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  #1  
Old 11-20-2019, 04:46 PM
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P0171 & P0174 Lean codes with a twist!

I had a tear in my intake boot about 3 months ago that threw the P0171 and P0174 lean codes. I replaced the intake boot and the message cleared for a few months.

Over the last few weeks its come back. Ive checked all the obvious locations and everything looks really good and not very dry rotted. What has me confused is that the car is actually running really well. Power seems normal, it accelerates normal, and isnt really acting like there is a vacuum leak. No hard starts or misfires. Ive reset the codes a few times just to see if they pop back up and they consistently come back 45 min after resetting, without fail. The light typically illuminates while Im driving at 70mph on the highway. Is there anything obvious that this could be attributed to? Since the car is running well and Im not noticing any real MPG changes Im kinda baffled as to what it could be. My current plan is to:

Replace DISA o-ring (it wasnt super hard to pull the DISA unit when removing it for the intake replacement)

Test CCV and see if it needs to be replaced (it was replaced along with the valve cover gaskets 30k miles ago)

Clean MAF (possible replacement)

Pre-Cat 02 Sensors replaced

Fuel Injector Cleaner

Fuel Filter replaced

Fuel Pump (possible replacement)

Anything else youd address? What order would you go in to solve the problem?
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  #2  
Old 11-20-2019, 06:54 PM
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I'd first check the boot again. Maybe it was not clamped on perfectly - which would be a pretty easy thing to not get right.

Or maybe it tore again. Really. When I got one of those codes, I quickly found the boot with about a 1" tear in it. Seeing records from the PO, it was replaced only 25k miles earlier (and I belive that due to the low wear on it in general), and it was a genuine BMW part too. I don't know, but it seems that if things are clamped in place skewed, there may be some stress on it that would make it tear faster than usual ??? So maybe that's your twist?
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Old 11-21-2019, 02:57 AM
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Check your ccv hoses, too, particularly the one that goes to the dipstick tube. Some are buried and hard to see, but they're also a source of vacuum leaks that don't pop the codes right away. Failing the visual check, get your hands on a smoke tester, which will out the source of the leak quickly.
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Old 11-21-2019, 08:53 AM
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Could be that the fuel pump is not able to keep up with the demand of the engine when the truck is driven at 70 mph for an extended amount of time. I would look at the fuel trim when you are driving at 70 mph. You can use a scanning app such as obd fusion to log fuel trims data while driving. log the speed while you are logging fuel trim so you can see what the fuel trims are for a given speed.
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Old 11-21-2019, 10:25 AM
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Pull apart this connection (red circle) and make sure you still have the large, ribbed, O-ring on the MAF exit side. A lot of times, it gets crunched up and stuffed in there or falls off which leaves a gap for unmetered air to enter causing the lean code on both banks. If this is the culprit, give the plastic intake tube a spritz inside with dry silicone spray to ease it over the O-ring forming a tight seal

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Old 12-01-2019, 03:09 PM
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Quote:
Originally Posted by e39_touring View Post
Check your ccv hoses, too, particularly the one that goes to the dipstick tube. Some are buried and hard to see, but they're also a source of vacuum leaks that don't pop the codes right away. Failing the visual check, get your hands on a smoke tester, which will out the source of the leak quickly.
I resealed the intake boot along with a new DISA oring. Im still getting the Engine Service Soon light about 45 min after a reset. Ill take a better look at the CCV hoses and may even pull the intake manifold off. Could it be anything simple like the gas cap not sealing?
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Old 12-01-2019, 08:42 PM
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Quote:
Originally Posted by PSpuza View Post
I resealed the intake boot along with a new DISA oring. Im still getting the Engine Service Soon light about 45 min after a reset. Ill take a better look at the CCV hoses and may even pull the intake manifold off. Could it be anything simple like the gas cap not sealing?
Wishful thinking, but to answer your question NOPE. A loose gas cap will just give you an evap code.
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2006 Infiniti G35
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Lotus Europa 1970 Destroyed by fire
Lotus Europa 1970 S2 Renault Powered
Lotus Type 52 1970 Twincam Webers Powered
PORSCHE 911 Targa 1982 The Garage Queen
Audi Avant donated to Kars for Kids
BMW 525IT Sold
Audi 4000CS Quattro Sold
Jensen Healey Lotus Powered Sold
Opel 1900 Sold
Triumph Spitfire 1971 Sold
Triumph Spitfire 1968 Sold
Plymouth "Cuda" 340 Six pack SOLD
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