Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community - FT86CLUB - View Single Post - Forced Induction and MAF readings, as well as Fuel Trim?

brzperson · 02-19-2022, 12:29 PM

Hello everyone.
I just bought a turbo BRZ, with a SBD kit on it.
Freaking stoked!
I understand why people love these cars so much.
I feel like I'm driving a shifter kart around town, and I just love being in the car.
Even in normal, everyday situations in low rev ranges.
There's really nothing quite like it.

It's been running DD on the kit for 70k+ miles, and nothing about it seems like it will not continue doing so.

However, there are some things that are a bit concerning to me.

The STFT and LTFT are somethings really high (in the positive direction), but never throw a code.
This tells me that the car is lean, but if it really was, wouldn't my AFR be off?
My AFR is always good. around 1 stoich +/- .004
.085 under boost, and 1.3 when throttle cuts off.

TLDR SCROLL

I compared engine vacuum to maf readings by using a fancy thing I found here on stack exchange: https://mechanics.stackexchange.com/...af-calibration

Essentially, I ended up with a MAP reading of 32kpa.
After converting to engine vacuum (opposite of MAP-baro), I get about
20.37hg in vacuum.

Since my car idles at 892 RPM, I converted that to sucking in 14.86 LItres a second.
Finally, 0.9868 (sea level baro) - 0.682 atmospheres (20.37hg converted to atm), I get what should be a MAF reading of 4.56 g/s.

However, my maf is reporting 2.34 g/s.

TLDR
My fuel trims are wonky (+ double digit percentages LTFT), and my maf is reporting half of what it should as g/s airflow.

BUT my car runs perfectly fine, and my AFR is on point.

The car is boosted and tuned.

I have heard that on boosted cars, maf readings essentially go out the window unless they are specifically tuned for.

Should I not worry about it, and just trust the AFR readings, or could the engine be compensating for a very lean condition, while still keeping a good AFR?

Again, there's NOTHING wrong with the way the car runs now.
It has a ton of power, has been running for at least 66 hours with no code, etc.

BUT if something is wonky, maybe i should look into it now.

The way to know for sure is to just get a smoke machine, which are pretty cheap, or go to a place that can smoke machine for me.
But I'm really just trying to wrap my head around all of this first, before I do something like that.

Though if I own a car that has introduced many more intake pipes, I might get one just in case I need to know if I ver need to replace a pipe clamp or something else.

02-19-2022, 12:29 PM	#1
brzperson Member Join Date: Feb 2022 Drives: 2013 BRZ Location: Texas Posts: 14 Thanks: 0 Thanked 3 Times in 2 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	Forced Induction and MAF readings, as well as Fuel Trim? Hello everyone. I just bought a turbo BRZ, with a SBD kit on it. Freaking stoked! I understand why people love these cars so much. I feel like I'm driving a shifter kart around town, and I just love being in the car. Even in normal, everyday situations in low rev ranges. There's really nothing quite like it. It's been running DD on the kit for 70k+ miles, and nothing about it seems like it will not continue doing so. However, there are some things that are a bit concerning to me. The STFT and LTFT are somethings really high (in the positive direction), but never throw a code. This tells me that the car is lean, but if it really was, wouldn't my AFR be off? My AFR is always good. around 1 stoich +/- .004 .085 under boost, and 1.3 when throttle cuts off. TLDR SCROLL I compared engine vacuum to maf readings by using a fancy thing I found here on stack exchange: https://mechanics.stackexchange.com/...af-calibration Essentially, I ended up with a MAP reading of 32kpa. After converting to engine vacuum (opposite of MAP-baro), I get about 20.37hg in vacuum. Since my car idles at 892 RPM, I converted that to sucking in 14.86 LItres a second. Finally, 0.9868 (sea level baro) - 0.682 atmospheres (20.37hg converted to atm), I get what should be a MAF reading of 4.56 g/s. However, my maf is reporting 2.34 g/s. TLDR My fuel trims are wonky (+ double digit percentages LTFT), and my maf is reporting half of what it should as g/s airflow. BUT my car runs perfectly fine, and my AFR is on point. The car is boosted and tuned. I have heard that on boosted cars, maf readings essentially go out the window unless they are specifically tuned for. Should I not worry about it, and just trust the AFR readings, or could the engine be compensating for a very lean condition, while still keeping a good AFR? Again, there's NOTHING wrong with the way the car runs now. It has a ton of power, has been running for at least 66 hours with no code, etc. BUT if something is wonky, maybe i should look into it now. The way to know for sure is to just get a smoke machine, which are pretty cheap, or go to a place that can smoke machine for me. But I'm really just trying to wrap my head around all of this first, before I do something like that. Though if I own a car that has introduced many more intake pipes, I might get one just in case I need to know if I ver need to replace a pipe clamp or something else.