I have a 97 F-150, 4X4, 4.6 (W code) that is running roughly. PO401 and PO303 codes showed up. PO303 shows #3 cyl missing (replaced plugs last summer) I have replaced the ignition coil, did not help. I tested the DPFE, no voltage on one side on vac. Replaced DPFE, still running roughly. I will be installing the old coil onto the other side to test old coil. Does anyone have any other ideas? I have tried to get the EGR valve off to clean, but the bolt will not budge. Mech friend advised me NOT TO BREAK BOLT! Thanks for any advise.

I put the old ignition coil on the other side, took truck to Auto Zone (they downloaded the codes the first time) and this time they showed no codes but the truck still runs roughly. I have the EGR valve loose, but not off. I could not get the copper looking nut off (big nut holding brass looking tub onto bottom of EGR valve) I hooked hose to vac port on top, it took a little sucktion but the ball valve broke free. Mach told me to spray carb cleaner through the side that connected to manifold, NOT to spray any on the top side where vac port is. Waiting on carb cleaner right now. Any other ideas? I have checked all vac lines I can find and I see no issues. Those I can, I put suction on to be sure it holds.

 

Get some PB blaster and soak that EGR bolt. Remove the entire intake elbow and give it a good cleaning with some throttle body cleaner, get some pipe cleaners/flexible gun rods with a wire brush attchment and clean the EGR ports out REALLY good.

 

Hello

Most of the time i say "most" tis will come down to a vacuum leak somewhere
sometimes it will be a small leak. so look carefully

 

is it possible you could have reversed the line on the dpfe. has happened before.

 

hoses are differant sizes so hopefully they are not switched.

 

any ideas on tracking down a vac leak?

 

How about the plug wires for the P0303?

A high failure item that causes a vacuum leak is the PCV elbow behind the throttle body.

 

any indea Where to look for that elbow? hi, low, side? Thanks

 

Follow the lines back from the PCV valve, it's not a small hose, it's almost as big around as a heater hose. It's almost touching the firewall. JBrew has some pics around here somewhere.

 

I think I found it and it looks fine.
I am switching the #3 wire to the other side to see if that code shows back up. Letting truck cool down and changing (attempting) the fuel filter.

 

what kind of plugs did you put in when you replaced them? also have you done any 4wheeln latey? or muddin??

 

No 4wheeling for a while. It just stated missing on the highway and just slowly got worse. I put in a set of Motorcrafts a little over a year ago. One of the codes showed a miss in #3. I just changed that plug and switched the wire with the other side. Starting on changing the fuel filter then will drive to see.

 

take #3 plug out and look and it also look whats inside that chamber ive had plugs misfire bc it was raining and a lil bit of water got in a chamber and it wouldnt work right. either my wires suck and wont miss a seal or something but i hate spark plugs. lol if not that maybe injector? i donno much bout them but maybe its fowled out and not enogh gas is getting threw? do you use fuel injector clean stuff?

 

Changed #3 plug, no luck with fuel filter. Backside came off easy, front side would not budge. I pried, twisted, everything but cuss at it. I will breakdown and have someone change fuel filter. When I pulled it out of the garage, I listened to it afer shutting it off. The item infront of the DPFE was making a vac sound. ????? Not sure what it is, but it sure had a suction sound right after turning truck off. Sound slowly stopped. ???????????

 

humm whats the DPFE? the vaccum hose could be off a lil bit and cause that to happen or a small hole. . i had the tool to get off my fuel filter and the fuel line was even caked in mudd took a lil for the front one but it came out. do you have that lil tool to get inside the fuel line to pop that off? As for #3 umm maybe the wire? i dont know what else would make it do that as i stated b4 i've said every time i mention spark plugs i wanna drop a 7.3L diesel in my f150 just so i dont have to deal with spark plugs lol. *dont have the time or the money!*