1990 Toyota Corolla failed smog test- California

CIAO

MEMBER
1990 TOYOTA COROLLA
4 CYL
FWD
MANUAL
177,574 MILES

Failed smog test today due to high NOX at 1409 (max allowed is 815) and HC of 153 (max allowed is 124) at 15mph but passed both at 25mph. Also failed timing at 22BTDC. Mechanic said for $20.00 he would time it and that may make it pass. It passed fine 2 years ago but since I have had a new distributor and spark plug wires put in. I did nothing to the car before taking it to be tested today. Commute in the car is 5 miles of city driving daily and never on the freeway. What can I do to help pass the smog test? New air filter, change oil, change plugs, freeway driving before the test, take the car in when hot from driving? EGR is $200.00 so I am not wanting to replace it if not needed. Can scanners test for it before blindly replacing it? Can they be cleaned rather than replacing it? Does a 1990 corolla have the capacity to be scanned? Any other solution to the problem? Thanks, BB

2 Replies

RASMATAZ

MECHANIC
75,992 POSTS

NOX failures are usually EGR-related, since the EGR system is primarily responsible for reducing oxides of nitrogen. But NOX emissions can also be caused by a bad three-way converter or a computer control system that remains in open loop

Hydrocarbon failures mean unburned gasoline is passing through the engine and entering the exhaust. The three most common causes include ignition misfire, lean misfire and low compression (typically a burned exhaust valve). Ignition misfire can be caused by worn or fouled spark plugs, bad plug wires or a weak coil. Lean misfire results where there is too much air and not enough fuel, so check for vacuum leaks, dirty injectors or a fuel delivery problem. In addition to these, hydrocarbon failures can also be caused by oil burning due to worn valve guides, valve guide seals and/or rings.

Give it another tune-up