i'm new to this site and was wondering if anyone can help me...i have a 1998 Ford Expedition 5.4L 4x4 ...my check engine light came on in my truck last night and the light starts to flash once in a while...when im at a stop in gear the truck idles really rough and when i first acelerate it putters and moves very slowly till about 20mph then its fine....im thinkin it maybe a oxygen sensor but i have replaced one before but have never seen the check engine light flash....im taking it to the mechanic tomorrow to try correcting the problem..does anyone have an idea of what else it maybe....also the truck has 91K....i know this is bad but i have never had a tune-up, flushed the tranny fluid, or the radiator fluid...none of that....i know i need a tune up so i might get that done along with the check engine light....any suggestions on plus and wires....also ive heard people say dont change the tranny or radiator fluid if you never have it before cause it may cause more problems....is that true...should I do both of those or not.....if anyone can help me I would appreciate it a lot....

Thanks
Joey

 

Welcome Joey!

A quick guess is that your problem lies in the number 4 cyclinder's COP (Coil Over Plug). The coil is malfunctioning causing a misfire in that cylinder, which is what the vehicle's computer is telling you when the check engine light flashes.

If your mechanic's fix coincides with this diagnosis are amazed at why we know what the problem is and what cylinder it is in, check back with us andwe'll tell you why we know.

 

While it might be #4, it could be any of them.

The flashing CEL indicates a severe misfire (any one or more cylinders), one significant enough to likely cause other problems including catalyst damage.

Have the codes scanned. The codes will indicate which cylinder(s) is the immediate cause of your misfire.

Be prepared to have all the plugs and at least one COP replaced. This will cost you at least several hundred dollars if you have it done.

If it happens to turn out to be #4, have the mechanic address the leaking heater hose directly above #4's COP, usually just by tightening the clamp.

Steve

 

I had similar issues with my 97 with the 5.4L and the light eventually started flashing too. I sure sign it had gotten worse, lol. I changed 6 of my 8 plugs because I just could get to the back two on one side and had to change one of the coil packs as well. That took care of the flashing light issue, but mine still stays on all the time. Take it to Advance Auto or Auto Zone and let them run the codes for you. With the codes, you tell what is the malfunction and hopefully correct it. Ask a lot of questions and the guys will surely help you out.

 

tlcohen, did you disconnect your battery to reset the computer?

 

yeah i did unhook the battery to reset the codes and they eventually come back on.

 

i first want to say thanks for everyone that helped me with my problem....i changed the fuel filter, pcv valve, spark plugs, (8) COP, and the check engine has gone off and it seems to ride fine....but i am still having one problem....when im idleing in any gear it seems that the RPM's drop a little and the truck vibrates enough that you can feel it pretty easily, not as bad when the check engine light was on.....sorry to ask again....but does anyone have any ideas.....the thing is there is no more check engine light....work on the truck was done today and i only drove it for about 10-15 minutes so far......i was thinking to drive the car for a day or two to see if it goes away....thanks again everybody....ohhh by the way #4 COP was the error code coming up.....



Joey

 

Thanks for the update Joey. It sounds like you may need a IAC (Idle Air Control) valve; however, considering the work just performed it is possible that a vacuum hose has been tugged loose. This problem creates a vacuum leak, which should cause the idle to rise, not drop. Nah, now that I think of it, I don't think it's a vacuum leak. Did this condition appear only after the tune-up? If not, I'd stick with the IAC.

So Joey, are you a police officer?

 

it seems like the problem wont go away....after driving yesterday for about 10 minutes....check engine light is on again and the same really rough idleing when im in gear........take it back to the mechanic and the computer test shows COP # 4 is the problem AGAIN....so the mechanic switches COP #4 and #5 and the light turns off...he tells me to drive the truck and let me know by tomorrow if it turns on....before i get home the light is back on......im going to drop it off tomorrow again and hopefully he can figure it out.....i guess i have no luck.....i know this is getting repetitive.....any ideas????....ohhhh by the way im not a police officer.....


Thanks Again
Joey

 

Well, if #4 COP set a MIL code (like P0304), and your mechanic swaps #4 COP with #5 COP and tells you to drive it, then the Check Engine light comes on again, logic would hold that you would get a P0305 code this time you scan it, suggesting that specific COP's resistance in either primary or secondary is out of range.

Target that particular COP and test its resistance to see if its in spec. If not, then you've found your root cause.

 

Gibson's got the right idea here; if moving the COP moves the problem, then you can be virtually certain it's the COP. I'm not sure I understood your previous post, did you get 8 new COPs for the tuneup? If so, I would suspect that the new one isn't bad and that something else is causing the misfire. It could be a wiring problem (including the connector) or perhaps a PCM problem. It could also be fuel; an injector. But in spite of all this, it sounds like the folks you have working on it are doing the right thing trying to narrow it down.

I know it can be discouraging, but it will get resolved. Then look at it this way, you'll have this wonder experience you can share with someone else who comes here seeking advice.

 

Look at your Coils, do they say motorcraft on all of them? Where did he buy the ignition coils? Did your mechanic really change all the coils? Man, I could give you so many stories of trusted Mechanics that led their best customers down a dirty road.

If he replaced all 8 of your COPs, you are looking at a minimum of $420 in parts. That would be purchasing from Autozone or Advance Auto. If he bought them through Ford, it will run you $650 for all 8.

My guess is, he moved the ignition coils around because he figured it would work just to replace the plugs. The spark plugs should be about $5 each.

 

i have the same issue with my 98 expy 5.4.....Still doesnt work.

Replaced more items then you can name over the past 6 months. (didnt do much over winter to cold)

checked vacuum
EGR valve
IAC
EGR pressure sensor
all oxygen sensors
Fuel pump
Fuel pressure regulator
Plugs wires coils ect ect

probably a few other things i have forgotten

Still runs rough typical vibration from missfire throws a code tells me the bank and cylinder but nothing i can do fixes it. runs rough at idle and missfires but not so much while driving. its been sitting for almost a year now and the frustration is getting worse. Someone just post a list of things that they can think of that causes missfires and i will replace what i havent. I really think there is something wonky about some expy's and missfires.

 

I have found, a couple of times, that the rubber boot between the COP and the plug fails due to heat and deterioration of the rubber. When the misfire code is thrown, the immediate assumption is that the COP is bad, when in fact, the failed boot is grounding out the secondary. Now, whenever I get a misfire code, in addition to checking the primary and secondary resistance of the COP, I always inspect the boot carefully for any cracks or breaks, or if the spring inside is corroded. A replacement boot kit is available at parts stores for about $5.

Just a thought.

 

finally after $400 in parts and labor......my problem is finally gone.....it was a wiring problem with COP # 4....it was replaced and the problem has gone away....i was outta town for the weekend and had my dad drive the truck....no problems yet.....and i have to say the truck is riding as good as when i bought it......thanks again for everyone who put there info in......