I would start with pulling codes from pcm. Autozone will pull them free. You would need a fuel pressure gauge to check for excessive pressure, but this would generally affect all cylinders so its not likely your problem.
Do you remember which cylinders had the fouled plugs? if you dont, unplug injectors one at a time trying to locate miss] I would start there with a compression test, backfires are usually valve timing related. This engine can spit a cam follower off, especially cold &/or using the wrong oil [requires 5w20], not changing it often enough [sludge]
let me know what you find and I will continue helping you.
A fuel pressure gauge would ge helpful to check for leak down. See if they loan any out.
John it should be around 150 . Just keep posting your results and I will keep helping you. I try to check my questions at least every couple hours.
John you need to check compression on #7..I attached the tsb that I think might have happened. Its not the cat converter!
Some vehicles equipped with a 4.6L, 5.4L, or 6.8L engine may exhibit a rough idle/miss after start-up in cold ambient temperatures (less than -12°C/10°F). This may be caused by a roller finger follower(s) being dislodged from the valve. This may result in damage to the camshaft, roller finger follower, valve, retainer, etc. A procedure is now available to service this condition.
Inspect and replace any worn or damaged engine valve components and install new retaining clip and lash adjuster for service. Refer to the following Service Procedure for details.
Perform normal engine diagnostic routines before opening valve covers. If the valve train is suspect, remove the valve covers and look for Roller Finger Follower(s) (RFF) that may have become dislodged.
Replace damaged parts as necessary.
John, you know it might be faster just to pull that valve cover and inspect it. The popping back noise just has to be a valve issue.
If you do the compression just compare it to 5 & 6.
John the only thing you can due is soak it down with pentrating oil. If you can heat it up with torch would help. I don't know if you have air tools, we would use a long air chisel to break the nut loose. See if you can hit your wrench with a hammer. Straight into nut, not trying to losen. [you will strip it otherwise] I'd tell ya to take the exhaust manifold off but you will probably have just as much hassle with all those studs.
You may end up having to replace that EGR exhaust supply line. I think they are around $40
WHEN you do get the cover off, just inspect the cam, the lash adjuster and end of valve for damage. They RARELY damage anything else. You can pop them back in with a hammer and dull chisel. ARE you using 5w20 oil???? if not, GET some and change it. Is there any sludge build up??
I live in Texas and dont have to deal with this often. I have to work sat, but I will try to check on your question every couple of hours.
Is the rocker OK? no flat spots on roller, spins with no binding. The cam not worn or rough? Is there any sludge build up?
You will need to bump engine over and get the cam lobe straight up for that valve. Your suppose to use a valve spring compressor tool to push the valve down a little so you can slide that follower [is what its actually called] IN . It's hard to explain, you get it on the valve side right up to the lash adjuster and basically pry it back in while pushing down on the valve a little.
If you want to private message me your phone number I'll try to explain it on the phone.
That's Great to hear, I would definitely use the 5w20 in the winter, This engine has very tight tolerances when new [measured in TEN thousand's] that is why it calls for such a thin oil. AND never over the 5w30. You might get better mileage with the 20.
We use nothing but the 5w20 at my dealership and we are in texas as I mentioned before. I see alot of trailer hitches and no problems from heat.
The truck runs great. No more missing and I do have 5-20 in the engine now. Is it the valve that sticks open that causes the follower to fall out? How many times have you seen this happen in other triton engines? You should give me your E-mail for future reference. I plan on keeping the truck for awhile and I also have a mercury Villager mini-van with 155,000, so I think I might be busy working on these vehicles as they get older. Do you know anyone that knows anything about older BMW's? The OBC won't turn on the passager side headling on a 1991, 535i.
Thanks again, I will be able to help you on the villager but post those bmw questions to the general cars section. You can always private message me from this site.
The problem seems to be caused by lack of oil flow, thats why I kept asking about sludge. and yes it is common.