Issue I'm very confused by.. misfiring in 4th/5th gear.

[thebigrooster]

My Explorer's fuel gauge doesnt work, and I plan to replace the fuel pump soon. Because the fuel gauge doesn't work, I've probably ran the truck out of gas at least 10 times since I've owned it in the past year. Its a good fuel pump...

Anyways, I thought it was dying recently because I got on the highway and about the time i hit 55mph it started missing pretty badly, I thought it was starving for fuel and the pump was dying. So I slow down and it just keeps on going, occasionally missing here and there. Found out soon after that if I keep the speed under ~48 mph it doesn't miss very muchl, and I don't think it has missed at all under 40 mph.

And today I had to drive it about 1 hour round-trip and kept it at about 45 mph. Missed occasionally, maybe 15 - 20 times total for the trip.

I understand that it shouldn't miss at slower speeds and will miss at higher speeds when you shift up because the engine is at a higher load to maintain speed, therefore will require more fuel. The thing that confuses me is right before I got home today, I ran it through first WOT and second up to about 44 mph and it didnt miss at all, seemed to have full power.

I would think 1st and 2nd at WOT would pull more fuel then crusing at 50 mph in 5th gear.

Any thoughts guys?

 

[///Manuel]

Check your plugs to see if they all look similar. That could narrow down your problem to one cyl. Go from there.

 

[1991explorerEB]

im pretty sure thats your coil pack. highway speeds are comin for misses when your coil pack is going out

 

[thebigrooster]

Could it possibly be a leaking intake gasket? The truck does leak a little oil, maybe a qt every 1k or so. I'm almost positive the oil leak is from the intake, it runs all the way down the back of the block (I saw that when I had the clutch out)

 

[thebigrooster]

I took out every spark plug but #3 because its a pain in the ass and I have to go to work in 20 minutes. I took pictures of each, all came out fine but number 3 was a real bear to get out. Seems like it got hotter then the rest. And number five looks awful, worst spark plug Ive ever seen.. These plugs only have about 6k on them. What's up with number 5?
Number 1 Cylinder

Number 2 Cylinder

Number 4 Cylinder - was the hard one to remove, seemed to have gotten hotter.

Number 5 Cylinder - something's wrong here.

Number 6 Cylinder

 

[cogs]

From:
http://www.explorerforum.com/forums/archive/index.php/t-202479.html

On this website you may notice that oil accumulation on the spark plug of cylinder #5 is due to a bad intake gasket that is allowing oil to be sucked into this cylinder port. This is not true.

A bad lower intake gasket will allow oil to be sucked into intake ports, (not always necessarily #5) which will cause carbon to build up in the cumbustion chambers. Too much carbon build up can increase the compression enough to degrade the engine's performance, as this engine does not have a knock sensor. Excessive build up will eventually cause pinging.

But, I have replaced my lower intake gasket twice and I still have the same problem with oil accumulation on the spark plug of cylinder #5. The oil is coming from the pcv system. Cylinder #5's port in the upper intake is directly across from the pcv valve port. I have had my intake off enough to know that the oil is coming from the pcv system. I even took the throttle body off and I could see a puddle off oil in the very back of my upper intake. Yes, my pcv valve and air filter is new. I have already ordered two K&N valve cover breathers to do away with the pcv system. Also, if your mechanic has suggested replacing the lower intake gasket based on oil accumulation on the spark plug of cylinder #5, it will not have any effect on our temperature fluctuation.