Head Gasket change and P0420 1997 2.7L Write Up

Hey Everybody,

I bought a project taco a couple weeks back. It ended up needing a new head, and that whole replacement went fine. This is the second head gasket project i've bought. Both of the ones I've bought have turned out to be hairline cracks in the top of one of the cylinders. In this case it was the #2 cylinder.

I did learn a few handy things during this process that might help somebody in the future. I apologize for not taking pictures, but ill describe the couple issues as best I can.

1. The first cylinder head I bought was built up by a machine shop, so when I got it back it already had the "cups" (Thats what the dealer calls them) that sit in the block where the fuel injectors go in. The second one I bought was from Autozone (ended up being about $200 less). But I learned if you buy the cylinder head new it will most likely not come with these cups. These are a very brittle plastic, so removing them from the previous cylinder head is not a option. So if you do one in the future you will want to order these ahead of time from the dealer (dealer only part). They weren't overly expensive, but they did take a week to arrive which delayed the process. (Couldn't find the cups on any diagrams)

2. The fuel line that attaches to the fuel rail has two small metal gaskets. I would order a spare one of these little gremlins as well. And definitely pack some rags or something under the line when going to re-install them. On this truck the line from the fuel filter to the fuel rail was a bit tighter and this is kind of a hard spot to get that bolt on due to the electrical harness running right next to it. I dropped and searched for these little fuckers several times and it was beyond frustrating. They only cost $4 from the dealer, which is crazy expensive for a small metal gasket, but after dropping it several times and losing one, only to have to order it and wait for it to come, I would have paid $50 bucks for that thing on the spot. So I would order those two parts from the dealer. Heres the diagram:


3. After getting everything put back together I started trouble shooting the P0420 code (Catalyst below threshold efficiency). First bet was the O2 sensors. I attached the excerpt from the FSM so you can see which terminals to test and what the reading should be.

So I had to cut the bolts and got the sensors off no problem. When I test the first one it showed 0 ohms. I tested the downstream sensor and got the same thing. 0 ohms. I did show continuity between the terminals though. So I went to the auto parts store and tested a brand new O2 sensor and got the same thing, which I thought was weird. But I got the same reading from all three, so I eliminated that.
Next I removed the Cat, which was a pain in the ass since the angle grinder only fit in two cut off two bolts, the other two were a combination of the dremel and a hand saw. Once I got the Cat off I inspected it and it looked fine. Nothing rattling around, no discoloration or anything like that. But I figured that was the bad piece.
So i ordered a new Cat from Rock Auto and it came with a handy little guide:

I wanted to do this post because I my research I didnt find posts that addressed some of these issues they list here. My exhaust manifold does have a crack in it, actually a couple which I didnt associate with the P0420 problem. Ive got a new Manifold on order and will replace it next weekend once the part gets here. Il update and let you know if that fixes the problem!
Hopefully this will help somebody with these issues in the future.
Thanks!

 

thought I'd chime in on your post re: fuel injector 'cups'. Yup, they're a PITA and 'valve grind' gasket kits do not include them. I bought a set through 'Engine Monster' for $20-took 3-4 days to receive them (Engine Monster located in Colorado Springs, Colo.) The 'cups' were listed as 'cylinder Head Fuel Injection Spacer Cup Bucket Holder's.("new, oem").

Excellent post, btw. Much useful info there, good of you to share. Cheers!

 

Awesome, thanks for the intel!

 

I just picked up a fixer-upper 06 with a 2trfe. Came with p0420 but I have a feeling a bad head gasket is causing it. I found black oily residue in the over flow tank, .5 qt low in the radiator, and it shoots out a black liquid splatter on cold starts that leaves a nice 1ft splatter pattern on the pavement. Im thinking the o2's are getting bad readings from all the moisture in the exhaust system.

 

Are you getting any white smoke or is the oil milky looking? You found oily residue in the coolant overflow tank?

Have you ruled out an oil leak or a coolant leak?

 

Yea, oily residue in the coolant overflow tank. No white smoke and no leaks. Ill be draining the oil and coolant today to get a better idea.

 

Awesome, ill be curious to hear what you find

 

The first picture is coolant drained from the petcock. It looks clean aside from some particles but no oil. The second picture is fluid drained from the over flow tank and its quite different. Very thick and black. Someone might of poured a stop leak product in the tank. Interesting note tho, the third pic is my radiator cap and it looks damaged. I believe its missing its spring mechanism that allows overflow. This might have prevented the cooling system to vent to the tank and thus isolating the oily mess from the rest of the fluid. Do you think the damaged cap would cause excess pressure in the system and blow out a seal? (water in tail pipe)

 

Im not really sure on that one. I tell you what i would do though is replace the fluid, get a new radiator cap and clean out the overflow tank real good. Also make sure and blow out the overflow line in case theres something restricting flow in there. Then dirve the truck for a day and see if you have anything in the system.

How does the oil look?

 

The cups are called spacers by Toyota, and there's an o-ring that fits between the spacer and head, so don't forget those either.

 

Just got done with the fluids and although the oil was filthy there was no water. I ended up changing out the spark plugs and while I was in there I noticed a 3/4" vacuum hose that connects from the valve cover to the upper intake was disconnected. Im not sure if this is the PCV but I did a search on "p0420 PCV" and it seems they're commonly linked together on other cars. I cleared the code and will see what happens.

 

That looks like it may be your issue. Write back and let us know if that fixes the issue. Nice job on the pictures too by the way

 

Literally just got done doing this exact thing on my 2rz-fe this week. Good post.

I used Allied Motor Parts (cylinderhead.com) head. All OEM remanufactured, great people to deal with. $455 shipped to my door, complete with cams, valves, shims, buckets, the whole 9 yards.

Paid $20.65 for the spacers from Toyota, gotta be careful installing those. I used the wooden end of a hammer to LIGHTLY tap them in. And still chipped a little piece off the edge on one, but doesent matter cause its just on the lip.

If I may add something; I highly recommend getting the top end "valve grind" gasket kit from Toyota. With the TacomaWorld discount from Gunny at Camelback Toyota its about $200. Includes everything you will need except for injector spacer cups. No messing with aftermarket stuff, all OEM, fits perfectly.

Also it makes things a lot easier if you bolt the water outlet on the back of the head on before installing the head. Not much room back there, just makes things easier.

 

Just trying to contribute to your p0420 issue so Ill check back in if my code stays clear.