94 suburban NOx and timing

[Txfirepro]

Hey all,

A couple of quick questions. Truck has a 5.7 liter engine.

I went for my annual emmissions test today and found out I failed the NOx test. Test station said they would replace the cat converter and it will pass.

Whoa I said, let me take it home and fix it myself for less.

Readings at 25mph

HC(ppm) 40 OK
CO% .20 OK
CO2% 18.7 OK
O2% .2 OK
NOx (ppm) 902 FAIL (706 standard in Texas)

OK, so I go home and replace the EGR, simple but cheap.

Retest shows,

HC(ppm) 22 OK
CO% .18 OK
CO2% 18.7OK
O2% .2 OK
NOx (ppm) 1048 FAIL (706 standard in Texas)

NOx was higher after EGR replacement.

OK, so its hotter than hell here, but I trudge on, sweat and all....

Timing, next on the list.

Checked timing and its off of the scale at idle. I estimate 20 degrees with a light on #1.

OK, I had the intake replaced two years ago, maybe its was set wrong.

Out comes the wrench, and according to the data plate on the radiator, 0 degrees is the right timing, so I set it up that way.

Man, what a dog that is. Idles great, but not drivable.

OK, so where the hell am I going wrong here?

Can someone explain the timing issues?

And what are the suggestions on the NOx?

Thanks in advance,

JT