1984 Chevy Truck, C20 Pickup, 5.7L, 8 Cylinder, failed ignition timing, NOx and HC.

NO - readings: Max 2273, measured 3351, at 15 mph

NO - readings: Max 2196, measured 2836, at 25 mph

HC - readings: Max 122, measured 129, at 15 mph

HC - readings: Max 77, measured 119, at 25 mph

Failed ignition timing as well.

Timing was at 22 degrees BTDC, Should have been at 6 degrees BTDC. Did inspect EGR Valve post test, and working properly, although found carbon buildup on intake manifold port where EGR valve mounts. What could possibly be contributing to these failed readings?

Answer:		You must...must...must... Correct the ignition timing first and have your 1984 Chevy C20 truck retested. Ignition timing is your truck's biggest problem at this point. All the reading will change with the correct timing. We can't determine if your truck will pass the test with the correct ignition timing but we can guarantee the emissions results will change. At that point you can continue with your diagnosis if needed. posted by SmogTips Support