So, a perplexing issue.

[Alisaihin]

Seems everyone here is stumped :V cause no replies!

Anyhoo, I was checking over the fuel system and whatnot. Injectors look fine (though I need a new set of O-rings on the 4th one), cause they aren't leaking fuel, and all of their resistances are a mere 3 ohms (likely because there's very minor connector corrosion, which is quite the shock!), fuel pressure is fine (I tried crimping the return line to see if it improved...nope, only got worse, so pressure is okay), and honestly if the FPR s*** the bed it would have after the Walbro 255 install (that and the vacuum line for it is free of fuel after running). So I looked, and researched, and looked some more.

I was finding nothing and felt at a loss!

Until someone had their 2005 Sentra's swirl control valve freeze, but in the open position. I was explaining to him what it does and then it hits me...

My intake runners have a good coating of carbon (I know because I have had the upper manifold off). The EGR had a sizable coating of carbon. And I would lose power up at the top, and it'd choke at 4500 at WoT. To confirm my suspicions, I checked to see if anyone ever had their Secondary Butterflies seize up in the closed position...because I know it's SUPPOSED to default to open at anything other than idle or low load/low rev conditions. And I found one hit, where someone in a thread said they once had a friend whose KA24E was choking at 4500 RPM (about where I do), and they'd lose power above 2000-3000 ish (which I sometimes do, car can't hold revs on highways uphill at 3100, and it slowly bogs down to about 2300). It all seems to make sense, yes? Close off half the stock runners and what do you get...you are getting the ability to only move half the air you need! At idle/low revs, that's fine, because the higher velocity allows for better charge fill, letting it burn better...but at higher revs, you aren't getting all the air you need. So it starts burning richer...and richer...until it can't burn, which it's merely burning off excess for a second until it resumes to normal.

So, I have begun the monumental undertaking that is unhooking the lower intake manifold from the block (it's easy enough...for the most part. The power steering pump and the support bracket are going to make this just a pain in the a**), just to see if my suspicion is correct. And if it isn't, well, I have a fresh gasket for it, and I can re-organize some of my wiring, lol. I'm also going to take this opportunity to maybe replace some hoses because I think due to removing the upper manifold I think I incidentally caused a couple small vacuum leaks that are making it run hideous thanks to old hoses...that and it'd just be wise to do so anyway.

[Alisaihin]

I utterly despise the intake manifold used on the KA24E. I CANNOT understate how needlessly complicated it is to remove.

It's still not 100% out, as a hose that apparently Nissan decided needed to run UNDER the coolant feed part of the manifold (which goes to the water pump) in a manner that is a complete b**** to remove. I was able to feel, and it feels like my secondary butterflies are actually open (though given the carbon buildup I felt I wouldn't be surprised if I may have knocked them back open).

I'm gonna fully remove this though, because I am NOT going to have fought this thing just to slap it back on. I also need a new plenum gasket because apparently the one I used destroyed itself (might explain why it was running like complete a** after emissions removal).

[Alisaihin]

Guys, I'm pretty sure injector 4 is shot.

https://www.dropbox.com/s/ik45segxrlrlz ... 4.jpg?dl=0
This dumped out of the intake manifold when I finally got it off...
https://www.dropbox.com/s/40128c8d11uzl ... 7.jpg?dl=0
Holy s*** those intake valves on cylinder 4 are SOAKED.
https://www.dropbox.com/s/kz3wq1ys9tkh3 ... 8.jpg?dl=0
...Injector 4 (the furthest right one here) probably hasn't been merely suffering from bad O-rings. Resistance-wise it seemed fine but I guess the internals are f***.

SCV is freed, so I know it works in keeping them open (at least now, I'd say). Just...I doubt I'll let it try to operate...I don't think the vacuum solenoid will be able to hold a vacuum because the armature that actuates the butterflies has the little airtight accordion thing (whatever it's called) just absolutely destroyed. That and removal of the butterflies can't happen until I can find a way to torch the screws out because they have all but three stripped themselves out entirely in attempted removal...so I'll just leave the SCV alone for now.

This isn't done, because I also need a new crankcase evap hose. I noticed it's extremely loose at the connection to the crankcase and is likely creating a fair bit of a vacuum leak. Plus side?

Removal of this damn manifold will be much easier next time, and it's going to let me clean up the engine bay a bit more.

[Alisaihin]

God, this thread feels so lonely.

Well, an update. Due to a loose PCV/evap hose from the crankcase to the intake I decided to remove it and get a replacement...it snapped in my hand. Huh, no wonder it loosened up badly.
The hose leading off the back of the thermostat was stuck on hardcore, and I was forced to cut the damn thing off. So needing a replacement for that too. Eff.
Apparently nobody can source the valve cover breather hose or the one that leads from the intake arm to the hardline that handles the IACV and Air Regulator. These two I might just see if I can't find a decent stock of emissions hose and use those.
I might get a few new hose clamps as some of the stock ones are kinda in bad shape...
I'm getting a full set of new intake manifold/plenum gaskets. For whatever reason the Felpro ones I ordered practically destroyed themselves from the first reinstall of everything. I thought Felpro made good gaskets...
And, of course, I got my new injector. I'm also waiting on a fresh set of O-rings and insulators for all four (not taking chances!).

I also did some things while I have been idle...primarily cleaning out the intake runners. They were...nasty.
https://www.dropbox.com/s/g7npjbreps512 ... 5.jpg?dl=0
Absolutely destroyed one of the el cheapo white washcloths I got from WalMart.

[Alisaihin]

Okay. Intake is put back together. The runners are cleaned out. The crap injector is gone, and I know the butterflies are open for sure.

BUT HEY, SAME ISSUE STILL. One thing I might want to note-I took the FPR off vacuum, and plugged up the port that supplies the FPR vacuum. The car seemed to run...exactly the same, minus one thing. When the FPR is hooked on, the car stumbles initially on startup.

I'm at a loss here. Is there something completely obvious I'm missing? Is the FPR somehow causing this? I'm so confused...