1. I've been steadily replacing COPS as they go bad since I've owned my '97 5.4L 4wd. It now has 170K, 5 newish COPS, motorcraft plat plugs with about 60K on them and a miss under load, but not enough to make the computer code. Is there a good way to diagnose which cylinder is missing? Took it to several mechanic shops that hooked up their scanner (usually the snap-on one) but it could not give them a misfire count. They claimed this Expedition has a proprietary system that only Ford can get the finer details out of. Last time it did this, I took it into a plowed field and drove it around until the CEL came on, but I don't have any fields close by right now. Ford charges $75 for a diagnosis that I wouldn't really trust anyway. If it comes to that, I'll just replace the remaining 3 coils and hope one of my old replacements hasn't gone bad.
2. Also, it sounds like my passenger side cat is leaking or has a hole. I'm enjoying the sound of flowmaster exhaust, but know this cannot be a good way to continue. The Cat is welded in the pipe from where it bolts onto the manifold flange all the way down into the wye where the two exhaust pipes join. Is this whole part usually replaced, or do most of you cut out the cat and weld a new one into the existing pipes? Where is a good source for the cat converter?
3. I want to replace the original O2 sensors. Can I do it at the same time I replace the Cat? Do all 4 need replacing? Has anyone has success with cleaning an O2 sensor?
Many thanks

 

If you want to see the actual misfire counts you'll have to use a scanner that can read the ECM's mode 6 data.

If this leak is upstream of the fuel control HO2S, that hole can cause the exhaust to suck oxygen into the pipe between exhaust pulses. The HO2S interprets this oxygen as a lean condiction and the ECM richens up the mixture, which might cause a random misfire.

 

Anybody done this replacement of the passenger side cat before? I'm sure this is going to be expensive and it seems like most parts on this vehicle are better if you use OEM rather than aftermarket. Anyone have any experience to the contrary?
Will -- Bryan, TX