newbie that's not so new

A little more history may be needed. I've been trying to figure out where this thread should be and how to move it to there. I have not posted before. I've always just been able to figure out whatever it is I've been trying to do by reading other peoples threads. But I'm stumped here.

Before I installed the new manifold, I had very noticeable loss of power on an interstate road trip. I use cruise and while climbing a long medium grade, it downshifted and the engine raced. I quickly disabled the cruise and worked through the grade climb with lower engine speed and mostly normal power and range. But then it did it again and I noticed the power seriously drops at RPMs above about 2500-3000 and gets weaker as RPMs climb. During the trip it threw codes for failed upstream O2 sensor. I figured the exhaust leak must have damaged it. No big deal. Order O2 sensors and replace them with the exhaust manifold.
when i replaced the exhaust manifold I also:
replaced upstream and downstream O2 sensors Denso. Since I cruised the 355 nation threads and found that some of the aftermarket brand O2 sensors don't play well in our trucks.
When I removed the old manifold, there were wasn't any catalyst in the resonator. I thought that odd since no one except the dealer would have removed the manifold. That was done with the recall for the valve/ cylinder misfire. That was an ordeal in and of itself. Anyway.......
New exhaust manifold (with catalyst), new upstream and downstream O2 sensors (Denso), cleaned MAF (with appropriate cleaner), cleaned throttle body, may as well while it's apart anyway, new PCV tube (because the old one was disintegrating). Still no change. Extremely poor power and fuel consumption stinks.
New air filter....same.
New fuel filter.....same.
Removed the exhaust manifold and tested for obstructions in exhaust flow.......free flowing exhaust.
Removed catalyst from new manifold.....why not, the old one didn't have it anyway, so may as well try it.
Put everything back together.....same.
Cruising the threads today. Found many folks found similar issue due to exhaust camshaft actuator soleniod. So I removed it to check, it looks brand new. Cleaned it a bit anyway, with throttle body cleaner, gently blew it out with air, re-installed it. I don't expect it to change anything but I'm hopeful.

cart7881 said:

Welcome back.

You removed the exhaust manifold and found there was no catalyst and no reason for it to be missing. Did you check to see if maybe it deteriorated, broke up and ended up downstream in the rear converter?

Click to expand...

Thanks for the welcome.
I did verify as best as I could. I believe the exhaust flow is unobstructed.
Since the old manifold was cracked in a couple places I snapped it apart to inspect. There wasn't any sign there had ever been catalyst in there. No scratches or other markings to indicate they had been removed and no pieces or remnants in there.
Since the issue continued after the new exhaust manifold and O2 sensors (US and DS) were installed, I was concerned that maybe it did disintegrate and clog up the downstream catalytic converter. I don't have a scope to look down the pipe so I took the manifold back off and fished around down the exhaust with a clear rubber hose connected to my shop vac down to the DS coverter. I could not pick up any particles from that direction. Then I connected the shop vac, full force, to the exhaust at the back and it seemed free flowing, and had good suction when I placed my hand over the open end where the exhaust manifold connects. Then connected the shop vac at the other end, at the manifold connection, and applied full suction. It seemed to be free flowing and when I placed my hand over the exhaust tip it had good suction, just as if it were at the end of the shop vac hose. So I don't believe there's exhaust obstruction.
Anyone have experience with O2 sensor trouble? New ones being faulty.

I installed the following O2 sensors (2005 3.5 liter) from Rock Auto:
Upstream DENSO 2344119
Downstream DENSO 2344285

My neighbor is out of town so I haven't been able to borrow his scan tool.

I experimented today by unplugging the vacuum line from the fuel pressure regulator. Absolutely no change in performance on a trip to the grocery store and back. Plugged it back up and test drove again. No noticeable difference in performance. I'm going to try a new fuel pressure regulator and see if it helps.
Anyone have any thoughts on this idea?

A bit more info:
About 100k miles ago, at about 130-140k miles, the fuel pressure regulator sprang a fuel leak. I replaced it with whatever the cheapest option was at one of the big chain auto parts shops. Maybe it's gone, or going bad?
I also tried unplugging the MAF and the MAP (separately) not even drive-able with either of those unplugged. Immediately shut itself down.
The engine does surge under light acceleration, and total loss of power under heavy acceleration. It just sounds like it's sucking air when the throttle is opened up under any load. But the engine does fine at 70-85 mph as long as you don't give it enough accelerator to make it downshift.

I have a rather expensive Autel, but I probably wouldn't recommend it to anyone. Some of the touchscreen icons don't work and Customer Service leaves much to be desired. I have heard some good reviews for Thinkcar scanners. Some Pros that I follow are happey with them and they have models that cover a wide range of functions and prices.

If you are planning on dropping a few hundred, do some serious research. Check to see how updates are accomplished and how much they cost. I think all the tools will work without constant updates, but if you work on more than one vehicle you might find them necessary. Last year I paid $365 for a one year update plan. Am now skipping at least one year.

If you can work with the cost, a scan tool with bi-directional controls is very handy. I use those all the time.

Amazon has a huge selection of scan tools that you can investigate to find out particulars and tool brand websites are a good source for specifics.

Good luck. Beware those that say "Brand X" is the best. There is no such thing as the best, unless you are prepared to spend thousands for the particular Manufacturer's dedicated tool. With that you are locked to one brand of vehicle.