I have recently run into a problem with my 1998 F150 4X4 (5.4L). Sometimes it starts up and runs fine but other times it misses repeatedly for a period of time. Before I let a dealer figure this on out (only go to dealer for repairs), I would like to troubleshoot it myself. I haven't done anything thus far and think maybe I should start with the fuel filter and plugs. Any suggestions? I had the ecm read at a local Auto Zone.

 

Both banks running lean is normally caused by unmetered air getting to the engine so I would start by inspecting all of the rubber lines connected to the intake, a common failure is the back side of the 90 degree elbow in the PCV hose will crack letting air in.

 

Thanks I will check it out.

 

I had the same problem you are having and found out the there is a small 90 degree vacuum tube on the back left of the motor that connects the EGR vacuum system to the plenuum that may have a hole in it causing most of the miss/vibration and letting alot of air into the intake. I am still working on a small vibration that maybe an ERG or the regulator.

 

Mine is idling bad too, what is the plenuum?

 

i think he is refering to the PCV elbow not egr... its on the back of the intake and is a common failure. just follow the black tube from the PS valve cover around to the back of the intake and u will feel it.

 

Yea , I think someones confused as hell

 

How many miles on that 98 ? Do your coils have the GREEN tags on top?

That's good thinking about changing the fuel filter first - Knock the easy stuff out first . The filter could very easily be the problem.

 

I have a 98 4.2 efi with 196660 miles.
Same problem I had, Check the small 90 degree hose on the back upper left of the plenuum looking from the front of the truck it's kinda hard to get to but I changed that out and took care of 90% of the problem. Got to put a new EGR on to take cake of it all.
Hope this helps

 

Before putting a new EGR on I would check the EGR ports inside the throttle body elbow, they are very prone to clogging up wth carbon and causing the EGR system to not function properly.