Unknown engine issue

Asked by Aug 19, 2017 at 03:58 AM about the 2007 Ford F-150 XL

Question type: Maintenance & Repair

I am experiencing a problem with my 2007 Ford F-150, V-6 4.2L 2wd. My
engine has no power, can barely get it to 50mph, it occasionally backfires,
some days more often, high gas consumption and a strong fuel smell from
exhaust. No one seems to be able to figure it out and was wondering if
anyone else has/is experiencing this problem. I have changed the 2 rear O2
sensors (can't get front ones off) replaced air filter, EGR valve and gave it a
tune-up. Still same problem. Any suggestions or help?

6 Answers


Have your coil pack tested. Make sure fuel injectors are clean. Do a full engine service including fuel & air filters, Spark plugs oem motorcraft, stay away from the plugs with hype. Use the better set of plug wires. Have your cat checked for clogs. If any check engine light are on tell us what the code set is. These engine have little vacuum boot elbows under the upper intake that either split or come off and need replaced often causing poor engine performance, the front one when bad causes mostly idle problems the rear one causes overall performance issues, both are hard to get too and neglected often, also the PCV is in the passengerside valve cover near firewall make sure it is seated properly and the vacuum hoses to it are in good shape and installed fully, it goes to rear underside upper intake also. Unless you have real tiny hands use mirrors, flashlights and tools to access the tight areas. May be a good idea to remove the throttle body to access the vacuum elbow on the one on the front underside and while its off take the IAC out and clean both the throttle body & IAC with CRC throttle body cleaner while using assorted nylon brushes (no Metal Brushes) reinstall with new gaskets. The thermostat is easy to change out also with throttle body off but I do not reccommend nothing but Motorcraft thermostats as replacements as the others are junk and your OEM original is likely fine. While checking the PCV clean it with the throttle body cleaner and its vacuum hose out real good. Also clean out the open upper intake while the throttlebody is off same deal just nylon brushes. The vacuum leaks on the upper intake also throw O2 sensor codes so thats likely why you changed them.

1 people found this helpful.

May need to use some bolt spray on the threads of those two front O2's, spray with different products until it comes loose without breaking it. Just spray and walk away and do so every now and then for a few weeks and give it a try one day.


Btw I added the full tune up and filter to the above for others sake as many people will read this need to know to do so, If you already replaced those as mention in question the disregard and also use dielectric grease on the inside of spark plug boots both ends.


If you have a Check Engine light that is on, have the codes read and let us know what they are... before replacing more parts!

I have a check engine light on, had codes pulled from a couple different places and they come up different. One is O2 sensors, one says running too lean. Had a mechanic check for leaks and said there are no leaks in vacuum. He suggested the parts I changed and also suggested the fuel pump and speed throttle as my speedometer has stopped also. Was thinking about bringing to Ford dealer to have them run the codes. I appreciate all y'alls help. I will get on spraying those upper sensors regularly.


Lower intake gaskets are weak and can suck air too.

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