2001 Expedition- 5.4- 4x4 -74k miles.

Truck stumbles at random RPM , no pattern. When a code is generated it is the infamous and non-discript "Random Mis-Fire". Fuel pressure tested at rail shows 32 at idle, when placed in gear to simulate load and run up to 1500rpm, the fuel pressure goes from 32 to 40 then drops back to 32. Happen to have access to another 2001 exp, basic same configuration and the pressure runs at 35 on idle, and runs to 40 and stays there when under a load. My information calls for a pressure between 35 and 55, so I am under the norm to begin with and then it does not maintain under load. Fuel pump and strainer have been replaced, fuel filter replaced, no leaks found by smell, visual, or otherwise. Regulator "appears" to be o.k.

Since this is random I do not suspect any one injector, coil pack, etc...And then there is the question of the fuel pressure. Any suggestions or past experience with similar???

Also, code can be cleared and then not show up for some time but the vehicle still has pressure issues, performance issues, and the stumble, just like a mis-fire.

Please don't tell me I need a new ECM...but I'm afraid that may be coming.

And...what about the fuel return side and vapor valve operation?

Thanks, please help.

 

Your fuel perssure is a little low.Did you try to do a fuel quanity test to see how much fuel your fuel pump can supply. Pressure is not the only thing you need you also need to have enough fuel.If that check out ok it is hard to say where to start with out the proper tools.I work at a ford dealer and i would start by using WDS to do a cylinder balance test to see what cylindres are droping out then i go from there after i dertermin if it is a injector problem or a ingition problem.

 

Thanks for response.

I would hope volume is not an issue since filter,strainer and pump have been replaced. No line "kinks" it's a 4x4 but the wife drives it so it hasn't been abused, except for the inside ofcourse! Anyway, do have access to WDS and was also suggested that a balance test be run while driving, as well as testing fuel pressure while driving (racerguy suggestion). I have crawled over this thing inspecting routes, connections, etc... Nothing to be seen, smelt, or felt. Only other history (bought new) is 2 bad COP's, one bad plug, and a CD changer died, but that's it. Maintanance is not an issue, I own 4 (2- exp, 2- F150) there good vehicles, 2 with over 100k, no "major" issues, and I do all my own service/repair. This is the first time with one of these that I have been truly stumped.

Thanks greatly, and anymore suggestions??