The valves in my 4.2 have been rattling like crazy w/ an empty truck and just barely having the throttle cracked goin down the interstate and approaching a mild grade. It has 142k and has good low end but looses some power shortly after. Also, when cruizin down the hwy, it feels like it will drop 2-3 cyl's all at once for a split second. It does that pretty often. The other symptom is on startup. Its not smooth. It lights right off no problem but sounds like it's detonating on startup as well. I've got intake upper/lower but i think i'm gonna just try intstalling the plenum gaskets first to see if that cures it. I'm assuming this is all from a vacuum leak. I saw what appears to be a light dust trail on the inside lower half of the plenum when i split it but then again that could have shook off during disassembly. Any other ideas that might help? I know the 3.8/4.2's are trash but I'm tryin to milk this one as it was a freeby. I've splent plenty of hours working on both tryin to repair head gasket failures. This is def some of fords worser engineering.

 

Im not sure why you think the 4.2 is such a horrible engine??? They have proved very reliable with the exception of the 97-98 intake manifold gasket issues?

As for your loss of power I think your on the right track with the vac leak... this is something you culd have checked before tearing it down though. It would have been a big help to check that first instead of tearing into it without a clue what your looking for. To the rest of you reading this dnt just jump into exploratory surgery on your truck because you have some power loss ask some questions and try to diagnose the problem before tearing your engine apart and bitchin about the motor because you dont know how it works or how to fix it

 

ease up little paul, pick your battles a little more carefully. Not worth pitchin a fit over.

 

Make sure the EGR ports are clean. I have a 3.8 Windstar that would ping its tail off then it developed a skip at cruising speeds. Sure enough, the EGR ports were nearly clogged except for 2 or 3. Cleaned them out and it runs great no more pinging.

 

That is gonna be my next approach. I found the dead skip to be a bad coil pack that had a cracked housing. Replaced that and she's back to full power and smooth as a button but I still have that detonation issue which I will investigate next. Thanks for the help!

 

On My 4.2 I replaced My Cam Position Mod. yesterday. The truck has been running ruff with no power. It seemed to help, but still not as good as when I bought it. I was impressed with the 4.2 until it started to miss and lost power. Now I'm stopping in to A-zone about once a week and having them do a CEL test. Every time it's something different.

 

I would definately remove the coil and at least give it a visual to see if it has any cracks of any kind. It seems that they are only good for about 100k or so, at least thats what my research/experience has shown me.