1998 Ford Explorer makes a thumping noise

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  #1  
Old 03-21-13, 09:33 AM
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1998 Ford Explorer makes a thumping noise

Recent history: Failed emissions for O2 sensor. This was replaced. Failed emissions AGAIN for "lean" codes. I cleaned the MAF sensor and replaced the air filter, but still have the code showing. Immediately after cleaning the sensor and replacing the air filter, my truck now makes a "thumping" noise when braking and it hits 1rpm. Any idea what this could be? It has never done this before. Must have something to do with what I did to it last (sensor and air filter), right?! Ugh. Frustrating!!! I really appreciate any help and suggestions.
 
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Old 03-21-13, 10:09 AM
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YankeesGirl,

Is the thumping noise coming through the throttle-body?

Are you saying the thumping noise is a misfire?

What are the actual error code numbers that are set?
 
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Old 03-21-13, 10:19 AM
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The thumping feels like it is at the front end of the truck (under my feet). I have never had a car backfire, so I am not sure what it feels/sounds like. This noise is a dull thump.

The codes are: P0171- System Too Lean Bank 1
P0174- System Too Lean Bank 2
 
  #4  
Old 03-21-13, 12:38 PM
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Causes A code P0171 may mean that one or more of the following has happened: The MAF (Mass Air Flow) Sensor is dirty or faulty Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry. There could be a vacuum leak downstream of the MAF sensor Possible cracked vacuum or PCV line/connection Faulty or stuck open PCV valve Failed or faulty oxygen sensor (bank 1, sensor 1) Sticking/plugged or failed fuel injector Low fuel pressure (possible plugged/dirty fuel filter!) Exhaust leak between engine and first oxygen sensor
Possible Solutions
A lot of times, cleaning the MAF sensor and finding/fixing vacuum leaks fix the problem. If you're on a tight budget, start there, but that may not be the fix for certain. So, possible solutions include: Clean the MAF sensor. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling Inspect all vacuum and PCV hoses, replace/repair as required Inspect all hoses and connections in the air intake system Inspect and/or test the intake manifold gaskets for leakage Check for a dirty fuel filter and proper fuel pressure Ideally you'll want to monitor short and long term fuel trims using an advanced scan tool If you have access, you may want to run a smoke test


Same goes for the other code, just for the other O2 sensor.
Basically, you running lean on fuel.

I do not think it has anything to do with Thump Down There at almost a halt. That sounds more of suspension/brakes issue, unless it does misfire, like others said.
 
  #5  
Old 03-21-13, 12:51 PM
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YankeesGirl,

You’re making yourself crazy and getting frustrated because you are making a classically typical mistake that most people make.

That mistake is to just throw parts (and or sensors) at a problem just because an error code (or codes) are set.

Check out the links below to see why it is not always necessary to replace parts (and or) sensors
just because an error codes (or codes) are set.

OBD-II DTC: P0171 System Too Lean (Bank 1)

OBD-II Trouble Code: P0174 System Too Lean (Bank 2)

Thank You
Amy
 
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