Greetings,

I failed a pretest a few weeks ago due to NOX and a failing harmonic balancer. I replaced the balancer, plugs, rotor and cap, cleaned the flame trap and associated hoses, changed the oil and replaced the air hose from AMM to Throttle body, as the old one had a slit in it. All vacuum hoses are good.

At the recommendation of another brickboarder, I sealed off the vacuum line going into the CIS, hoping to drop the NOX low enough to pass. No such luck.

Timing is 20 BTDC and the NOX actually increased slightly at 1783RPM (1180, max allowed is 791). NOX at 1822RPM decreased from 733 from the last test to 571.

I'm wondering if I need to throw in the towel and put on a new cat and O2 sensor, or if there are other things I can do to correct the NOX and pass. I have never altered the timing, could plugging the CIS vacuum line cause this? I was under the impression that the timing on my model could not be changed. I don't have a timing light and have never done this.

Any assistance is much appreciated.

Stormie - '88 240DL (475,000 miles) + 765T (243,000 miles)