Problems with precats removed?

fstsven · May 24, 2004, 15:14

Ok guys, don't flame me for bringing this up again...
I know there's loads of info on precats and precat removal, but still, I have a question... s:roll: :roll: s:roll: s:)

s:)

I'm seriously considering getting the precats gutted on my '00 roadster, since it's out of warranty anyway. However, since I'm the nervous type s:oops: :oops: s:oops: , is there ANYBODY out there where this has given problems afterwards (like CELs, O2 sensor problems, engine management,... or whatever) s:?: :?: s:?: s:?: :?: s:?:

Or is it a completely foolproof method without any drawbacks at all?

The mechanic I asked (not a Toyota one) didn't seem too eager... s:? :? s:?

Thanx in advance. Cheers[/i]

Slacey · May 24, 2004, 15:17

Well I did mine yesterday, and so far there is no problem - the car runs fine with no CEL's, so I'm happy... or at least would be if I hadn't cross-threaded one of the O2's s:roll: :roll: s:roll:
For a more informative opinion, try Grant (GSB) or jonboy, both of whom have been running without for a while.

crankshaft · May 24, 2004, 15:26

What hapens with the ECU ?? - the O2 sensors measure before the PreCats and after the Cats, so is the ECU expecting to see a reduction in emissions and if not does it not set a flag somewhere or adjust mixture / timing etc to accommodate it ??

Crankshaft

markiii · May 24, 2004, 15:58

02's aren't used for emmisions on teh header, they are used for fuel trim and sit before the pre-cats

GSB · May 24, 2004, 17:03

I've done 2000 miles now with no problems other than a sheared stud when I did the job. You wont have any problems, heres why...

The O2 sensors are used purely for fuel-air mixture adjustment, They sit before the pre-cats so that the ECU can get an accurate sample of unmolested exhaust gasses. As a secondary function (health monitoring rather than the business of actually running the engine), The ECU then takes a reading from the 3rd O2 sensor downstream, and compares it to the reading taken by one of the O2 sensors in the manifold. It's looking for a change in reading, which would indicate that the cats are working. If the reading is the same, it consider's that the cats are no longer functioning and flags this up as a CEL.

By removing the Pre-cats you are removing less than 20% of the cars total ability to catalyse all the nasties in your exhaust gas. The main cat is more than capable of taking up the slack, and the ECU is particularly generous in what it considers to be a good reading from the 3rd O2 sensor, as clearly Toyota would rather not have to many of these errors coming up. The proof of the pudding comes when you consider this:

If there was likely to be a problem, do you reckon Toyota would sell these?

(Its the TRD header, note the lack of any pre-cats s:wink: :wink: s:wink: )

loadswine · May 24, 2004, 19:46

All seems to make sense to me, It seems I'm not the only one to have had problems with the thread on theO2 sensors, the worst one for this is on the offside as the heatshield seems to cover more of it.Be careful with these, especially if you inspect the precats regularly. s:wink: :wink: s:wink:

Tem · May 24, 2004, 19:51

Quote from: "loadswine"All seems to make sense to me, It seems I'm not the only one to have had problems with the thread on theO2 sensors, the worst one for this is on the offside as the heatshield seems to cover more of it.Be careful with these, especially if you inspect the precats regularly. s:wink: :wink: s:wink:

I never had an issue with these...then again, I've killed so many threads in the past, that now I'm always tightening everything by hand as long as they go. It's pretty easy to notice if things go wrong, when you're not really applying any power...and you only need to turn some 1/4 turn with the socket after the handjob...oops...that last word kinda came out wrong s:oops: :oops: s:oops:

Anonymous · May 24, 2004, 21:39

i was luck enough to have the garage that fitted my engine do mine for me. i have had no problems whatsoever.
it might be just me wishful thinking but it seems to run better without them especially when the weather is hot (compaired to when they were in before) the only downside is that it seems to use more fuel than before but i have not put a full tank in to test it yet. as for emmission i have my first mot next week so we shall see if they make any difference but judging by previous posts it should pass with no problems (fingers crossed).

Anonymous · May 25, 2004, 20:13

Quote from: "GSB"I've done 2000 miles now with no problems other than a sheared stud when I did the job. You wont have any problems, heres why...

The O2 sensors are used purely for fuel-air mixture adjustment, They sit before the pre-cats so that the ECU can get an accurate sample of unmolested exhaust gasses. As a secondary function (health monitoring rather than the business of actually running the engine), The ECU then takes a reading from the 3rd O2 sensor downstream, and compares it to the reading taken by one of the O2 sensors in the manifold. It's looking for a change in reading, which would indicate that the cats are working. If the reading is the same, it consider's that the cats are no longer functioning and flags this up as a CEL.

By removing the Pre-cats you are removing less than 20% of the cars total ability to catalyse all the nasties in your exhaust gas. The main cat is more than capable of taking up the slack, and the ECU is particularly generous in what it considers to be a good reading from the 3rd O2 sensor, as clearly Toyota would rather not have to many of these errors coming up. The proof of the pudding comes when you consider this:

If there was likely to be a problem, do you reckon Toyota would sell these?

(Its the TRD header, note the lack of any pre-cats s:wink: :wink: s:wink: )

Note the price: appr. 850 Euros s:!: :!: s:!: s:? :? s:? s:!: :!: s:!: s:? :? s:?
(order from the US) - any cheaper source

Tem · May 26, 2004, 07:25

Quote from: "Eifel-Roadster"Note the price: appr. 850 Euros s:!: :!: s:!: s:? :? s:? s:!: :!: s:!: s:? :? s:?
(order from the US) - any cheaper source

Not really, they do cost a small fortune...

GSB · May 26, 2004, 08:55

Quote from: "Tem"
Quote from: "Eifel-Roadster"Note the price: appr. 850 Euros s:!: :!: s:!: s:? :? s:? s:!: :!: s:!: s:? :? s:?
(order from the US) - any cheaper source

Not really, they do cost a small fortune...

And you have to ask yourself, seeing as they follow the design of the stock manifold so closely, using identical pipe routing, diameters and lengths, with the only real change being an absence of pre-cat chambers, do you think its performance gains come from:

a) Advanced design using carefully tuned primary and secondary pipe lengths.

OR

b) The fact that there are no dirty great lumps of ceramic material blocking the exhaust...

Thats not to say that you'll equal the TRD manifold by simply gutting your pre-cats, I would guess that the empty pre-cat chambers on a stock manifold cause enough flow anomolies to make the TRD a better performer, but not by much.

If you're after a "performance" manifold, I'd look elsewhere.