Dreaded P0171

[Gotta_Go_Fast]

Hello everyone,
I’m seriously struggling to figure out what’s wrong with my car. It’s got a P0171 with long term fuel trims peaking into the mid +30s. I’ve checked the purge system, PCV system, replaced the MAF sensor, smoked the intake and had no leaks at all, O2 sensors appear to operate normally.
What’s even weirder is that they’ll spike to around 30 when I come to a stop and slowly start to drop back down into the teens. It does this every time and hits mid 20s in between shifts. Any ideas?

 

[efaily]

It's got to be an air leak with that behavior. The spike at idle is because the percentage of air leaking is higher at low RPM. The common PCV failure points are the rubber nipple coming loose in the intake manifold, which then leads to the rubber diaphragm in the intake manifold tearing. Did you try pulling the oil dip stick with the engine idling to see if there's vacuum in the crankcase?

 

[JoelD]

In idle pull the dip stick. Put your finger tip on the hole where the dip stick goes. There should be a bit of suction you can feel on your fingertip which is normal. If you pull the dipstick and hear it "shoot" out pressure, then the PCV problem needs to be fixed before seals are blown. I'm no mechanic. It happened to me two weeks ago leaving work. Good luck.

 

[Gotta_Go_Fast]

In idle pull the dip stick. Put your finger tip on the hole where the dip stick goes. There should be a bit of suction you can feel on your fingertip which is normal. If you pull the dipstick and hear it "shoot" out pressure, then the PCV problem needs to be fixed before seals are blown. I'm no mechanic. It happened to me two weeks ago leaving work. Good luck.

Yep already did that. I have the V3 of the PCV fix kit installed already. Dipstick suction is strong

 

[Gotta_Go_Fast]

These are a list of my current mods. I forgot how to update my signature lol.
MPfab Intake, Bypassed the Bypass, Ported Intake Manifold, PCV Fix Kit v3, Trifecta Elite (Flex) Tune, Custom 2.5" Exhaust, BNR Downpipe, RacerX FMIC, RacerX Shifter Bushings, TurboTech Trans Mount, MSD Blaster Coil Pack, BKR7E Plugs @.26, BNR Shifter Clamp, OTTP Motor + Trans Upper Mount, OTTP Stainless Clutch Line, OTTP Short Shifter, ZZP Lowering Springs, ZZP Metal Sway Bar Links, ZZP Rear Sway Bar, Rally Armor Poly Mud Flaps, ZZP Flex Fuel Kit, Bosch 42# Injectors

 

[Gotta_Go_Fast]

It's got to be an air leak with that behavior. They spike at idle because the percentage of air leaking is higher at low RPM. The common PCV failure points are the rubber nipple coming loose in the intake manifold, which then leads to the rubber diaphragm in the intake manifold tearing. Did you try pulling the oil dip stick with the engine idling to see if there's vacuum in the crankcase?

Tons of vacuum in the crankcase. I double-checked the burst disk on the part of the PCV hose that is connected to the turbo and that's good. Double checked to make sure the fix kit plug was still sealed and it very much is. The diaphragm on the valve cover is good as well. No leaks coming from any of the hoses in the fix kit either.

EDIT: PCV fix kit v3 is installed

 

[efaily]

You've already used a smoke machine connected to the intake and didn't see any smoke anywhere? P0171 is a lean condition. Either unaccounted for air getting past the MAF, or not enough fuel. In this case, with the fuel trim spiking at low RPM, that indicates air leak rather than fuel obstruction. Did you try the smoke machine with the engine warm, or cold? Did you notice a difference in the fuel trims with the engine warm or, cold?

 

[Gotta_Go_Fast]

You've already used a smoke machine connected to the intake and didn't see any smoke anywhere? P0171 is a lean condition. Either unaccounted for air getting past the MAF, or not enough fuel. In this case, with the fuel trim spiking at low RPM, that indicates air leak rather than fuel obstruction. Did you try the smoke machine with the engine warm, or cold? Did you notice a difference in the fuel trims with the engine warm or, cold?

Yeah 0 smoke, not even a whisp anywhere. Engine was cold since its worse when the motor is cold. The fuel trims tend to be happier when the motor is fully warmed up. Sometimes it even sits at like 8 or 9 on the LTFT after I've been driving for 20-30min before it stumbles slightly then cranks back up to like 15.

 

[efaily]

That leads me to think it's a crack or split hose. Something temperature sensitive if it behaves differently from cold to warm. It sounds like it's got to be a vacuum line somewhere. Under the intake manifold maybe?

 

[efaily]

Or maybe a gasket somewhere in the intake system?

 

[Gotta_Go_Fast]

That leads me to think it's a crack or split hose. Something temperature sensitive if it behaves differently from cold to warm. It sounds like it's got to be a vacuum line somewhere. Under the intake manifold maybe?

I was thinking the same thing, wouldn't that yield smoke from the test though if one was cracked or loose?

 

[Gotta_Go_Fast]

Plus I would think that would leak boost as well. Did a pressure test at 20 PSI and it seemed perfectly normal. Pressure took a long time to drop and there was no hissing or audible air movement.

 

[efaily]

Yep, it should have shown up with the smoke test. I just thought it might have been in an obscure location where you might not have noticed it. I recently had the P0171 code on the Sonic RS I just bought for my son. It turned out there were two hoses leaking. I missed the second one under the intake manifold the during the first smoke test.
You're correct, the pressure test is an even better indicator. If it held 20 PSI with no noise and very slow pressure loss, it doesn't seem like an air leak. The symptoms you described seem backwards for a fuel issue, but maybe I'm wrong? It's a bit of work, but maybe have the injectors flow tested? I didn't think to ask, but how does the car run? At idle, compared to under load or at speed? Maybe it's an sensor issue, and not actually air flow or fuel? If you're able to datalog, maybe Trifecta would be able to review the logs and help with suggestions?

 

[Gotta_Go_Fast]

Yep, it should have shown up with the smoke test. I just thought it might have been in an obscure location where you might not have noticed it. I recently had the P0171 code on the Sonic RS I just bought for my son. It turned out there were two hoses leaking. I missed the second one under the intake manifold the during the first smoke test.
You're correct, the pressure test is an even better indicator. If it held 20 PSI with no noise and very slow pressure loss, it doesn't seem like an air leak. The symptoms you described seem backwards for a fuel issue, but maybe I'm wrong? It's a bit of work, but maybe have the injectors flow tested? I didn't think to ask, but how does the car run? At idle, compared to under load or at speed? Maybe it's an sensor issue, and not actually air flow or fuel? If you're able to datalog, maybe Trifecta would be able to review the logs and help with suggestions?

That’s actually a great idea. The day I smoked it it was pretty windy so I’ll jack it up tomorrow and test again but look from under the car. It did the same thing on the stock injectors so I put in the Bosch 42# greenies. No change sadly. Then I switched to E85 and still no change. Was hoping there would be some variability there to see if it was a fuel pump issue.

 

[Gotta_Go_Fast]

At full throttle the STFT is at a perfect 0 with the long term at 17

 

[Gotta_Go_Fast]

Ran another boost leak test while it was really cold out this time. Looks like air is spewing out of the oil cap and leaking oil slightly! I ordered the updated one that has the filler neck now. It should get here tomorrow and will update if anything changed

 

[efaily]

Hope that fixes it!

 

[Gotta_Go_Fast]

Installed the new oil cap with the filler and nothing changed. Went to the dealership today and got a new valve cover. Threw that on thinking the cover was warped around the oil fill cap and still no change

 

[Gotta_Go_Fast]

Just ran a boost leak test on it. Took exactly 1 minute to go from 20 to 10 PSI. No sounds of leakage at all

 

[Gotta_Go_Fast]

Honestly at this point I might as well throw a new oxygen sensor at it. Not sure when it’s been changed and when I was graphing it it seemed lazy