i need advice on an intermittent problem. truck is a 98 f150 4x4, 4.6 liter, automatic, 131,000 miles. have had an on-again/off-again misfire since 11-08. the c.e.l. has only came on two times for the problem. once in 11-08, and once on 02-12-09. always happens when i first start the truck and the engine is cold. will run rough and seems to hesitate and miss when i put it in gear and try to accelerate. seems to go away after the engine warms up. i can still feel a slight "miss" when sitting at a traffic light at idle. had plugs and wires replaced about 10,000 miles ago. used motorcraft platinum plugs and motorcraft wires. replaced plugs only in early january 09. replaced with autolite platinums. replaced fuel filter. replaced pcv valve. still happened. looked for vacumn leaks. found a dried and cracked "hvac"? line that ran to the throttle body near the back of the firewall. replaced that and it seemed to run better, but still had the slight "miss" at red lights, etc. the c.e.l. light reset itself in one day of driving. i dont know what to do next. ive been told that it might be the #5 cylinder sticking. ive been told it might be a coil pack or a bad plug wire. what should i try next. i took it to a ford dealership, but was told that it was running okay at the time and to bring it back when they could see what it was doing.
Going to start with engine basics, do a compression check to see if cylinders are with in 10% of each other. Vaccuum leaks can cause idle roughness, check hoses especially hose elbows to PCV valve. Spray intake joints with choke cleaner and listen for idle speed variations. Have read on here about the COP being intermittent. Others will have to recommend proper means of testing. Do not understand #5 sticking?
thanks for the advice bill. my truck doesnt have cop's. it has coil packs. do you happen to know if a coil pack can function okay one day and malfuntion the next? as for the cylinder sticking.... i dont understand either. that was just what someone told me since the misfire has been detected twice in the #5.
greenwizard13 - You can try switching the coil packs around to see if the misfire follows the move. My truck just recently had a misfire on cyl 5 (I had the shaky idle/acceleration and flashing CEL). I thought it was a plug or a wire, and put a new one of each on as a test and it still had that dead miss on #5. I moved the coil pack, and sure enough the misfire moved. Replaced the coil, and she runs like a top again. Only a $55 part, so it wasn't tough on the pocket book either.
ok. i changed out the coil pack on one side ( side with the #5 plug wire ). started the truck and it idle'd great. no hesitation. smooth idle. thought all was well. didn't drive it right away. truck sat for a couple of days. first time that i started it to drive it, it started with no problem and idle'd great again. none of the hesitation and misfiring when cold and first accelerating. but, i got about 2 miles down the road and the misfire and hesitation seemed to move to the 45-55 mph range. it really started hesitating bad. then, i got on the gas and it came out of it. did it for a few more miles, but never set off the c.e.l. then, the slight miss came back like when sitting at a red light with it in drive and your foot on the brake. should i replace the coil pack on the other side? havent had any misfires on that side, but it appears as if both were the factory original motorcraft coil packs. truck has 131,000 miles. ive never cleaned the egr ports, maf sensor, etc. any thoughts on my next move?
update. changed out the other coil pack. cleaned m.a.f. sensor, cleaned i.a.c., cleaned as much of the t.b. as i could without removing it so the egr ports did not get checked or cleaned. checked pcv valve line. found rubber connector on it that was cracked and appeared almost completely collapsed inward. replaced the rubber connector. i took out the spark plug on the #5 cylinder since that was the location of the misfires. the plug was clean. i checked the gap on it. it was not set at .054. it was more like .43 or so. i didn't check any other plug gaps. truck idles great in park or neutral. the hesitation between 40-55 mph range is gone. still have the problem with the engine shudder and miss while sitting at idle with it in gear and foot on the brake. the tack shows around 500 with it in gear at idle. moves up to around 700/750 when i put it in neutral with no miss or shudder. anyone have any suggestions? could it be plug wires. they have about 10,000 on them, but ive heard that they can go bad. its driving me crazy. any advice would be appreciated.