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Mike Kelly
Mike Kelly, Auto Mechanic
Category: Car
Satisfied Customers: 5470
Experience:  17 years experience as a auto mechanic,foreign and domestic.5 years running my own repair business.
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2002 Lincoln Navigator: P0171..running fine..a trip..restarted..rough

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My 2002 Lincoln Navigator just came up with the following codes: P0307, P0304, P0174 and P0171.
The symtoms are; went from running fine yesterday on a trip, stopped to eat and when I restarted the motor it was running very rough and uneven feeling.
I was able to nurse it home (100 miles).
What would likely cause this combination of codes.

Thank you,
Hi,how are you? p0307 -cylinder 7 misfire , p0304 -cylinder 4 misfire ,p0174 - system too lean bank 1 , p0171 - system too lean bank 2 , all of these codes are most likely being caused by a bad mass air flow sensor.
Also the mass air flow sensor is located at the air filter housing.
Customer: replied 7 years ago.

Hi Mike,


Thanks for getting right back to me. Help me through this one and I'll be sure and tip well.


How can I determine for sure that it is indeed a mass airflow sensor?


Some additional info about the problem:

Last week, 2 or 3 times when I started the car it stumbled and and ran rough for 10 or 20 seconds, then smoothed right out and ran fine.

Then today when it went all out and only ran really rough, I nursed it home for 100 miles or so and the entire time the "Service Engine Soon" light was going between staying on and flashing. It seemed to not run as rough when I put it in O.D. and increased the RPM's. I thought it might be the catylectic converter or oxygen sensor (of course, I am only a casual weekend mechanic).


What are your thoughts on this?


Thank you,



one of the most common causes of Ford P0171 and P0174 lean codes is a dirty mass airflow (MAF) sensor. graphic. The MAF sensor should be protected from outside dust and debris by the air filter, but sometimes the air filter doesn't fit real tight inside the housing and allows unfiltered air into the engine. Dirt can stick to the MAF sensor wire and form a coating that slows the response of the sensor to changes in airflow. The MAF sensor can also be contaminated by fuel vapors that back up through the intake manifold and throttle body when the engine is shut off. The vapors can leave a waxy coating on the sensor wire. This causes the MAF sensor to under report airflow, which in turn misleads the powertrain control module (PCM) so it doesn't add enough fuel to maintain a properly balanced air/fuel ratio. As a result, the engine runs lean and sets a P0171 and/or P0174 code (see Ford TSB 98-23-10 for details).

If the MAF is dirty, the fix is easy enough: just clean or replace the MAF sensor. In many instances, the MAF sensor can be successfully cleaned by spraying the sensor element with electronics cleaner. Do not use any other type of cleaner as this may damage the sensor.

Disconnect the air inlet tube just ahead of the sensor, and then spray the electronics cleaner through the screen at the wire element in the center of the little MAF sensor. Let the cleaner soak in for several minutes, then give it another shot of cleaner. Let it sit another five minutes, then reconnect the air inlet tubing and start the engine.

If the lean codes keep coming back, the MAF sensor may have to be replaced.The mass air flow sensor can also cause the vehicle to run rough and create random misfires.


  1. Using a multimeter, check for voltage by backprobing the MAF sensor connector.
  2. With the key ON, and the engine OFF, verify that there is at least 10.5 volts between the VPWR and GND terminals of the MAF sensor connector. If voltage is not within specification, check power and ground circuits and repair as necessary.
  3. With the key ON, and the engine ON, verify that there is at least 4.5 volts between the SIG and GND terminals of the MAF sensor connector. If voltage is not within specification, check power and ground circuits and repair as necessary.
  4. With the key ON, and the engine ON, check voltage between GND and SIG RTN terminals. Voltage should be approximately 0.34-1.96 volts. If voltage is not within specification, the sensor may be faulty.
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Customer: replied 7 years ago.

Hi Mike,


Thanks for the trouble shooting directions.


I'll test my MAF sensor tomorrow and if it turns out to be the problem, I will be sure and add bonus to my payment.


If it is not the mass airflow, could it be the catyletic or something else?


Thank you,

Yes let me know if the sensor turns out to be fine,then we will check the egr valve,this would be where to look next.
Customer: replied 7 years ago.

Thanks Mike!


I'll be in touch tomorrow night.



Ok sounds good,thank you.
Customer: replied 7 years ago.

Hi Mike,


Okay, so far I took out my MAF sensor and cleaned it with electrical cleaner. Re-installed it and still have the problem. I have not checked the sensor with a multi meter yet.


After I put it back together and cleared the codes, I drove the vehicle for about 10 minutes (still the same sputtering syptoms). I then checked the codes again (service engine light did not come on during myXXXXX the 2 codes I got were #4 and #7 cylinder misfire.


Based on that, do you still believe that I have a MAF sensor problem? The Navigator has 130,000 miles with the factory plugs. Could these 2 plugs be the problem? Or the EGR?


I appriciate your feedback.


Thank you,


Hi,i am still leaning towards the maf,but it certainly would not hurt at 130,000 miles to replace the factory plugs.These would be inexpensive and it would rule this out.
Customer: replied 7 years ago.

Okay. I will go ahead and pick up a MAF sensor tomorrow and install it.


Evidently, the 2002 Navigator is a real project to change the spark plugs. I was quoted $600 by the shop that changes my oil. I'm told my car takes extensive labor to change out the plugs.


Do you have any shop instructions on how to get to my plugs?


Thank you,


This is the only info it gives.

Ford Excursion, Expedition, Lincoln Navigator 2000-2005

Spark Plugs

Inspection & Gapping

Check the plugs for deposits and wear. If they are not going to be replaced, clean the plugs thoroughly. Remember that any kind of deposit will decrease the efficiency of the plug. Plugs can be cleaned on a spark plug cleaning machine, which can sometimes be found in service stations, or you can do an acceptable job of cleaning with a stiff brush. If the plugs are cleaned, the electrodes must be filed flat. Use an ignition points file, not an emery board or the like, which will leave deposits. The electrodes must be filed perfectly flat with sharp edges; rounded edges reduce the spark plug voltage by as much as 50%.

Check spark plug gap before installation. The ground electrode (the L-shaped one connected to the body of the plug) must be parallel to the center electrode and the specified size wire gauge (please refer to the Tune-Up Specifications chart for details) must pass between the electrodes with a slight drag. NEVER adjust the gap on a used platinum type spark plug.

Always check the gap on new plugs as they are not always set correctly at the factory. Do not use a flat feeler gauge when measuring the gap on a used plug, because the reading may be inaccurate. A round-wire type gapping tool is the best way to check the gap. The correct gauge should pass through the electrode gap with a slight drag. If you're in doubt, try one size smaller and one larger. The smaller gauge should go through easily, while the larger one shouldn't go through at all. Wire gapping tools usually have a bending tool attached. Use that to adjust the side electrode until the proper distance is obtained. Absolutely never attempt to bend the center electrode. Also, be careful not to bend the side electrode too far or too often as it may weaken and break off within the engine, requiring removal of the cylinder head to retrieve it.


Removal & Installation

4.6L, 5.4L & 6.8L Engines
  1. Disconnect the negative battery cable.
  2. Remove the coil on plugs as outlined under Ignition Coil in this section.
    NOTE Remove any foreign material from the spark plug wells with compressed air before removing the spark plugs.
  3. Remove the spark plugs.
  4. Inspect the spark plugs
  5. Adjust the spark plug gap as necessary. Proper gap is 0.52-0.56 in. (1.32-1.42mm).

To install:

  1. Install the spark plugs and tighten them to 13 ft. lbs. (18 Nm) for 4.6L and 5.4L SOHC engines. For 5.4L DOHC and 6.8L engines, tighten the spark plugs to 15 ft. lbs. (20 Nm).
  2. Install the coil on plugs.
  3. Connect the negative battery cable.
Also,these tune ups is the 4 plugs on each side of the engine,it's just there is not much room to work with,you will need some extensions.
Customer: replied 7 years ago.

Hi Mike,


Okay, I cleared the codes and then installed a new MAF sensor. The problem still persist.

I drove about five miles, as soon as I started up a small hill the "Service Engine Soon" light began to flash and when I returned home and pulled the codes, I got P0171, then the P0307 and P0304.


What do I check next?


Thank you,

Hi,you need to remove the coils and have them tested,or take the vehicle to a shop to have them tested,this would be the next step,if you decide to remove them yourself.

Removal & Installation

4.6L, 5.4L SOHC & 6.8L Engines
  1. Disconnect the Coil On Plug (COP) electrical connectors.

    Click image to see an enlarged view

    Fig. Disconnect the Coil On Plug (COP) electrical connectors

  2. Remove the bolts.
  3. Remove the coil on plugs.

    Click image to see an enlarged view

    Fig. Exploded view of the coil on plugs-4.6L and 5.4L SOHC engines

To install:

NOTE Apply silicone brake caliper grease and dielectric compound to the inside of the coil boots.
  1. Install the coil on plugs.
  2. Secure with the retaining bolts and tighten to 44-62 inch lbs. (5-7 Nm).
  3. Attach the coil on plug electrical connectors.

5.4L DOHC Engines
  1. Disconnect the negative battery cable.
  2. Remove the bolts and the ignition coil cover.
  3. Disconnect the electrical connector from the ignition coil.
  4. Remove the ignition coils.
  5. Installation is the reverse of the removal procedure. Tighten the ignition coil cover bolts to 9 ft. lbs. (12 Nm).