup for the TB (inc. fixed SAS, TPS and IPS). Checked for air leajs - nothing. No change of Situation whatsoever.

    What we found:
    - base idle barely at 650 rpm [acc. to workshop manual] but ISC has 0 steps and base idle screw fully closed -> not correct
    - no leaks in exhaust or intake piping, no hissing sound etc.
    - even though the IPS/TPS is setup correctly the ECU does not sem to get the IPS signal - it always displays IPS = off.
    - the injector time is slightly going up from 1.8ms to 2.0ms seconds

    We then disconnected the FPR from the solenoid driven pressure source and connected a manual vacuum/pressure pump. Neither with 0.5 bar vacuum nor with 0.9 bar pressure the AFR changed. So now we are kind of clueless. I tend to believe that the ECU tries to get this "lean conition to be rectified but it cannot reduce air more (because ISCV is at 0 steps already = fully closed) and even with longer injector opening times it does not get more fuel.

    Does that mean, the FPR is the culprit? Why is it working spot on under WOT or hard accelerating then? When cruising the car perfectly fine swings around 14.7 AFR. When on WOT it gets 11.5 without issues.
    What does the IPS signal trigger inside the ECU? Is the factory FPR capable to handle a 255lph Walbro on constant 12V (e.g. if I am going to bypass the resistor pack in engine bay?

    In fact the situation does bug me. It's kind of "luxury" problem I am chasing, as it's only happening during idle but I know it's not correct and it will be an issue for next year's MOT/emmission test. So any ideas are very welcome....IMG_1139.JPGIMG_1140.JPG

  5. #45
    crazydriver81's Avatar

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    Quote Originally Posted by swinks View Post
    Stefan @crazydriver81 did you "park" ISCV by MUT or Evoscan according to workshop manual? From your description it is not parked properly. If you need more abot procedure, search for the same with Evo (easy Google).
    Yes @swinks - we did park the ISCV with help of MUT-III before trying to adjust the base idle.
    @kc427 I read through your posts and understood that injector cleaning did solve your problem. However - I already have cleaned and flow matched injectors installed. So I assume there is no problem there.

  6. #46
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    I have two more things to follow:

    - When and how does the ECU trigger the switched voltage for fuel pump? Can anybody help?
    - Changing the ECU coolant temp sensor. I found that the blowers do not engage fully so I think ECU temp sensor is on its way out. This sensor is used for fuelling too...

    One thing I realize more and more is, that ECU seems to reduce RPM on idle if stationary after a few seconds. I know this "feature" from other 8G Galants too (owned a few). So what happens is, that if sitting on idle stationary, car tries to get to 14.8ish AFRs which it almost gets - but then drops RPM's a bit and starts leaning out. I also found that the ISCV is on 0 steps at that point - so fails to reduce air more. I suspect the car does not get enough fuel on idle rather then having an air leak somewhere (mede the air leak test a number of times already with no leaks to show up at 1 bar)

    WOT is fine, cruising is spot on - it only happens if car is stationary, warm and on idle...

    If out of gear and letting car idle (e.g. while going down a hill, it keeps AFR's at 14.7ish...

  7. #47
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    Finally the issue has been solved. After changing the coolant temp sender, the leaning out has disappeared. when warm the idle AFR's are between 14.7 and 15.1 - spot on! YEAH!

  8. #48
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    Great news Stefan. Great detective work.
    '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

  9. #49
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    That is a great result Stefan

    I feel there maybe a need for many people to swap out the ECU coolant temp sensor (2 wire).

    I don't imagine they cost much.
    Stefan do you have the part number and price of the sensor.

    I think this would be helpful.

    Sent from my MI 5s using Tapatalk

    Bye for Now!

  10. #50
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    If it was indeed the coolant temperature sensor giving an incorrect reading to the ECU, then good spot!

    The part number is MD177572 or MD182467 and is around £14 at the time of writing.

    Viamoto

  11. #51
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    did your temp guage in the car misread as well?
    @Crazydriver81

    Last edited by TAR; 12-12-2017 at 08:50 PM.

  12. #52
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    Quote Originally Posted by TAR View Post
    did your temp guage in the car misread as well?
    @Crazydriver81

    There is a separate sensor for the dash gauge.
    @Crazydriver81 did you log the other temperature sensor with EvoScan, and if so, what kind of values were you seeing which caused this issue? Was it over-reading, under-reading?

  13. #53
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    @Confused - the ECU was under reading actual temp, so it slightly leaned out to get the dsired engine temp (my theory what caused leaning out tho)

    I came across that possible cause for my failure, cause the rest had been refurbed before already. While sharing a beer with @foxdie in Berlin last year, he pointed me towards the ECU fuelling adjustment by coolant temp. So I just bit the bullet and replaced the temp sender after checking with Evoscan and dicovering some strange readings and blower fan rpms being too low for my liking..

    Btw, I wnt for the OE Mitsi sensor which came in at approx 60 EUR plus tax.

  14. #54
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    Great news

    I never thought of this before, as I logged the coolant temp by EvoScan and compared with my external Defi gauge and they are very close.

    Actually, I just re-visit Evoscan web site, and found that the the injector insulators can leak. I assume my case was caused by the insulators, and when I cleaned my fuel injectors, I also changed new insulators, o-rings etc, and maybe it is the reason why I could fix the issue on my car.

    BTW, is there any FAQ section in the forum so that we could consolidate all kinds of problems and solutions, especially these kind of wired problems, it's a nightmare actually.



    Quote Originally Posted by crazydriver81 View Post
    @Confused - the ECU was under reading actual temp, so it slightly leaned out to get the dsired engine temp (my theory what caused leaning out tho)

    I came across that possible cause for my failure, cause the rest had been refurbed before already. While sharing a beer with @foxdie in Berlin last year, he pointed me towards the ECU fuelling adjustment by coolant temp. So I just bit the bullet and replaced the temp sender after checking with Evoscan and dicovering some strange readings and blower fan rpms being too low for my liking..

    Btw, I wnt for the OE Mitsi sensor which came in at approx 60 EUR plus tax.

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