Failed emissions on a 88' help please...

My fiance took her 88' 4.0 in today for inspection. Emissions failed for high NOx standard was 1300 and some change she read 1700 and some change. Now emissions is not my strong suit so a) what is NOx in the first place, and b) what causes it and better yet what can be checked to try and correct. Other then the NOx issues she's running in tip top shape and would pass. Little help guys, :banghead: would hate to have it off the road for this small issue.

check the operation of the EGR
check the functionality of the cat.

both of those are what is supposed to control the Nox.
The EGR works to lower combustion chamber temps=lower nox

the cat is supposed to clean up the rest.
is this an idle test or a dyno test?
Renix won't use the EGR if it's an idle test, leaving you with a cat that's most likely bad.

NOx

NOx is (are) different forms nitrogen oxides they are some of the main contributors to acid rain.(some of the NOx's bond with water in the atmosphere to form nitric acid) in my experience the main cause of unusually high NOX emmisions is a faulty EGR valve. other than that unfortunatly any one of a dozen factors could cause incomplete combustion of the air fuel mix and could lead to the same results.

hope some of that helped.
good luck

87manche said:

is this an idle test or a dyno test?
Renix won't use the EGR if it's an idle test, leaving you with a cat that's most likely bad.

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Dyno test...

I am pretty sure a bad cat can not cause high NOx. A bad EGR can cause high NOx for sure, and is the usual suspect, especially if the other numbers were all OK.

Ok, that makes me feel better that it's probably not the cat.. and yes everything else was fine and dandy.

extremely lean cyl. can also give localized hot spots that can increase NOx levels, but not really affect driveability. I would also look for a small exhaust leak near the engine that may be allowing unburned fuel to burn in the Cat.- that too can give high NOx readings.
EGR is primary culprit, but if not..... check others!
--Shorty

Shorty said:

extremely lean cyl. can also give localized hot spots that can increase NOx levels, but not really affect driveability. I would also look for a small exhaust leak near the engine that may be allowing unburned fuel to burn in the Cat.- that too can give high NOx readings.
EGR is primary culprit, but if not..... check others!
--Shorty

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Shorty,

Good first point, I am thinking a partially clogged injector that is not metering enough fuel. Fuel injector cleaner maybe???

On another point, a lot of fuel additives tout that they get close, almost passed systems over the hump on an emmissions test. Also fuel grade (premium instead of regular since it burns a little cooler and slower) and quality, like Chevron with Techron, might make a little difference, enough to make or brake a close NOx test?

I am not all sure what you are getting at on the exhaust leak near the engine???? I would think a small intake leak on one cylinder right at the intake header gasket, making it run lean, too much air in one cylinder, might do it, but what would an exhaust leak do?

I may be totally off base on it, but I was under the impression that the heat required to generate NOx can also be caused by the unregulated introduction of oxygen ahead of the cat. allowing the unburned fuel to continue burning as it travels through the exhaust.

it's been 14yrs since I had to pass a smog test, but I seem to recall if everything else passes, but NOx is high chances are good there's high combustion or exhaust temps causing it.

you make a good point on the intake leak as well--would definitely lean out a cyl. and increase temps-- didn't think of the obvious:doh:

--Shorty

Seafoam claims on the back of it that it will help you pass an emissions test...so give it a try.

Another trick that I've been taught.....Run your fuel tank nearly empty, then dump in cleaner of your choice (seafoam, chevron, acetone, etc....) with ~5 gal. of fuel. This will run the cleaner through at 200-300% concentration, and will do a quick and mean job of cleaning everything. When done, just fill up as normal

SeansBlueXJ said:

My fiance took her 88' 4.0 in today for inspection. Emissions failed for high NOx standard was 1300 and some change she read 1700 and some change. Now emissions is not my strong suit so a) what is NOx in the first place, and b) what causes it and better yet what can be checked to try and correct. Other then the NOx issues she's running in tip top shape and would pass. Little help guys, :banghead: would hate to have it off the road for this small issue.

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how did i forget that you posted this. im a douche

sorry boys. guess i already had help. but as you can see, NOTHING was done to my poor old whitey. hasta