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  1. #1
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    TUNING FOR DUMMIES PART 1

    Welcome to anyone who wan't to learn about these cars. To begin the journey of "tooning" there are few thing you should understand at first such as "Fueling", "Ignition also known as timing" and "Boost control". In most cases if you tune anything else besides BMW and few Audi counterparts you are going to run into something known as "closed loop" and "open loop". I know you are thinking its an overload of info and we haven't even got started but don't freak out, just stick with it.
    What is Open loop?
    99% of cars use 2 stage process of operation Open Loop and Closed Loop. Close loop operates from O2 sensor reading and knows the lambda which then is converted into AFR(air to fuel ratio) and references the info with the fuel table for the bank its working with. Let's say you started your car and you table target is 14.7 (stoich) for the 30-40 load and 800-900 rpm (cold start) but the car is dumping fuel and O2 reads labmbda of 0.918 which is 13.5 AFR, what its going to do is compensate and you are going to see STFT going into negative area aka pulling some fuel out (Note: STFT - Short Term Fuel trims that make adjustments according to the lambda reading from O2 sensors). Once fuel is pulled the AFR(lambda) adjusts to your desired target as per current table. There are certain problems that arise with such system as bad O2 can cause all sorts of roller coaster ride. The other reason it is not ideal, because certain conditions must be met before O2 can read properly aka warm up period to certain temperature which varies on vehicles. We are not going to cover addition ECU programming aka Warm up Enrichment (E85 and winter conditions), spool table (to increase turbo spool etc).
    The other logic that most cars use is called OPEN LOOP. This is where MAF sensor comes into play. MAF stands for Mass Air Flow which measures, you guessed it, air. Let's say you put a massive CAI (cold air intake) on your car or change turbo size, change cams to suck in more oxygen the MAF has to be calibrated. Some standalone ECUs are advanced enough ***cough cough AEM Infinity*** To see VE (Volumetric efficiency and recalculate thing a bit for you however you still have to make certain changes to get desired result. Think LS motors for a moment. When you shove a NightFury cam on it, car won't start because of improperly calibrated MAF so when the tuner makes adjustments he will adjust MAF to that cam (Usually base table that he came up with over the course of tuning multiple cars on that cam) and then adjust it further from logs or in person. For Emissions and Fuel Economy purposes cars with both Open and Closed loop will switch between both. You are going down the street and car measures maf etc and then you pull up to a stop light with this nice BMW and ... well its green and both of ya'll punch it. What is going to happen? In most cases car will switch to closed loop and read of appropriate table in ECU. Switch can be triggered by different things: TP(throttle position ), Speed, Warm up cycle, tuner manually set you to one mode etc. Once you let off car normally goes back to Open Loop and you are chilling. Again, this is set by certain conditions aka timer, tp, load or whatever your vehicle is using.
    Interesting note: Some tuners prefer to stick to one or another mode to eliminate complication of tuning both. IE if your O2s are bad or if you have an EVO, NA-T (Naturally aspirated car that got boosted),Spray.Really no way of saying one is better over the other as everyone does it differently but everyone has an opinion for one over the other
    Now that we covered some basic stuff lets jump into other things.
    FUELING:
    Fuel is always measured in lambda as lambda is universal principle for any fuel. Each type of poison in your tank has its own stoichiometric ratio. Stoich-Perfect burn mixture between oxygen and injected go go juice knows as equilibrium. So when we look at lambda of 1 for each one of the different types of fuel will have different picture:


    Click here to enlarge


    For PI cars you would usually run max power rich but again depends on you or your tuner. For DI cars (Direct Injected) you would stick to max power lean or even leaner. I tune in lambda sometimes as it is a bit easier then recalculating the afr each time. Most modern Wideband O2 sensors are calibrated to 14.68 aka pump gas so your afr in log would show up as 12.0 even if you are on E85 but that isn't really 12.0 AFR because pump stoich is 14.7:1 (where ONE is LAMBDA) and E85 in perfect world is 9.765:1. It sounds complicated but its not. If you look at the table above you will get it more. If you want to figure out what your AFR actually is then you would do this 12.0/14.7(14.7 is what your O2 is calibrated to) you would get lambda of 0.816. Since we are on E85 we need to find what that lambda actually equates to on this fuel. We take 0.816*9.765(stoich for Ethanol) and get 7.968 afr. Some aftermarket wideband sensors can be calibrated for type of fuel you are using in order to read real afr.
    Even though your O2 is telling ya that you are running 12.0 afr in reality you are spewing 7.968 afr which is good. So how do you know its good ? Reference table (Credit to hotrod.com)

    Fuel A/F Lambda (λ)
    Pure Gasoline Stoichiometric 14.7 1.000
    Pure Gasoline Max Power Rich 12.5 0.8503
    Pure Gasoline Max Power Lean 13.23 0.900
    E10 Stoichiometric 14.08 1.000
    E10 Max Power Rich 12.0 0.8523
    E10 Max Power Lean 12.7008 0.9020
    E15 Stoichiometric 13.79 1.000
    E15 Max Power Rich 11.75 0.8521
    E15 Max Power Lean 12.4362 0.9018
    E85 Stoichiometric 9.765 1.000
    E85 Max Power Rich 6.975 0.7143
    E85 Max Power Lean 8.469 0.8673
    Ethanol Stoichiometric 9.0078 1.000
    Ethanol Max Power Rich 6.429 0.7137
    Ethanol Max Power Lean 7.8 0.8659
    Methanol Stoichiometric 6.45 1.000
    Methanol Max Power Rich 4.0 0.620
    Propane Stoichiometric 15.7 1.000
    Propane Max Power Rich 13.18 0.8395

    You are basically sitting in the sweet spot between Max power rich and Max power lean.
    Term max Power lean is when the fuel burn out but some oxygen is left over and it comes out as hot air. It is good for spool in moderation, can make more power as well.
    Negative effect: Overdue it and you go KABOOM, Melted pistons, holes in the block, Misfires.

    Max power Rich: Great for cooling as ambient temp of injected fuel takes heat away from cylinders, Economy is complete sh*t, safer.
    Negative: Can wash a cylinder (washes off oil that sits between the Piston ring and wall to create compression), hydro-lock, puts out spark causes misfires.

    In perfect way to put it, moderation is the KEY!!!

    This is part one. I am out of time today and will walk you through timing in the next one. This is basic concept so people can begin to understand their car better.

    PS: N54 has not MAF sensor but instead uses calculation to calculate MAF. If you have any questions, ask away

  2. #2
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    Do you not have the open and closed loop stuff backwards? My understanding was that closed loop is used for idle and low load situations, and open loop is a predetermined map where o2 sensors are ignored (in something like an LS). There is a local LS tuner here in town and his tunes blow for driveability but are great for WOT because he just forces the car into open loop all the time and runs a set afr. It's fun cruising on the interstate at 11:1 everywhere lol.

    I also thought our cars' DME is different and even WOT is closed loop with the o2s being used the whole time.

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    Car usually start in Open loop and some stay there until the O2 warms up and it goes into closed loop. Fuel is strictly determined by airflow in open loop. Some cars stay in Open loop for low load and cruise etc and switch to closed at certain load, temp, tp etc. There are 2 sets of tables both for Open and Closed loop. When you are in closed loop you still reference the fueling table but ecu makes ST adjustments and LT adjustments(stored in memory for future reference) to bring the fuel closer to whatever you are trying achieve. Usual value is +-25% but some ECUs swing more.

    I think you got confused cuz I made an example of closed loop only system which is not ideal. Those work off timer usually or use temperature sensors to determine which table to use

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    1 out of 1 members liked this post. Yes Reputation No
    Cars that use a narrow band 0-1 volt sensor are usually open loop on cold start until 02 heater gets the sensor warmed up, older cars stayed open loop until coolant got to a certain temperature. They also go open loop at wide open throttle because the sensor is not accurate at that flow/temperature. All cars with catalytic converters will be in closed loop at idle and at cruise if the system is working properly.
    The N54 is only open loop during cold start and when some type of failure causes fuel trims to go to max (34%) for a certain period of time or some other failure that affects fuel control (FMEM failure mode effects management) FMEM will cause open loop under these conditions. Until the next restart where the computer will attempt to control closed loop fuel again but drop into FMEM again if the fuel trims cannot be maintained or the same fault is detected. N54 uses a wideband 02 sensor so they are in closed loop at wide open throttle.(if everything is working properly)

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    Here's my load
    And boost log
    My afr on high rpm is 12.2
    I'm driving with 100ron
    What can be that load problemsClick here to enlarge
    Attached Images Attached Images  

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