I have a 2000 Expedition with the 4.6 in it. It was a great truck up until recently. A few months ago it started missing pretty steadily. It threw up the CEL and a code pulled showed that number 7 cylinder was misfiring. A little reading online revealed that the number 7 cylinder is apparently a common problem.

So I bought all new platinum MC plugs, and went ahead and had the number 7 coil pack changed as well. It seemed to fix it ... for a while. But it started missing again, but felt not as bad. I went to have the codes checked to see if anything was showing. Nothing. So I started to think that it might have been a fuel issue instead of a coil pack.

Well, as I debated which it could be, a couple of weeks and about 300 miles went by, and then it blew out a plug ... on number 7. So I disconnected the #7 connector for the coil pack and injector just to be safe and drive it home and then to the shop. The fix they suggested was a heli-coil repair with a new coil pack. It sounded good to me and I had read some good reviews on that type of repair, so I went for it.

But within the hour after picking it up it started missing horribly. At this point I'm pretty frustrated. I'm thinking surely it's not #7 again. This time the CEL starts blinking. I knew that was not good. I could already smell the catalytic converter burning. I took it to have the codes pulled and it was a misfire ... on #7, again.

So now I'm at a loss. I've already had #7 repaired twice. However, I'm starting to suspect that the shop may have seated the heli-coil too deep into the head, letting the spark plug get fried or beat to death. I want to pull the plug and check, but it appears I'll have to take the fuel rail off to do that, and since I've never done that, I'll need a day set aside where I can fool around with it.

But (after writing all that) my question is basically: What's my next step to fix this thing? And ... in the meantime, I still need to take and pick-up my daughter from school (1 mile round trip), so i was wondering, will it help to disconnect the electrical connectors from the #7 coil pack and injector for now to keep spark/fuel from getting to cylinder 7? I just don't want to burn up my cat while I wait to get this fixed.

Any help is GREATLY appreciated.

 

No replies?

I'm still driving it as is to take/pick-up my daughter from school. Catalytic converter still cooking away, even with that short drive.

If anyone here can help in any way with my two questions, I'd really appreciate it. I tried disconnecting the injector and coil pack electrical connections to #7 and it cranked and idled without stalling ... still really rough though. I just don't know if I can temporarily drive it that way or if that even helps to not burn up my cat.

Please help. Thanks.

 

Some people get this wrong so I have to ask.
To you, which cylinder is #7?

 

By #7 cylinder, I'm referring to the one that is next to last on the driver side.

4 8
3 7
2 6
1 5
Front

 

Why are you disconnecting the COP?

And disconnecting the fuel injector is going to let the O2 sensor on that side see a big hunk of exhaust that is loaded with unconsumed oxygen. The PCM is going to compensate by going rich on all cylinders on that bank to ry and use up the oxygen. That will fill your cat with hydrocarbons and cook it.

Do a compression check on the engine to be sure there isn't a mechanical problem. Then swap the #7 injector with #6 and see if the misfire follows. (Might want to also swap the COP with #5 and the plug with #1 and see if/where the misfire moves to.)

 

I just figured that if it was bad, and there was no fuel going to it (from the disconnected injector connection), that it was better disconnected than sending intermittent spark. But that's part of why I'm here ... to find out if actions like that are good, bad, or just pointless.

That kind of sounds like I'm damned if I do, damned if I don't. Leaving it connected is dumping excess fuel into the exhaust and then burning it in my cat. But if I disconnect it, the PCM just compensates for it and still burns up my cat.

I'll have to take it in for a compression test when I have a little more money. But I can probably swap the coils and plugs myself. Is it possible to do that without removing the fuel rail? I'll try to run through all of those tests asap and see what comes of that.

I was hoping there was an easy temporary work-around way to drive for the next two weeks (for the aforementioned drop-off/pick-up of my daughter) without burning up my cat (or it catching fire) or doing any further damage to the engine. It's definitely frustrating having the same code for #7 occur again and again.

I appreciate the help.

 

My '98 F150 with 4.6L and twin coil packs has been chronic since new meaning ignition wires seem to last a year. They corrode at the spark plug end. Also - I've learned spark plug insulators get hairline cracks during installation or due to poor handling during packaging and shipping. Those hairline cracks you cannot see will bite you. Closely inspect your spark plugs. I run only Motorcraft platinum tip plugs. Nothing else will work. Weird but true...

 

If u are still having this steady misfire, I believe its a faulty injector. When an injector is barely working it will cause a miss and the pcm won't detect that. An everyone automatically accume spark plug. Even if u but a mechanics scope on the injector to hear it , u may still here a steady click like the injector is working when its not. So I could be wrong but I believe the culprit is the injector.

 

Okay, that makes sense. Like I had said, we had the truck in twice for cylinder number seven, having changed plug and COP twice (including the heli-coil). But the one common denominator that *wasn't* changed (or even checked to my knowledge) was the injector.

The injectors are a cheap enough part that I'll just go ahead and replace it. I've never had to remove the fuel rail before ... is that a relatively easy task?

I appreciate everyone's help on this. If I get this thing solved, I post the results. In the meantime, hopefully I won't burn up the cat.

 

Usually a knock that doesn't go away an doesn't throw a code for the coil the culprit is the injector. I have had cars that I attempted to repair mess with me like that. I am not shore on how hard the task is but I believe the rail is right up top shouldn't be hard. Make sure u use new o rings. That's to avoid leaks. Hope it helps.

 

I just blew #7 and put in an insert but now my check engine light is flashing saying I have a miss fire...it was fine before I blew the plug...the car still runs good but it shakes a little bit when I give it gas and it acts like it don't want to pull hills.....I pulled the plug it's sparking but it's wet...I disconnect the wire from the coil a and there is no change in the way it runs...could I have not put my insert deep enough and the plug isn't deep enough? It looks like it's bottomed out though...please help me out

 

Switch COP with another cylinder and see if the misfire moves. Don't forget to dry everything out.

 

You sure you didn't leave any debris in the cylinder before firing it up?