Pre-cats??? help widen my knowledge?

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Pre-cats??? help widen my knowledge?

Post by Sparkie » 26/07/09 13:45

What is the problem with them? Why do they mess up the engine??

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Re: Pre-cats??? help widen my knowledge?

Post by Howlin_Mad » 26/07/09 14:02

Taken from here:

http://toyotaownersclub.com/forums/inde ... e=threaded

Whilst the MR2 Roadster has very few flaws as either a fun cheap sports car or as a precision tool to hit the track with, there is one thing that we as a Club feel every owner should be aware of, and that is the pre-catalytic converters (or pre-cats for short). There have been a huge amount of questions on here since the forum began regarding these, and this thread is here to hopefully answer any and all questions that have cropped up about the pre-cats, as well as dispel some myths about them.

*Please note: The Club neither encourages nor advocates the interference with emissions equipment on any motor vehicle, and we take no responsibility for any action taken by any person as a result of reading this article. All text and pictures here are for information purposes only.*

What is a pre-cat?
To put it quite simply, the pre-cats sit before the main catalytic converter in the exhaust system and help to keep the harmful emissions as low as possible for a short period after you start the car up. Of course, there is slightly more to it than that…

The main catalytic converter in the Mk3 works best at converting the harmful compounds contained within the exhaust gas at high temperatures: However, since the engine takes a while to heat up to it's optimum running temperature, there is a time when a great deal of harmful emissions are allowed to simply pass straight through the cat and are dispersed into the air. Toyota obviously wanted to keep these emissions to an absolute minimum to enable the car to be classed as a ULEV (Ultra Low Emissions Vehicle) to allow the Mk3 to be sold in California (they have practically the most stringent rules on car emissions anywhere in the world there!), so between the engine and main cat they placed two pre-cats contained within the main manifold itself. The manifold itself looks like this:

Image

The four headers run into the two chambers containing the pre-cats, and then they're passed onto the main cat to let it do its job. The pre-cats are made from a ceramic material, which whilst excellent at absorbing the noxious gasses at low temperatures, is also highly brittle…


Why are we worried about them?
As stated above, the pre-cats themselves are not the strongest material known to man, and they have been known to break down and enter the engine, causing serious damage to the internals. When this sort of damage has occurred, you are almost certainly looking at needing a new engine.


Woah, wait a minute! How can the pre-cat get back into the engine: Surely the exhaust flow pushes it all out?
True to a certain extent, but here's the clever bit…

The 1ZZ-FE engine (Toyota's designation for the engine inside the MR2 Roadster) is a very clever piece of kit, and arguably its main party piece is the VVTi, or Variable Valve Timing Intelligent. This increases engine response all over the rev range by altering the timing of the cams, allowing for differing amounts of valve overlap in order to give great low-down torque as well as good top-end power. The 1ZZ also uses it's VVT to perform EGR (Exhaust Gas Recirculation) functions without the aid of a specific valve like other cars. Under certain operating conditions (usually steady cruise) the cams are timed to scavenge some exhaust gas back into the cylinders, as a way of reducing the high hydrocarbon emissions that modern petrol engines generate at certain times.

Unfortunately, when you combine this with some very sharp ceramic pre-cat particles, you can imagine what happens: The pre-cats start breaking down, and get dropped into the main cat which then causes excessive pressure, leading to oil blow-by in the engine. When the VVTi kicks in, the pre-cats are sucked back in and scratch and score the cylinder walls, leading to more oil passing by the piston rings and being burnt off without you even realising it. No oil in an engine leads to massive failure as every moving part grinds against metal, and in short you end up with a practically useless engine. When this happens the situation is compounded by the fact that hot oil is now allowed to drip directly onto the pre-cats and break them down even quicker, which in turn allows large chunks to block the main cat even more, which then stops any smaller pre-cat material escaping at all and sucks even more back into the engine to cause even more damage… A vicious circle of the very worst kind.

Some common symptoms of pre-cat failure are extreme oil loss, very noticeable lack of power all the way through the rev range, and horrible noises coming from your engine bay. Essentially, if you've got any of these problems and they are directly related to pre-cat loss, then it's too late. Even the oil warning light won't save you here, as by the time it comes on there's almost zero oil left in the engine anyway.

For more information on how an engine works in general, please click here for a link to HowStuffWorks.com


But I've read elsewhere that the pre-cats themselves are fine, it the piston rings which are the weakness…
This is where we come across a real conundrum, and a question to which no-one has a definitive answer. It's true that on very early MK3s there was a known problem with the piston rings themselves on a 1ZZ, and Toyota issued a technical document to the dealers around the world stating as such. They also changed the design of the piston rings for the facelift version of the Roadster, which became available in 2003.

Now whether it's a case of the piston rings failing, oil dripping onto the pre-cats and breaking them up, or the pre-cats self destructing and taking the piston rings with them, we just don't know. All we do know for certain is that whilst you can't take the piston rings out of the engine, you can remove the pre-cats from the manifold. No pre-cats = Nothing to get sucked back into the engine.


Okay, so the pre-cats are obviously a bad thing, but what can I do about it? Is there any way to tell if they're okay on my car?
There is only one sure way of telling, and that it to remove the entire manifold and check both the top and bottoms of the pre-cats for any signs of damage. This is the only 100% way.


I'm not very mechanically minded, so is there another way? Even if it's not 100%?
Yup, and this is the way 99% of people do it (myself included). It's very simple, and requires nothing more than a 22mm O2 sensor removal socket (Available from here for one, but you can get them at many other places as well, this is just an example), a can of PlusGas or similar penetrating oil (WD40 will do at a push, but it's a lot easier with the PlusGas), and a torch.

Image

The picture above shows the heatshield which covers the manifold itself, and is how your car looks when you open the engine bay. Coming out of either side of the heatshield are the O2 sensors, which need to be removed to see the pre-cats from the top only.

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

2. Spray the PlusGas liberally onto the joint where the O2 sensor meets the manifold. Leave for 10 minutes, then spray it again. You cannot use enough of this stuff, trust me! Don't worry about the steam coming off; it's not doing anything any harm.

3. Being very careful not to burn yourself on the heat shield, use the O2 socket to remove the sensors, Unplug them first from the plastic clip (it's a simple push-tab-and-release connection), and make sure you turn them anti-clockwise. If you have an older vehicle, you may find that these are very stubborn, but do persevere and don't be afraid to give it a little elbow-grease!

4. Pull the sensor out of the socket and place carefully on the floor, away from your feet. You don't really want to tread on it now you've done the hard part, do you?!

5. Take the torch and shine it into the holes. You're looking for a completely solid honeycomb matrix with no cracks or large holes in it, like this:

Image

6. When you've finished checking (and hopefully found that they're still intact), simply screw the O2 sensor back in and nip it up with the socket. Oh, and you may want to plug it back in too.


My pre-cats look fine! I'm safe! *dances*
Not quite: They're still very fragile, and remember you can't see the bottom of the matrix from that angle either. All this means is that your engine is still fine and you're not in any immediate danger of the pre-cats failing.


Oh, okay. So what's the next step then?
The only 100% sure way to protect your engine is total removal of the pre-cats from the manifold. This isn't a particularly hard job, but it is more involved than simply removing the sensors.

Heres how I removed the cats...

Note: Clearly, neither I nor MR2-ROC can condone you ripping lumps of emmisions control equipment out of your car. Its safe to say the the warranty on my manifold at least and probably my main cat as well have now been well and truly voided, so the same will go for you. Basically, if you decide to go down this route as I have, you're on your own... On the plus side, if its not in there, it cant break.

Toolkit required

Trolley Jack
Axle Stands
10mm spanner
10mm socket on 6" extesnion
12mm spanner
12mm socket and various extensions
14mm socket
Hammer
Vice
Long flat bladed screwdriver
High pressure water or air supply
Large vocabulary of swear words

In order to remove the precats, you first have to remove the exhaust manifold from the car, Care should be taken to apply penetrating oil to the various nuts and bolts some time before undoing them

1/ Jack up the rear of the car and place on axle stands.
2/ Remove the splash guard from under the rear bumper
3/ Remove 3 bolts from the forward splash guard to let it hang down.
4/ Remove the 3 14mm nuts that secure the main cat pipe to the manifold

In the engine bay;

5/ Using a 22mm O2 sensor socket, remove the 2 O2 sensors from the manifold.
6/ Remove the 4 bolts securing the manifold upper heat shield
7/ Remove the 2 bolts that secure the lower part of the manifold to the engine block. These are 'behind' the manifold and not readily visible. ! of them is 12mm, the other 14mm.
8/ Remove the 5 nuts securing the manifold to the cylinder head.

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

Decatting the precats...

Actually getting the precats out is pretty simple, here's what mine looked like from above and below before I started, you can see some of the degradation thats taken place in the first photo:

Image

Image

And here are the surgeons tools

Image

Removal is simply a case of attacking the precat matrix with hammer and screwdriver until its broken up into lumps small enough to be able to get them out through the lower exhaust port. The ceramic material gives up very easily, it only takes 1 or 2 taps on the screwdriver to do this...

Image

After digging around for a while you will also expose the glass fibre that surrounds and supports the cat matrix, this has to come out too.

Image

Once out you'll have a big pile of very useless, but rather expensive catalytic material left over. I beleive some places do recycle this stuff to reclaim the precious metal content, so if your now feeling guilty about your effect on the environment, this could be a way to ease your concience

Image

Once its all out, you'll be left with an empty manifiold like this;

Image

You now need to clean it, as there is still an awful lot of potentially damaging dust and particles left inside. I would recommend high pressure water like a jet wash or an airline for this, as an chemical residue from solvent cleaners may have a damaging effect on the O2 sensors.

Once clean and dry, re-building is simple the reverse of the process used to take the manifold out in the first place.

Happily, I've not noticed any increase in noise level from removing these. Performance certainly isnt any worse, and in fact the car may have benefitted in the form of slightly increased torque, but I cant say for sure... What is certain though, is that the pre-cats are going to have a hard time damaging my engine from the workshop bin, and I'm a lot happier now that these ticking time bombs are not a problem...MOT tests wont be a problem, as I still have the main cat in place, which is more than capable of doing the work. I dont have a ULEV car anymore, but I do have one that with a bit of luck will last a bit longer.

This has been re-produced by permission from Ekona (as it is his work) and the committee of the MR2 Roadster's Owners club.. www.mr2roc.org

Just cut and pasted the lot with images for over here but all taken from the Toyota Owners Club and previously MR2ROC.org.

HM
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Re: Pre-cats??? help widen my knowledge?

Post by vanilla.coffee » 26/07/09 16:42

Cheers Kieren. Have stickied this. :th:
They'll take the internet off us if people keep doing this.

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Re: Pre-cats??? help widen my knowledge?

Post by jimi » 26/07/09 19:05

If we can get permission to use this, I could put it in Know Your 2 ;)
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Re: Pre-cats??? help widen my knowledge?

Post by Sparkie » 26/07/09 20:46

Cheers Kiz. :th:

Dont know why but couldn't toyota of just used pre-cats on the us models though.???
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Re: Pre-cats??? help widen my knowledge?

Post by JohnnyC » 26/07/09 21:33

Sparkie wrote:Dont know why but couldn't toyota of just used pre-cats on the us models though.???
Baffles me too, AFAIK the 1ZZ-FE in the Celica doesn't have the pre-cats :confused1:
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Re: Pre-cats??? help widen my knowledge?

Post by kevindean » 16/08/09 10:04

So if I do nothing whats the chance of my engine blowing up ? small, medium or high?

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Re: Pre-cats??? help widen my knowledge?

Post by kentsmudger » 28/08/09 11:32

kevindean wrote:So if I do nothing whats the chance of my engine blowing up ? small, medium or high?
Chances are quite small, but potential cost is very high - A whole new engine!. The prevention above is virtually free AND lets a few more bhp out to play.

No-brainer - Gut the manifold or, even better, get a nice aftermarket one.
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Re: Pre-cats??? help widen my knowledge?

Post by David_F » 09/07/19 11:58

Just wondering what the current thoughts are re emission controls? I know that if they find that if the pre-cats have been removed it is an automatic MOT fail. My car is a very late MR2 mk3 so wondering if it is worth worrying about? I do little mileage anyway.

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Re: Pre-cats??? help widen my knowledge?

Post by ken platt » 31/08/19 11:35

How do you get through MOT with pre cats removed?

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Re: Pre-cats??? help widen my knowledge?

Post by SonicSW20 » 31/08/19 15:46

ken platt wrote:
31/08/19 11:35
How do you get through MOT with pre cars removed?
With ease.

Its impossible to tell they're removed externally, and they are there to improve emissions during engine warm up.

With the engine fully up to temp, your main catalytic converter is doing the heavy lifting and is more than sufficient to keep emissions below limits.
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Re: Pre-cats??? help widen my knowledge?

Post by Elektronic » 01/09/19 9:00

With all the catalytic material removed, what happens with the retained exhaust sensors. Meaning does it affect their operating range......meaning will error messages be flagged ?

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Re: Pre-cats??? help widen my knowledge?

Post by SonicSW20 » 02/09/19 9:15

Elektronic wrote:
01/09/19 9:00
With all the catalytic material removed, what happens with the retained exhaust sensors. Meaning does it affect their operating range......meaning will error messages be flagged ?
Won't make a difference. The two in the manifold are before the precats and control fuelling in closed loop mode. The one after the main cat checks post cat emissions and tells the ECU if the cat is working or not. The precats won't affect this.
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Re: Pre-cats??? help widen my knowledge?

Post by Elektronic » 02/09/19 12:37

Thanks SonicSW20, understood.

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