P0171/P0174 Help!

[helosailor]

Vehicle is a 2007 Tahoe LS, 4.8 2WD with 138xxx miles and a K&N CAI.
I get a CEL with P0171 and a P0174 after slowing down from being on the highway for a while. This triggers a C0561 in the Stabilicrap system. The vehicle still runs just fine. I was able to get freeze frame data from the P0174. Does anything jump out as being far off? I'm thinking a small vacuum leak somewhere.
I have recently replaced the Throttle body and the MAF.
Fuel Sys 1 CL
Fuel Sys 2 CL
Calc Load (%) 19.6
ECT(*F) 194.0
STFT B1(%) 5.5
LTFT B1(%) 23.4
MAP(inHg) 12.1
Eng RPM 724
Veh Spd(mph) 6
Spark Adv (*) 9.0
IAT(*F) 77.0
MAF(lb/min) 0.8
TPS(%) 16.1
Run Time(sec) 1216
Command Evap 24.3
Fuel Level(%) 51.8
Warm Up DTC clr 2
Clr Dist(miles) 34
EVAP VP(in HSO) -1.020
BARO(InHg) 29.5
CAT Te 11(*F) 1202.0
CAT Te 22(*F) 1261.4
ECU Volts(V) 13.746
LOAD Value(%) 18.0
EQ Ratio 0.999
Rel TPS(%) 2.7
Ambient(*F) 73.4
TPS B(%) 16.1
ACC Pedal D(%) 18.8
ACC Pedal E(%) 9.4
Command TAC(%) 3.9


Thanks, and I owe you beers.

[kdventura73]

Can you watch live data with the scanner? Long Fuel trims are way high indicating lean condition. Reset the fuel trims if you can. If they stay normal(less than ltft +15 for those codes to set and stft +/-5%) might just needed to reset the trims. If they start rising,bring the rpms up to 2500, if they start falling back to 0 you have a vacuum leak,probably intake or gaskets. If they don't start dropping look at fuel pump/supply problem.

[helosailor]

Long Fuel trims are way high indicating lean condition. Watch the fuel trims and bring the rpms up to 2500. If they start to drop and become normal sub +/- 15 you have a vacuum leak. Probably intake or gaskets

Thanks! That was kind of what I was thinking. I'll definitely have a look at it.

[JC316]

Intake gaskets have a tendency to go bad on those motors. That is where I would start looking.

[helosailor]

Intake gaskets have a tendency to go bad on those motors. That is where I would start looking.

That's kind of what I'm leaning towards. I'm going to check the fuel tables on the way home (they were reset since the parts were changed, so it's fresh info), and go from there. Tomorrow is leak finding day.

[shumpertdavid]

Fuel trims usually don't reset with a code clear, did you have the battery disconnected for at least 10 minutes to clear the keep alive memory? Do you get bank 2 fuel trims as well, I assume since you have 171 & 174 that both banks are indicating lean? As stated, intake gaskets are common failure. Usually I see them running rough on first start ups for the first 10 seconds to a minute but generally only in cold weather times.

[helosailor]

I had the PCM flashed after I replaced the throttle body. The battery was disconnected when the MAF was replaced, but the high LTFT has persisted since both. I don't have any freeze frame data for the other bank, but I suspect it to be close to the same. I'm going to stay hooked up for the drive home today and see what it's doing. The symptoms really do sound like a small intake leak.

[kdventura73]

If you do change the intake or gaskets, I would also check the knock sensors and wiring harness while you have the intake off. If they are corroded or have water pooling in the holes change both the knock sensors and harness with oem parts. I remove the rear foam insulator and build little rtv dams to divert the water towards heads so the water can escape.

[helosailor]

Well, it turns out it was something that just got overlooked, multiple times. The intake gaskets are fines, and all of the sensors are doing their thing. It turns out this little bastard had gotten uncapped somehow. I put a new cap on it, and all is well. LTFT numbers are where they should be, and no codes at all. Thank y'all for giving me a direction to look in.