I have a S4 NA with the following mods -

Street Port
Intake (K&N)
Header and catback
RTEK 2.0

I installed a different AFM in my car recently. I can see on the RTEK that I am getting error #4 - Intake air temp sensor failure. This is the temp sensor that is in the AFM. I have a couple questions. The ECU now assumes that the intake temp is 66.9 degrees all the time. This is the default behavior for the #4 error.

1 - Is this sensor replaceable if I have a good one out of another AFM?

2 - Would this sensor failure drastically affect my AFRs as intake temps change?

I was at a track day last weekend, and when I started a run the car was at 12:1 AFR under load. By the end of the run the car was at 16:1 AFR under load and power dropped off noticeably. This was over a 20 minute period, the car slowly tapered leaner and leaner. I know the intake air temp will change probably 30-40 degrees or more over a run. It was about 70 degrees outside.

The only difference from before was the AFM and I had to retune the car for the new AFM because my old AFM was broken. The main problem is that the car won't stay consistent.

Thanks,
Ashley

 

It makes sense that the ecu defaults to 1 temp, Mazda probably picked something that wouldn't throw in too much fuel, and something that wouldn't cause dangerous lean conditions.

Though I am a bit surprised that your car leaned out over time vs getting richer.

 

1. yes, its actually really easy. once you pop the top off the afm (the black plastic one, and be careful it needs to go back on) the temp sensor just pops out

2. it should change fueling. if you really wanna know do some searching for henrik. but anyways the ecu takes afm signal and the air temp signal and combines them into "load" , fueling is based on load.

 

It should run richer if the default temp is lower than the temperature of the air the engine is seeing. You said it was getting leaner and leaner throughout the track day makes me think fuel system related possibly? Maybe crap in the tank was getting disturbed and slowly clogging the fuel filter during the day causing fuel pressure to drop? Just a thought.

 

The fuel system is good. Fuel filter and the in tank prefilter are both clean. Fuel pump is good and fuel pressure regulator is good. I can make the car run 11:1 AFRs under high load if I add fuel via the RTEK, so I don't believe this is a fuel supply or delivery issue.


Also, I tried to drive it yesterday and it was in the low 50s ambient. The car was running very very rich (10.1 AFRs) at light load, around 3K RPM. The car was warmed up by idling in the driveway. I drove down the street and turned around because it was nearly undriveable because it was so rich. Maybe I need another AFM entirely.

 

You can try and see if it helps. I'm sure it will.