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Code p0171 p0174

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12 Jul 2019 09:20 #31726 by Ortiz
Code p0171 p0174 was created by Ortiz
Have a 2013 camaro 3.6 L with trouble codes p0171 and p0174 . Says that both banks are running lean and upon looking at fuel trim numbers stft is running steady up and down near 0 while my Ltft is super high steady at 38 % . I thought it may been a vacuum leak put a vacuum gauge to it and read normal and oddly enough only when you turn on the a/c the vacuum drops below normal . Also heats up immediately when a/c is on. This is really weird to me don’t think it’s normal. Any ideas on what it could be . Appreciate any help in advance

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12 Jul 2019 11:01 #31728 by Crombie
Replied by Crombie on topic Code p0171 p0174
Would clearing the codes reset the LTFT, this new phone code reader I got can record, would allow to view stuff after driving around

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12 Jul 2019 11:38 #31729 by PDM
Replied by PDM on topic Code p0171 p0174
You’re either getting a lot of air or not enough fuel. Unmetered air can enter in the intake stream without affecting manifold vacuum. In addition to a leak, a stuck open EGR or evap can cause a lean condition. If you don’t have a loss of power at heavy throttle, it’s probably not a fuel supply issue.

Can you look at o2 sensor data? Are they stuck lean? Can you drive them rich with WOT?

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12 Jul 2019 13:46 #31734 by Ortiz
Replied by Ortiz on topic Code p0171 p0174
Car runs great all around normal startup, no perceived loss of power, engine runs smooth but only when a/c is turned on the vacuum gauge drops below normal then engine gets hotter. I should also mention with a/c off and idling not all the time but a few times the engine gets shaky . I also did try the water test everywhere including where the manifold gasket is and nothing changed. The main thing that is throwing me off is why i lose vacuum when a/c is on. As for the O2 sensor i didn't check how they were responding but i will check now and ill keep you posted.

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12 Jul 2019 13:47 #31735 by Ortiz
Replied by Ortiz on topic Code p0171 p0174
Not sure I Might have to try that

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12 Jul 2019 13:59 #31736 by PDM
Replied by PDM on topic Code p0171 p0174
The a/c adds load to the engine. The shaking is a misfire. You can also add propane to the intake and see if the o2 sensors will respond rich.

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12 Jul 2019 16:13 #31738 by Crombie
Replied by Crombie on topic Code p0171 p0174
on my car I taped the throttle body closed, took off the brake booster hose and blew vape/e-liquid into the intake manifold, I expect you wouldn't see it if its an EGR problem, unless it would go out of the exhaust not sure, this was with the engine off. found I had a throttle body gasket leak

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12 Jul 2019 16:16 #31739 by Crombie
Replied by Crombie on topic Code p0171 p0174
it will go out of the exhaust anyway if the exhaust valves are open, but it worked for finding my vac leak

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14 Jul 2019 08:42 #31775 by Tyler
Replied by Tyler on topic Code p0171 p0174
Losing vacuum with the A/C on isn't unusual, as the PCM opens the throttle body more to bring the idle speed up with the additional load on the engine.

Can you observe fuel trims at idle and 2500 RPM? That'd give us a better idea of what kind of lean condition you're looking at.

Any aftermarket intake parts installed?

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14 Jul 2019 10:19 #31786 by Ortiz
Replied by Ortiz on topic Code p0171 p0174
Ok here’s what I’ve found so far at idle my LTFT on both banks is at steady 35% which I believe is abnormally high even when driving LTFT went up as high as 42% when raising up the rpm
Numbers did not improve much it did drop down to the lowest I saw whuch was 26% which is still to high. Next thought being i have 2 faulty O2 sensors unlikely but I checked their graph data on the scan tool and both were responding well and were reading normal. Also would like to mention as I was looking at the data and someone else was driving my stft which was normally around the regular + or - 5 jumped up to 15% and this happen intermittently whether or not we were at a stop light or WOT. I am completely lost with this car information is not pointing me to any direction . Could I be missing anything here. If not my only explanation is that this car not only may have a vacuum leak but also a fuel delivery issue which would explain such high percentages at both idle and high rpm.

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14 Jul 2019 10:26 #31787 by Ortiz
Replied by Ortiz on topic Code p0171 p0174
Please let me know if I’m overlooking or missing something here also if there’s any tests I could do that can help me pinpoint the problem. Also the car has no cold air intake everything is stock. The purge valve on this car was changed out a year ago due If that helps any.

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14 Jul 2019 10:35 #31788 by Tyler
Replied by Tyler on topic Code p0171 p0174
Thanks for getting back to us with the fuel trim numbers. Definitely too high, even at their lowest. :silly:

I think your next easiest step would be a visual on the intake tubing and the MAF sensor itself. I see it's all stock, which is good. You're looking for loose clamps, disconnected PCV hoses and the like. Cracks in the intake tube. Anything that'll allow unmetered air into the engine.

With the MAF, we want to get eyes on the sensor element itself. The opening on the left is what we're after:



Any debris/insects/whatever will screw with the fuel metering and cause lean trims. It doesn't take much.

Let us know what you find. :)
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