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Old 02-15-2014, 02:55 AM   #1
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Codes P0171 and P0174

Bank 1 and Bank 2 too lean

Installed a new AOS during the rebuild as there was oil in the intake tubes

Took the oil filler cap off at idle and there was a little vacuum in the crankcase. 2 fingers and little effort maybe three or four ounces of force to get the cap off, as it was definitely getting pulled by a vacuum when it was removed and installed.

I searched this forum and believe I am looking for a fairly substantial vacuum leak.

Anyone have experience with this?
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Old 02-15-2014, 08:25 AM   #2
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Bank 1 and Bank 2 too lean

Installed a new AOS during the rebuild as there was oil in the intake tubes

Took the oil filler cap off at idle and there was a little vacuum in the crankcase. 2 fingers and little effort maybe three or four ounces of force to get the cap off, as it was definitely getting pulled by a vacuum when it was removed and installed.

I searched this forum and believe I am looking for a fairly substantial vacuum leak.

Anyone have experience with this?
The codes are for overly lean conditions on both banks, which would be indicative of an intake air leak in the main intake area (throttle body, plenum connector hoses, etc.) as it affects both sides of the engine.
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Old 02-15-2014, 08:56 AM   #3
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Bank 1 and Bank 2 too lean

Installed a new AOS during the rebuild as there was oil in the intake tubes

Took the oil filler cap off at idle and there was a little vacuum in the crankcase. 2 fingers and little effort maybe three or four ounces of force to get the cap off, as it was definitely getting pulled by a vacuum when it was removed and installed.

I searched this forum and believe I am looking for a fairly substantial vacuum leak.

Anyone have experience with this?
I employed my un-patented "Jamesp Extreme Super Smoker" which runs on cheap cigars, which has become my current aroma. The leak is on the forward right corner of the engine under the manifold in front of the vacuum reservoir. I cannot see the exact point of exit for the smoke though. Any thoughts on how to proceed?

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Old 02-15-2014, 09:41 AM   #4
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I employed my un-patented "Jamesp Extreme Super Smoker" which runs on cheap cigars, which has become my current aroma. The leak is on the forward right corner of the engine under the manifold in front of the vacuum reservoir. I cannot see the exact point of exit for the smoke though. Any thoughts on how to proceed?

Not to be overly obvious, but take it apart and see why it is leaking.
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Old 02-15-2014, 10:33 AM   #5
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I was hoping there might be a common failure in a component in that area. I'm modifying a web cam to see if I can see where the smoke is originating.
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Old 02-15-2014, 10:35 AM   #6
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check the boot that holds the resonance tube in place - it mught be cracked or folded somehow underneath. when you have the resonance tube off check the secondary air injection system - it has a couple of vacuum connections in that area.
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Old 02-15-2014, 03:04 PM   #7
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check the boot that holds the resonance tube in place - it mught be cracked or folded somehow underneath. when you have the resonance tube off check the secondary air injection system - it has a couple of vacuum connections in that area.
Done. Everything looked good. Tried to blow through the spagetti tubing and all the valves must be closed because there was no airflow. Is it common for the air injection cut off valve or the vacuum reservoir to leak? Could that be the source of the vacuum leak?
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Old 02-15-2014, 03:08 PM   #8
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Done. Everything looked good. Tried to blow through the spagetti tubing and all the valves must be closed because there was no airflow. Is it common for the air injection cut off valve or the vacuum reservoir to leak? Could that be the source of the vacuum leak?
Definitely, the vacuum reservoir and its lines are common problems. If you have a hand vacuum pump, you can disconnect the reservoir and pump it down to test it.
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Old 02-15-2014, 04:11 PM   #9
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I like the "Jamesp Extreme Super Smoker" that's a great idea.
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Old 02-16-2014, 06:04 AM   #10
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Pumped down everything south of the vacuum check valve by connecting a vacuum source (the Extreme Super Smoker in reverse - turning out to be handy) to the check valve itself and pulling a vacuum. pulled the check valve off after about 30 seconds and there was plenty of vacuum. Checked the actuator for the butterfly valve in the resonance tube and it's tight. Can the air injection cut off valve have a constant leak that shows up in a smoke test??? I blew into the tube and that valve is closed at present. Can the butterfly valve stem have a leak?
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Old 02-16-2014, 06:53 AM   #11
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Pumped down everything south of the vacuum check valve by connecting a vacuum source (the Extreme Super Smoker in reverse - turning out to be handy) to the check valve itself and pulling a vacuum. pulled the check valve off after about 30 seconds and there was plenty of vacuum. Checked the actuator for the butterfly valve in the resonance tube and it's tight. Can the air injection cut off valve have a constant leak that shows up in a smoke test??? I blew into the tube and that valve is closed at present. Can the butterfly valve stem have a leak?
Yes to both questions.

Rather than pull a vacuum and then listen to see if any is left, you need to be testing with a unit that allows you to pull a known level of vacuum and watch for any changes:



Sometimes the vacuum leaks that cause these codes are slow but continuous ones.....
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Old 02-16-2014, 07:11 AM   #12
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Thanks for your reply JFP. I used time instead of a gauge. If the system holds a low vacuum for a full 30 seconds my sense is any leak is less than a pinhole. I think I'll go check it for a full minute though. I did listen for a hiss as well and did not hear one. I bought a plastic vacuum pump similar to the one you show to bleed the clutch as it was marketed for use in brake jobs. It would have been a better tool if it was compatible with brake fluid.
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Old 02-16-2014, 07:54 AM   #13
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Thanks for your reply JFP. I used time instead of a gauge. If the system holds a low vacuum for a full 30 seconds my sense is any leak is less than a pinhole. I think I'll go check it for a full minute though. I did listen for a hiss as well and did not hear one. I bought a plastic vacuum pump similar to the one you show to bleed the clutch as it was marketed for use in brake jobs. It would have been a better tool if it was compatible with brake fluid.
I don't care for vacuum brake bleeding tools at all, I prefer the pressure style like the Motive system because it pushes clean fluid downward and through the system without any chance of pulling air in, which a vacuum system can quickly do.
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Old 02-16-2014, 03:28 PM   #14
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I don't care for vacuum brake bleeding tools at all, I prefer the pressure style like the Motive system because it pushes clean fluid downward and through the system without any chance of pulling air in, which a vacuum system can quickly do.
I'll pick up a pressure system next time I'm messing with the hydraulic system. Put everything back together and working on getting through a driving cycle. I think it was a poor seal between a rubber seal and a plastic tube on the manifold. A rookie mistake, but I have an excuse. With luck, it's good to go.
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Old 03-17-2014, 12:26 PM   #15
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i had the same issue. My AOS was bad, and i also had a kink in one of my boots, which was hidden underneath, and not visible. i also found that there was a hose that came loose below the resonance flap, and a screw had fallen out, which caused it not to work 100%. upon replacing AOS, all 4 boots and clamps, fixing the resonance tube and butterfly valve, and replacing the MAF the codes stayed away. I bought a smoke tester from a local guy who makes them in his garage. here is a link to my thread. i had the exact same codes p0171 & p0174

Replacing Boots (Intake Manifold to Resonance Tube)
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Old 03-19-2014, 11:28 AM   #16
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I like the "Jamesp Extreme Super Smoker" that's a great idea.
I like it too. I've got that I think Harbour freight transfer pump?

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Old 03-19-2014, 05:09 PM   #17
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I like it too. I've got that I think Harbour freight transfer pump?

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That is exactly what that is. It is also a vacuum pump to check the integrity of the vacuum reserve.
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