New 4Runner, bad exhaust Valve, what to do

Logically, no, actually. O2 sensors measure the concentration of oxygen in the exhaust pipe, ie: the ratio of air to fuel. Since exhaust gas (assume a static oxygen ratio) is pressurized at the manifold relative to the ambient air, very little additional air (if any) should be introduced to the system since it would be escaping (high -> low pressure). Hence, the ratio stays the same and is read as the same at the sensor.
Less mass <> leaner reading.

If anything, the cracked valve would allow unburnt fuel during the injection phase through the exhaust pipe causing a rich condition, thus leaning the engine. But that's after it's already cracked.

FWIW wet intake is normal.

 

If any air did get introduced, it would be due to venturi effect on the closing end of the exhaust pulses. But its unlikely it would be enough to significantly influence the ECU's fuel correction. In this event, ECU would richen, which wouldn't cause damage.

 

So explain how it makes a lean condition? I'm all ears.

Treyus30, thanks, that makes sense on ruling out the ECU detecting any change in o2 concentration due to a cracked exhaust manifold.

 

Stock or stainless valves will work fine for your app. Titanium is reserved for the bad ass of the bad ass engines with extreme usage intentions. Actually I believe poster for the titanium valves was joking around. With todays machining, calabrating, laser measuring, etc. sky's the limit. Good luck on this project, as for the manifold, if you want to have it fixed, take it to a welding shop and have them weld the cast iron manifold with nickel welding rod/wire. We welded a cast iron cylinder in a fairly rare block, the machine shop was pissed, machining nickel is tough (it is HARD). Engine still running!

 

Thanks for the advise. Since this is my first time doing this. I'm going to replace the two exhaust valves with oem and lap the rest as suggested. in the future I will definitely invest on better performance parts if needed. On the exhaust manifold, I've recently seen a video with someone replacing it with a better exhaust manifold from the Tacoma part# 17141-75080. Is this a good idea or should I stick with stock?

 

If the Taco guys consider it a better part...it's probably a better part. It's a genuine Toyota part number. As long as it hooks up the same and all, I would use it.

Lots of parts out there are better revisions of parts but aren't updated by the dealer to show they fit all possible applications.

 

Just stick with stock. It's not going to gain you anything, even if it is different (guess I need to check mine now, never noticed a difference). I'm working on a Tacoma head rn as well, I plan to polish the heads and lap the valves in addition to a gasket replacement. I'd love to do performance upgrades, but they're overpriced and out of budget.

 

Also for the record I should add that getting titanium valve springs will do nothing for you without a shim-under-bucket conversion as well (~$800 from LCE). You need both to raise the redline. (+ECU ofc)

 

Hey how'd the rest of this go? Did you replace all valves both sides? or just the problem ones and clean up rest? I'm currently dealing with the same exact issue. Did you resolve the cracked manifold too? I bout it with the misfire hoping it was a simple fix. I'm about to take it to a machine shop and have them resurface the 2,4,6 and do a valve job for it. I'm worried about the cause though.

 

Should be checked for clearance at 150k - 200k miles as they tighten up over time

It's neglect that causes issues especially on the exhaust side otherwise the 3RZ is bullet proof so no concern for "cause"

Just wear and tear over time