Can changing fuel pump cause misfires on 2007 Expedition?

Asked by Feb 15, 2017 at 02:33 PM about the 2007 Ford Expedition Eddie Bauer 4X4

Question type: Maintenance & Repair

I replaced the fuel pump and filter in my 2007 Expedition and immediately the
next day got codes for misfires on cylinders 3 and 4.  Could the fuel pump
change have caused misfires?  I thought perhaps some moist air got into my
tank while it was open and exposed (I live in Seattle), and perhaps got too
much moisture in my fuel.

5 Answers

FWIW, I had the spark plugs changed a few months ago by the dealer.

17,725

You can add Sea foam or some other fuel additive that removes small amount of moisture. I do not believe it is caused by a fuel pump change. and if water in fuel from the new pump install would not be just on 3 & 4 it would be on all. Look at coil pack for moisture in it or loose electrical connections. Use some dielectric grease on all spark plug boots & electrical connections. May have to test the coil pack & plug wires may be arching together.

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Best Answer Mark helpful
50,755

Please post the codes. Miles on the vehicle? Have the coils on plug ever been changed?

The codes are P0304, P0303, and P0300. Mileage is 146,000. The coils have never been changed. The plugs were changed about 3,000 miles ago. I called the dealership who did the plugs and they told me they did not do the coils.

After a lot of reading, I suspected it may be some old ignition coils. I replaced the coils on the 2 offending cylinders and it appears to have done the trick. After driving all weekend, the check engine light is gone, and the engine is as smooth running as ever. I was surprised at how easy the coil change was. Even changing out #4, which everyone says is the hardest one, I had the job done in 20 minutes.

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