MAF and Fuel Trims Wisdom Needed

[VBSTANG06]

2006 GT with BBK not so cold air intake, Pypes long tube headers, cattless x-pipe/pypebomb axlebacks, Hitachi MAF (new), NTK upstream O2's (new w/downstream O2's turned off), clean stock 24lb injectors, OEM spark plugs/coils, stock intake manifold w/ OEM PCV hoses hooked up to it, and a Dyno tune.
It will start in open loop (lambda 1.00) w/STFT between -5 to +5 and LTFT slowly going + until O2's warm up (about 30 seconds) and switch to closed loop with lambda still at 1.00, stay in CL for 1 min, then OL again w/an immediate lambda of nice and rich (as low as .84 and as high as .98 just depends on ambient air temp I guess?) At idle while warming up and at operating temp (190° to 195°) my LTFT is both banks +22%, always in open loop with LTFT trending to zero under load (+3%). WOT is .82 lambda and decel is 1.05 lambda. O2's read .85 to .92 volts depending on what I'm doing.
MAF sensor reads .60 lbs/min at idle w/air conditioning off and .74 lbs/min w/ air conditioning on. Values increase with throttle and everything feels great while driving or idling.
My question is - Is my engine ok as is (running lean possibly due to mods/tune)? ECM is compensating for things appropriately. I have an OBD2 code reader w/live data stream to monitor behavior.

 

[VBSTANG06]

Forgot to mention that it goes into CL on start up and stays there for about 1 min then switches to OL and stays there. So it's start up, OL until O2's warm, CL for 1 min (still at 1.00 lambda here), then OL again w/lambda immediately nice and rich. Is that a healthy 4.6L 3 valve?

 

[VBSTANG06]

 

[Dino Dino Bambino]

The ECU should go into closed loop within a minute or so after a cold start up 'cause by then, the front O2 sensors should have warmed up sufficiently to send a voltage signal to the ECU. In closed loop mode, the O2 sensor voltages should fluctuate continuously between about 0.1-0.9v in order to maintain a stoich air:fuel ratio.

The STFT shouldn't be more than ~25% in either direction (+ or -) and the LTFT should be near zero. I'd expect the WOT lambda (open loop) to be in the 0.85-0.90 range.

Your engine's definitely healthy and nothing is out of range, but the tune doesn't appear to be properly optimized. I think the injector pulse width needs to be increased slightly to bring the STFTs closer to zero during closed loop mode. The fact that the ECU is adding fuel (STFT +22) suggests that the programmed injector pulse width is too short and the CL operation requires enrichment. The WOT fueling is slightly rich (opposite situation to CL), so it appears that this needs to be leaned out a bit. I suggest you contact Lito by email to [email protected] and discuss a possible tune revision with him.

 

[VBSTANG06]

Sup Dino thanks for the info! It's LTFT that's +22 for me and STFT hovers very close to zero. It's also only at idle that it goes LTFT +22. It has good power too. I'm new to fuel trims and MAF readings and wanted to see what someone thought of these numbers. Does MAF lbs/min look right to you at idle?

 

[VBSTANG06]

O2 voltage cycle very quickly in CL also with fuel trims just a few numbers away from zero. My car idles very rich (must be the tune for OL?

 

[VBSTANG06]

My OEM MAF read .74 lbs/min w/air conditioning off and .88 lbs/min w/air conditioning on but that MAF looks like there is black stuff caked on the inside of that won't come off with MAF sensor cleaner. I replaced it with Hitachi MAF and numbers read different now. I did the KAM reset after changing and have driven about 150 miles now. Before I changed MAF LTFT was +6 at most, changed MAF, now LTFT +22. I thought the MAF was bad so exchanged it but got same readings as the other Hitachi MAF. Thanks for the help

 

[Dino Dino Bambino]

Does MAF lbs/min look right to you at idle?

It looks a bit low to me. I'd suggest you get the genuine Motorcraft MAF sensor (part no. 3L3Z-12B579-BA. In fact, I'd recommend OEM for all sensors and electrical/electronic components. See where your fuel trims are with the OEM MAF sensor and go from there.

 

[VBSTANG06]

I'n a bit ill get a pic of what my scanner is saying. Idle rpms are 796-807, timing is 15.5-16.5° w/mid-grade fuel (89 octane here). I get pretty good gas mileage too (23-28 mpg with mild/moderate driving)

 

[VBSTANG06]

Oh do you know where the AAT sensor is on these? Does front bumper need to come off because I can't find it.

 

[VBSTANG06]

At cold start
At idle in OL warmed up
At idle just after start up in CL


CL at idle

OL at idle getting up to temp

OL commanded lambda at idle warmed up

 

[Notthenow]

Did you ever figure out the high LTFT?

 

[VBSTANG06]

Yes I did it was the Hitachi MAF. These engines are super sensitive to all values related to air and it wanted the motorcraft MAF. Now my LTFT values are -10% roughly on both banks and runs great. The Hitachi MAF lasted about two weeks before my car started backfiring/missing at idle. Swapped MAF sensors and have had no driveability issues since.

 

[GlassTop09]

Oh do you know where the AAT sensor is on these? Does front bumper need to come off because I can't find it.

Hi VBSTANG06,

On the 05-09 S197's for sure, maybe 10 as well but not sure on this, there is no physical AAT sensor used. With these MY's the AAT is inferred from the MAF IAT readout using math in tune calibration\OS while the car is moving to prevent bad calcs from under hood heat soak while car is stationary. So, any AAT reading thru a scanner is the last reading the ECU calc'd & updated........this isn't a real time readout.

Hope this helps.

 

[VBSTANG06]

Thanks GlassTop09 just saw your reply. What do you think these 4.6 3 valve engines make for horsepower if it's got long tube headers, no catalytic converters, and cold air intake with Dyno tune? I was told my car was tuned when I bought it ( no check engine light with rear O2's turned off, no CAT'S, and BBK cold air intake ). My guess is 300hp to the wheels? Commanded lambda is always around 9 unless I'm flooring it then it goes 8.4

 

[Dino Dino Bambino]

Yeah, ~300rwhp & ~315rwtq sounds about right.

 

[GriffX]

One reminder, the read out of the fast changing values like STFT and O2 voltage depends on the scan tool and the way it gets connection to the ECU. Some scanners have very high dwell times to get the data so it is possible to miss the maximum and the minimum values.

 

[Thatblack03]

It looks a bit low to me. I'd suggest you get the genuine Motorcraft MAF sensor (part no. 3L3Z-12B579-BA. In fact, I'd recommend OEM for all sensors and electrical/electronic components. See where your fuel trims are with the OEM MAF sensor and go from there.

What would you suggest for a custom setup? I'll be using a built 3v in a new edge chassis on the stock 03 gt ecu. I already know the maf is different, so I can swap in the slot style that the s197 has. I'm just not sure if my ecu will like it.

I'm also in the process of learning HP Tuners and recently heard that you really don't even need a maf. Speed density seems to be the better way to go and it runs off a map sensor I think? I've only just began researching and learning about tuning, so forgive the ignorance.

Last thing, could one of you maybe explain what exactly STFT and LTFT are? Those are your short term and long term fuel trim right?

 

[Dino Dino Bambino]

What would you suggest for a custom setup? I'll be using a built 3v in a new edge chassis on the stock 03 gt ecu. I already know the maf is different, so I can swap in the slot style that the s197 has. I'm just not sure if my ecu will like it.

I'm also in the process of learning HP Tuners and recently heard that you really don't even need a maf. Speed density seems to be the better way to go and it runs off a map sensor I think? I've only just began researching and learning about tuning, so forgive the ignorance.

Last thing, could one of you maybe explain what exactly STFT and LTFT are? Those are your short term and long term fuel trim right?

Yup.
STFT = Short term fuel trim
LTFT = Long term fuel trim

You'd be correct that a speed density system runs off a MAP (manifold absolute pressure) sensor that's usually placed in the intake manifold plenum. On an N/A set up the range would be roughly 0.0-1.0 Bar (sea level) or 0.0-14.5psi. For an FI set up, the range would be 0.0-2.0 Bar (0.0-29.0psi) for maximum boost up to 1.0 Bar. The MAP sensor output voltage varies linearly with manifold absolute pressure, making it easier to tune especially on FI set ups. It avoids two drawbacks of the MAF sensor (namely the necessity to place it in a non-turbulent airstream, and its sensitivity to intake tube diameter/intake tube leaks).