Just bought a 1994 MX3 GS

:
1994 Mazda MX3 GS
Got this car for $500 and has 164K.
It is a one owner car and I have all the manuals, past maintenance records and original window sticker.
Car looks great and drives although Manual Shifter is loose as hell. Will be changing bushings next week
I do have some issues with SMOG however. I would like to get advice from anyone that can help.


It is on its third CAT and has failed California Smog more than 4 times. Resolved with new CAT 3 times.
It is running high NOX and high HC at 15 mph.

Any suggestions to resolve issue would be of great help. It seems to me that there is something causing the CAT failure that has been overlooked.

Getting car ready for Grandson who is a Marine at 29 Palms right now.
 
......Any suggestions to resolve issue would be of great help. It seems to me that there is something causing the CAT failure that has been overlooked.

Getting car ready for Grandson who is a Marine at 29 Palms right now.

Have you tried this Forum site??? www.mx-3.com

There is a wealth of information on that site that might be useful.
 
:
1994 Mazda MX3 GS
I went to the suggested site and appreciate the input and guidance. The site however has a lot of information but couldn't find a way to sign up and ask questions. I will try again later when I am not so frustrated. I am still left with the same problem and haven't got a significant answer regarding the problem. Before I go any further I need to resolve a couple of questions however. In the process of TRYING to analyze the root problem I am leaning towards the EGR valve. I do know that on a OBD11 vehicle it will throw a code for the EGR system but this vehicle has an OBD1 system and I do not have any CEL's. The vehicle runs excellent without any operational problems.

I am going to do the Jumper test on the OBD1 system to see if there is a hidden code but still not convinced I am looking in the right direction. Based on what I have learned about the car thus far and questions I have gotten answers for I am leaning in the direction of a CHEAP CAT. Supposedly, a cheap CAT last about a year and in California, the SMOG Test is every two years i.e. CAT could have gone bad prior to the failed test. I have thought about using a cat cleaner but more inclined to get a good Magnaflow or Walker CAT thus the questions.

Does anyone have educated experience with my problem that can provide support or non-support of my theory? All input including answers, opinions, guesses, and etc would be appreciated. I am 74 and getting older each day. I hope to solve this while I am still looking down at the daisies. When I start looking up, the problem will be solved immediately. Thanks in advance for and input.
 
I understand the frustration...similar vintage myself!!!

Go to this page and register to use the forums.....http://www.mx-3.com/phpBB3/index.php. It will have a Register click through option at the top of the page,

My car is the JDM market equivalent of the MX-3 (Eunos Presso) imported second hand. It has none of that Smog mitigation stuff fitted to it (no EGR) and we dont have any Smog testing here ...yet. I am sorry I cant help as I just don't have any experience of CAT issues and Smog testing and the like.'
 

mazdadude

ZOOOOOOOOOM ZOOOOOOOOOM
:
'16.5 Mazda CX-5 Touring
Got this car for $500 and has 164K.
It is a one owner car and I have all the manuals, past maintenance records and original window sticker.
Car looks great and drives although Manual Shifter is loose as hell. Will be changing bushings next week
I do have some issues with SMOG however. I would like to get advice from anyone that can help.


It is on its third CAT and has failed California Smog more than 4 times. Resolved with new CAT 3 times.
It is running high NOX and high HC at 15 mph.

Any suggestions to resolve issue would be of great help. It seems to me that there is something causing the CAT failure that has been overlooked.

Getting car ready for Grandson who is a Marine at 29 Palms right now.

My first thought was the fuel injectors. (uhm)

Kudos to you for getting one of these on the road again. The smallest V-6 that was ever mass produced! They are butter smooth when running right.
 
:
92 Mazda MX-3 GS
Are you on facebook? Join the "MX-3.com" group. the online website forums are quite inactive.

If you haven't already, consider ordering parts from Rockauto.com
They're often the most affordable parts source.

Cheap catalytic converters are basic ceramic core converters that are prone to early failure. However a year is extravagant.

One of the most common catalytic converter killers is running lean.


If you haven't already, some common maintenance items -
Replace Front and rear O2 sensors.
Check the intake tubing and vacuum lines. The "accordian" intake tube often tears underneath, causing unmetered air in. Some of the solenoids behind the intake manifold break, or the vacuum chambers underneath the intake manifold also break.

Fuel Injectors - the side feed injectors sit inside the fuel rail. sometimes they can fail and stick close. One easy trick is to pull the rails off the intake manifold (but keep them connected to the fuel rails) and place a cardboard box underneath the injectors and crank the engine. You should get 6 wet spots. It's a bit of a hack way of checking but hey... it saved me hassle when I ended up with 5 wet spots.

When you replace the CAT, Look in the old catalytic converter. does it look pretty gummed up? You could just have an old, tired engine that's slowly burning oil and ruining the converter.

Best of luck!
 
:
1994 Mazda MX3 GS
Are you on facebook? Join the "MX-3.com" group. the online website forums are quite inactive.

If you haven't already, consider ordering parts from Rockauto.com
They're often the most affordable parts source.

Cheap catalytic converters are basic ceramic core converters that are prone to early failure. However a year is extravagant.

One of the most common catalytic converter killers is running lean.


If you haven't already, some common maintenance items -
Replace Front and rear O2 sensors.
Check the intake tubing and vacuum lines. The "accordian" intake tube often tears underneath, causing unmetered air in. Some of the solenoids behind the intake manifold break, or the vacuum chambers underneath the intake manifold also break.

Fuel Injectors - the side feed injectors sit inside the fuel rail. sometimes they can fail and stick close. One easy trick is to pull the rails off the intake manifold (but keep them connected to the fuel rails) and place a cardboard box underneath the injectors and crank the engine. You should get 6 wet spots. It's a bit of a hack way of checking but hey... it saved me hassle when I ended up with 5 wet spots.

When you replace the CAT, Look in the old catalytic converter. does it look pretty gummed up? You could just have an old, tired engine that's slowly burning oil and ruining the converter.

Best of luck!

Since I don't have a Check Engine Light I am confused. Would all of the above, except for CAT, throw the CEL. Keep in mind the system functions correctly. I did find that the Spark Plugs, although functioning, were all carboned up. Primarily from city driving at slow speeds. I did change them from autolite to NGK.

I am still in the process of visually inspecting and try to get access to EGR valve to do function test. It is a PITA. I did do a compression check and all cylinders are at 170.

Also had an adventure with the muffler shop. They told me that the car has two CATS. After a heated discussion they did find that there was one model that had one CAT. Don't trust them anymore.


I am still amazed at the car regardless of problems. It runs like a dream and there still is no CEL. Haven't check yet but will be checking for hidden OBD1 codes with jumper next week.


Don't have a lot of time right now. Wife going to Hawaii for two weeks on Monday. In other words, she is going home for a few days. While she is gone, I will have more time then.
 
Last edited:
:
92 Mazda MX-3 GS
The OBD1 system doesn't have a very robust monitoring system.

O2s in particular will just misreport readings, affecting air fuel ratio most of the time without triggering a code.

In particular, I had a set of O2s which caused my MX3 to run rich. We monitored the voltage which wasnt throwing a code, and was fluctuating causing my HCs to run high (we test HCs and CO in my county).

I tricked the system by intentionally creating a vacuum leak to lightly lean the mixture out. I originally ran around 230ppm HCs which was a fail. Once I replaced the O2s though, it adjusted to around 150ppm HC.

If you do replace O2s, which I recommend you do, NTK/NGK brand was OEM. Highly recommended. And order from rockauto.

Most of the later model 90s transitioned from a single cat to a single cat, and a pre-cat right below the exhaust header log. If the header comes from the heads, combines 3-1 and immediately flanges to the down pipe, then no pre cats. If there is a cylindrical unit on the header log, you have a front and rear pre cat... But they are really mostly useful on warmup.
 
:
1994 Mazda MX3 GS
The OBD1 system doesn't have a very robust monitoring system.

O2s in particular will just misreport readings, affecting air fuel ratio most of the time without triggering a code.

In particular, I had a set of O2s which caused my MX3 to run rich. We monitored the voltage which wasnt throwing a code, and was fluctuating causing my HCs to run high (we test HCs and CO in my county).

I tricked the system by intentionally creating a vacuum leak to lightly lean the mixture out. I originally ran around 230ppm HCs which was a fail. Once I replaced the O2s though, it adjusted to around 150ppm HC.

If you do replace O2s, which I recommend you do, NTK/NGK brand was OEM. Highly recommended. And order from rockauto.

Most of the later model 90s transitioned from a single cat to a single cat, and a pre-cat right below the exhaust header log. If the header comes from the heads, combines 3-1 and immediately flanges to the down pipe, then no pre cats. If there is a cylindrical unit on the header log, you have a front and rear pre cat... But they are really mostly useful on warmup.

Will the PRE-cat cause my problem with High HC and NOX? I have changed the plugs and ordered the Sensors. Probably here Friday and will change Sunday. What does the EGR tube accomplish? It appears to be connected to the Pre-Cat. Will the Pre-cat cause other problems?
 
:
92 Mazda MX-3 GS
EGR will help reduce NOx emissions a bit. But the pre cat mainly assists during the warm-up from cold start. Any time you emissions check, you want the car running at normal operating temps, and the pre cat does little to assist when it's hot.

The high HC though is going to be because of a bad air fuel mixture and a poorly operating catalytic converter.

That's where o2 sensors play an important role in emissions and also catalytic converter longevity
 
Top