348 - MAF adjustment and open loop? | Page 3 | FerrariChat

348 MAF adjustment and open loop?

Discussion in '348/355' started by Ferrarium, Jul 27, 2020.

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  1. m.stojanovic

    m.stojanovic F1 Rookie
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  2. Ferrarium

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    #52 Ferrarium, Sep 3, 2020
    Last edited: Sep 3, 2020

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  3. Ferrarium

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    OK, Trying to wrap my head around why I saw no AF change with the CO screws at idle. My 19/19.5 AF at idle I suspect is a symptom of not enough flow to generate a good reading. the exhaust pulses blow and suck and swamp the 02 sensor with air. If that's true then that explains why changing my CO screws did absolutely nothing to the AF at idle, simply not enough flow to read. In fact it would not get into the 14.x region until >2500 rpm. I suspect trying to set 465mv or 14.x AF at idle is just not advisable.

    The manual does not exactly say what rpm to set the CO screws with. But it does say to go to 2500-3000 to check the vacuum, then it mentions to adjust the CO screw after that, it never states return to idle to do CO adjustments after revving to 2500-3000 leaving me to believe it is actually 2500-3000 to see the effect. That makes sense with my observations.
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  4. m.stojanovic

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    #54 m.stojanovic, Sep 3, 2020
    Last edited: Sep 3, 2020
    In my previous post, I stated that there was no mention of unplugging IACs in the manual but those instructions are for 2.5 (no IAC motors). The instructions for 2.7 state "disconnect the 2 idling speed regulators" - disconnect the wire connectors from them with no requirement to remove the IACs and plug the hose. When the wires are disconnected from the IACs, they will still conduct air through but at a fixed flow, i.e. at the IAC's default opening. If they are removed and the hose plugged, the engine will not have enough idle air to run.

    I think you are right about the mixture being richer with the CO pot at higher Ohms (turned clockwise). Until you mentioned it, I was following the info I found on the internet that lower Ohms cause richer mixture (seems wrong). I did see the instruction in the manual "clockwise thickens" but I took it to mean that clockwise will reduce the Ohms (without actually checking the pot operation) and concluded that it meant the same as the internet info.

    Just checked the CO pot operation on my new spare 348 MAF - clockwise increases the Ohms. So, if it is not an error in the manual (it has some other errors and bad translations from Italian), then higher ohms mean richer mixture.

    In this case, when I turned the CO pot to 400 Ohm (turned clockwise) and had detonation, it was not due to leaner mixture (as I thought) but due to richer mixture which makes more sense.

    I checked the Italian word for "thickens the air-fuel mixture". It states "ingrassa" (translated as thickens) but the Google translates it as "greases" which certainly means richer mixture.
     
  5. Ferrarium

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    We can measure the 02 sensor voltage, they generate voltage with no power. Reference voltage of 450 mV. represents an air-fuel ratio of 14.7:1 or stoichiometric. Excess air (lean) will send the O2 sensor voltage signal low (under 0.450 volts) and lack of it (rich) will send the voltage signal high (over 0.450 volts). So we can determine richer or leaner CO with voltage from the 02 sensor.

    Seems there is a big variance in CO numbers based on plugs and what not. https://www.ferrarichat.com/forum/threads/how-to-set-the-maf-screw-accurately-on-motronic-2-5.202083/

    Here Marco says "had one MAF at 343 and the other at 370 to hit the magic number on the O2 sensor output."
    Then 2 posts down he said
    "Bank 5-8 520 ohm, 1-4 430 ohm to balance the O2 output on new set of plugs."

    I question 14.x at idle I don't see enough exhaust flow to measure, I got 19.x which is very common at idle for cars due to inability to measure due to lack of adequate flow. I think you need to do it a light cruise 2500 rpm or so.
     
  6. m.stojanovic

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    Does your wide band sensor have an internal electric heater? As I understand, O2 sensor needs to be heated-up to certain temperature (more than 300 C) to operate correctly. If your wide band is not heated, I don't think it will get enough heat from the exhaust gasses at idle. The max. EGT I measured at idle was 265 C.
     
  7. Ferrarium

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    You bet, its a 6 wire Bosch LSU4.9 oxygen sensor. I plugged it in and powered it outside the cat and touched its hot alright. I don't think there is enough exhaust flow, there is too much air in the exhaust until the engine is humming at light cruise.

    Marco had 343 then 540 on the same bank to hit the target depending on the plugs. I suspect the 383 is a safety margin to account for degradation. If not Marco never would have had THAT different a reading on the same bank by changing plugs. Not sure I'd want to set it at 540 then when plugs degrade who knows whats happening. Who wants to reset that CO screw for every plug change or what not. I suspect its a factory "good enough" for most cases compromise value. Not suire sure I'd change it because something like changing your plugs would throw it off your previous perfect adjustment.
     
  8. m.stojanovic

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    I found an article on the wide band sensor and on how its readings can be affected at idle by the camshaft durations, i.e. by their overlap. At idle speeds, the cam overlap intake-exhaust (around the TDC) causes some air to pass directly from the intake manifold into the exhaust affecting the sensor readings (too much oxygen).

    The article was about an engine with 219 Deg. intake camshafts (the overlap not mentioned) and the wide band was reading 16:1 to 17:1 at idle. The 348 (CAT) intake cam has 248 Deg. duration (244 Deg, exhaust) with overlap of 22 degrees. With higher 348 intake cam duration (and probably higher overlap) than the mentioned engine, there should be more pass-through air in the case of the 348 at idle thus producing even higher error in wide band readings. It seems that you have to keep the engine at certain constant lower-mid revs to get the correct AFR readings.

    Another factor that would significantly affect the AFR readings is if the air injection (suction actually) system is not properly closed but it is unlikely that you have this issue. And if there is some leak pass the air injection valves, it would probably be on one bank only which would cause the recorded AFRs to be different between the banks. Perhaps you can plug the air injection hoses just to eliminate this possibility.
     
  9. m.stojanovic

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    Spark plugs affecting AFR?!. And to the extent of change of the CO pots 343 to 540? I don't think this is possible. New spark plugs, compared to old, could very slightly improve combustion but not to the extent requiring CO pots readjustment. The setting at 343 Ohms would have to have been with very worn, long overdue for change, spark plugs causing random misfiring to result in the shift to 540 Ohms with new plugs.

    On the other hand, Marco said that the CO pot should be turned very slowly which suggests that even small Ohm changes have significant effect on the AFR. If this is the case, then changing from 343 to 540 would be huge change in the AFR.

    I intend to continue my EGT tests and see if I can establish what number of Ohm change causes recognisable EGT change. This time, I will turn the CO pot anticlockwise (leaner) and not clockwise anymore to avoid re-occurrence of my detonation.
     
  10. m.stojanovic

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    The EGT test continued, 383 Ohm both CO pots, pics 1-5 are warm-up, last picture with closed loop. I ran the engine the previous day for some 20 min. from the battery reconnect and left it connected. Presumably, the ECU learning phase had been completed.

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    Similar differences as in my first readings ~20 days ago. Left the engine off for around half an hour and took 3 more readings:

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    Initially, the left (always lower EGT bank) showed a bit higher temp. Later was somewhat lower but remained rather close to the right EGT. Perhaps the ECUs learned further.

    Tomorrow, I will first do one more test from cold with both COs still at 383 to see whether the EGTs go back to the left bank always lower by similar degrees as the first test today or whether they are closer (and perhaps the left initially higher). After that, when the engine cools down, I will start again with the left CO pot anticlockwise this time (somewhat lower Ohms) and see what happens. Will not go to any Ohms higher than 383 which, at 400, caused detonation.
     
  11. Ferrarium

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    I agree everything about that post is confusing. More and more leaning towards leave it at 383. Btw I found in the manual 30 min for ecu learn, which was news to me, always read 10 min out here.

    Bought new gauges and will balance intakes.

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  12. m.stojanovic

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    Very interesting info, the 30 minutes. I think I reached (and exceeded) a total running time of 30 min. during the EGT tests today, I'll see whether I have more equal EGTs tomorrow from cold while still at 383.

    Perhaps 10 min. is sufficient to start driving but the full learning cycle completes after 30 min.
     
  13. Ferrarium

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  14. m.stojanovic

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    The same section of the manual, at page C73, mentions the 10 min. for relearning but this appears to be for the purpose of car driveability (preventing engine from stalling etc.). For our "sophisticated" tests, we should use 30 min.

    I think I found why you have too much oxygen reading on your wide band sensor - when the original O2 sensors are disconnected, the air-injection is reactivated allowing secondary air into the exhaust causing the false AFR readings that you get.

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    So, you need to plug the secondary air system or, if the control valves are closed with no vacuum acting on them, just disconnect (and plug) the small vacuum hoses.
     
  15. m.stojanovic

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    Did one more EGT check today and the readings, starting from cold, were as before: left bank ~10C lower than the right during the warm-up (open loop) and ~5C lower after the loop closes.

    I then moved to checking the vacuum, left & right; currently, bypass valves both at 2.5 turns out. With the engine at operating temperature, I stopped it, unplugged the connectors from the IACs and restarted. The idle speed went, from previous ~1000 rpm, to ~1300 rpm. According to the manual, the idle speed should actually drop to 850 +/-50 rpm. Anyhow, I proceeded with the intake vacuum checks and got the following results:

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    I then had to turn the left bypass valve, from 2.5 turns out, by 1.5 turns in to equalise the vacuums. Left bypass at 1.0 turn out, right at 2.5 turns out:

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    Since when disconnecting the IACs my idle speed goes up instead of down, I will next have to do the "geometrical balancing" - have a look at the throttle butterflies and make sure that they are both closed with exactly the same gap between the butterfly edge and its bore of 0.02 - 0.05 mm. It seems that my butterflies are not closing down to the said gap (causing the idle speed jump up with the IACs disconnected) and that my left butterfly has a slightly bigger gap requiring its bypass valve to be closed more than the right one to equalise the vacuums.

    Once I complete the geometrical balancing, re-adjust the TPS-s and redo the vacuum synch, I will see again what EGT readings I get and only then go to the CO screws (if necessary).
     
  16. Ferrarium

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    Yes definitely saw that but when those kick on you can hear them, I never heard them growl once the shut off when the cats came up to temp. Perhaps clamping the vacuum is a good idea regardless but the steps for doing the adjustments in the manual never mention doing that. I am waiting for new 02 sensors, Fedex lost them should have been here 2 days ago, arg.
     
  17. m.stojanovic

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    I will not be disconnecting my O2 sensors but I can confirm that the secondary air (growl heard at the air intake openings) is not only active when starting from cold (for ~3 min. or so) but also when restarting a warmed-up engine after some 5-10 minutes. In this case, the growl lasts much shorter i.e. only until the O2 sensors heat-up again to some 300C (the engine temp is already more than 50C). So, the info I attached above makes sense. Non-functioning O2 sensors, either because they are not hot enough or disconnected, call for secondary air.
     
  18. SoCal1

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    I got rid of the exhaust valves into the manifold, made sure the cross venturi would seal 100% then synced each bank. Smoke tested and resealed everything that sucked. Those exhaust valves are horrible with intermittent leaks day to day to weeks to months.
    That made all the adjustments very responsive

    Got all my ITB stuff ready to go on just need to make a new rear deck lid that will fit them, maybe a clear bubble hehehe

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  19. m.stojanovic

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    To follow up from my finding that I had to set the left air bypass screw to 1.0 turn out and the right one at 2.5 turns out to get equal vacuum in both banks.

    1. Checked the gaps of the butterflies - left was good (0.05 mm) and the right was slightly more open at 0.1 mm (could see that its adjuster screw had been tempered with) so I set it to 0.05. This was obviously not the reason for the left air bypass screw having to be open less as it was the right butterfly which was open more that would normally require its bypass screw to be open less.

    2. Had a look at my IAC-s (Idle Air control motors) - they looked identical but had different Bosch numbers. One was 1993 (my car is 1991) and the other 1998. When I compared their default air port openings, I could see that it was bigger on the left IAC and this was the reason why the left idle air screw had to be closed more.

    Installed new IAC-s that I had - Löwe Automobil, Germany, p/n 580505.

    3. Adjusted the TPS-s as per the manual - 400-600 mV, 80 mV max. difference left to right. The manual states to measure the voltages between ECU pins 19 and 53 but it is much easier to do it on the TPS connector:

    Left TPS - between Pins 1 (-) & 2 (+): 5 V ; Between Pins 1 (-) & 3 (+): 400-600 mV
    Right TPS - between Pins 1 (+) & 2 (-): 5 V ; Between Pins 2 (-) & 3 (+): 400-600 mV

    Although the TPS does not have slotted mounting holes for adjustment, it can be rotated a small amount which was sufficient, in my case, to bring the mV readings difference from initial ~ 60 mV to just 30 mV.

    I then set both idle air bypass screws to 2.0 turns out, started the engine and straight away got equal vacuums left-right. As the vacuum gauge needles were just touching the "green" segments, I closed both idle air bypass screws to 1.0 turn out and got the needles into the "green".

    I opened-up one of the old IAC-s to see what's inside. The IAC does not have a stepper motor but just a normal electric motor with only 3 segments on its commutator and 3 brushes. It is connected to the roto-valve which controls the air flow. The valve is spring loaded in both rotational directions which keeps the valve at certain default opening. The motor does not rotate but is just turned a small amount clockwise or counterclockwise (acting against the valve springs), as commanded by the ECU, to increase or decrease the valve opening.

    The default IAC opening is near to the fully closed position (~2 mm valve gap) and has much more travel towards fully open. This means that it is designed to control the idle air flow more by increasing the valve opening from the default (ign. off) position than by reducing it. In view of this, the idle air bypass screw should not be opened too much as it will cause the IAC to go out of its small "closing" range which will cause high and/or unstable idle. I found that the idle screw should be somewhere at 1-1.5 turns out. At my setting of 1 turn out, I get perfect idle and very good idle rpm response to the engine load changes caused by the AC compressor switching on and off.

    My special tool for TPS voltage measurement:

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  20. Ferrarium

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    #70 Ferrarium, Sep 16, 2020
    Last edited: Sep 16, 2020
    I set both my TPS to 1 or darn close to it I think there were like .005 mV difference between them when I was done. There is some plastic flashing inside the TPS mount holes that you can remove to enable a bit more twist. https://www.ferrarichat.com/forum/threads/348-throttle-position-sensor-adjustment.453969/

    The the gaps of the butterflies.... is that the gap between the stop and the flap?

    Super interesting on the IAC I assumed it was magnetic with a charge to increase or decrease opening but the apparent operating range is very good Intel, thanks!
     
  21. m.stojanovic

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    I saw the plastic flashing but I did not go to removing it as I managed to set them with much smaller difference than what the manual states. Getting them to exactly matched voltages voltages is probably not necessary since the ECU-s, I believe, calibrate themselves to the base voltage readings Left & Right (as long as they are not different by more than 80 mV) at ignition "on" and go from there having correct "pictures" of the actual butterfly angles.

    The gap (0.02 to 0.05) is measured between the butterfly edge and the bore (wall) of the throttle body, like so:
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    The IAC is basically electromagnetic, although it looks like an electric motor with permanent magnet stator. Its 3 commutator segments, via 3 brushes, are linked to the IAC Pins 1,2 & 3. The centre pin (2) is conected to +12V and the currents to the ground of the other two pins (1 & 3) is alternatively regulated by the ECU (via its pins 4 & 22) causing the motor to turn, by small angles, in one or the other rotational direction. This actuation may be by PWM (Pulse Width Modulation) or by simple analogue current regulation circuits of the ECU.
     
  22. Ferrarium

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    Did you adjust the butterfly Gap with the throttle stop on throttle body itself? I did my vacuum today and got them both the exact same at about 1 and 1.5 rurns however they're just outside the green I couldn't get them into the green which leads me to believe the butterflies are open too far I'm assuming it's the throttle stop on the tb that I need to fine tune that with?

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  23. m.stojanovic

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    The green on my gauges starts at 18 inches and I got the vacuum to ~18.5 to 19.

    The butterfly adjuster screw is at the bottom of the TB. You can check the gaps in-situ but you will need to remove the TB-s for any adjustment.

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  24. Ferrarium

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  25. m.stojanovic

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    Did a check of the ECU signal to the IAC-s with an oscilloscope and established that it is PWM, appears to be 200 Hz. The graph below is at idle (1050 rpm) with the AC off. I had very similar duty cycles left and right meaning that my "geometrical balance" of the left & right throttle bodies and the air bypass screws was good.

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    I then switched the AC on to see how the IAC responds to the changing load (recorded in wider scale):

    AC off, duty cycle is 28% (7 of 25 points on the scale):

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    AC on, duty cycle increases to 32% opening the IAC a bit more (8 of 25 points on the scale):

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