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.
What were the other emissions readings and limits?
When you replaced the plugs, cap, rotors, and wires, what brand parts did
How many miles are currently on the truck?
Yes, a cold engine could have caused an emissions failure.
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
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.
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