I've got 160K on my 250 and just changed the fuel pump out over the weekend. Poured the gass back in and started and ran fine. Start up Monday AM fine drove it to work and gassed up on the way no issues (20 miles to work on the new gas). Head home from work and the truck runs like junk. seems to be missing on one or two cylinders. I changed the fuel filter at the same time as replacing the fuel pump. Thinking it might be the PCV elbow has collapsted again (great deign Ford - NOT) or the PCV is dirty. Any other thoughts? I did not clean out the tank, it looked real clean and did not see the need. No check engine light. Just real rugh idle clears up some around 2200 RPM and gets noticable at higher revs or at idle. Was thinking about running some injector cleaner through the tank but really not sure what next step to take. Fuel pump was dead but this is a mystery now.

Thanks for your thoughts.

APEXDUCK

 

Get an OBD ll reader and check for reason codes. Many parts stores loan them in their parking lot.

Sometimes, you can get codes without a CEL coming on. If it doesn't prompt for a P0300 series code to determine the exact cylinder or even a random misfire code, Pull you COP's out of each cylinder and inspect for cracks in the boots. These cracks will allow the spark to travel to ground and misfire that plug.

Also, if you have a slight intake manifold leak and antifreeze slowly enters that plug hole, you'll start to also get misfires. Get a flashlight and mirror to start the process. Blow out or vacuum out any moisture in that plug hole before removing.

Re coat the COP end with dielectric grease as it can sometimes run again for months or years.

 

What does your IAC look like?

 

I have not checked the IAC but did replace the PCV and checked the hose to the throtle body for cracks and it did nothing to help. Did stop at the part store and get the P0300 code. Nice to have a code but that just tells me I have an engine missfiring and check everything! I work for a parts company so thinking with the age of the vehical I can swap out a few things without too much financial pain. Guess I just need to make a list and keep swapping things. IAC, MAF, ??? what else? Will check the COP this weekend but thinking this is more intake/fuel related since I just started in and I just changed the fuel pump.

Thanks for the help

APEXDUCK

 

Gve the truck to my local mech who specializes in big trucks. COP was bad and boots need to be replaced. He's doing the plugs as well since he has it there. More costly than me doing it but I don't have the time and by the time I do the extra gas it has been burning running rough will pay for his labor.

Thanks for all the help folks.

APEXDUCK