1994 Pontiac Sunbird failing on NO PPM.

[miguellatigo]

I have a 1994 Pontiac Sunbird LE 2.0 Coupe. It has been failing the canadian emission test on NO PPM. The limit is 526 and my reading is 871. I have spent so much money on it already to no avail. I have changed the following...

(1) New Radiator
(2) Spark Plugs
(3) Catalytic Converter
(4) Oxygen Sensor
(5) New Brake Pads and Rotor (This is irrelevant but might as well put it here)

I have also done the following,

(1) Changed oil and filter
(2) Engine Tune up
(3) Clean Throttle body

After replacing and doing all of these things, it still fails. I went to emission it 4x during this repair time frame and my reading are always 800 and above. I am hoping that this site can lead me to the right direction as to what to do next. I am in desperate need of help as this has consumed alot of my money and time and days off work.

Thanks.

[old_master]

Excessive NOX is caused by excessive combustion chamber temperatures. That can be caused by several things but the most likely/common is a malfunction with the EGR valve. Make sure the passages are clear and the valve is working. The valve on your engiie is controlled by ported vacuum and exhaust backpressure, both must be correct for the valve to operate.

[miguellatigo]

I forgot to mention that I also replaced the EGR valve already.

[danielsatur]

But did you clear the EGR passages on the intake?

[miguellatigo]

I will try to clear the EGR passage tomorrow. But since I will be opening it up again, anything else I should check. Hoses or wires maybe?? Exhaust??
Anything that might contribute to the NO PPM being excessively high.

Thanks.

[old_master]

Make sure the EGR valve is getting vacuum when it should and that the vacuum hose is good back to its source. Exhaust backpressure also needs to be correct or the valve will not open. Engine at operating temp, EGR should have vacuum, in varying amounts, except when at idle and at WOT.

[miguellatigo]

OK, I opened it up again yesterday and verified that the EGR valve is getting vaccuumed. I am retrying the test again today. Crossing my fingers.

[old_master]

With the engine at idle, if you manually open the valve, (with your fingers) the engine should stall. If it does, you know that the passages are clear. When the engine is at operating temp and at idle, increase speed to 2500 RPM and the valve should open. If vacuum to the valve is good, and the passages are clear, and it doesn't open, there is not enough backpressure in the exhaust system.