2014 Chevy Malibu 2.5 ecotec p0171 with freeze frame with very high LTFT

Symptoms p0171 code
Hesistation
Somewhat rough idle but definitely not normal
Struggling acceleration especially re-acclerating after de-accelerating

What i have done already:
New MAF sensor
New intake and exhaust solenoids
New engine air filter
Oil Change with new oil filter

Have not tried smoke test to check for vaccum leak due to no smoke machine


Freeze Frame Data pulled from Torque App for android
Vehicle Manufacturer: Chevrolet
Vehicle Calibration ID: 126

Freeze frame information:

---

Fuel Status = 0 byte
Engine Load = 15.686 %
Engine Coolant Temperature = 172.4 °F
Fuel Trim Bank 1 Short Term = -1.562 %
Fuel Trim Bank 1 Long Term = 39.844 %
Fuel pressure = 43.511 psi
Intake Manifold Pressure = 3.916 psi
Engine RPM = 1,200.5 rpm
Speed (OBD) = 42.253 mph
Timing Advance = 42 °
Intake Air Temperature = 26.6 °F
Mass Air Flow Rate = 4.46 g/s
Throttle Position(Manifold) = 20.392 %
Fuel trim bank 1 sensor 1 = -1.562 %
Run time since engine start = 392 s
Fuel Rail Pressure = 688.929 psi
Fuel Level (From Engine ECU) = 50.196 %
Distance travelled since codes cleared = 264.083 miles
Evap System Vapour Pressure = -270.25 Pa
Barometric pressure (from vehicle) = 14.359 psi
Catalyst Temperature (Bank 1,Sensor 1) = 1,198.4 °F
Voltage (Control Module) = 15.251 V
Engine Load(Absolute) = 13.333 %
Commanded Equivalence Ratio(lambda) = 1
Relative Throttle Position = 10.196 %
Ambient air temp = 26.6 °F
Absolute Throttle Position B = 20.392 %
Accelerator PedalPosition D = 30.98 %
Accelerator PedalPosition E = 15.294 %

Any help would be appreciated!

Fuel Pressure is low. Spec 50-94psi.

When running real time data my scanner is reading 50, where it should be? Does anyone know if this could be a simple o2 sensor issue with the freeze frame data provided above? I could use a little more info to guide me in the right direction so I'm not replacing a bunch of unnecessary parts. Thanks!

intake air snorkel torn?? engine speed says its almost at idle. do you hear a hissing sound like vacuum leaks?

I'd start with monitoring the data during a test drive. Do the trims remain high during acceleration and cruise? Your symptoms suggest they will, but it's good to have data for confirmation. Knowing this will help narrow down your list of suspects.

I have a couple known good captures off a 2013 Malibu with the same 2.5L engine, for comparison. Have a look. Keep in mind that ShopStream Connect (the Snap-On desktop software) skipped a decimal point on the Fuel Pressure Sensor PID. It always shows in the hundreds. Add one decimal point to get the real value.

Idle:
www.scanshare.io/share/AAQFM8j4MEeEtG_aUaYtmA#0,34,35

Test drive:
www.scanshare.io/share/IHiHV2HovE60-zkRdMSyBw#0,20,21,34,35

It would appear that your fuel pressure reading of 43 PSI at idle isn't unreasonable. Monitor the same PID under load to make sure it's not dropping off. Monitor the rail pressure as well. It should be able to clear 1500 PSI easily under load. Most will do closer to 2000 PSI at WOT.

Definitely inspect the air intake tube as Cheryl suggested. Your MAF reading at 4.4 g/s is low for 1200 RPM.

If you mean the tube after the maf sensor it is fine. Took it off and no cracks or anything. The housing for the air filter seems loose but doesn't seem disconnected. I brushed it off as normal but I don't even know how to get to it, maybe under the wheel well on the passenger side.

Fuel pressure at idle seems to be sitting around 43 to 45 at idle, fuel rail 420 to 455 at idle, when I rev up to 2500 to 3000 rpm the fuel rail only seems to reach a steady 8 to 900ish but if I give it one quick rev it goes up to 1700+

Forgot to mention yes ltft stays high while driving. It will drop tho while I'm in park and rev it up to about 3000 rpm, it will dip lower about 10% and when I let off the gas it just goes right back up

Sounds like the low and high pressure fuel system is good. I'd go for a WOT test drive and watch Calc/Absolute Load and the upstream O2. Calculated should be 99-100%. Absolute should easily go over 90%, maybe over 100%.

Good Loads and a lean upstream O2 would suggest a fuel quality issue, i.e. ethanol fuel in a non-Flex vehicle. Dunno if this Malibu is Flex Fuel, or if they sell E85 in your area. :silly:

Control module voltage 15.251? Isn't that a little high?

Desmond6004 wrote: Control module voltage 15.251? Isn't that a little high?

Technically, yes? But it's a late model GM, and they'll charge at whatever rate the BCM feels like. :silly:

Tyler wrote:

Desmond6004 wrote: Control module voltage 15.251? Isn't that a little high?

Technically, yes? But it's a late model GM, and they'll charge at whatever rate the BCM feels like. :silly:

Code:

https://www.remyautomotive.com/dam/jcr:5d7303a6-36a2-4ec8-9335-f1d81bce2d24/2)%20Technical%20Service%20Bulletin%20-%20June%202015.pdf

Ok, like the Toyota I had the other day. Newley fitted driving lights kept blowing bulbs but headlights were fine.
I checked charging at over 16 volts for a minute after start-up, dropping to 12.8 after 10 minutes. I scoped the headlight bulbs
and after start up they received pulse width modulation feed to compensate. The driving lights were connected directly
to the battery through a relay so the 16v was blowing the bulbs.

Just an update, I've also changed both PCV vales and upstream o2 sensor. (Sensor was definitely burnt), I'm on mobile quick reply or I'd upload a photo. Neither of these brought down the fuel trim. I do have a downstream o2 I'm going to replace since the upstream looked rough I'm at 64k miles roughly, so it wouldn't hurt. I know the thing here is to not be a parts changer but I'd be lying if I said I'm not enjoying the knowledge I'm gaining from doing these things. Plus it's not breaking the bank, these are all fairly inexpensive parts. I'm pretty much down to manifold gasket and/or fuel injectors/pump (hopefully not pump) issues. But I'm strongly leaning towards manifold gasket which was my suspicion to begin with.. I'm not educated on TPS sensor, does anyone know if that can throw a p0171 code? I'll keep the updates coming because I don't see much of this engine with resolved problem codes on the internet so the people will get what they need from this post in the end.

SixOneFour wrote: I know the thing here is to not be a parts changer but I'd be lying if I said I'm not enjoying the knowledge I'm gaining from doing these things. Plus it's not breaking the bank, these are all fairly inexpensive parts.

No hate from me. As long as you're having a good time!

I'm pretty much down to manifold gasket and/or fuel injectors/pump (hopefully not pump) issues. But I'm strongly leaning towards manifold gasket which was my suspicion to begin with.

I doubt you're gonna find an intake issue, but I'm ready to be wrong. :silly: The fuel trims staying high while driving points more towards fuel delivery. You could always go for the classic ScannerDanner water test?

I'm not educated on TPS sensor, does anyone know if that can throw a p0171 code?

Unlikely. A dirty throttle body, maybe. But again, that won't matter when driving down the road (where the trims are still high).

I'll keep the updates coming because I don't see much of this engine with resolved problem codes on the internet so the people will get what they need from this post in the end.

Please do! I'm starting to see these cars roll in out of warranty, so this whole thread is valuable to me.

Have you tried watching the Loads and the upstream O2 during a WOT run? That'll allow you to check VE and fuel delivery, all in one test.

So did some more research on this one, and I may end up eating my words? Apparently it's very common for the intake bolts to come loose, and thus not seal against the cylinder head. :blink: Could be an easy fix if you put a ratchet on the bolts and they're loose!

If you find loose bolts, maybe try the water test beforehand? Just to see if it's a good way to find the problem. Then, snug 'em up and see what the trims do.

So did some more research on this one, and I may end up eating my words? Apparently it's very common for the intake bolts to come loose, and thus not seal against the cylinder head. :blink: Could be an easy fix if you put a ratchet on the bolts and they're loose!

If you find loose bolts, maybe try the water test beforehand? Just to see if it's a good way to find the problem. Then, snug 'em up and see what the trims do.

Tyler wrote: So did some more research on this one, and I may end up eating my words? Apparently it's very common for the intake bolts to come loose, and thus not seal against the cylinder head. :blink: Could be an easy fix if you put a ratchet on the bolts and they're loose!

If you find loose bolts, maybe try the water test beforehand? Just to see if it's a good way to find the problem. Then, snug 'em up and see what the trims do.

I’ve found that using an unlit propane torch works better when you are looking for intake leaks using fuel trim changes.

Wouldn't you still expect to see lower ltft than this at that rpm if there was an intake leak?

Sent from my Moto E (4) Plus using Tapatalk

"Have you tried watching the Loads and the upstream O2 during a WOT run? That'll allow you to check VE and fuel delivery, all in one test."

I will try this today. Most recent update now is that I've tried the water test around the tubes and around the intake, I did not hear any water being sucked in nor did I hear any idle change (which is already pretty rough) I did however notice for the first time that while my positive long term fuel trim was high my fuel trim went very negative about -15 to -20ish (rich?) while in park/idle and then it went back to doing what it normally does. I felt like the car wanted to stall for a second but it didn't.

Here's a few screen shots at WOT if I did this correctly. I'm still a noob on this forum. Upstream and Downstream o2 sensors, I noticed the downstream taking a dive in voltage when letting off the accelerator from WOT coming to a slow or stop, then it will go back up to around 0.8ish and stay. Keeps doing that. I have a new downstream sensor but have yet to replace it, the upstream is brand new. All parts I use are OE