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I have a 99 Superduty with the 5.4 that stumbles and bogs down intermitently. It acts like the fuel filter is clogged but I changed it. While it is doing this I can shift to nuetral, shut the truck off, start it right back up (while coasting or at stand still) and it starts running fine again for a period of time. Anybody seen this before? I am thinking maybe the pick up tube in the tank is being blocked and when I shut it off the pressure is relieved from the end and it becomes unblocked for a while? I would sure like to here some ideas before I attempt to remove the tank and inspect. Lets here it!
Winter condtions, 10 to 20 degrees outside temp. Treated tank with injector cleaner and Heat after the problem started. No error codes showing.
Have you hooked up a gas pressure gauge and monitored it while driving and during an 'episode'?
I hate to sound like I broken record (seems I've been posting this same post a lot lately) but this sounds JUST like my old issue. I went through the whole Cat Converter thing also......and the MAF.....and the TC lockup.....and the plugs....and the COPS....nada....
The reason it sounds like maybe yours might be similar is the fact that when you shut it off, it gets better for a while......like maybe you are giving it time for the gas pressure to build back up on the rails?
It's a long thread, but you will have to read it all to follow my path to repair.
I would check the Air filter first if you have a stock filter. I've seen the black plastic cone on these filters come unglued from the filter medium and get sucked up against the Mass Air flow mounting plate. The result was exactly what you described. Every time the engine was shut off the cone would fall and allow airflow until it was eventually sucked back up against the mounting plate.
I can tell you that my old shop cut out two Cat's on two separate vehicles trying to solve this problem, just to come to the conclusion that it was the filter, and having to weld the Cat back in. Over the five years I worked there I probably saw this on five to seven different Ford Trucks and Vans from what I remember off the top of my head..
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