QuestionI have a '90 Lebaron, 3.0 engine wi auto transmission. It failed the emission testing with the nox above acceptable range. I replaced the cat and had it retested and again it failed.
Test levels @25mph are:
HC 56
CO .04%
CO2 14.6%
02 .03%
NOX 4871ppm-FAIL (Standard 1206ppm)
I looked at the service manuals and I could not find an EGR valve except on the California models and I looked under the hood and still could not find one. I thought all cars had an EGR.
I will look at the vacuumm line and see if there are any problems. This problem is testing my patience with this car. Are there any suggestions about what direction I should go to remedy this problem? The car runs good and wouldn't you know when I am trying to sell it, this would happen.
Thanks
AnswerHi Pat,
You are correct that there is no egr except on the Cal-sold vehicles, but that would help it there were one. The other causes of high nox are mainly due to high temperatures in the combustion chambers. Is the engine running hot based on the temp gauge on the dash? If so, then checking out the thrermostat for opening at too high a temp would be in order. Also too heavy carbon deposits in the combustion chambers can cause high temps, so consider a fuel additive that claims to help remove those deposits. The timing may be too far advanced: it should be 12 BTDC with the engine idling, warmed up and the wire to the temp sensor next to the thermostat housing disconnected temporarily. The Catalytic Converter may be compromised is a possibility as regards its chemical "bed" being worn out.
The final possibility is that there is a leak around the exhaust manifold gasket or from the connections between the exhaust manifold and the cat. Also checking the intake vacuum lines for a leak would be good to eliminate if you find one.
Those are the causes of high nox.
Roland
