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Emissions Component

1994 Mazda MX3 GS 1.8 V6 High NOx and HC Failure

1994 Mazda mx3 GS 1.8 V6. After looking at past maintenance records, I find that this vehicle has history of High HC and NOX. Also, it is on its third Catalytic Converter. I just purchased the car and it runs great and does not have any CEL's and is an OBD-1 vehicle. I have been on many sites and still don't have a clear answer and also visited a Star Certified Smog Shop and was told that Mazda in general have high emissions.

I have to get the car smogged to register and after a visual on the car, I found that the Catalytic Converter is still fairly new.

I am reluctant to take it in for smog until I can determine why a history of High HC and NOX

It does have a pre-cat but I have been told that it is not measured however, no additional information. I am curious if that could be part of the problem.

I just changed the plugs with NGK and found the old plugs coated with carbon, all 6. I have concluded that the primary city driving is more than likely the culprit.

I have also ordered new Oxygen sensors, again ngk, and will be putting on the weekend.

I feel that I am over-looking something and really need professional guidance. I am a Disabled Vietnam Vet and now 74 years old.

Having work on Helicopters for over 20 years, I am confident that I can fix most things but it is difficult to resolve problems that I am confused about.

Also, I am even more reluctant to take it into a shop since I am on a low fixed income and when I hear $500+ it is demoralizing.

What do you think?? and thanks in advance 


Please see the following two pages below which discuss failures that may cause high NOx and high HC. If you've diagnosed the system and found the oxygen sensors to be lazy, then replacing them is your first step at correcting the air/fuel ratio which may be attributing to the high NOx and HC failure. The problem may be more complex than that though. Being an older model vehicle, carbon buildup and high compression may be the culprit as well. You'll need to conduct a cylinder compression test to determine this. Frankly, finding out the exact reason your Mazda's engine is producing high emissions will be time consuming and require the use of specialized emissions repair diagnostics tools.

posted by SmogTips Support

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