Our 200,000 mile F150 5.4 rwd pickup truck has had all plus more of the ignition coils replaced over the years, but a few weeks ago, there was a coil-like malady that has continued. To test for a coil issue, last week I removed and plugged the egr vacuum line, and the truck has been running well ever since. An hour ago, I reconnected the vacuum line, and the miss fire under load has come back. Sometimes, it runs right under load, but mostly it begins to miss fire as load increases. In order to safely drive on the freeway, I'll be plugging the hose again. Meanwhile, what do you think the egr issue is: a cracked tube, egr vale, or the dpfe thing? Could it be something else?

 

I forgot to mention that there are no trouble codes, except when I disconnect the valve, then it's the expected 0401. All help will be appreciated! I would like to avoid buying parts I don't need!

 

Does it knock at with the tube hooked up? I have a thread going now, 4.6 trouble codes. I think we are sharing some of the same things. Today I replaced the fuel filter. It was the origional one. 79k on the truck. I have a knock sensor in my hands but I am lacking motivation to put it in tonight. When I do I hope it gets rid of the knock. It feels like it may have a very slight miss. Runs great around town, highway but hill I have that knock. No codes now and no check engine lights.
I will be checking your thread and status. Thanks for reading and your time

 

The truck is a 1999. There is no knocking or pinging in either cases. The plugs are about 25k old with coil on plugs. It runs great with the egr vacuum line plugged, but I want to repair the issues, and reconnect the hose. It seems that with the hose connected, under load, the truck leans out to the point that most all cylinders start to lean miss fire, and the truck goes way off song and losses power.

 

I am no expert but that sounds like blocked passage in piece the throttle body is connected to.

 

FYI. If you are interested. I ran that saefoam through the other day. Still had my knock and like you I was losing power on hills. Really bad on the highway hills. Forward to today. Again I removed my egr valve and the 90 deg bend on the upper intake that it is bolted to. 1 of those ports were blocked again.
Cleaned that out and checked out the egr. I put the short end of a Allen wrench in the inlet. Pulled a vacuum on the diaphram. The first time I did not feel it move. With a vacuum and some pressure on the Allen wrench I felt it move. Did it a couple times without pressure and it moved freely.
Reinstalled everything and hit some back roads and highway and it ran great. With that said I just put new 285/16s on and the headers. Runs and rides a little different than 100%stock. But goodtonight.

 

Well, even with the egr vacuum line plugged, the truck eventually started the miss fire under load situation. Basically, it starts fine, and runs fine until you want to get past 45mph, then if you inch up, you can get up to 65mph, but any time you throttle up agressively, the power drops off and the engine runs rough. The facts were: several weeks ago we tanked up at the 76 station, and as we pulled out, we felt the engine stumble a bit. By the next day, it would run rough sometimes under load, and sometimes run well. The thing is, we only put a hundred miles a week on it, and as the tank of fuel got lower, it was running worse. Yesterday, with way under a quarter tank left, I started testing it again. I tried the egr on and off the circuit, same rough under load running. Suddenly, I started thinking what if it's the fuel? I went and got a bottle of Heet and some Chevron injector cleaner. Then put about 9 gallons of Chevron gas in. Mind you, I arrived at the gas station with the rough under minor load syndrome. As I pulled out of the station, it was already running stronger!
So now I'm peddle down and the engine is running strong! Today, we took an 80 mile round trip with it, and I was unintensionally speeding everywhere because it was running so strong. Who would have thought you could get a bad batch of U76? It might have had water in it, or maybe even kerosene? The last bad fuel I got was over ten years ago!