Pre-cats: The Official MR2-ROC Information Thread

[roger]

Yes, the sensors SHOULD be OK, but if they've been spurted with oil, you never quite know. If you can get them replaced under warranty go for it. And as Craig says, replace cat as well.

You have the chances of both messing it up all again or getting yourself a blockage so performance is lost after about 4K revs. Air MIGHT clean it out, but again its a risk.

[scipio]

The car only has 71K km's on her....I feel a good blow with compressed air in the opposite direction must dislodge any particles stuck there. My insurance won't pay çause it's "wear and tear"! I will clean the main cat and leave the sensors as they are. I am also having the rings and big-ends replaced. The cylinder walls look very good with no scoring and the original honing marks still clearly visible. She burnt an exhaust valve....reading up as much as possible about this but all roads seem to lead to pre-cats.

[benji89]

When one of mine fell through, I took the cat out and tried fir a few hours to unblock it, using a needle and compressed air. It freed up the airflow, but didn't cure it. When I took it to an exhaust specialist, they told me that the cat was nackered, so I had a sports cat as a replacement. Was a great deal cheaper than toyotas cat quote.

[scipio]

Just submitted a vote on "post pre-cat gutting - problems with 02 sensors" ...unfortunately had to vote ÿes".
Got the baby back from the Toyota dealer this afternoon. The mechanic said that she was idling fast, about 1500rpm. He suggested that it may be the gutting of the pre-cats that was causing the fast idle.
I noticed when she cooled down that the idle alternated between 700 and 1500rpm...when hot it goes to 1500 and when cold it idles normally...for a while!
To recap: I burnt a valve when a piece of precat lodged itself in the valve seat....when they had the motor in pieces I felt they may as well replace the big and small ends together with the piston rings and valves. She had been using oil since I bought her at 44k km and the valve burnt at 71k km's. I never noticed a difference in performance and oil usage never increased but she was using more than two pints per 1000km's. I had topped up the oil the day before the valve incident.
FYI the cost was about 950 pounds, R11500.00 (Just found out my pc has no "pound" key!...is that possible?!)
Has anyone have any ideas on the idling question?
I have seen a thread where someone suggested taking the main cat sensor wire and connecting it to one of the precat sensors...can anyone shed light on this?

[roger]

Just submitted a vote on "post pre-cat gutting - problems with 02 sensors" ...unfortunately had to vote ÿes".
Got the baby back from the Toyota dealer this afternoon. The mechanic said that she was idling fast, about 1500rpm. He suggested that it may be the gutting of the pre-cats that was causing the fast idle.
I noticed when she cooled down that the idle alternated between 700 and 1500rpm...when hot it goes to 1500 and when cold it idles normally...for a while!
To recap: I burnt a valve when a piece of precat lodged itself in the valve seat....when they had the motor in pieces I felt they may as well replace the big and small ends together with the piston rings and valves. She had been using oil since I bought her at 34k km and the valve burnt at 71k km's. I never noticed a difference in performance and oil usage never increased but she was using at least two pints per 1000km's. I had topped up the oil the day before the valve incident.
FYI the cost was about 950 pounds, R11500.00 (Just found out my pc has no "pound" key!...is that possible?!)
Has anyone have any ideas on the idling question?
I have seen a thread where someone suggested taking the main cat sensor wire and connecting it to one of the precat sensors...can anyone shed light on this?

Precat gutting made no difference to my idling, but a couple of jobs first time round..... Clean the MAF and reset the ECU (battery off for 30 mins). The dealer should probably have done both, but you're never sure.

[scipio]

Precat gutting made no difference to my idling, but a couple of jobs first time round..... Clean the MAF and reset the ECU (battery off for 30 mins). The dealer should probably have done both, but you're never sure.

I cleaned the MAF sensor a couple of weeks ago and the car definitely had it's battery out for a couple of days.....but will try both suggestions again....thanks for that Roger.

[manchestermatt1986]

Started the job todaqy of taking out old precat and fitting with a decat manifold. To make life easier i took off the exhaust and went to it from the back. Exhaust came off fine as i only fitted it 6months ago. The the problems started!!

Three nuts came out fine from the heatshield then the third rounded   s:evil: :evil: s:evil:   i tried vice grips, then chiselling so i could try a flat head, then filed the sides to get a grip with a spanner, then hammerd on a smaller socket and just basically buctehered it. In the end i just angle grinded the little  sfuck fuck sfuck er off.   s:twisted: :twisted: s:twisted:  

Any how, the precats look in tact   s:D s:D  .

Now, i the bolts holding the cat to the precat are stiffer than michael jackson in a nursery. and the five holding the top of the precats to the engine look like itd be easier to ice skate uphill.

I soaked all the bolts the night before and for a few hours in the morning, and it did diddly squat.

Anyone got any secret method to getting these buggers off?

The only thing i didnt do was raise the temp of the car before starting as i took the exhaust off thinking i was being clever and making life easier

[manchestermatt1986]

Just a word of warning to anyone who is going to do there precats themselves or repclace manifold. As a follow up to my above post, in total i had to chisel off 5 nuts. they were all rusted on and with the car being a 2000 i could blatenly see these had never been moved since fitment. The three nuts holding the cat to the precat are very stubborn, without a ramp it near impossible to get them off with the car just up on stands, two had to be chisseld off and the other needed some serious weight behind it to start turning. I found that when i took the heat shields off and lifted part of the cat up past the block i could bring the precats towards me and get to the nuts from ontop. Was much easier from then on.

[redcarblackhorse]

Hi All

Some really interesting reading. I have a 99 Jap import with about 70k miles and naturally worried now.
Can anyone recommend a good replacement manifold and where to get one? Want to change it before its too late.

Thanks

[Anonymous]

 m http://www.ebay.co.uk/itm/ws/eBayISAPI. ... 0410646673 m

[redcarblackhorse]

Thanks Richard,

Have you got this fitted to your car?

[swinglow81]

Hi everyone I bought a 99 mr-s a couple months back and to get through mot had a new head gasket done its only done 58k tho. I ran it in for over a thousand miles at 3000 rpm but lately noticed a noise coming from engine louder than normal and when I hit a incline in dies out and stugles to do 50-60 could this be the pre cats as reading all this has got me highly worried and if so does it sound like its to late for me??

[Maverikk]

Hey guys, I don't know much about cars (fair to say, I am "mechanically retarded"), but am planning on having a cat-free manifold put in very soon. I've done some basic research on this site already, but if someone can take a look at this one

 m http://www.ebay.co.uk/itm/TOYOTA-MR2-RO ... 483cb398aa m

and confirm whether or not it would suffice, and comment on the quality of the product if possible, that would be much appreciated!

Matt

[Jandaw]

Looks exactly like mine. It doesn't appear to have the heat shield lugs but the shields are not essential.
You can always wrap the manifold later if you wish.

It won't have a fixing to help support the manifold buy it will only weigh 4.5 kg compared with the original at 10kg.
I've made a bottom bracket but it was tedious to say the least.

You can use the bottom gasket but make sure you use a Toyota manifold to head gasket. Do not use the one supplied with the manifold.

I'm quite happy with mine, don't believe the blurb about extra power, just be glad to be rid of the precats.

Watch the tyres/wheels and keep reading the forum.

You won't go far wrong.

Welcome by the way!!

[Maverikk]

It won't have a fixing to help support the manifold buy it will only weigh 4.5 kg compared with the original at 10kg.
I've made a bottom bracket but it was tedious to say the least.

Am I correct in assuming that this fixing is an absolute necessity with the new manifold, despite it being lighter? And is that something any mechanic/garage worth their salt will be able to sort out?

[spit]

I'd say its necessary. Unsupported, it'll still work, but on an aftermarket manifold this isn't so much about supporting the weight. Its more about keeping stress off the pipework by having both flanges firmly attached to the engine block.

[Maverikk]

Ok, I see. Thanks for the advice.

[Maverikk]

Does anybody know what size dimensions the bolts/screws (two of them) are on the top of the heat shield covering the pre-cats? The ones on top of mine have suffered heat degradation quite badly (turned into a brittle, plastic-like substance...) and I know that, once removed, they will not go back on, so I don't want to remove them without a replacement!

[fulmar/88]

does the MK3 from 2003 still have the pre-cat problem?

[AndyM]

does the MK3 from 2003 still have the pre-cat problem?

You'll find more detailed information if you have a bit of a search around on here but my understanding is that the facelift included some small changes that help prevent the root cause of the precat failure (oil control ring thingy).

However some facelifts have still suffered from the same issue. It purely lessens the chance slightly.

I believe there was also a small revision again in 2005 (?) or 2006 that once again improved it.

[fulmar/88]

many thanks.

[Anonymous]

Greetings all...I have a 2001 MR2 with 37k on the clock. 1 previous owner, serviced every 6000 miles...wish to avoid the dreaded pre-cat problem - anyone know of a garage in Surrey in the Epsom area who would remove them for me?

OR

Is it better just to buy a new manifold and get someone to fit it for me?

(I watch a lot of 'wheeler dealers' but my mechanical skills aren't exactly on the same level as Edd China's alas!) Easy job?

[6100art]

Hi and thanks for a good explanation Ekona.

I have recently bought an 2003 MR2 from my friend who had it from new, it had done some 29000 miles. I have recently found this forum and read your article about pre cat failure, and would like to know how the 2003 car is better, ie does it have metal substrates in the pre cats. As I dont want to take out the pre cats for no good reason, but if they are ceramic I will definitly take them out.

I probably ought to say that I am retired from an high performance engine design and development background.

Thanks again for your input.
6100art

[Jandaw]

They are definitely ceramic. You can check and determine condition if you take out the sensors.

Have fun! Heatshield and the three manifold to exhaust pipe fixings can be little sods.

[6100art]

Thanks Jandaw. I will take them out.
6100art