1990 Catalytic converter failed

Have a 1990 Miata. Failed emissions test. Too much NOx ppm. Failed before and I replaced the cat. Is there something that would make the
cat fail besides it being a cheap one. Not sure how long I am going to keep the car so don't want to spend a ton of cash on a new one. Any ideas on what causes them to fail early and a good cheap replacement one. Thanks.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 12/2/2011 6:51 PM, Mac wrote:

The one and only time that my 1990 Miata failed emissions (at about 120,000 miles) it turned out to be the dreaded timing pulley, which had been installed incorrectly after a previous timing-belt replacement. YMMV.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 12/2/2011 6:51 PM, Mac wrote:

why it fails after 21 years? probably somebody can answer that better then me, but besides age (mine failed because the heat shield started to rattle at 10 years and I could not stand listening to it anymore) but a car that is burning oil can clog up a cat pretty quickly and make it useless at doing its job. the point being that before replacing the cat you may want to make sure the engine is running smoothly and not throwing up error messages from various sensors...
i replaced the cat in my '95 in april last year. i found lots of really cheap cats on the market but they were the in-line type that required cutting the flange off the header and the cat-back sections of the exhaust. i didn't want to do that. i found a direct fit replacement made by magnaflow, model 23696, that is just like the oem mazda cat (complete with flanges) but it lacks the bolts that come standard with the oem cat. I paid $85 delivered from performancepeddlar.com (after submitting a low ball offer they came back with this low price). this was at least $200 less than the discounted price of the oem part from finishlineperformance.com and so worth the effort for me to find my own bolts to install it. but a couple of notes: i am not certain that the magnaflow 23696 is also for your '90, so check it out. you will need new gaskets and bolts to install it. i do not think it meets california requirements but it has passed new york state inspection multiple times. and i don't know why but i could not get it installed completely silent (i periodically get a rattle from it - wonder if it is internal?), but it isn't horrible, and god knows that a miata with 140k is a symphony of noises anyway. ;)
let us know how it works out for you.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 12/4/2011 5:36 PM, Christopher Muto wrote:

the '90 cat is a different animal than the '95... so much for the suggestion for the magnaflow. finislineperfromance.com sells one made by bosal for your '90 for $149.95. they used to offer free shipping if you spend over $150 so add an oil filter or something to your order.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It should meet emissions with the cat removed.

Yes, Cats fail from over use, if they have a continual stream of unburned fuel they'll overheat and fail. Your NOx PPM might be due to mis-firing plugs or similar, that causes the cat to have to burn up the unburned fuel and eventually fail. Have the rest of the car checked before replacing the cat.
--
XS11E, Killing all posts from Google Groups
The Usenet Improvement Project:
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Replaced the cat and car passes. Before nox ppm, 2433, allowed 1512, new cat 178. not sure what is caused the cat to fail but $100 every year or 2 is not bad. I drive this car everyday and will continue to until it cost more than a car payment to keep it running. Thanks for all the advice.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 12/16/2011 5:06 PM, Mac wrote:

A 1990 is well up in years and usually mileage. Oil consumption may be a factor.
Besides and beyond, plugs, wires, points, distributor cap, and rotor should be considered likely suspects. (assuming a 90 has such things.)
At least it's not a 99 with suspect intermittent coil packs.
Another question has to do with mixture. If you are still getting good mileage, it's unlikely that the mixture is a problem.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Thanks again for all the help. It does have high mileage but still gets around 30mpg. Going to drive it until is won't run anymore.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
replying to Mac , JC wrote:

2 other problems I didn't read here is that your timing may likely be advanced. Get your timing checked & corrected with a timing light. A second problem may be bad valve oil seals that allow too much oil to be turned, causing the catalytic converter to get ruined. These 2 things were the problem for my 1990 Miata. By the way, if you live in California, you need to ensure that it says California legal and that it's for 50 states. 49 States means that it's not legal in California.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.