i have a 97 f-150 4.6 v8 xlt 66k miles and recently it started running really rough besides when i get up to around 60 then i can't really notice it. the check engine light comes on and starts flashing every once in a while. my dad who has just about the same truck had the same problem recently and he told me the mechanic said it was the egr valve so i changed mine. i unhooked my battery, let the computer reset and everything was great. this was about 3 weeks ago and today it started doing the same thing. autozone told me it was reading that my #4 plug was misfiring. any suggestions?

list of things that were recently done

spark plug wires changed about 3 months ago(msd 8mm)
spark plugs changed about 8 months ago(bosch 4 plat)
k & n air filter cleaned
fuel filter changed about 4 months ago
egr valve changed about 3 weeks ago

 

I see you changed your plugs.

I had the same problem with my #1 spark plug on my 5.4 a few weeks back. Same problem, any engine I guess. Anyways, I changed the plugs and haven't had the problem at all. Let me tell you though, it took me near 7 hrs to change the plugs. This was the first time there were changed since '97. They were hard to get to and pretty bad when I pulled them out, but in went the new plugs and everything has been perfect so far (knock on wood).

 

Here's your likely problem. Replace these with the correct MotorCraft replacements which can be identified at www.motorcraft.com Boshe plugs have been identified as the cause of misfires so many times that getting rid of them is the first thing to do.

EGR valves very seldom go bad. Only one that is stuck open will cause faults, but their symptom does not match your report. DPFE sensors, OTOH, .... different issue.

Inspect the overhead coolant line for leaks onto the #4 plug. Tighten the clamp as needed.

Changing the plugs on a 4.6 of this vintage is extremely easy compared to the 5.4. No comparison, really.

The #4 misfire (or any other type A misfire) is almost always the plug, the wire, or the coil pack. These will cover about 99% of the ocurrances.

Steve

 

My experience with the Bosch plugs is that the plugs don't fire, but the spark jumps from the spark plug terminal (where the plug wire attaches) to the base of the plug (where it screws into the head) leaving a "carbon track" down the side of the the spark plug insulator (and possibly along the inside of the spark plug wire boot as well). Once the carbon track is established, the spark continues to follow the path of least resistance and the misfire becomes more prevalent. Inspect your #4 plug to see if you have carbon tracks running along the insulator. If you do, and you replace the plug without replacing the wire, you may have the problem repeat itself because of the carboned plug wire boot. To reiterate what was said above use MOTORCRAFT plugs. The problem described above with the Bosch plugs seems to occur on "wasted spark" ignition systems. I don't know if that is the system your engine uses.

 

what motorcraft plugs would you suggest? are any of them better for performance or gas mileage?

 

Go to the website indicated and look up the correct plug. There will be only one current plug (and possibly several obsolete listings), although under several possible stock numbers, ie, singles, 4-packs, 6-packs, etc....

I'll tell you where to look for relevnent inforamtaion, I'm not going to do it for you.

Steve

 

I replaced my old motorcraft plugs with motorcraft "finewire" plugs. Let me tell you, my engine never ran better. It's alot smoother, and I can feel a slight increase in power.

I replaced the wires with 8mm Autolite Professional Series wires. They're high quality wires that meet or exceed OEM standards.

Link to the plugs: http://www.oreillyauto.com/EW3/Produ...riptionId=2691

Link to plug wires: http://www.partsamerica.com/ProductD...e=5004&ptset=A