greenwizard13

i need help, please. i have a 98 ford f150 xlt xtended cab 4x4. has a triton 4.6 liter v8 with 129,000 miles. for last month or so, it has been running rough when first started. engine hesitates at idle and then really hesitates when first accelerating. gets better when it gets warm, but not completely. had motorcraft platinum plugs and wires installed 12000 miles ago. ran two cans of seafoam through two consecutive tanks of fuel thinking i had gotten bad gas. no help. on a really cold day ( 40 in florida ) it was missing really bad and backfired within a mile of driving. check engine light began flashing then went solid. took it to goodyear and scanned it. code 305 misfire in #5 cylinder. took it home and changed the #5 plug. check engine light did not reset. changed fuel filter. no change. had engine light turned off and codes cleared. problem continued, but no check engine light came back on. took it to ford dealer and was told i needed to drive it til check engine light came back on to get a code. had spark plugs changed last week. went with autolite platinums. mechanic said he didnt see a real problem with old plugs. still have same problem. changed pcv valve. looked for signs of vacumn leak, but could not find one. its driving me crazy. especially when i feel it hesitate in the brake pedal when im idling. feels like it wants to cut off, but doesnt. ive been told so many things from: cylinder sticking, plug wires, coil packs, etc. nobody appears like they want to diagnose the problem without having a code to go by. i thank anyone in advance for suggestions.

IA_F150

I'm dealing with similar symptoms. I'm currently awaiting a fuel injector rebuild kit that is to be delivered Monday. I narrowed it down to this after someone on here suggested I try switching the injectors on two cylinders and see if the trouble code followed the injector. In my case it did indeed! I also recently changed my Idle Air Control Valve due to poor idling in cold weather. Now it idles fine too.

Ace White

i am having the same problem with my 02 f-150 4.6 turns out i have a compression problem with cylinder four run a compression test it might lead you to your problem

blizzard63

you also might wanna check to make sure you locked the plug boot on the plug and coil
i had the same problem and thats all it was

torkum

Not sure that this is it but would be good to check, EGR valve. The EGR valve could be stuck open and would explain why its better when warm. If you have a hand vacuum pump hook it up to the EGR and try pumping it up while the motor is running cold. If the motor runs worse the EGR is working but if it doesn't change that would be a sign that the EGR is not working.

Fiver000

i need help, please. i have a 98 ford f150 xlt xtended cab 4x4. has a triton 4.6 liter v8 with 129,000 miles. for last month or so, it has been running rough when first started. engine hesitates at idle and then really hesitates when first accelerating. gets better when it gets warm, but not completely. had motorcraft platinum plugs and wires installed 12000 miles ago. ran two cans of seafoam through two consecutive tanks of fuel thinking i had gotten bad gas. no help. on a really cold day ( 40 in florida ) it was missing really bad and backfired within a mile of driving. check engine light began flashing then went solid. took it to goodyear and scanned it. code 305 misfire in #5 cylinder. took it home and changed the #5 plug. check engine light did not reset. changed fuel filter. no change. had engine light turned off and codes cleared. problem continued, but no check engine light came back on. took it to ford dealer and was told i needed to drive it til check engine light came back on to get a code. had spark plugs changed last week. went with autolite platinums. mechanic said he didnt see a real problem with old plugs. still have same problem. changed pcv valve. looked for signs of vacumn leak, but could not find one. its driving me crazy. especially when i feel it hesitate in the brake pedal when im idling. feels like it wants to cut off, but doesnt. ive been told so many things from: cylinder sticking, plug wires, coil packs, etc. nobody appears like they want to diagnose the problem without having a code to go by. i thank anyone in advance for suggestions.


WOW! Exact same problem here. Tell me you figured it out cause I need answers for my 2006 4.6 f150

greenwizard13

it ended up being a bad spark plug wire. i looked many times, but never saw it arcing. one day my engine was wet, and i saw the arc. new plug wires installed. problem solved.

jumbofisher

My 4.6 does the same only when it warms up. Starts and runs fine when cold. Haven't scanned it. Had trouble with antifreeze leak taking out #4 spark plug not too long ago. Hopefully it's a wire or remaining plugs. Running fine until it warms up makes me wonder a bit. Any Ideas would be appreciated.

red98

I just had a similar problem last week.
I changed the #8 plug wire and was done.
I'll change the other seven when I have time

joncelk

Hi, I have a 1998 f150 4.6 4x4 stepside and bought it new at dealer turned 173 386 miles and last few months has been getting worse milage and now began running rough and no power and idling rough sounds similar to others . I decided to work this week with price of gas!!! on it and changed the plugs to new motorcraft , new plug wires two new coil packs, cleaned neg and pos battery posts /connection , cleaned air intake and k&n ,cleaned mas with proper mas cleaner, cleaned air elbow to throttle body,changed pcv valve, changed gas filter for the first time ever and is dirty realize now every 30k to change gas filter,so was thinking strongly after this work I did made it run better but still not right and was going to change injecters ,ran 1/3 tank gas a can of seafoam , then someone told me do compression test before spending more money, bought compression tester and cold not get it to thread where the plugs are 4 inches deep and no one in town had a adapter to extend tester , so didnt get the test done . so thinking today I need to go back to fuel related issues . and as dirty as the filter is I can dump dirt out of filter , thinking to check fuel pump pressure, maybe I need another new filter or and any ideas sure would be greatly appreciated ,Thanks Jon