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failed emission high NOx

My 89 Toyota pickup recently failed emission test for high NOx (1483 std reading 2954). I checked out the egr system as per the service manual and didn't find anything wrong.. I changed plugs, cap, rotor, wires, pcv, air filter about 20K miles ago and the truck rund fine. I did however have to wait over an hour in the line and had the engine shut off. By the time I got to the emissions test, the engine was pretty cold. Could this have caused this? Thanks for comments.

Reply to
RZ
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What were the other emissions readings and limits?

When you replaced the plugs, cap, rotors, and wires, what brand parts did you use?

How many miles are currently on the truck?

Yes, a cold engine could have caused an emissions failure.

Reply to
Ray O

High NOx is caused by high combustion temps. You say you checked the EGR, which is important as the exhaust gasses actually cool the combustion temps. If the EGR is proven ok, you need to look at too lean a burn, etc.. It probably has a feedback carb, and it's possible the system has a problem and is not properly metering the air to the system. I'm fairly sure in this case if it is a feedback carb, the air is metered rather the fuel. IE: it may be pulsing way too much air than it should be due to a faulty system. This very lean burning will drive NOx scores through the roof. Also make sure the engine is not carboned up as that will lead to lean burns and higher combustion temps also. Anyway, you need to check that whole system for proper operation. Do not waste money on a new cat converter.. Cure the lean burn and the NOx should drop. Also.. a trick... Retarding the timing will slightly reduce NOx scores, and can get you over the hump if you are borderline. But your problem is not borderline.. :( BTW, the engine being cold would not effect this.. It probably gets worse the warmer the engine gets. MK

Reply to
nm5k

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