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Car expert, ASE Certified Technician
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Experience:  ASE MASTER TECHNICIAN,30 YRS EXPERIENCE
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Hi. 1990 Montero LS. California.

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Hi.
1990 Montero LS. California. Low speed - 15mph - NOx readings only just pass! 25mph readings are right on average. Same for the HC reading also. Low speed (15mph) just makes it. High speed (25mph are right on the average. Read your info - 2010-01-21_210326_1.pdf. Very informative. Anything else I should look at please?
Thanks.

Patrick T.
Welcome to just answer.com. I'm here to help you and your 100% satisfaction is my goal.If this could be a faulty catalytic converter but most commonly because your other readings are good and it's only The nox That is too high checked the EGR System be sure the valve is working properly remove the EGR valve be sure all passages are clear and they're not plugged up or they go into the cylinder heads . If you have a lack of EGR flow this will raise the cylinder temperatures to the point Where they will produce excess if nox gas,Check the temp of the catalytic converter in the front and rear, there should be at least a 100 degrees temp increase at the rear
Customer: replied 6 years ago.
Hi Sean.

It's not only the NOx that's high! See my question - "" Same for the HC reading also. Low speed (15mph) just makes it. High speed (25mph are right on the average. "" Might this also be associated with the EGr system? And finally. The best solvent to clean carbon from the EGR valve?

Thanks.

Patrick T.
if they are both high most likley you have a cat that is going bad but ck the egr first its much cheaper
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