Air Volume?

[Ozy44]

I understand My 2012 3.8L GDI does not have a MAF sensor. Soooooo, how does the ECU measure the air volume coming into the intake in order to adjust the amount of fuel being injected? Reason I ask is, my Jenny Sauce is wanting to stumble and nearly stall at stop lights while in D. I've had this happen on other cars, and cleaning the throttle body and MAF would almost always remedy the problem. Throttle body has been cleaned, air filter replaced, PCV valve replaced, and I've done a smoke test for evap leaks. I am getting an occasional code of P0100 indicating an air flow problem. The old girl is at 191k miles. Any help would be greatly appreciated.

 

[Gunkk]

What are your fuel trims at idle (warm engine, closed loop)?

 

[Gunkk]

To answer the original question, TL/DR: lookup tables.

To determine fuel demand, your car's ECU uses a combination of inputs: engine RPM, throttle body position, manifold air pressure, 02 sensors (when in closed loop), and Intake air temperature and/or pressure, and coolant temperature. ECU sifts all that through a few lookup table to determine fuel demand. Then it commands injectors to deliver fuel to meet the calculated demand. O2 sensors measure actual output, and any differences between commanded and actual are compensated via long term and short term fuel trims (shown as %), the sums of which (ST+LT=total) for each bank should average near zero plus or minus a few percent. If fuel trims are more than +10% or less than -10% then there is a problem.

Contrast to MAF cars which directly measure the mass flow rate (grams/sec), which the ECU then does a similar lookup to calculate fuel demand. MAF systems are more accurate at edge cases where the MAP/IAP aren't perfect, but 99+% of the time MAP/IAP work just fine as they did for decades.

As to troubleshooting your stalling/rough idle in gear, from the manual (ref: https://cardiagn.com/2012-14-hyundai-genesis-fuel-system-3-8l/ ):

ECT = engine coolant temperature

EDIT: the emission control section of that same 2012 3.8L manual suggests that there is a MAF combined with the IAT downstream of the throttle body, so unless the manual is wrong it might be using the same code for that sensor whether or not it has an actual MAF? Sorry I'm not a 3.8L guy. Ref: https://cardiagn.com/2012-14-hyundai-genesis-emission-control-system-3-8l/

 

[Ozy44]

Yikes!! Looks like both my downstream sensors aren't cranking out any data. I may try replacing them, but I have a bad feeling this is CAT issues. I use the car on a 100-mile commute daily, and I drive it pretty hard.

 

[Gunkk]

High fuel trims suggest an air leak (O2 sensors are getting too much oxygen, which the ECU thinks is running to lean, so it adds fuel). This is consistent with poor idle performance. This condition, if left unfixed, will cause to accelerated wear-out of of the cats among other issues. Time to go see the mechanic.

 

[Ozy44]

I decided to order the downstream sensors and will replace them when they come in. Lots of miles on my car so hoping they failed one at a time and need replacing.
Gunkk, any chance you could let me know what temp your cats are running at under load, say 70mph on the highway? I'm reluctant to visit a mechanic due to the age and value of the car. The car has been fantastic to own, paid $10,500 in 2019 with 70k on the clock and it's at 192k now. Pretty sure I got my money's worth out of it! Lots of items failing now; Front crank seal leak, rear diff leak, valve cover gaskets starting to weep, suspension bushings cracking and it needs a starter. Just looking to keep it running a little longer while shopping for a newer car.

 

[Gunkk]

I don't have my cars anymore, sorry. Gave my last '12 to one of my kids.

Firing a parts cannon at a rich-running car is a waste of money, IMO. But if you must then stick with OEM or you'll compound the problems.

 

[Ozy44]

I'm thinking of it more as a maintenance item than a parts cannon situation. If I change them and it doesn't resolve the issue, well.... they probably needed replacement due to age/mileage anyway. I'll get back with results once I get the issue resolved, and let everyone know how many times the cannon was fired and how much it cost me