1998 4.6l with pretty bad misfire on cylinder #3 (code #PO303). changed all plugs, all wires, coil and checked fuel injectors. misfire still there, engine seems to run fine when first cranked up but begins to shudder after driving for about 5-10 miles. misfire seemed to get somewhat better for a day or two after plugs and wires were installed but eventually returned to stay. any ideas.
thanks

 

Are you sure that you firmly seated all your plug wires on both ends? Seems strange that it ran ok for a couple of days then went back to missfiring. Did you blow out that the junk with compressed air prior to changing your plug.

What plugs did you use?

Have you done a reset yet? And is the code for #3 still appearing?

This exactly happened to me...same plug. New wires and plugs fixed it for me although I still can't figure out how to get back there to replace #4 (Passenger rear). Heck #3 was hard enough for me with all the good tips from this forum.

 

used autolite platinum pulg. boots are seated good I even swapped wires with the same results. I did use compressed air. I think my next step is to find a lake to dirve it in........

 

Nope. That won't help. Keep your chin up. The answer is elusive not impossible.

Seems like you are doing the right things. You can try putting another new plug in that #3. Be very careful not to foul that plug going in (#3 aint the easiest). Do you use a length of fuel hose to get the plugs started? Its cheap to replace that plug again...right? Stranger things have happended. You've already bought new wires so the its only the cost of another plug.

Hang in there bro.

Have you seen this thread? You can solve this!

https://www.f150online.com/forums/sh...d.php?t=235693

 

I seen that thread before

 

I did explain a few things in your other post, you started two threads -same issue. As you are probabaly figuring out , that doesn't work out in your favor.

My 98 won't run on Autolites- I don't know why exactly Use MotorCrafts to play it safe -- Use NGK's to play it safe +1 -- Theres a few more good ones out there. All the info you need with the issue your having is behind the search bar. Check it out if yuh get the chance.

Good Luck

 

I work at a Ford Dealership and have seen it possable for 1 section of a coil pac to fail. Try swaping coil pacs and see if the miss moves to another cyl.

 

Trprofera...Undo the 4 screws that hold the power junction to the fire wall and let it drop down the firewall. Now you have room to reach back there.

 

Yup!! go to eBay , you can get new OEM parts there 75% below dealerships prices . That's what I eventually did, friends have done and allot of good people from this site as well. When your in a bind and need to down on some of the expense to make it happen - eBay . .

Jefal - You have a 98 , Change your system out with new - unless your selling it . Your ignition problems will become ongoing if you don't - get new and be done with it.

I paid $130 for a total COP's kit- Motor-craft spark plugs were even included lol..




Coil packs - same thing o eBay..

 

my 98 does not have C.O.P.'s it has two coil packs that run four plugs each. both of these coil packs have been checked and all are firing good. I did take the number three plug out last night, it looks like that cylinder is getting someking of moisture in it. looks and smells like antifreeze to me. any ideas how this could be happening?

 

You may (as suggested before many times on this forum) have a heater hose that is leaking. You will notice there are a couple of hose that live over the #3 & #4 plugs. You may be on to something. Keep at it.

TexfordD....Thanks for the hint on getting to #4. I will try that.

 

I know it doesn't have COPS - that's why I said in my post you get the same deals on coil packs at the bottom. I was making a point.

 

bad head gasket?/

my 97 did on the #4cylinder did the coils plugs wires was fine for few weeks
then bam right back to misfire
changed the plug again and has been fine ever since
and before you drive it the lake send me your transmission