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Discussion Starter · #1 ·
2005 Toyota Sienna XLE Limited, 3.3L V6 AWD
Hi All!
I’m new here, and fairly new to auto repair overall! I am planning on doing an engine overhaul on our van, and have already begun doing a lot of the prep work (such as disconnecting hoses, wiring, and manifolds). However, there are a few things I want to make sure I have figured out before going further. I apologize if any of these questions have been asked before, this is my first post.
  • Does the transmission come off before the engine is lifted out? Does it come out with the engine? Is it unbolted and left in the vehicle? Will a transmission jack be necessary? The transmission is kind of blocking my access to the rear exhaust manifold at the moment…
  • Is there anyway around discharging the A/C system? Can I just unbolt the compressor and set it aside? Don’t really want to deal with the hassle and expense of discharging it, but I will if I have to. If it does need to be done, is it better to have a professional do it, or is it better to get the supplies and do it yourself?
  • One of my most confusing challenges at this point is the wiring harness. Do I try to remove the harness completely from the engine area, or can I just unplug all of the engine connectors, and set it aside.
  • Can I determine if the engine needs machining by myself, or does a machine shop have to evaluate it?
  • What kind of tools do I need? I know I need things like a valve spring compressor, ridge reamer, engine hoist, and a stand. However, I have never rebuilt an engine before, so I have no idea what kind of things would be good to have. Any Toyota special tools that I’d need.
Thank you!
 

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Let’s start with why you want to overhaul the engine. Then, can it be overhauled properly? Some modern engines have cylinder finishes that cannot be practically restored. I don’t know where you are but retail machines shops have disappeared from many metropolitan areas. Hard to find someone to properly inspect and rebuild cylinder heads. More common these days to find a good used engine.

Sixto
‘04 LE FWD 195K miles
 

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I've done an engine swap on the 2GR-FE, which I would say is not rebuildable (by me). You can take a look at my posts. The 3MZ is a simpler engine, but I would read up on rebuilding it first. You might be able to find a good used 3MZ engine at LKQ - if they have a yard near you, they will often ship the engine of your choosing for free. Send me a PM if you want the ins and outs of buying a used motor. I was told that an AWD minivan motor swap was one of the more complicated engine swaps that you can do.

First, you're going to need to do a lot more research - IMO no one will be able to tell you off the top of their head what you will need and how to do it. It took me almost a week (working 8 hours a day) just to swap motors, although that included a transfer case rebuild. Having done it, it would probably take 4 days now, but I have been working on cars for decades and have many tools (inc. cordless impacts & ratchets). You can get an idea of the steps for the 2GR-FE at tsienna.net.

Regarding your questions:

You raise the front of the van and drop the cradle that holds the engine, transmission and drivetrain out the bottom onto a dolly. Then you separate the engine from the transmission and cradle/engine mounts before lifting it out (I used a shop crane).

I was able to hang the AC compressor on the radiator support with a piece of cardboard between the compressor and the radiator.

I unplugged the wiring harness from inside the glovebox and fed the harness and main connector through the firewall as the engine was lowered (or maybe before).

Regarding machining, only you will be able to determine whether you can handle that.

You're going to need a factory service manual showing the rebuild procedure, and from that, you will be able to determine the specialty tools based on the engine damage that needs to be repaired from the above step.

From the very beginning, I labeled every connection I removed (both ends) with numbered tape labels, and reconnected them in reverse order. I had several plastic bins that I used to store parts in order, and just took the bins in reverse order during assembly. I used plastic bags to organize fasteners in the bins for each piece that I removed.

Good luck with your project!

PS: check out the Wikipedia listing for the 3MZ engine: https://en.wikipedia.org/wiki/Toyota_MZ_engine

It lists all the vehicles that the 3MZ was used in. If you could find a low mileage used engine out of one of these vehicles (preferably with rear end damage), all you'd need to do is a swap. The rebuild parts alone look like $600. The risk involved in "getting it right" the first time when doing the swap/rebuild myself would put me off rebuilding an engine. You can look for used engines on LKQOnline.com
 

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Discussion Starter · #4 ·
Let’s start with why you want to overhaul the engine. Then, can it be overhauled properly? Some modern engines have cylinder finishes that cannot be practically restored. I don’t know where you are but retail machines shops have disappeared from many metropolitan areas. Hard to find someone to properly inspect and rebuild cylinder heads. More common these days to find a good used engine.

Sixto
‘04 LE FWD 195K miles
Well the primary reason I am deciding to do the rebuild is just due to normal wear. The engine and car has been sitting unused for about two years now. The valve cover gasket seemed… dried out I guess? It was cracking and broke easily, so I am afraid other gaskets are in similar shape. It was a bit sludgy under the valve cover, and the vehicle was used daily. The belt that drives the alternator and A/C appeared to be in rough shape. There are several signs that point to wear on the exterior of the engine, and I imagine the interior is in similar shape. I think new bearings, rings, and gaskets would only help the engine, and it would also be a great opportunity to do things like the timing belt. I have plenty of time to repair this vehicle, and doing it right and keeping it on the road for as long as possible are the primary goals here.
The original cause of the break-down was exhaust-related FYI, either O2 sensors or catalytic converters.
 

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Discussion Starter · #5 · (Edited)
I've done an engine swap on the 2GR-FE, which I would say is not rebuildable (by me). You can take a look at my posts. The 3MZ is a simpler engine, but I would read up on rebuilding it first. You might be able to find a good used 3MZ engine at LKQ - if they have a yard near you, they will often ship the engine of your choosing for free. Send me a PM if you want the ins and outs of buying a used motor. I was told that an AWD minivan motor swap was one of the more complicated engine swaps that you can do.

First, you're going to need to do a lot more research - IMO no one will be able to tell you off the top of their head what you will need and how to do it. It took me almost a week (working 8 hours a day) just to swap motors, although that included a transfer case rebuild. Having done it, it would probably take 4 days now, but I have been working on cars for decades and have many tools (inc. cordless impacts & ratchets). You can get an idea of the steps for the 2GR-FE at tsienna.net.

Regarding your questions:

You raise the front of the van and drop the cradle that holds the engine, transmission and drivetrain out the bottom onto a dolly. Then you separate the engine from the transmission and cradle/engine mounts before lifting it out (I used a shop crane).

I was able to hang the AC compressor on the radiator support with a piece of cardboard between the compressor and the radiator.

I unplugged the wiring harness from inside the glovebox and fed the harness and main connector through the firewall as the engine was lowered (or maybe before).

Regarding machining, only you will be able to determine whether you can handle that.

You're going to need a factory service manual showing the rebuild procedure, and from that, you will be able to determine the specialty tools based on the engine damage that needs to be repaired from the above step.

From the very beginning, I labeled every connection I removed (both ends) with numbered tape labels, and reconnected them in reverse order. I had several plastic bins that I used to store parts in order, and just took the bins in reverse order during assembly. I used plastic bags to organize fasteners in the bins for each piece that I removed.

Good luck with your project!

PS: check out the Wikipedia listing for the 3MZ engine: https://en.wikipedia.org/wiki/Toyota_MZ_engine

It lists all the vehicles that the 3MZ was used in. If you could find a low mileage used engine out of one of these vehicles (preferably with rear end damage), all you'd need to do is a swap. The rebuild parts alone look like $600. The risk involved in "getting it right" the first time when doing the swap/rebuild myself would put me off rebuilding an engine. You can look for used engines on LKQOnline.com
Good tips there, it sounds quite complex, but educational for sure! Where would you recommend getting a factory service manual from?
 

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Well the primary reason I am deciding to do the rebuild is just due to normal wear. The engine and car has been sitting unused for about two years now. The valve cover gasket seemed… dried out I guess? It was cracking and broke easily, so I am afraid other gaskets are in similar shape. It was a bit sludgy under the valve cover, and the vehicle was used daily. The belt that drives the alternator and A/C appeared to be in rough shape. There are several signs that point to wear on the exterior of the engine, and I imagine the interior is in similar shape. I think new bearings, rings, and gaskets would only help the engine, and it would also be a great opportunity to do things like the timing belt. I have plenty of time to repair this vehicle, and doing it right and keeping it on the road for as long as possible are the primary goals here.
The original cause of the break-down was exhaust-related FYI, either O2 sensors or catalytic converters.
Everything you described is a normal wear and maintenance item. I would get the vehicle back on the road before deciding to take it apart.

The outside of an engine an drivetrain can look terrible but the inside is perfectly fine.

I don't know where you can get a manual, but you might check ebay.

There's a good chance you can just do normal maintenance and have a much more reliable vehicle than if you were to take it apart.
 

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Discussion Starter · #7 ·
Everything you described is a normal wear and maintenance item. I would get the vehicle back on the road before deciding to take it apart.

The outside of an engine an drivetrain can look terrible but the inside is perfectly fine.

I don't know where you can get a manual, but you might check ebay.

There's a good chance you can just do normal maintenance and have a much more reliable vehicle than if you were to take it apart.
You know what, that is probably good advice, and it is probably best to follow your suggestion. Timing belt was done about a year before the breakdown, so that's probably okay, right? Replace a few belts, figure out exhaust, drain/flush fluids, and see what happens?
 

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You know what, that is probably good advice, and it is probably best to follow your suggestion. Timing belt was done about a year before the breakdown, so that's probably okay, right? Replace a few belts, figure out exhaust, drain/flush fluids, and see what happens?
I quite agree with DC_Dave. How many miles on this Sienna?
 
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If you're fairly new to auto repair, you will DEFINITELY want to start with an easier job than semi-rebuilding a FWD Toyota V6 from a mini-van. Pick up a 70s RWD truck or sedan and work on that. You'll be much happier! If you were to go ahead and do the work on your motor plus all the "Might as well since I'm here" jobs, I'd anticipate $10-15k in parts going into the job. Replace the belts, valve cover gaskets, intake gaskets and throttle body gasket, throw in 6 new plugs and the 3 rear coils and button it all back up.

A couple other points... Sitting for two years isn't the best thing for the gas in the tank. You may end up needing to drop the tank, drain out the old gas and refill with fresh. If it had 1/4 tank or less, you might just fill it with fresh gas, just because. All that said, before you do anything else (or even any of the above repairs), check the engine bay for signs of wiring damage from mice/rats. A sitting car is the super-ideal home for countless critters who love nothing better than chewing. After that, charge up the battery with a trickle charger for at least 24 hours. It might not hold a charge, but just keep the charger on it. You should have enough juice to be able to connect a scan tool and find out exactly what the codes are that caused it to be parked. If it was the cat or O2, it should have a code. Once you know the codes and have put the van back together, you can put the charger to "jump start" and try starting the motor. I'd bet it will start right up and run just fine, if all else was done properly. Once you have it started, you can check things like O2 sensor response, fuel trims, etc.
 

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Please keep us updated with your project.
 
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Discussion Starter · #13 ·
Hey there!

So I decided to put in new oxygen sensors, instead of jumping straight to cat replacement. Did the valve cover gaskets and tube seals, filled transmission fluid, remounted everything I took off and put in new oil. Well, after all that, ended up at a crank no-start. Very frustrating, but I know there is great advice here to be found. Let me give a little info on a few common problems to help narrow down my issue.
-Ignition system: We replaced the spark plugs figuring it would be the best move after all the miles on them.I checked and made sure all the coils got plugged in properly.
-Fuel: Gauge indicated fuel was completely empty, which was a relief (and not surprising, in a few weeks it'll be the three-year mark since break down.) Put new fuel in and it is reaching the fuel rails (at least the front one). Checked some ignition and fuel injection/pump fuses and relays, all seem okay.
-Air: Put in new air filter, I don't have any reason to believe the issue is in this system.
-Battery: Healthy 12-12.8 volts, but there could technically still be a problem, with either the battery or terminals, correct?
-Starter: It is engaging fine, and the engine is turning, but could the starter be a bit too weak?
-Cooling System: I did not fill coolant yet, as I didn't want to deal with it if more work was necessary. I didn't plan to run it long without coolant, but I wanted to see if it'd start. Could it be sensing that there isn't coolant, and preventing start-up? I read that it isn't likely, but it could happen in some vehicles.
Could the real problem here be the catalytic converter, could it cause an issue like this? Could the engine be out of time?Thank you!
 

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Do you have a fuel pressure gauge to use on the rail Schrader valve? There should be a healthy spray if you tap the valve pin.

If you suspect clogged cats, remove the upstream O2 sensors which will provide enough exhaust bypass to start the engine.

Is it possible you’re using a key that isn’t authorized by the immobilizer? Is the security light beside the radio solid off when you’re cranking? I don’t know why the immobilizer lets you crank the engine but it does.

Sixto
‘04 LE FWD 196K miles
 

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Discussion Starter · #15 ·
Do you have a fuel pressure gauge to use on the rail Schrader valve? There should be a healthy spray if you tap the valve pin.

If you suspect clogged cats, remove the upstream O2 sensors which will prove enough exhaust bypass to start the engine.

Is it possible you’re using a key that isn’t authorized by the immobilizer? Is the security light beside the radio solid off when you’re cranking? I don’t know why the immobilizer lets you crank the engine but it does.

Sixto
‘04 LE FWD 196K miles
No I don't have that gauge, but I could look into it, probably wouldn't be bad to have. How much do they usually cost (I know it probably depends).
Willing to try removing the sensors, thanks for the idea!
We tried two different keys that we have for it, but that doesn't necessarily mean the immobilizer isn't preventing start-up. I can check the light tonight.... Just to clarify, it will stay solid red when cranking if the immobilizer is the issue? Thanks for the tips, I'll let you know what happens.
 

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Good tips there, it sounds quite complex, but educational for sure! Where would you recommend getting a factory service manual from?
techinfo.toyota.com

$20 for 2 days, $90 for a month, $480 for a year. Has factory service manuals for all Toyota and Lexus vehicles since like 1987. Plus all tech tips and service bulletins.

You can save as much of it as your like for future reference. It’s allowed by the license terms for personal use to do so. You click the print button and you can either actually print or you can use the “print to PDF” built into Windows to save as a PDF.

Only downside is you must print/save each individual section. You can’t just save an entire service manual in one click. I get the two day and save all the sections I need for a particular job I’m working on.
 

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With the level of disassembly you have, it could be anything. However, the first quick-check thing to do is make sure you have the small, inconspicuous wire block at the cowl plugged in. With that unplugged, you'll get no fuel. Also, make sure your battery terminals are clean and tight and that you have a charge in your battery. After that, you'll have to step through the process to see if you have spark and fuel. You'll want to pull a front-bank coil and check for spark and then pull the plug and see if it's wet with fuel. My guess is one of those two will be your failures. I assume you didn't drain the fuel tank and add a couple gallons of fresh gas? If not, you're working with 2 year-old gas that may have gummed up the fuel pump pretty badly and/or clogged the injectors when you tried to start it.
 

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Some pages may be out of order but I think it's complete, and the search function works. It's for 2004-2006 3MZ so the title's not correct for the North American market. I saved each section as a PDF.

It's picky on which browser you use. It works with Brave. Ignore all the "click on this" distractions, which of course you won't have after saving the PDFs.

2004-2007 Toyota Sienna Service Repair Manual + Wiring Diagrams
 

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Discussion Starter · #19 · (Edited)
So I have bittersweet news! I tried Sixto's suggestion and pulled only the front upstream oxygen sensor, and it started! It sounds pretty good, although I cannot run it for long yet as I am still waiting to receive a cooling system part. So since I left the rear upstream sensor in and pulled the front one, does that mean the front catalytic converter is the only clogged one? Should I attempt to clean the cat, or should we just save ourselves the hassle and buy a new one? Last question for now, after running it for about 30-40 seconds, I looked at the tailpipe, and saw that it was letting out a bit of smoke after shutting off the engine. Is this normal considering that it hasn't run for awhile, is there a good chance that it'll clear up with more time running, or should I be concerned? Really looking forward to running this for a bit longer and making sure everything is good to go!
 

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Discussion Starter · #20 ·
With the level of disassembly you have, it could be anything. However, the first quick-check thing to do is make sure you have the small, inconspicuous wire block at the cowl plugged in. With that unplugged, you'll get no fuel. Also, make sure your battery terminals are clean and tight and that you have a charge in your battery. After that, you'll have to step through the process to see if you have spark and fuel. You'll want to pull a front-bank coil and check for spark and then pull the plug and see if it's wet with fuel. My guess is one of those two will be your failures. I assume you didn't drain the fuel tank and add a couple gallons of fresh gas? If not, you're working with 2 year-old gas that may have gummed up the fuel pump pretty badly and/or clogged the injectors when you tried to start it.
Gauge indicated fuel was completely empty, so I just added about 2-3 gallons of fresh gas. Hopefully any traces of old gas will blend in with the new gas and I won't need to worry about it, right?
 
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