OK so i have a 99 f150 4.6l 4x4 with 144,000 miles on it. Almost 6 months ago it started to missfire on me. I continued to drive it because it only did it while the engine was under heavy load. It would never do it cruising around like highway driving or on level ground. Once you hit a hill though it would start to shudder and missfire. The check engine light is not on, and the one time i hooked it onto a computer it showed nothing.

Now heres the intresting part, the problem will go away for about a week if i replace the spark plugs, or the plug wires, and i mean completly go away. It will slowly start to return afterwards. I also put new coils in it but that did nothing.

The one other thing wrong with this truck is it smokes bad on start up. i have had a few people tell me this is bad valve seals. It will only burn oil on startup and depending on if the ground is level or not it may not smoke a drop or it will look like i just did a burn out for 10 minutes. Could these problems be related?

ANY help would be greatly apreciated. I dont want to spend 700$ at the dealership.


thanks

 

I have no answer but I have a similar problem but with my 97 4.2 it seems more noticible with the air on ,no codes with the air off its barelly there, friend told me I needed to get ecm reflashed but havent got to dealer yet to empty my wallet ,just curious if your problem is similar..

 

I'm having a very similar problem with my 98 4.6. I did plugs in it and a mufffler (Magnaflow) and noticed that it started to ping high in the RPM band. So i thought it might be the NGK plugs and put a new set of stock motorcraft plugs in. She ran great with them. No pinging, idled smooth. Now, about 3 days later, the ping is back, when i rev it off idle she shudders a little, and when im under a load and acceleting she'll shudder then too, almost like the tires are losing grip or the clutch is slipping, but theres no change in rpm. Its hard to describe. I'm trying to diagnose it now and I really dont want to go replacing stuff for no reason. Any advice??

Mike

 

Try moving your wire harness away from your accumulater - this will reak havoc on our truck and cause the problem you discribe.

 

Had the EXACT same problem here on a 99 4.6, but replaced 1-5 wires last night. Didn't have time for 6-8, gonna hit them today or tomorrow. Saved the best for last, lol. Plugs and fuel filter were done a couple months ago.

Regardless, my shuddering was gone this morning . And I had power back. Used to run around 2000 RPM when accelerating past 40 mph, now it stays closer to 1500 RPM at my usually rate of acceleration.

How close is too close to the accumulator? Does it affect 1-5, or just 6-8 that pass right under it (if I remember correctly). Curious as to how it affects them, too. I'm still a bit of a noob at this stuff.

And, what's the best route for the new wires?

Thanks!

 

I Am Having The Same Misfire On #4 And Also Received A Evap
Emmisions Error (big Leak). New Motorcraft Plugs And Wires 24k Ago. Intermittent Skip With Flashing Check Eng And Then Steady.
Pulled Wire And Went To Check Plug. Socket Came Back Out With Oil All Over It But The Boot Is Clean. Plug Is In Real Tight So Am Waiting To See If It Seafoam Cleans Out The Water If That Is It Before Proceeding With Plug Removal But The Source Of The Oil Around The Plug Has Me Stumped And Worried More.

Any Ideas?

 

I think i know the answer, it sounds like youre having the same problem i did on my 99 extended cab f150. The hoods on the 98-99 f150's had a bad problem with sealing and when it rains they let in water and moisture and over time you start to get stuff down on the spark plugs and in the plug wires, try cleaning out the plugs and wires and then if you have a tuner clear the codes and see how you run after that.

 

Hey Guys,
The oil around your plug could have been just a mishap that slid buy yuh during an oil change - it happens...The two lines above #4 are known leakers and it's hard to tell until #4 gets compromised.
What I'm not seeing in your posts is the most important steps when -New Plugs, New COP'S , Coil-packs, Wire's ETC- are installed , without a jar of dielectric grease , it's a waste of time and money.. You definitely NEED that stuff on there before the first rain - One humid night , there cooked. They will never be the same after that.

Look it up

 

Your theory about the di-electric grease makes sense, but I was told it wasn't needed by the Autozone guys since the Duralast wires I bought were pre-greased. Flyer said so, and it was visible, as well.

Is the stock grease just bad quality? Or not enough? Should I get a better set of wires?

I did notice the boots didn't quite seal off the top, and the new wires had two locking tabs for the ignition coil, as opposed to one.. and they didn't want to clamp on too well.

Thanks!

EDIT - 10/19/2006: Put some grease on the wires last night, figured what the heck. It worked! No more shuddering/bucking at 40 mph when coming out of overdrive. Hope it holds up.