Okay, I had a list of small problems with my 4.1 which was motivating me into the 4.9 swap, but I figured I would see if the easy fix worked and that would take pressure off having to do the 4.9 under duress.
Problems were: periodic lean error (E44) after warmup, uneven acceleration after warmup (but not cold that was fixed separately), vacuum pump getting louder as temperature increased, and oil analysis showed higher than normal levels of dirt and coolant. I also had a long-term problem with random oil consumption, and low compression. The failure that would explain all of this was a leaking intake gasket, but I also thought there could be some other problems, so I had a mechanic run some tests.
He tried the easy and obvious thing first which was to monitor the O2 sensor, and sure enough it showed good, but it was also showing the temperature bouncing around a bunch, even to the point where the car was dropping in and out of closed loop on the highway.
On to the serious tests. A leakdown test showed that one cylinder has minor exhaust valve leak, while three cylinders have minor blowby issues, but nothing major. There was no coolant leak. The exhaust system also tested fine. The engine core is solid, which is good news and kind of surprising for HT4100 with 138k miles.
So given the history of intake gaskets, I had the mechanic install a new Felpro, and also gave him new valve cover gaskets. After he got the lid off he said that the existing one actually looked fine with no visible damage. However I am hoping that some micro leaks were fixed anyway, and maybe the bolts just needed a good torquing. One of the engine shops I talked to said that the manifold probably needed to be resurfaced, but that was after the fix.
Anyways... he buttoned everything back up, reran some tests and ... O2 still showing wild temperature readings. Shit. So he started doing some more tests, and traced the leak down to the butterfly valve connector rod which had excess play from a crack. I picked up a replacement TB from a yard for $60 (remans are $200-400 btw), and it took care of the problem.
I took it out for a long drive this morning and the problems with lean error and uneven acceleration are gone. I will not know if the consumption problem is fixed for a while yet. I assume the high dirt content is resolved, and am guessing that the high coolant levels were from spillage and blow-off getting sucked into the TB.
I still have a couple of small problems--uneven bubbly at highway cruising, and wanting to stall at red lights sometimes. However I think those will be fixed with replacement TPS and ISC, which are both old. I also need to have the timing bumped up again. Otherwise I am told (again) that my engine has +60k miles left on her...
TPS is a fun one to have fail, Had I not have known mine was broken I would have had a heart-attack when I couldnt accelerate above 20 mph with the engine revving and the pedal to the metal. lol Would have definately thought transmission, but a new $30 TPS was all it needed.