Pre-cats don't damage engine?!

[Anonymous]

This is going to be a long post, so if you need to use the toilet, go now.   s:wink: :wink: s:wink:   Also, I have almost zero idea how engines work, so some the post may not make strict sense, as I'm just going off memory. Still, is interesting reading...


My car is due for it's first service on Monday, and after reading all the potential problems with regard to the pre-cats I thought that it might be an idea to get the technicians to check mine while it's at Mr T's. So off I trundle to my local dealer (Hill's in Bishops Stortford) where it's booked in.

The main reason I went in there was to ask one of the service guys which bolts needed undoing to allow access to the O2 sensors (I know there are many photos on here, but I prefer to be shown in person: no offence all!) so that I could give them a good oiling over the weekend to try and prevent any of them shearing off, and causing them major headaches. So far, so good.

I spoke to the actual service manager about this (didn't get his name), and was basically advised not to bother having the pre-cats checked, as they don't exist on the MR2. This puzzled me slightly, so I asked him to go into further detail. In a condensed version, this is what he said:


1. There are no pre-cats on the 1ZZ-FE engine; there is only the main CAT material itself.

2.  The honeycomb you can see through the O2 sockets is simply the main CAT which starts at the top of the manifold just after the O2 sockets, and ends down at the 3rd sensor.

3.  If any pre-cat/cat material was broken up in the manifold, there is almost no chance at all that it could get back into the engine, as the valve that let's the exhaust gas to escape is only open for a split-second, and is pushed out with such force that there is almost zero chance of any back-suction.

4.  The problem's that some owners have found with their engines blowing up is NOT caused by anything to do with the pre-cats: The reason for the increased oil consumption followed by the engine going to that great scrapyard in the sky is because the pre-facelift engines had a problem with the pistons working so hard that they started boring out the cylinders themselves, eventually leading to the oil problem and the engine breaking. This is the only known problem with the 1ZZ-FE engine, and was addressed in the facelift model so it shouldn't happen again.

5. The only time it's worth checking the pre-cats/cat is just before the warranty expires, as that's the only time they'll do any investigation into any possible engine damage. Checking the pre-cats/CAT regularly isn't worth it, as the risk of snapping a thread/O2 sensor itself far outweighs any benefit.

6.  The other reason they don't recommend the checking of the CAT is that even if there is evidence of damage to them, how far back do they go to investigate? Do they strip the entire engine block just on the off chance that there is any damage? That's a lot of labour time just for a 'what if?' scenario.



Plenty of talking points there, I think you'll agree. Let me state for the record now that the guy was very helpful, and more than willing to spend as long with me as necessary to explain everything in as much detail as I wanted, and even went to the lengths of going into the workshop and coming out with the manifold from a Previa just to explain things a bit clearer. I have no doubt he was trying to be as helpful as possible. He was also quick to order a couple of new wheels for my '2 as they are blistering, without even wanting to inspect the car.   s:D s:D  

Regardless, there are a couple of other things I noticed from my visit. First, when I said 'pre-cat' to him, he looked genuinely baffled. After 5 minutes of explaining, I gave up and just pointed him to a few of the pictures recently posted in this forum; that was when the whole 'That's not a pre-cat, that's just the main CAT itself" thing came about.

Secondly, just how much of a worry ARE the pre-cats? If there is no chance of them getting sucked into the engine, then why are we gutting them? If Toyota were aware of a problem with the 1ZZ (as in the 'piston boring out the cylinder' scenario), and have corrected it, why should we still be concerned? Ok, so that last point is moot to all pre-facelift owners, but still...


Have I been fobbed off here, or does the guy actually have a point?

[GSB]

The man speaketh from his arse...

1. There are no pre-cats on the 1ZZ-FE engine; there is only the main CAT material itself.

Yes there are. And they are clearly detailed within the official Toyota workshop manuals

2. The honeycomb you can see through the O2 sockets is simply the main CAT which starts at the top of the manifold just after the O2 sockets, and ends down at the 3rd sensor.

No it isnt... See my photos in the precat removal post for proof

3. If any pre-cat/cat material was broken up in the manifold, there is almost no chance at all that it could get back into the engine, as the valve that let's the exhaust gas to escape is only open for a split-second, and is pushed out with such force that there is almost zero chance of any back-suction.

Cobblers... Gas can go in as well as out under certain closed throttle conditions. The thing you need to search for is "valve overlap"

4. The problem's that some owners have found with their engines blowing up is NOT caused by anything to do with the pre-cats: The reason for the increased oil consumption followed by the engine going to that great scrapyard in the sky is because the pre-facelift engines had a problem with the pistons working so hard that they started boring out the cylinders themselves, eventually leading to the oil problem and the engine breaking. This is the only known problem with the 1ZZ-FE engine, and was addressed in the facelift model so it shouldn't happen again.

Aside from the obvious question of do the pistons in a later engine do less work? He has a point regarding oil blowing past the rings. Toyota have updated the engine in this area.

5. The only time it's worth checking the pre-cats/cat is just before the warranty expires, as that's the only time they'll do any investigation into any possible engine damage. Checking the pre-cats/CAT regularly isn't worth it, as the risk of snapping a thread/O2 sensor itself far outweighs any benefit.

Thats the only time its worth checking if you have to foot the labour bill for your customers concerns. If its your car, its worth checking a little more often...

[SteveJ]

There are cases of post-facelift engines having this problem, so that's one point that he's got wrong for a start.

He also doesnt seem to know what happens when the VVTi kicks in. Basically the exhaust and inlet valves are open at the same time in order to allow more of the exhaust gasses to escape. There are however times when the piston starts to descend before the exhaust valve closes. This means that gas CAN be drawn back into the cylinder from the exhaust tract, and with the PRE cat being so close to the top of the manifold if anything were to come loose (as we have allready proven on multiple occasions it can do) it would be sucked back into the engine. Given that the ceramic material is extremely abrasive even a tiny amount in the cylinder bore will cause a scratch leading to increased oil consumption.

[heathstimpson]

Steve maybe you should get a job at Toyota mate  s:wink: :wink: s:wink:  U know what your talking about  s:wink: :wink: s:wink:

[mph]

Semantics eh?   s:roll: :roll: s:roll:  

I'll tackle these in order:

1. & 2.

There are three CAT 'cells' on the Roadster - two in the manifold and a larger third. They are made of the same construction.

We refer to the two cells within the manifold as pre-CATs. For *current* emissions they are not needed, the third cell is large enough to handle the exhaust output. The two smaller cells are deliberately placed as close as possible the engine in order for them to heat quickly from cold (the catalytic process requires a bit of temperature!) and this is to meet the Euro 2005 emissions standard which tests engine emissions from cold.

3.

During over-run during certain cam timings the exhaust valve is open during start the intake stroke. Combined with the exhaust gas pressure wave 'stuff' (which is way beyond my understand) it's quite feasible for 'debris' to be sucked in from the exhaust side. This is all beyond me to prove, and unfortunately I'm under non-disclosure with my source of information.

4.

There is a documented problem with the oil scraper rings on the original spec engine. I am certain this has caused engine failures, but this does not in itself otherwise disprove the 'pre-CAT problem'.

5.

From his point of this this is quite valid. Equally, 'we' would recommend otherwise.

6.

Understandable. I personally viewpoint is that if they check and document (always get everything in writing!), and later have an engine failure (ie, post warranty), coupled with further degradation of the CAT, you could make a case that the CAT was the failure point.


Overall, while we may or may not agree with his views, I'm glad you have a dealer that is taking a customer service seriously and dealing with your queries in detail.

[Anonymous]

Change the mechanician!  s:lol: :lol: s:lol:

[Anonymous]

if that is the case then why was the left hand chamber of my 'so called non-existent pre-cat' totally empty of any honeycomb substance when i had my engine replaced and the majority of what was left was either in the engine block or the main cat.
even the mechanic who fixed my car said that the was no reason for them to be there except for the low emissions and he recomended that they be removed so they dont break down again and get sucked back into the engine via the vvti unit.
shame i didnt act more on stevej's diagnostic instead of a toyota trained tech, might have saved myself £2000.

[markiii]

I think it's all been said, but basically good intentioned and friendlty as he may have been the man is talking out of his arse.


If you doubt it, net time your there ask him to sjhow you where in the worksop manual it says thats it'sall one cat and that the precats don't exist.

I can even give yiou the relevant page numbers to quote him.

Failing that collar me at JAE as I wil bring teh workshop manuals with me,.

[Anonymous]

Thanks for all the replies people: I was never quite sure if he was wrong or not, as I'm not that mechanically minded, but I think I'm pretty straight on it now.

I know that this is a job that a lot of people have done (and do) to their cars themselves, but I'm still not too keen (despite the excellent guides!   s:oops: :oops: s:oops:  ), so while the car is in for it's service, do you think that I should insist on the pre-cats being checked (bearing in mind the service managers attitude towards the problem; not that I'm suggesting all the guys in the department are the same)? Or should I use a different dealer (How's the one in Chelmsford?), or just wait until the car is almost at the end of warranty? After all, that's the only time I'll worry because it'll get expensive after then!   s:lol: :lol: s:lol:

[Bongo]

While my car was in for warranty work i tried to get them to check the pre-cats as it's coming to the end of it's warranty.

I'd forgotten to mention this when booking the car in originally so i went in and added it to the list of things to be done, unfortunately neither of the 2 people i usually dealt with were there. Anyway i explained what i wanted done as best as i could - it turns out the bloke who worked on the car checked the performance of the main cat once it had warmed up   s:lol: :lol: s:lol:  

At least they did the work, even if it wasn't what i wanted. (NB: i read the description of the work to be done (afterwards) and it wasn't clear, so no blame on the mechanic).


Moral of the story: make sure the guy booking the car in understands exactly what you want done.

[Anonymous]

Valve overlap, my friend.  Part of that environmentally sound philospophy, eating one's own waste.  Sport Compact Car did an investigation into certain NISSAN engine failures... very similar to the situation with our cars.  They proposed that valve overlap in the NISSAN engine was an integral part of their self-destruct problems.

Precat material is very hard ceramic and it makes perfect sense to me that it could get into the cylinders.  Sloppy bores is another thing I believe.  How about warped rings due to lean burning?  I believe that one, too.  I heard that from a Honda mechanic who sounded like he knew his stuff.  Precat failure followed by kerpoof is a sad tale that is repeated over and over.  Precat failure + valve overlap seems to be what "turbocharges" the destruction process... and may be THE or ONE OF THE things that kicks it off in the first place.  I'm a pessimist.  I think there were and maybe still are multiple things wrong with the design.  There will be a 2ZZ in my car someday, maybe even a Lotus 2ZZ.

[Tem]

1. There are no pre-cats on the 1ZZ-FE engine; there is only the main CAT material itself.

2.  The honeycomb you can see through the O2 sockets is simply the main CAT which starts at the top of the manifold just after the O2 sockets, and ends down at the 3rd sensor.

I must be a bit tired...couldn't stop laughing after these first two  s:lol: :lol: s:lol:  

Reminds me of the Star Wars Jedi powers...  s:twisted: :twisted: s:twisted:

[Anonymous]

Pre-cats don't damage engine?!

Well I for sure will soon find out...

Check out Toyota's official "MR2 New Car Features" in which they explain very clearly how the VVT-i system operates. (p.41-44.) [You can order this excellent book at any Toyota dealer for 10 quid, juste quote: Pub. No. NCF180E]

Well, here is just a quote from the table of operation states: "At medium load" - "Increasing overlap to increase internal EGR for pumping loss elimination" - "Better fuel economy. Improved emission control"

In fact, overlap (for internal EGR) takes place at just about all operating states except during idling; at low temperatures; and upon starting/stopping the engine.

So in effect, this is official Toyota evidence that ceramic particles from a collapsing pre-cat (or warm-up CAT or front CAT - whatever Toyota wants to call them) can enter the cylinders; especially if the main cat is blocked as the difference in pressure between exhaust and intake will be massive.

I'm starting to wonder if Toyota isn't using the MR2 Roadster as a "test bed" for this new technology... A relatively low production car (to minimise the risk of damaging their reputation if this car gets a bad name on reliability); a type of car that will be driven "hard" (not like your average Yaris driven by mum).

My wife being in New Product Development for a very large company, I have heard of cases similar to this. After all, the Toyota engineers who designed the engine and the pre-cats must be completely aware of the potential risk/problems. If they feel the technology isn't 100% safe for say a "normal lifespan" (e.g. 100k miles), they will not use them on the mass produced models. Not until the technology has been made reliable enough.

Well, all I can do now is wait until the engine gets checked out... But I'm a wee bit less optimistic now.   s:( s:(

[Anonymous]

I said the exact same thing about it possibly being a "test bed".  Why put more environmentally friendly stuff on a sportcar (OK, "sporty car")?  Lower production means lower cost to fix if it has problems.

[Anonymous]

Beanie, I think you are right about the spyder being a test bed for new emissions technology. If only a few people make a fuss about blown engines then Toyota isn't really hurt by that. Time will tell. Look and see if precats using this type of material are being used on new models. I'll bet not!! I think that hybrid....followed by totally electric is the way things will be going. We are a dying breed.....

[Anonymous]

Not sure about this, but you may be able to adjust valve overlap with Power FC if you change the VVT (Variable Valve Timing) map.  Someone on SC (I think it was LittleRocket) said that one of them (exhaust I think) has fixed timing?  I forget.  Messing with VVT is not something I feel up to.

[Anonymous]

A very interesting thread. Can I ask what oil consumption rates owners of pre-facelift models get? My 2 is just over 3 years old and has pretty low mileage, 9,500 when I bought it last September, and about 13-14,000 now. Having had 2 Toyotas previously, ( my Celica, a K reg, and my wifes new Yaris) both of which used hardly any oil between changes, I was very surprised to have to put nearly a litre in the other day to bring it back up to the full mark.  s:? :? s:?   Is this normal?

[SteveJ]

I said the exact same thing about it possibly being a "test bed".  Why put more environmentally friendly stuff on a sportcar (OK, "sporty car")?  Lower production means lower cost to fix if it has problems.

IMHO the reason for the additional "environmentally friendly stuff" is to allow the vehicle to be sold into the US market (particularly California) due to the tighter emissions controls.

The problems that are showing up are because the car is such a low volume seller the cost of the parts needs to be kept low - hence the use of cheap-shit ceramic cats instead of the metal ones that should have been used that close to the engine.

[kanujunkie]

The problems that are showing up are because the car is such a low volume seller the cost of the parts needs to be kept low - hence the use of cheap-s**t ceramic cats instead of the metal ones that should have been used that close to the engine.

an interesting and if somewhat contraversial theory, remember that in a lot of engineering items nowadays that involve heat, the ceramic items are the best and normally only open to the elite products because of the costs involved in manufactuer and R&D.

Ceramics normally dissipate the heat a lot better than metal and at that distance where they are in the hottest area by not absorbing it in the first place. The problem in my mind is the metal case, which is expanding and contracting at a resonably fast rate, whilst the ceramic interior isn't. When the metal is expanded outwards, ie its f-ing hot, is the ceramic core becoming loose? and likewise once its cooled is it compressing the ceramic core?

[Comer]

So off I trundle to my local dealer (Hill's in Bishops Stortford) where it's booked in.

I was going to put my car in for servicing there on Fri / Sat but once again I ask myself why bother  s:shock: :shock: s:shock:  

The main reason I went in there was to ask one of the service guys which bolts needed undoing to allow access to the O2 sensors (I know there are many photos on here, but I prefer to be shown in person: no offence all!)

It is very easy (3 mins max) and if you come to JAE I'm sure it will be repeated many times.  There's no number of bolts apart from the acutal bolt holding each sensor.  The only thing you need to 'worry' about is disconnecting each lead and having an o2 socket but each time someone buys one on here they get cheaper so have a search for the latest post.

I spoke to the actual service manager about this (didn't get his name), and was basically advised not to bother having the pre-cats checked, as they don't exist on the MR2.

Was he a fairly big bloke? because I think I spoke to him about changing my rusting wheel nuts and he was friendly enough.  But I do get the impression even from ordering hardtop fixing parts, that because the MR2 is not serviced / fixed as much as say the Yaris, that you won't find anyone with sufficient knowledge unless they have a manual in their hands.  

It's a shame he didn't have a manual to illustrate what he meant because he may have changed his views pretty quickly  s:shock: :shock: s:shock:

My first reply to him would have been so you say only one cat but there is 3 sensors, WHY?

[markiii]

I beleive thats why the ceraminc sits ina glassfibre cocoon to allow for expansion

[GSB]

The problems that are showing up are because the car is such a low volume seller the cost of the parts needs to be kept low - hence the use of cheap-s**t ceramic cats instead of the metal ones that should have been used that close to the engine.

an interesting and if somewhat contraversial theory, remember that in a lot of engineering items nowadays that involve heat, the ceramic items are the best and normally only open to the elite products because of the costs involved in manufactuer and R&D.

Ceramics normally dissipate the heat a lot better than metal and at that distance where they are in the hottest area by not absorbing it in the first place. The problem in my mind is the metal case, which is expanding and contracting at a resonably fast rate, whilst the ceramic interior isn't. When the metal is expanded outwards, ie its f-ing hot, is the ceramic core becoming loose? and likewise once its cooled is it compressing the ceramic core?

I dont think thats the problem... The cat is suspended within the metal case by a jacket of glass-fibre matting. This jacket is able to absorb any differential expansion and prevent damage to the cats. Also the extrnal edge of the cat matrix is particularly thick in comparison to its soft centre, making it quite strong.

The problem I think is the exhaust gasses themselves. Look closely and you will notice that the top of the precat is subjected to high velocity gas pulses coming from alternate directions. A normal cat further downstream only has to deal with gasses coming straight into the matrix at a more favorable angle, usually flowing straight into it. The rpecats though have the gas flow coming in from an angle, first one way with one cylinder, then from the opposite direction with the other cylinder. The forces that this imprts to the very thin and vrittel walls of the cat material is, I believe, what causes the failure.

[Anonymous]

The forces that this imprts to the very thin and vrittel walls of the cat material is, I believe, what causes the failure.

then surely every '2 should suffer from failing precats and not just a small percentage?

[kanujunkie]

I beleive thats why the ceraminc sits ina glassfibre cocoon to allow for expansion

and that shoots my idea down in flames then!  s:? :? s:?

[Anonymous]

I get the impression from inspecting different photos of pre-cats that the earlier models ('00-'01) have thinner walls (or perhaps less catalytic material coated on the walls) than later models. The holes on later models look more "round" and earlier models more "square".

Maybe it's just a photographic effect due to focus/lighting/angle of incidence; but I think it's mainly earlier models that have suffered from this problem.