I've been reading all of the posts on this forum and you guys sound very knowledgable. My Expedition was working great, no problems until this last weekend. Going down the interstate when all of a sudden I lose power and the service light flashes and then stays on then flashes again and I also notice that there is a knock-like sound coming from the engine. I used to be a motorhead in my early years and experience tells me its not a hard mechanical knock, it sounds more like air, like an exhaust leak but harder. Anyways I run the reader and it tells me misfire on #1 and#6. So by suggestion of a reliable parts man I replace the coil and plugs on both cylinders. I still have the noise so he tells me to replace all the plugs since the truck has 83k. Still had the noise and no light. After that so I took it around to a couple of shops. One tells it could be a rocker off the push rod. Couple shops told me it could be a severe misfire with more coils failing and not tripping the "service soon" light. And the one that made the most sense to me was the mechanic at ford. He said from what I told him about the misfires, and the noise he heard coming from the truck and smell of the rich exhaust, I have a crack in the channel between #1 and #6 in the intake manifold. He said he couldn't verify it for sure until he put it on the computer but he thought there was a 99% chance that is the problem. He said he would have to look at the fuel trim readings and do a propane test to know for sure. Does this sound right? I thought they corrected this problem in the late 90's. Any input would be helpful. Thanks

 

you know... i could be dead frickin wrong here... and i probably am lol but, to my knowledge.... OHC motors dont use pushrods... i thought that was the biggest advantage of using an OHC motor... no rocker arms or adjustments... just plain old cam on valve spring action.... am i wrong for thinking this way? if so, how does the OHC work?

 

bigrr - does you 5.4 have the plastic manifold or the aluminum?

If it is plastic, then it could definitely crack. But if you have the aluminum manifold, I don't see that cracking under normal use.

 

ford man says they are plastic. thats what he told me. did they go back to aluminum?

 

They've used a composite intake manifold since the switch to "PI" heads, I'm pretty sure. Try to put a hand down near the intake at idle (without burning yourself) and see if you can feel the engine vacuum. If you can, you've got a cracked manifold. If not, look for faulty vacuum lines elsewhere. Another thing to try is cycle your coil plugs with a new one and see if that doesn't take care of things (replace each of the coils with the new one in succession until the symptoms go away or nothing happens, then you can rule out coil packs).

Good luck!
-Flea

 

Ford started with aluminum and then went to plastic (with an aluminum crossover I think).

 

Double post.

 

You could have a broken valve spring since you were on the interstate. Have you checked compression on 1 and 6? There isn't much shared between those cylinders. Get back to basics before you go too crazy. Hook up a vacuum gauge. Sounds like you have used one before. The readings still mean the same. Just because it has a bunch of wires running everything it is still a four-stroke internal combustion engine after all. Hope this helps keep us informed.

Robbie

 

You could have a broken valve spring since you were on the interstate. Have you checked compression on 1 and 6? There isn't much shared between those cylinders. Get back to basics before you go too crazy. Hook up a vacuum gauge. Sounds like you have used one before. The readings still mean the same. Just because it has a bunch of wires running everything it is still a four-stroke internal combustion engine after all. Hope this helps keep us informed.

Robbie

Oh yeah, if the check engine light "flashes", it is under a misfire condition! Only thing that makes the light flash is a misfire.

 

You could have a broken valve spring since you were on the interstate. Have you checked compression on 1 and 6? There isn't much shared between those cylinders. Get back to basics before you go too crazy. Hook up a vacuum gauge. Sounds like you have used one before. The readings still mean the same. Just because it has a bunch of wires running everything it is still a four-stroke internal combustion engine after all. Hope this helps keep us informed.

Robbie

Oh yeah, if the check engine light "flashes", it is under a misfire condition! Only thing that makes the light flash is a misfire. Also the firing order is 1-3-7-2-6-5-4-8 so I believe when number one fires, number six is on its intake stroke.

 

I don't know when COP came out. On the older waste spark DIS systems, 1 and 6 share a coil. Ignore this if they were already COP.

 

Bigbronc I think that ford guy might be right about the manifold since the the truck runs great above 2500 rpm and there is no noise. If memory serves me right if it were mechanical the noise would get louder the higher the RPM's am I correct?

 

I will go into more explanation on what the ford tech told me and you guys can respond. He said the plugs fouled out from the rich mixture of the injectors trying to compansate for the extra oxygen coming in the cylinder. And when the plugs foul out the coils burn up in a matter of time and even faster going down the interstate. That makes sense bigbronc about the "service soon" light flashing since it hasn't flashed since I replaced the coils. The tech said I will have to replace those spark plugs again after fixing this problem. He said the injectors are dumping fuel in there as we were speaking and they will foul the plugs again and and burn up the coils again if they were not replaced.

 

deleted dup post

 

I've been using this forum to get some Ford product knowlege. I've posted some things that have turned out to be embarassingly wrong. Here goes today's attempt.

1. On the highway (O2 sensors warmed up, closed loop, off idle) a vacuum leak (cracked manifold) would not cause an overall lean condition, the PCM would notice using the O2 sensors, add fuel appropriately, and it wouldn't cause any highway drivability problems due to the mixture.

2. Air in the manifold is air in the manifold. It doesn't care whether it comes in through the throttle body, a cracked vacuum line, or anywhere else. After the engine is fully warmed up, in closed loop, pull the brake booster vacuum line, far bigger than a crack in the manifold. Go for a drive. At idle, it may after 10 or 20 seconds get to the limit of the fuel trim and run some lean. On the highway the only way you can tell is you will need less throttle. This only applies after the engine is in closed loop.

3. Slight hedging on 2. Any air added to the intake manifold anywhere will reduce the vacuum, increase the manifold absolute pressure, everywhere in the manifold. Just like the air came in the throttle body. If the engine has intake runner manifold with long tubes specific to each cylinder (or pair), the drop won't be exactly even like it would be in a single plane manifold. But the difference would be far less than the pressure drop from the throttle body to the intake valve and that is very, very little drop.

4. The fuel trim in any misfire will go positive, that is a misfire in any cylinder will cause all cylinders on that bank to get more fuel. This isn't because of the vacuum leak, it is because unconsumed air from the misfire is being sensed by the O2 sensor. Again, this only applies in closed loop. If the misfire is from no spark, the aggregate fuel trim will only go up to 5-10%. If the misfire is from no fuel, the aggregate fuel trim will go up 25% or more and could cause carbon fouling of the other three plugs on that bank. Excuse, me, you have a misfire on both banks so all 6 other plugs.

5. A carbon fouled plug has LESS resistance to ground than the spark across the gap. If it didn't, fouling wouldn't hurt plug performance. In short, carbon builds up on the ceramic in the plug's well around the center electrode. This makes a low resistance path from the center electrode to the side (ground) of the plug. Spark takes this path instead of jumping the gap. This would put LESS strain on the coil instead of more. An open plug or too wide a gap could damage a coil but a carbon fouled (rich) plug wouldn't.

Someone please correct any mistakes I may be making here.