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Discussion Starter #1
Got 2 codes.... Engine runs fine.. only difference i notice is a little decrease in power and mpg.... Im thinking my oxygen senors are bad but are not sure... can any1 help me out here?

Thanks in advance
 

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Discussion Starter #4
I believe it was replaced 30000 miles ago... somewhere in the 40s or 50s. I replaced the downstream o2 sensor. I'll be taking a long drive tomorrow so ill post up the results.
 

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Discussion Starter #5
Just want to update this, I believe the downstream o2 sensor fixed the po420 code but still have the po171.

Any1 got any advice?
 

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Just want to update this, I believe the downstream o2 sensor fixed the po420 code but still have the po171.

Any1 got any advice?
A p0171 on it's own is usually never a bad o2 sensor. You could still Change it as maintenance if you want to but it most likely will not solve the issue..........here is a good link explaining the code.
http://www.obd-codes.com/p0171
 

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P0171 is the car running lean ... sucking air in somewhere ... check for vacuum leaks, cracked or broken vacuum/PCV hoses.



 

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It's most likely the PCV vacuum line. You should be able to find a ton of threads about PCV lines going bad on older Zetec Foci. Clean the MAF also, and you might want to go through the A/F reset when you're finished which is simply disconnecting the negative battery terminal for 10 mins, reconnecting, starting the engine, and then allowing it to idle for 6-7 minutes so the timed A/F test can be completed by the ECU.
 

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Discussion Starter #9
had a feeling most people would jump to that conclusion.. I already replaced the hose and valve bout a year ago. Its not a vacuum leak and because of that, it kinda has me stumped. I feel like I've checked everything. I haven't done the fuel filter but it has been done within the last 30,000

Any1 know how to tell if the MAF sensor is shot or not?
 

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Discussion Starter #10
I have a replacement filter here.. guess its from the previous owner. I read the directions over fuel filter replacement and I suppose I'll give it a try. Gonna do that and spray the MAF sensor with cleaner. We'll see what happens.
 

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had a feeling most people would jump to that conclusion.. I already replaced the hose and valve bout a year ago. Its not a vacuum leak and because of that, it kinda has me stumped. I feel like I've checked everything. I haven't done the fuel filter but it has been done within the last 30,000

Any1 know how to tell if the MAF sensor is shot or not?
I have a replacement filter here.. guess its from the previous owner. I read the directions over fuel filter replacement and I suppose I'll give it a try. Gonna do that and spray the MAF sensor with cleaner. We'll see what happens.
To change the fuel filter back you car onto carramps. pull the fuel pump relay or fuse and start the car until it stops, on my 2002 the filter bracket was held onto the body by 1 bolt then the filter was held in the bracket by one bolt. look at the clips carefully and you will see how to disconnect them.

pull the maf and make sure it is cool before cleaning it. buy the crc maf cleaner, spray it good do not touch the wire at all. let it dry thoroughly. make sure you air filter is good and the intake is clear. I don't remember if you have the oiled air cleaner, they can cause issue with the maf

look for vacuum leaks.

if that does not solve the issue you might want to consider a new maf. I do not know how to test it. I have tested coilpacks with a MM and other things and they tested out fine but where still bad.........

a p0171 by itself is almost never the o2 sensor..........it is the o2 sensor doing its job
 

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I have a replacement filter here.. guess its from the previous owner. I read the directions over fuel filter replacement and I suppose I'll give it a try. Gonna do that and spray the MAF sensor with cleaner. We'll see what happens.
oh and with 4,000 posts you should have a more detailed signature about your car ;)
 

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There are other ways aside of the PCV line that could cause a vacuum leak, and it could be an air leak after the MAF.

You asked if Bosch sensors were good for Fords, and they are not. We've had more than a few who were disappointed in the performance of their Bosch O2 sensors. Typically we've seen excessive fuel use, or just bad sensors/heaters.
 

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Discussion Starter #14
Thanks for the input fellas. I didn't get to doing the filter today. Took us 7 hours to replace rear leaf springs on a 89 ranger. Hell of a day. We'll see what tomorrow brings.
 

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Thanks for the input fellas. I didn't get to doing the filter today. Took us 7 hours to replace rear leaf springs on a 89 ranger. Hell of a day. We'll see what tomorrow brings.
No sawzall?

If replacing the Bosch sensor with a Motorcraft doesn't fix it, then you might want to start searching for more elusive vacuum leaks. Intake leaks, leaks around injectors, EVAP leaks, and so forth don't always make loud enough hisses to be heard over typical engine noise. A clogged injector can do it as well, but for that diagnosis I'd use spark plug analysis to verify. It's more difficult with plat/irid plugs, and that's the reason I run standard plugs. If you can't figure it out, and tons of injector cleaner doesn't work- swap to standard plugs, and run it for a couple of months. You should start seeing deposits if you have a problem.

Didn't you say that you unplugged the vacuum line to the fuel sensor and smelled fuel? If very strong, that's a sign of a bad fuel sensor, but those are hard to diagnose and not cheap. I'd want to see all 4 spark plugs showing lean condition deposits before I replaced that dude.

You can also get lean conditions from a fuel pump that is going bad, but that issue tends to accelerate fairly quickly.

Finally, for parts you can wait on, or want to save big on- check out RockAuto. In our Vendor Group Buys, and Special Discounts forum there is a Rock Auto thread that gives us a 5% discount. Look for the most current discount thread, and if you order more than one part- watch to be sure you're shipping from the same locations if possible.

I was bored, here's a link Rock Auto Discount Code
 

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Discussion Starter #16
Replaced the fuel filter... So we'll see what the end results are after my 100 mile drive today.

Might pull the plugs this afternoon to see what they look like... Might throw a bottle of fuel injector cleaner in the tank.

I want to see if my maf sensor is bad... its clean as a whistle and I just cleaned it again. There has to be a way with a volt meter to see if one is bad
 

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Discussion Starter #19
I tested the MAF sensor, tested good. Pulled the plugs and they look shot so I'm picking up a new set wednesday. The car ran pretty weak but no code yet.
 
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