PO174 and PO171 codes, 2000 Mercury Sable

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On Sun, 4 Jan 2015 12:44:12 -0800, "Jeff Strickland"


It's not the octane rating, or the fact that it is premium gas - He needs to try ethanol free gasoline - and Shell Premium has no ethanol - which is why I recommended it for troubleshooting purposes If the car is not designed for E10, or worse yet E15 fuel, the engine will run lean with the adulterated fuel

He is better off to just buy a simple code scanner for his purposes. Same price and no downloading, and no compatability problems if he doesn't have the right kind of phone.

me as being that technically inclined (no offence intended)
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Sam Seagate wrote:

Exactly. So take it to someone who knows what they are doing. A cracked/damaged vacuum hose is highly probable on something that old but so is a leaking intake manifold gasket. The first step is to monitor, verify, and manipulate O2 sensor operation using graphing mode on the scan tool. If the lean condition is only at idle, a vacuum leak is most likely. If the lean code is at cruise, then fuel supply/delivery is suspect.
and it's not an OH it's a 0. P0171, etc. GW
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Those codes mean that the car is detecting a LEAN condition, there is more air than fuel.
When the system works right, air enters and goes past the MAF (Mass Air Flow) sensor. Some manufacturers use a different device that does essentially the same thing in another way, so do not get bogged down on the exact name of the device. The idea is that the MAF measures the quality of the air -- density and temp -- to help the computer set the fuel delivery so that a ratio of 14.7:1 is attained. This ratio is not critical for the engine, but the CATs need the ratio so that the exhaust molecules are divided evenly to convert the crap in the exhaut into basically air, water, and carbon dioxide.
That's the plan.
The error you are seeing says that there is too much air in the contents of the exhaust. Either this is false or there really is too much air. Assuming there is too much air -- by far the most common reality -- then you have a leak somewhere after the MAF, but before the intake manifold. Basically, the MAF is measuing air, then additional air is getting into the intake that has not been measured, and therefore there is insufficient fuel delivered and the result is LEAN.
Since the issue began after some other service, then it is safe to assume that something -- a hose or duct -- broke during the service and air is entering through the hole that results.

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THIS IS WHERE YOU START YOUR DIAGNOSTICS.
Since the code came after service, then be sure the service was competent and correct before you satart looking for parts to replace. The First Rule of Auto Repair states that you should do the simple and cheap stuff first. This includes fixing stuff that was "fixed" a week ago.
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On Sun, 4 Jan 2015 12:48:33 -0800, "Jeff Strickland"

WILL cause the problem - and has been the cause of those codes before (including on my wife's car - same model but 2 years newer)
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On Sun, 4 Jan 2015 12:34:03 -0800, "Jeff Strickland"

You know what ASS U ME means, right?? Make no assumptions. Just as likely something else went wrong unrelated to the oil change. The light was on when he picked it up - car had not been driven since the oil change enough to go closed loop and check the sensors and cats.
I've had too many customers come back and say things like "you just changed my wipers and now the muffler fell off - You must have done something to damage it" or You put new tires on last week, and now the engine is smoking and knocking - what the H%$$ did you do to my car?"
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