TL;DR The small engine bay on the 4runner with the V8 means there's about 0.5" of space between the rearmost bolt securing the Check Valve and the firewall, making it literally impossible to extract. We resorted to draining the coolant, disconnecting both air ducts from the pair of valves, and dislodging the bracket to which the valves were mounted (couldn't fully remove the bracket because of an electrical connector being mounted to the back of it). Now, the biggest challenges after mounting the check valves to the bracket will be to reinstall the bracket and connect the two ducts that mate to the valves (each with 2 screws that are really difficult to reach, even with several extensions on a ⅜" drive wrench)

I recently got myself a 182k mile 2008 4Runner Limited with the 4.7L V8. The seller disclosed a few items that would need attention upon sale: cracked exhaust manifold, failing fuel sending unit, and CEL due to a broken SAIS Check Valve (seller had a Hewitt Bypass Gen1 installed). I knew I would order a set of DT shortie headers and have a shop install/weld them to the cats, and the fuel sending unit is a DIY job I should be able to take care of in a few hours.

At first, the check valve replacement seemed like a feasible DIY job and a relatively less costly one (~$100) than the more frequently talked about SAIS pump replacement (~400). I found plenty of great references from people who'd done this work on larger platforms (Tundra, Sequoia, LX/GX), so I ordered the parts, called over my father in-law and we got to work.



Once we had the intake plenum removed, we could not figure out how to get to the two bolts securing the check valves. We tried many different ways of finagling wrenches through the narrow opening between an encased wiring harness and the firewall. We eventually pivoted and resorted to removing the bracket to which the valves were mounted, which entailed draining coolant from the radiator and disconnecting the line that routed through the right side of that bracket.







While I had got the intake off, I confirmed that both the SAIS Pump and the AIR Switching Valve both work.

Has anyone done this job before? If yes, do you have any tips or suggestions to make reinstalling the check valves more feasible?

IMPORTANT NOTE: OBD2 reader gave me the following error codes:
P1442: SAIS Switching Valve No.2 Bank1 Stuck Closed
P1445: SAIS Switching Valve No.2 Bank2 Stuck Closed
P2441: AIR System Switching Valve Stuck Closed Bank1
The part I ordered was "Switching Valve No2" but it seems to me that it was actually No1 that was malfunctioning. Once both were removed, I compared the plunger movement with vacuum applied. My old Check Valve No2 functioned identically to the new part. In Check Valve No1, the plunger barely moved and the diaphragm didn't hold the vacuum at higher pressures like the new part. I've ordered a new Check Valve No1 and will compare it to No2.

I will update when the new part arrives and again once we've reassembled everything (I hope).

I'm wondering why there was a failure despite having the bypass?

Regardless, there are a few videos online and a thread here that are helpful.

Good thread with a great linked video.
Guide: Starter, Knock sensor, SAIP replacement 2UZ-FE VVT-i

And forum member @mtbtim recently posted his experience, and tips which is awesome as usual
Toyota Lexus 2UZ-FE Starter Replacement (With the Secondary Air Injection System 2005-2011) (Part 1) - YouTube

I haven't done this myself, but I would probably replace the whole setup (although very pricey) or at least both check valves for sure and probably bypass it immediately so I don't have to go back again. I would also consider replacing the starter since you've done the hard part (those check valves!)

This video from Timmy the Toolman proved to be EXTREMELY helpful. He replaces the starter, check valves and SAIS pump. He notes this is one of the most infuriating jobs he's ever done.

As it turns out I was correct in that, despite the error codes stating Check Valve No2 was malfunctioning, it was actually No1. It wasn't holding enough pressure when the vacuum was engaged to allow the valve to open sufficiently. We ended up installing both of the new check valves since we had already come this far.





In removing the old check valves, we managed to tear both of the breather tubes on the starter motor for which I was able to source replacements from the dealer (see pic in original post, red arrows).

Here's the list of parts I used to do this job:
25720-50020 SAIS Check Valve No. 2
25720-50011 SAIS Check Valve No. 1
16341-50020 Coolant water gasket for under bracket (x2)
17377-50010 Pipe Gasket (for Check Valves) (x4)
17171-50030 Engine Intake Manifold Gasket (x2)
96761-24019 Coolant O-Ring (for metal pipe that connects to bracket of check valves)

Do you watch this one? He has some tips. https://m.youtube.com/watch?v=9vKyVQa-pjk

I did. It was helpful in getting the intake off, but the big difference is how much space there is between the check valves and the firewall. In the Tundra/Sequoia (shown in that video), there's enough room to get a hand and a wrench back there to loosen the two bolts that secure the check valves.

On the V8 4Runners this isn't possible to do without removing the bracket with the coolant line running through it. There's only about ¼ inch of space between the top of the bolt head and the firewall.

I'm not sure why the CEL came on while the bypass was installed.

We had already removed the bracket with the coolant line running through it the check valves mount to by the time we found this video. It ended up being the most helpful resource for completing the job and putting everything back together.