Hello Guys ! Heres my problem. I hope someone can help !

I have a 1999 Expedition 4.6L (113000 miles)
It has been misfiring for about a month now. PO302 code. #2 misfiring... Ok ! I have replaced 2 coils (has 2-4packs) I have put 2 sets of 8mm wires on, 2-sets of spark plugs, and #2 injecter... Ford house says "maybe" valve problem. 1400.00 to rebuild 1 head and labor.... Ouchhhhhhh ! "and hope its fixed"
I find it hard to believe that a valve would act up one day and 30 minutes later it runs great. Have I missed anything ? Thanks in advance !

 

Well, you seemed to cover all of your bases with the changes you've made. It is an electrical problem most likely. I had #3 misfire, but I had an oil leak fill up the spark plug cavity and cause my plug and wire to short. Try another reputable shop and have them diagnose it without giving them any info and see what they say.

 

I forgot to mention that I also put in a new fuel filter . I have no leaks. Antifreeze stays full and allways change oil @ proper times.
What electrical part would cause this intermitting misfire ?


Thanks again for your answers.

 

since it is registering a code the problem is not mechanical it is electrical. and that you already replaced the coil and plug on that cylinder you may have to look at the injector being clogged. when you replaced the filter did you find anything unusual in the fuel? if it had any discoloration or debris in the fuel that came out of the filter that same debris may be clogging that injector. i have run into this problem fairly frequently in vehilcles that fuel up at mom and pop gas stations that have not had there tanks checked or replaced. down here in VA there are a lot of them. if, heaven forbid, you should have to replace the head, which i doubt, there are websites that you can go to to get a cylinder head for a lot cheaper than what the dealer would charge.

 

The computer uses a sensor that detects the speed-up/slow-down of the crank as the cylinders fire. If it doesn't see enough crank-acceleration when it should, it registers a misfire.

It has nothing to do with whether or not it's mechanical. If the cylinder misfires for ANY reason, the computer will see it.

The only thing no one has mentioned is a vacuum leak - Check the vacuum/PCV hoses, especially the elbows and other rubber hose - Ford used some pretty sad rubber for the hoses. It's just possible that it's on the hairy edge, you have worn O2 sensors, so it's already running rich to mask most of the vacuum leak, and there we have an intermittent one-cylinder misfire. Or the intake is leaking right at that cylinder's intake port.

Maybe

Other than that, there are two other ways that you can get a misfire with good coil/wire/plugs and good injector: The computer is not driving the injector or coil correctly.

But, since this is only effecting one cylinder and you have 4-post coil packs, I gotta say, it could be the computer not firing the injector, which means, electronically, something is wrong with the computer.

You need a good mechanic/diagnostician to check for pulses coming from the computer for that injector when the misfiring happens.

Good luck with it.

 

Thanks for the very informational post there krewat! Im going out right now to get some carb spray and see if I do have a vacume leak.

Ron McCafferty: I have changed the injector on # 2, then swapped it out with #1 after....

Im going to save the new computer for last... Thanks Guys ! I will keep ya upto date !

 

Yes, please post back with the solution, or to keep working on it.

The dealer should be able to do a compression check and be able to say "Yes, there's loss of compression in that cylinder and it's a valve" or "it's the rings". I could do it in my backyard in the dirt and tell you whether or not it was a valve or compression problem within an hour...

Find another dealer or go to a local "good" shop.

 

The intake is a possibility but I have a 5.4 right now that has a dead misfire and is not registering a code. Turns out had a burned valve. Can't always go by a computor. Have to go back to basics. And a leaking intake is one of the basics.But, if the cylinder is still actually firing and not completely dead it won't register a code.

 

Checking compression today ! I sprayed carb cleaner all over it last night, its hard to tell, I put cleaner in tank, cant tell if the once in a while smoke is from cleaner or carb cleaner, My buddy was standing next me away from Expedition and said he heard the motor idle up when I was spraying. ( I guess thats a good sign).... One last FYI, I got mad @ the car and unhooked #2 plug and injector for 10 minutes, plugged both back in and the damm car ran normal for 15 minutes and back to missing. Boots have greese in them and all connections have been checked a 100 times. Could a valve reseat it self like that ? Dang dealer keeps pushing me to the head problem. Thanks again !

Every other day I have the code PO302 erased, and it comes back within hours now. :-)

 

Keep chasing that vacuum leak, if there really is one!

Check the rubber PCV hoses, etc... I know the "dreaded PCV elbow" problem happens on the 4.6 too

 

WHAT A TRIP !
Ill keep it short ! It boils down to I had a "hairline" crack on 2 spark plugs. I guess I cracked them putting them in or they came like that. #1 and #2 sparkplug were cracked but only reading the #2 code. I took if for compresion test, 100 lbs, needle didnt move.

Its running like a champ again ! Thanks for all your help out there.

FYI, on the spark plug where the name is written.... example " AC 789ap had a line running down it, really only way of telling was from greese on it that showed up the line or if you run your finger nail on it, you can feel the lip on the crack.

Thanks again guys "and gals" !

 

Just another quick "THANKS !"... Expedition is still running great, Thanks again for all your input.... Great site !

 

Glad to hear it!

It's also a kick in the pants to have solved it yourself, I'm sure

 

well, good. always great when it is something simple and not so expensive. glad to hear that it is running well.

 

Take the cracked plug to the dealer who said it was a head problem and tell them to shove the $1400 where the sun don't shine. I hate crooked mechanics. It gives all the good ones a bad name.