superex87

hey guys im new to this fourm and i have an 98 expedition xtl 5.4 L triton
its ilding rough and missing under exceleration but when i give it alot of gas it wont miss
i have done some searching on these fourms and understand that it could be a vacume leak or a coil problem
i do hear a loud hissing sound which sounds like a vaccume leak but i cant seem to find it
the sound is comming from the back of the engine near the fire wall
to me it seems that the sound is coming fron the pvc hose area but i have checked it and didnt find any leaks
is there a particular thing that with crack (plastic) that is part of the vaccume system??
also where can i find a online manual for my expedition??
thanks in advance

 

00gtr1

Most likely the vacuum leak on high mileage expeditons is the pcv hose that runs from your pcv valve the the back of you inyake under the IAC valve. What happens is over time the rubber begins to swell and sucks in while the engine is running. They can suck in right at the pcv valve or at the back of the intake. I always replace the pcv hose assembly you can get it from ford for about 30 to 40 bucks. As far as the miss, expeditons are know for #4 cop going bad because of a coolant drip from the heater hoses. as far as online manuals I'm not sure. hope this helps.

mister_v_man

Here is a reply i posted elsewhere in this forum. maybe it will help. i had the same symptoms and it fixed mine:

Have any of you checked the vacuum hose connection to the IAC (Idle Air Control) Valve? My '98 EB Expedition was hard to start and ran really rough. I secured/sealed the hose to the IAC (with some RTV and a wire-tie) and the truck has been running great since. It has 120,000 miles and runs great just like the day we got it. I recently changed the spark plugs on it and have never had to replace a coil pack. For those of you wondering, the vacuum hose to the IAC valve is centered located as far back as you can reach near the top of the engine. It is approximatly 1/2" in diameter, and has a 90 degree elbow on it that looks similar to a small engine spark plug boot. Your hand will pretty much be touching the firewall when you get to it. You'll probably have to stand on a chair and lean over the engine bay to get to it. Make sure it's not loose. The intermittent rough idle could be caused if the hose loosens up during vacuum changes throughout the RPM range. Please let me know if this helps anyone out.