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PreCat Removal

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#1 OldMan



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Posted 01 December 2010 - 11:54 AM

This is an extensively revised, rewritten, & enhanced version of an article by Ekona. The original document was excessivly chatty & verbose, and contained duscussions either now out-of-date or not applicable to Spyder owners in the United States.The original document is available at the Midship Runabout website.

Pre-2003 Spyders are known to have issues with pre-catalytic (pre-cat) failure. 2003 & later cars do not seem to be affected. When the pre-cats fail they take the engine with them. The cause of failure is not known for sure, but the remedy is: The pre-cats should be removed. No service facility in the United States may alter the emissions system legally, so pre-cat removal is pretty much a do-it-yourself proposition.

The least expensive way to remove the pre-cats is to "gut" the existing stock manifold. An alternative to gutting the pre-cats is to replace the stock manifold with an after-market unit. The Che "header" is a popular choice, but replacement manifolds are available from other sources such as eBay, MonkeyWrench Racing, The Performance Division, PPE Engineering, Zero_Exhausts (pricy), and TRD (very pricy). In most cases, these after-market units offer little performance gain over a gutted stock manifold. Some after-market replacement manifolds come with a low-quality engine-to-manifold gasket. Don't use it. Use the proper Toyota gasket: Part# 17173-0D020.

There will be little, if any, increase in exhaust noise due to removing the pre-cats, and engine performance is essentially unchanged. One cannot say with 100% certainty that your car will pass Emissions Testing after pre-cat removal, but almost all treated cars pass. As long as the engine is at operating temperature during the test, the stock main cat is more than capable of filtering out any nasties from the exhaust gas. The pre-cats were installed to deal with emissions while the engine warms up so that the Spyder could be sold as an Ultra-Low Emissions Vehicle.

There is another way to remove the pre-cats, but it does get considerably more expensive…Turbo conversion. The Hass, C2, PE, and Top Secret kits do not include any pre-cats in their design. The TTE kit does employ pre-cats, but it is made of metal and is very resistant to breaking. Obviously turbo charging isn’t a solution for most people due to the cost involved, but it’s a fair point to mention.

Parts you will need:
One (1) Engine to Manifold Gasket: Part# 17173-0D020
Two (2) Manifold to Downpipe Gaskets: Part# 90080-43036

Parts that shouldn't be reused (even though some do):
Three (3) Manifold to Downpipe Nuts: Part# 90080-17187
Five (5) Engine to Manifold Nuts: Part# 90179-08228

Parts you won't need unless something goes wrong:
Five (5) Engine to Manifold Studs: Part# 90126-08037
Three (3) Manifold to Downpipe Studs: Part# 90116-10146

The following is a complete set of instructions for removing the pre-cats, based closely upon those originally written by Grant (GSB). Do it his way and you won’t go far wrong. Many thanks to Grant (and Ekona) for producing such a wonderful and complete guide.

In order to remove the pre-cats, you first have to remove the exhaust manifold from the car. You should apply penetrating oil (PB Blaster, Liquid Wrench, etc) to the various nuts & bolts some time before undoing them. Multiple applications over a period of days isn't a bad idea.

Tools you will need:
Floor Jack
Jack Stands
10mm wrench
10mm socket on 6" extesnion
12mm wrench
12mm socket and various extensions
14mm socket

* Use six-point (as opposed to 12-point) sockets & wrenches to avoid rounding-off the nuts.
O2 Sensor Socket (a long one)
Long flat-bladed screwdriver
High pressure water or air supply

This guide is focused on the technique for removing the pre-cat material from the stock exhaust manifold.
More detailed instructions on disassembly can be found here.

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The photo above shows the heatshield which covers the manifold. This is how your car looks when you open the engine lid. Protruding from either side of the heatshield are the O2 sensors (indicated by red arrows), which must be removed before the heatshield. The green arrows indicate the heatshield bolts to be removed.

1. Get the engine nice and warm first, it’ll make this job a lot easier!

2. Spray penetrating oil liberally onto the joint where the O2 sensor meets the manifold. Also spray it on the heatshield bolts. Leave for 10 minutes, then spray it again. You cannot use too much of this stuff. Don’t worry about the smoke coming off; it won't harm anything.

3. Unplug the O2 sensors from the wiring harness (it’s a simple push-tab-and-release connection). Being very careful not to burn yourself, use a long O2 socket to remove the sensors. Make sure you turn them counter-clockwise. They can be stubborn: be persistant.

4. Store each O2 sensor in a safe place. O2 sensors are delicate, so treat them gently. Take care to avoid getting foreign material on them.

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Heatshield removed, revealing the stock manifold.

The stock manifold has two cylindrical canisters, each fed by two of the exhaust pipes.
After-market manifolds do not have the canisters.
If your manifold looks similar to this one,
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a previous owner has already removed the pre-cats.
Put everything back together and drive on!

If your manifold has the canisters, peek into the holes where the O2 sensors were. A flashlight helps.
If you don't see anything in there, and your car is running well, a previous owner has already removed the pre-cats. Put everything back together and drive on.
If you see a gray/white honey-comb "barrier" on only one side, start saving for a replacement engine & main cat, and proceed with the next steps.
If you see a gray/white honey-comb "barrier" on both sides, your pre-cats are still in place: Proceed with the next steps.

5. Jack up the rear of the car and place on jack stands.

6. Remove the plastic splash guards (if present) from under the car. You may opt to forgo reinstalling these pieces later, as they are mostly appearance items.

7. Allow the exhaust system to cool until you can comfortably touch it.

From under the car;
8. Remove the three 14mm nuts that secure the main cat pipe (downpipe) to the manifold. Penetrating oil is useful here: These "Three Amigos" can be very difficult to remove.

9. Remove the 2 bolts that secure the lower part of the manifold to the braces attached to the engine. These are ‘behind’ the manifold and not easily visible from above. One of them is 12mm, the other is 14mm.
If you're installing an after-market manifold, loosen the bolts that attach the brackets to the engine block. It will make installation a little easier.

In the engine bay;
10. Remove the 5 nuts securing the manifold to the cylinder head. Here again, penetrating oil is quite useful.

The manifold can now be lifted out through the top of the engine bay.

Here’s what the pre-cats look like:
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^ from above ^
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^ and below. ^

And here are the surgeon's tools:
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Pre-cat removal is simply a matter of attacking the pre-cat matrix with hammer & screwdriver until its broken into lumps small enough to pass through the lower exhaust port. The ceramic material crumbles very easily. It only takes 1 or 2 taps on the screwdriver to do this…
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After digging around for a while you will expose the glass fibre that surrounds and supports the cat matrix. This has to come out too.
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When finished, you’ll have a big pile of useless, but rather expensive catalytic material left over. There are places that recycle this stuff to reclaim the precious metal content, so if you're feeling guilty about your effect on the environment, this could be a way to ease your conscience.
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You’ll be left with an empty manifiold like this:
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You now need to clean it because there is still a lot of potentially damaging dust & particles left inside. I recommend a high-pressure water spray like those found at do-it-yourself car-washes. Any chemical residue from solvent cleaners or penetrating oil may have a damaging effect on the O2 sensors.

Once clean and dry, reinstallation is simply the reverse of the process used to remove the manifold. Use new gaskets on both ends of the manifold. Apply liberal amounts of anti-sieze compound to all threaded fasteners. Be careful to put anti-sieze on ONLY the threads of the O2 sensor: If it gets anywhere else, it could foul the sensor; requiring it to be replaced. Install all nuts loosely. Tighten them finger-tight, wiggling (shaking) the manifold as you go. Finally tighten all nuts to the proper torque in stages.
Manifold to Head: 27 ft-lbf
Downpipe to Manifold: 46 ft-lbf
Manifold to EngineBrace: 27 ft-lbf
O2 Sensor: 32 ft-lbf

If something goes wrong and you have to replace a stud, you'll need a star socket for installing the new one. Star Socket sets are available from Harbor Freight, among other places.

This information should be heeded by every MR2 Spyder owner, regardless of year or mileage. Either Ekona or Grant (the original article is unclear on this point, but presumably Ekona) reports that the pre-cats on their 2003 car had started to disintegrate after only 15K miles, showing that it’s not just high mileage cars that can suffer pre-cat breakdown. Pre-cat failure is far more common in pre-2003 cars, but that doesn’t mean that you're immune if you have a later car: Remember, as soon as the pre-cats begin to fail your engine is more-or-less ruined, and by the time you notice the symptoms it’s usually too late…
Cars that have suffered pre-cat failure must have their engines replaced. Rebuilding the ruined engine is not cost-effective. The main catalytic converter must also be replaced because it will be plugged-up with the remnants of the disintegrated pre-cats.

Article and photo submissions are property of the contributing authors (Ekona & Grant, whoever they are).
Disclaimer: This documentation in no way replaces the Toyota MR2 Repair Manuals. It is only to provide supplementary information to MR2 Spyder owners. The authors may not be held responsible for any injury or damages that may occur as the result of practicing any of the methods or procedures described in this document.

If your Porsche is not anhydrous, there IS a substitute.

#2 OldMan



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Posted 01 December 2010 - 12:07 PM

DateLine Dec 04, 2010

mikecobra427 actually caught his pre-cats in the act of disintegrating!
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Full story here

If your Porsche is not anhydrous, there IS a substitute.

#3 Dogbreath


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Posted 01 December 2010 - 01:16 PM

I'll add 3 comments.

1. You will need a breaker bar for the 3 amigos.
2. You may need an abundance of epithets for the 3 amigos.
3. When re-assembling exhaust nuts/bolts always coat them with high temp RTV. You will thank yourself if you ever need to undo them in the future.
This post is guaranteed to be 100% content free.

#4 Anderson


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Posted 01 December 2010 - 01:39 PM

Stuck and locked as there should not be any more input or information on this as it is as complete as I have seen(not discounting anyone else's attempts)...

I have reopened per OldMan's request to have access to edit...

Lets keep this chatter free so that the editing process can be smooth. I will re-lock once he has signaled me that he is all wrapped up. Thanks for your patience...

Annnd we are done! Big thank you to OldMan for compiling all the necessary components and information to convey a clear and concise message for a PreCat removal process!

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