1991 Honda CRX Si with California emissions
retest smog because my car failed on 7/22
retest after replacing:
air filter
spark plugs (OE nickel core, gapped to spec, 1mm)
set timing to 18 degrees with "stop ECU from making adjustments" jumper in the blue plug @ passenger door hinge
adjusted valve clearances to spec 0.007 intake, 0.009 exhaust
replaced Cat before previous test @ 221,409 miles (NOX was getting high two years ago)
I took it to AAA Car Care Plus for a diagnoses:
-no vacuum leaks on intake side via smoke test
-8% leak down (which is very good)
-compression 138 psi for all cylinders (not sure if this is correct, I got 195 to 205 for the cylinders when I tested 2 weeks ago; the rebuilt engine I got had the head shaved 0.030 instead of the standard 0.002-0.003 for flattening, not sure if this could be causing a problem.)
222,322 miles on 8/19
1908rpm, 12.2% CO2, 2.8% O2
-- previous test 1872rpm, 12.5%, 1.8%
FAIL 15mph CO (max 0.58, ave 0.12, measure 0.87)
-- previous test 1.92
pass 15mph HC (max 94, ave 37, measure 61)
-- previous test 123 (was fail before)
pass 15mph NOX (max 847, ave 389, measure 11)
-- previous test 17
2087rpm, 12.8% CO2, 2.6% O2
-- previous test 2093rpm, 13.4%, 1.6%
pass 25mph CO (max 0.49, ave 0.10, measure 0.14)
-- previous test 0.29
pass 25mph HC (max 76, ave 30, measure 37)
-- previous test 58
pass 25mph NOX (max 786, ave 316, measure 9)
-- previous test 19
Tech said:
Replace rotor and cap?
replaced cap when I got home tonight(I had a spare), cleaned up rotor a tiny bit with a points file; rechecked timing, no change in operation.
Look at switching idle control valve? (car sometimes stalls because of slow idle when coming up to operating temp, but, not when cold; maybe,ICV is dirty?)
how can I get the CO at 15mph to pass?
Cat too cold durning 15mph part of test? (Run car for longer before testing? Need to test with hot cat.)
Answer:
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Your Honda CRX appears to be running very rich. This is indicated in the high CO at 15mph, when the load placed on your Honda's engine is at it's highest. We recommend conducting a "fuel feed back" test.
This includes ensuring the oxygen sensor is working properly, your Honda CRX's ECM (engine control module) is receiving O2 sensor signal, the ECM is computing the data properly and sending the correct signals to the fuel injectors to either increase or decrease fuel delivery.
The feed back test will utilize a 5-gas analyzer (usually a smog machine) and propane. Propane is introduced to the intake system while monitoring the oxygen sensor reading. This test should be done after the engine has sufficiently warmed up and while it is running at idle. The added propane should increase O2 sensor voltage output and the ECM should lower injector pulse rates. If there is no increase in oxygen sensor voltage, your Honda might have a defective O2 sensor. The sensor should be replaced and the test repeated. If voltage increase is present at the sensor output the technician needs to ensure voltage increase is also present at the ECM O2 input terminal. If voltage is present at the terminal as well next the technician must ensure the computer output terminal to the fuel injectors are lowering “injector pulse rates”.
At the end of the feedback test it will be know whether the high CO fault is electronic or mechanical, and the technician can further diagnose the fault.
Your Honda CRX also has other emission sensors which send vital engine information to the ECM as well, such as the TPS (Throttle Position Sensor), ECT (Engine Coolant Temperature Sensor) and the MAP or MAS (Vacuum/Pressure Sensor). These components should be inspected as well. They are also part of the "feedback test".
For more information... What Causes High CO?
posted by SmogTips Support
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FOLLOW UP:
After doing some more research on the web. It looks like it's my coolant temp sensor which has failed.
My car frequently stalls while warming up, cold fast idle is very low 700-800 when it should be around 1200-1500, I haven't noticed problems starting the car when the weather is cold. (but, the first two are symptoms of coolant temp sensor failure.)
Other things I'll do:
-check all the grounds on engine, thermostat, and transmission
-use electrical contact cleaner on coolant temp sensor connection
thanks,
PS, AAA said my O2 sensor was working correctly.
posted by SmogTips Support
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