My '85 passed the dyno test the other year w/ TRD Level 1 cam and a stock head. CO and HC were down near 0, NOx was high though. In my case, it was lack of EGR flow, probably due to a few things. One was the somewhat low RPM for the 15MPH test (around 1800) and the small EGR passages in the early heads. I cleaned and ported the EGR passages in the header and head to maximize flow for the re-test. Also filled w/ 91 octane gas, backed the timing 3-4 degrees and dropped the NOx about 60% to pass. I tested with a new cat and new O2 sensor.

r.c.brown@ieee.org
TruckEditor@tlca.org
Project: 4Crawler
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