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Old 05-08-2010, 01:09 PM
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Code P0171

Alright I went back to AutoZone this morning and had them rerun the diagnostic on the truck. The first time the guy kept telling me it was the Oxygen Sensor that needed to be replaced. This time I made them break it down and show me everything and print it all out.

Troubleshooting P0171
OEM Brand: Domestic

Definition
Fuel trim bank one condition

Explanation
The powertrain control module uses the oxygen sensor to calculate the Air/Fuel ratio of the engine. The computer has recognized a rich or lean condition on one engine bank only.

Probable cause
1. - If bank one and two codes set together suspect fuel pressure or MAF (Mass Air flow) sensor.
2. - Oxygen sensor defective
3. - Ignition misfire-repair
4. - Fuel injector problem

According to what he showed me on the screen, both 1 and 2 codes set together. So the AutoZone salesman said that it's most likely either the Fuel Pressure Regulator or the Mass Air Flow sensor. Then he started talking about replacing the fuel injectors?

The truck has, to me, a heavy idle. It's not the worst idle I've ever felt, but you can definitly feel it. That's the first thing the guy said to me, that it doesn't feel all that bad. I think that there is a misfire in the engine, you can just feel that when your driving. The salesman told me that he said there was a misfire in #4, I do not know how he came to that conclusion based off of what the machine read to him.

Now I am kind of lost, should I just go ahead and replace both parts?
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Old 05-08-2010, 11:59 PM
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KhanTyranitar KhanTyranitar is offline
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Autozone is great for the free code retrieval, but they are not qualified to diagnose you vehicle or get you the right parts. An O2 sensor is not going to cause a lean code. Here is where to start.

Since you have the code on both banks, a MAF is very probable, especially if you are using a K&N or other oiled filter. You can try cleaning the MAF element with some spray cleaner. In all probability, the sensor is toast if it is the fault. Replace it with a DEALER MAF sensor. RockAuto Auto Parts carries the Motorcraft brand. The other cheaper brands may be tempting, but I have learned that they do not work as well as the original. I have been through several aftermarket MAF sensors.

A misfire will cause such a code, but you would know if you had a misfire.

A bad injector can also cause this code it is true.

However, the most common cause of lean codes was completely ignored by the fools at Autozone, and that is vacuum or intake leaks. The rubber gets old, shrinks, cracks, and hardens, resulting in leaks. Check the areas around the PCV valve especially. The other area is the gaskets on the upper intake manifold. Same story, they get old and shrink and harden. This causes them to leak over time. Most guys on this forum with your code resolve the code by repairing these leaks.

Some will talk of a test where you spray a flammable gas or liquid around the intake. This test has been known to start fires, and has so far proven ineffective at accurately detecting leaks, so don't bother checking that way.
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Old 05-09-2010, 04:54 PM
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I am almost 100% certain that I have a misfire. You can feel it when you are driving the truck. Would a bad MAF cause a misfire?
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Old 05-09-2010, 05:12 PM
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Sorry for the double post but I should add that I do not currently use a K&N Filter, did in the past but not any longer.

Also, if I do replace the upper intake manifold gasket, should I break the entire manifold down and replace all 3? Has anyone done that or has it always been corrected through just the top gasket being worn down?
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Old 05-09-2010, 06:34 PM
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what codes do you have code p0171, and p0172, and p0304?

304 would be your misfire look at a possible coil
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Old 05-09-2010, 07:35 PM
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The only code the guy told me that the truck was pulling was Code P0171. He really would not let me look at the machine when he was using it so I couldn't really see it either way.
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Old 05-09-2010, 08:00 PM
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your best bet would be to go someplace else, but if he told you you had a miss on 4 then that could explain the miss you feel and the code p0171
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Old 05-09-2010, 08:03 PM
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Yeah I will probably go somewhere different after work tomorrow. The guy was not a ton of help, actually told me not to buy the parts there because the prices were to high.

I really need to just buy one of those OBDII readers, just have to convince the wife that it's a good investment.
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Old 05-09-2010, 08:07 PM
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it's easier to ask for forgivness then ask permission
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Old 05-09-2010, 08:37 PM
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I hear you

I am looking at MAF's online, both from Ford and the aftermarket one from Cardone. I am really trying to decide which way to go here as the Cardone claims to be made to exact Ford specifications with even higher testing involved then the OEM preforms on their own. I am going to give the Ford dealership a call in the morning to find out about the price they list. I am curious if it includes the core charge or not.
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Old 05-09-2010, 11:13 PM
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The Cardone is not even close to the Ford part. Motorcraft is the way to go. If you have a miss, you need to get that tracked down.
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Old 05-10-2010, 01:29 AM
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To be honest with you, the RockAuto sounds really great on their price but with their core charge I might as well purchase it straight from the dealer. Yes I can get the money back in the end but I still have to pay for shipping and wait, might as well save the time and effort.

I'd love to go OEM but with everything else it seems that I am going to have to replace, I don't know if I can afford that or not. Have to wait and see on that. If it's the only thing I have to replace then that will be no problem.
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Old 05-10-2010, 08:22 AM
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http://repairpal.com/OBD-II-Code-P0171-and-P0174
I found this site informative.
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Old 05-10-2010, 06:51 PM
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Thank you Jack, that was very informative, going to go out and look at it right now. I am feeling more and more like there is probably going to be a leak somewhere. Whatever I do I imagine it will be the last thing I find that will be the problem.
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Old 05-10-2010, 07:26 PM
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Quote:
Originally Posted by Tomcat7742 View Post
Whatever I do I imagine it will be the last thing I find that will be the problem.
well duh I sure hope you stop looking after you find the problem
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Old 05-10-2010, 07:26 PM
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