How OBD2 calculate the fuel flow rate and Mass Air Flow

I figured out that the formula stated in the paper for fuel flow below:

fuelFlow = (MAF * 3600) / (14.7f * 820) ; // l/h

is off by a single 0(needs an extra 0 added to the right of decimal).So we need to divide by 10, so the actual formula for fuelFlow now becomes:

fuelFlow = ((MAF * 3600) / (14.7f * 820)) / 10 ; // l/h

Apart from this the MAF calculated using the formula 1 below:

IMAP = RPM x MAP / IAT / 2 MAF = (IMAP/60) x (VolEff/100) x EngDisp x (MMAir/R)

probably results in a close estimation of MAF that is highly dependent on the accuracy of VE(Volumetric efficiency).I assumed it to be 80%.If there is some kind of way to calculate VE based of obd parameters not using mass air flow itself, then it would be great. Otherwise you just have to assume on VE percentage.

how does the ecu determine the load on the engine? [Archive] - The Subaru SVX World Network (subaru-svx.net)

The ECU needs to know the quantity of air it is getting, so it can work out the quantity of fuel to mix with it.

A MAF sensor measures it directly.

With a MAP based system you need to measure pressure and temperature and then calculate the quantity based on those readings. When you step on the gas, Mass Airflow changes almost instantly but Manifold Pressure lags behind. So you have to do TPS delta compensations to guess how the airflow is changing while you wait for the pressure to catch up.

MAF systems are faster to respond and more accurate. So they run smoother, especially at low rpm where precision is important. They suffer from less hesitation and provide better drivability. That's why most modern ECUs use MAF.

MAP tuning becomes a lot more useful when you increase the horsepower beyond what the manufacturer designed for. When your airflow exceeds what the MAF can measure, you either have to fit a bigger MAF (with reduced precision), or go to a MAP based system.

Some aftermarket systems like EcuTek RaceROM and Cobb Accessport can use MAF at low rpm and switch to MAP when the MAF gets maxed out. But obviously neither of those is available for the SVX.

Yes the Mass Air Flow sensor is far more accurate than the Manifold Absolute Pressure sensor, that was used before emissions demanded better fuel ratios. Though I think you have their actions, in reverse.:cool:

The MAP Sensor will signal the pressure change instantly, the MAF is slower as the air has mass, and pressure does not. When you floor the pedal, the pressure changes instantly, along with the fuel, but the air is not there to match it, so the ratio has to be compensated.

The MAF sensor reads the air mass that is entering the cylinder, so the air/fuel ratio can be set exactly to match the air.

Harvey.

Reference of MAP sensor

Fuel Injection Diagnosis: It's All About the Air | MOTOR

what is the ideal optimum coolant temperature for perodua alza

The optimum engine coolant temperature for Perodua Alza is about 82 ~ 85 degrees Celsius or 179.6 ~ 185 degrees Fahrenheit. 

At what temperature does the radiator fan to automatically turns on ? It should be around 93 Degree Celsius or  199.4 Degrees Fahreinheit.

What happen when map sensor is worn out or faulty ?

Worn out map sensor may cause rough idle and increase in fuel consumptions - as the diaphragm rubber that measure the absolute manifold pressure getting weaker over time due to aging. As the ECU will received lag / delay data from the MAP sensor it will command wrong fuel delivery for combustions.

Faulty map sensor may result in engine difficult to start or start but having the worst idle as if the engine going to stop and it cause the ECU to command more fuel and this is the worst fuel consumption you can have. Significant weakness in the engine and feels like going to stop when on idle and you can smell fuel coming out from the tail pipe. 

While worn out map sensor can be tricky and difficult to detect but failed (bad) map sensor can easily be detected using cheap OBD2 data. For Perodua Alza the MAP sensor on idle ranging from 4 to 6.3 psi or more stable one around 5.8 ~ 5.9 psi but if it fails it will go up to around 14 psi pressure and you can feel the car run very weak with fuel smell coming out from the exhaust tail pipe and engine jerking to almost stop.

Perodua Alza front wheel bearing size dimensions

Outer Diameter = 75mm 

Inner Diameter = 40mm 

Height = 39mm

Perodua Alza 3SZ-VE engine 4 holes fuel injector characteristics

Resistance range between 12.5Ohm ~ 12.9Ohm. Commonly 12.5Ohm ~ 12.7Ohm

O-Ring Size Dimensions: 11.6mm outer diameter and 2.1mm ~ 2.2mm thickness

Clicking / ticking noise from the cabin after installing new fuel delivery pipe (fuel rail) alza

After 13 years running the car never change or service the fuel injectors including the fuel rail system. The injectors have been clogged badly and caused misfires and lean combustions. This can be seen on the spark coloration where it is almost red which indicates more air burnt than the fuel. So cleaning the fuel injectors nozzles and check if any of them are leaking should be done.

Another small component called the fuel pressure pulsations damper (pulsation dampener) or FPD can also be faulty - and this may caused the car feeling choked or dull when accelerating. Ticking / clicking noise can be heard from the cabin when the car running on idle. 

The function of the fuel pulsation damper is to absorb pressure generated by the activities of opening and closing of injectors (recoil effect). These hydraulic pulses can cause an undesirable noise which can be transmitted to the passenger compartment. 

Experience of Fuel Consumptions Test:

Today 13-July-2022 an experiment after Fuel Pump, Fuel Rail (including pulsation damper), and fuel injectors have been replaced. Test drive was completed about 20 km it shows significant improvement to the overall health of the car as follows;

1. Intake Air Temperature - it used to be average around 55 to 65 degree Celsius and sometimes increase up to 80 to 90 degree Celsius. After all the replacement above the range is between 38 to 55 degree Celsius. This indicates that good fuel delivery have significant impact to the Air Intake temperature which also the same for the engine bay heat. Since the Alza car air intake pipe within the engine bay therefore temperature measured by the IAT sensor is roughly equivalent to the engine bay temperature.

2. Second improvement is steady reduction in the fuel consumptions - the car have been suffered too long from clogged fuel filter, weak fuel pressure, clogged fuel injectors, and faulty pulsation damper. It used to consumed around 12.7 Liter per 100km which is way beyond poor fuel economy sometimes it went up to 14 Liter per 100km. 

3. The oxygen sensor or O2 sensor readings starting to show steady oscillations of data between 0.1v to 0.7v ~ 8v and it used to be very inconsistent.

4. The spark plugs no longer looks reddish in color which indicates nearly stoichiometric (14.7 : 1) air and fuel burnt in the combustions. It looks more white and a little black now.

The most significant lesson learnt in this test drive experiment is about fuel pressure and fuel pulsation damper (FPD). After years of investigations of what went wrong with the car with the following assumptions in mind.

1. Because of the O2 sensor inconsistent data reading on the OBD2 apps - it was assumed that something wrong with it or already worn out. However this assumptions turn out to be wrong as the inconsistent data was caused by imperfect combustions due to lack of fuels.
2. The second assumptions was fuel injectors gone bad or clogged - but after testing the injectors resistance around 12.5ohm to 12.9ohm seems fairly good and cleaning the injectors doesn't really changed much of anything.
3. Replacing the fuel pump does increase the fuel pressure but it was not good enough as fuel still having issues not enough for good combustions.

So it turns out one last thing which is the fuel pulsation damper - it solved the issues significantly. So it is very true that the activity of opening / closing of the injectors could generate ripple effects that is repulsive in nature and that will disrupt the incoming pressure into the fuel rail. Therefore the function of the pulsation damper is to absorb that recoil effect of the fuel injectors and allow steady flow of fuel and its pressure into the fuel rail so that all the injectors have equal pressure to spray into the combustions chamber. However having that component faulty for so many years - I couldn't really figure out what was the problem until then. And now everything seems going back to where it should be. 

One thing to note: If you measure the fuel pressure on the hose that leads to the fuel pump is good - that is not enough. And there is no way to measure the pressure inside the fuel rail unless you drill into the fuel rail and install pressure gauge (perodua alza 3SZ-VE engine). So to know if the pulsation damper is the problem is to check one by one if the fuel injectors and fuel pump are doing OK. If they are okay meaning only one thing left which is the fuel pulsation damper.

Which one is Perodua Alza fuel pump fuse ?

Perodua alza fuel pump fuse is located in the front hood fuse box denoted by the 15A and written on the fuse box cover as (EFI fuel injection). See picture below. To be certain this is the correct fuse - you can test when the fuse is intact and remove by doing so.

1. When the fuse is intact (installed) - put in key and switch to "ON" position (not start) you will listen to the fuel pump noise.

2. Now remove the 15A fuse and - put in the key and switch to "ON" position (not start) - you will listen no noise of the fuel pump.

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