EGR cleaning - high NOx during emissions test

[mkoz]

I thought I would share my experience since I didn't find enough details when I searched for info:

My mother's '92 Eldo (PFI) failed its emissions test back in November. It was more than double the limit on NOx. CO and HC barely registered. Classic symptoms of an EGR problem. Car has 113K km (around 65K miles).

The EGR valve had been previously replaced prior to the November emissions test due to a code being displayed, but it still failed with a new valve. Car was parked till now. I ran some TB cleaner through it, burned through a tank of injector cleaner and went in for a retest yesterday. Failed NOx by more than 4x the limit (warmer weather). So last night I removed the throttle body, cleaned off all the carbon on it, then I went to town on the EGR system. The two tubes in the middle of the intake plenum were gummed up with carbon, I'd say 50% clogged. I snaked them with a mini drain snake from the dollar store, did the same thing on the EGR valve ports (left is exhaust source, right is intake which comes up those two tubes in the middle of the intake plenum). Finished everything with some TB cleaner and compressed air, then replaced all the brittle rubber hoses at the ends of vaccum tubes. In the process I discovered the reason for the harsh shifts. The hose on the vacuum transducer on the tranny was so aged the metal line loosely fit inside it. After reassembly I ran some home made seafoam through the engine, confirmed vacuum signal to the EGR valve (got 5 Hg in. at cruise with light load) and today I went for a retest. Car passed with flying colors. NOx were 75 and the limit is 320 if I remember correctly.

So, for those battling high NOx, it's not enough to replace the EGR valve, you gotta clean the all the channels which carry the exhaust gas to the intake.