Cracked Exhaust Manifold - Toyota Nation Forum : Toyota Car and Truck Forums

modain · 05-14-2008, 10:19 PM

I finally was able to get my 97 Avalon looked into regarding the high NOx emissions on its failed smog test. The EGR stuff is working fine, so that isn't the problem with the high NOx readings. The technician found a crack in the (firewall side) exhaust manifold which he says lets fresh air into the exhaust.

According to him the extra O2 in the exhaust never lets the cat-con get into an O2 starved condition which it needs in order to clean up the NOx gases. It makes sense to me, but I'd like to run this by you guys that know about emissions stuff for confirmation/objection before I spend $800 to fix this. ($311 parts, $400 labor) The cost seems right for the parts (manifold, gasket, bolts, etc.) and scope of work (four hours) - I just am not looking forward to spending this coin...

***toyomoho*** · 05-14-2008, 11:41 PM

An exhaust leak can cause high NOx.

Did the shop rule out everything else such as the converter, EGR, 02 sensors, etc.

modain · 05-15-2008, 01:38 AM

The O2 sensors are all new (detailed in another post). The EGR was checked out today and nothing was found to be wrong. Converter is original: this is the next point of solution if the exhaust leak doesn't fix the problem.

The shop is a Toyota dealership.

***toyomoho*** · 05-16-2008, 10:40 PM

Not sure. Would depend on how bad of leak, can you hear it?

The link below provides an example of a bad exhaust leak causing high NOx.

http://www.brickboard.com/RWD/volvo/...ual_cause.html

The Camry and a few other models use the same engine. Could find a used manifold at a junkyard go to a third party shop, the results would be to save money.

modain · 05-21-2008, 07:19 PM

Well, no joy. After the $740 repair there was no meaningful change in the NOX measurements. So, with new O2 sensors and no exhaust leak (even though it appeared not to have contributed) is the next thing to go for the cat-con?

On a side note, could the cat be bad? The car has no zip like it used to have. I have to put a lot more foot into the pedal to get around cars when passing, accelerating, etc. Could a clogged cat kill the performance as I have described and fail the emissions testing? The car (and original cat) has 175K miles on it.

cexsiman · 05-22-2008, 12:41 PM

sorry to hear that i didnt fix the problem, but it probably did help, and will help with gas mileage and all that. Its a strong possibility that the cat is clogged, with all those miles on the car (plus over the years all of the use that arent miles, aka, sitting at traffic lights, waiting in parking lots, drive in movies, etc.) really add up. it will help with performance by getting rid of all that carbon thats blocking the exhaust flow, you might want to look into ways of cleaning ur cat vs a new one, its cheaper and i have heard that it does an ok job. you will blow a ton of smoke out of the exhaust but it should take care of the problem.

modain · 05-22-2008, 05:07 PM

How does one "clean a cat"? It's worth a try if it'll keep me from spending yet-more money to get it to pass.

I have been looking on-line for replacement cats and most parts state they are not for sale for California registered cars (won't ship here, either). Hmm... I have a federal emissions car and live in CA. What are my "legal" choices?

TMack409 · 05-22-2008, 06:23 PM

The 3-way catalyst (modern CatCon) does more to reduce NOx than anything else you can repair - generally. In fact, a perfectly tuned engine (one that is low in HCs, CO and O) will be naturally high in its NOx readings. Only a properly functioning CAT Con can bring them down. That said.....NOx can be attributed to high combustion temps which can be due to overly advanced timing or poor condition cooling system or bad EGR. Or clogged CAT Con.

Replacing the CAT will result in its failure again unless you fix the problem - which in my opinion you already have by replacing the cracked exhaust manifold. FYI and FWIW Oxygen is briefly introduced into the exhaust stream on older cars (maybe modern too?) upon cold startup in order to lite off the CAT quicker [heat them up] and get them working efficiently sooner. I don't think the 1MZ-FE does this but I could be wrong. Point being however, your cracked exhaust manifold was constantly introducing Oxygen into the exhaust stream and probably frying the CAT.

Thanks for posting your findings as you go. They will be helpful to others down the road I am sure.

TMack409 · 05-22-2008, 06:30 PM

Quote:

Originally Posted by modain

How does one "clean a cat"? It's worth a try if it'll keep me from spending yet-more money to get it to pass.

I have been looking on-line for replacement cats and most parts state they are not for sale for California registered cars (won't ship here, either). Hmm... I have a federal emissions car and live in CA. What are my "legal" choices?

I forgot to mention that premium fuel can bring down combustion temperatures enough to pass emissions - if your readings for NOx are on the edge.

Unfortunately, the dealer is going to be your only option IMO. The junk yards can no longer legally sell you a used CAT. Your only hope would be to find a private owner who is parting out a 1MZ-FE engined Toyota of your same vintage. Have you looked on Craigslist?

***toyomoho*** · 05-22-2008, 07:30 PM

From my understanding the CAT can only be replaced by a mechanic if is known to be defective. Then needs to be replaced with one that has been deemed exempt by the California Air Resources Board or use an OEM CAT. From my understanding this rule is rarely enforced.

Given the high number of replacement Cats in service it may be impossible to tell one from another unless a detailed examination

Some online stores selling Cats state they are illegal to use on the car, not illegal to sell them in Calif. If your car is Federal emissions, this is what it will be tested to.

There is nothing to stop you from going to a local muffler shop that also does CAT replacement. From my understanding there are lots of outlets certified that do emissions tests, find one that will guarantee the car will pass.

Is this a Toyota dealer? If every thing is fixed, why isn’t the mechanic checking the CAT by taking exhaust samples before and after the CAT? Drill a hole in the pipe before the CAT and stick in the probe, compare the reading with the tail pipe.

modain · 05-22-2008, 09:42 PM

Quote:

Originally Posted by TMack409

I forgot to mention that premium fuel can bring down combustion temperatures enough to pass emissions - if your readings for NOx are on the edge.

Thanks for your (and everybody else's) help here. The premium fuel won't help because the measurements are *way* over (about 3x) the allowable range. [detailed in another post] So it has to be the cat. I don't think it's a combustion chamber temperature problem because the cooling system is working fine, the gauge still rides in the center where it has always been, and when I use a computer scanner the temp shows under 210*.

I'll shop my options to see what I can do without too much pain to my finances (if that's possible). Hopefully I can get a magnaflow or walker cat put on without any trouble and get past this saga.

I'll post the results when they come in.

TMack409 · 05-23-2008, 06:14 AM

Quote:

Originally Posted by modain

I don't think it's a combustion chamber temperature problem because the cooling system is working fine, the gauge still rides in the center where it has always been, and when I use a computer scanner the temp shows under 210*.

I am glad to see that you used the OBDII scan tool to verify engine coolant temps. The factory temp gauge on the dash is not accurate at all!!!

Good luck getting it sorted.

cexsiman · 05-23-2008, 08:10 PM

what type of computer scan tool did you use? a standard code reader? a usb plug that goes to a laptop? scangauge? ive been looking for a cool gaget like that. thanks.

TMack409 · 05-24-2008, 12:14 PM

Quote:

Originally Posted by cexsiman

what type of computer scan tool did you use? a standard code reader? a usb plug that goes to a laptop? scangauge? ive been looking for a cool gaget like that. thanks.

I bought an AutoEnginuity Scan Tool about 4 years ago @$199.00. It works in conjunction with my laptop via its USB port (my ThinkPad does not have a serial port - which is what it really uses - but adapter cables got me there).

Additionally, AutoEnginuity offers a Toyota specific upgrade for even more $$$ but the 1996 Avalon's OBDII diagnostic port does not support that many extra features that I cared about...However, if I owned a model year 2000 car or newer, I might spring for the Toyota specific upgrade. But that's going to have to wait for my son to graduate college!!

You could probably find (used) the old Pre-CAN enabled scan tools cheap now - since the new 'CAN' standard came into effect in 2006 IIRC. Or just get a new Scan tool since they are backwards compatible to older Pre-CAN enabled cars IIRC.

The modern scan tools will work with your Palm Pilots as well - just be sure to specify laptop or Palm when ordering. I think they even support BlueTooth now. But I believe they are about $300 these days.

No affiliation, bla bla bla.

modain · 05-27-2008, 05:23 PM

Quote:

Originally Posted by cexsiman

what type of computer scan tool did you use? a standard code reader? a usb plug that goes to a laptop? scangauge? ive been looking for a cool gaget like that. thanks.

I have a BR-3 interface from www.obddiagnostics.com, it was under $100 for the interface cable (uses a serial port) and the software is free. Some other products are more featured (at a higher cost), but this solution provides real-time monitoring, O2 sensor readings, saving/playback, and code clearing. That's enough for me at the moment.