1990 Honda Accord California smog retest shows CO% too high

Tiny
NICOLTONY
  • MEMBER
  • 1990 HONDA ACCORD
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 28,700 MILES
What causes Co% (max.63 Measured 1.57%) to be too high in only the 25 MPH Test?
Before this we had to replace the EGR Valve and reset timing from 8 degrees (BTDC) to 15 degrees (BTDC).
Since the test, I also found the Cap and Rotor was bad, so I replaced them, as well as the Plugs (Fair Condition), Air Filter (Fairly Dirty), PVC Valve, and it had an Oil change recently though the car sat a couple of months.
All other test scores are fine.
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Wednesday, November 19th, 2008 AT 11:22 AM

2 Replies

Tiny
KHLOW2008
  • EXPERT
Hi nicoltony,

I can think of a few possibilities that can cause the problem.
1. Throttle position sensor out of adjustment.
2. EGR passage partial clogging. When replacing the EGR valve, did you clean the passage under it?
3. O2 sensor working out of specs.
4. Fuel injectors.
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Thursday, November 20th, 2008 AT 2:24 PM
Tiny
NICOLTONY
  • MEMBER
Thank You KHLow. It seems the O2 sensor is part of the problem since I'm not getting any Oxygen readings at all in any tests so far. My retest produced worse results than the first, after a major tune up. The Co's / No's were even higher.
I found out that the ECU has ideal settings stored for the EGR Valve (which was properly cleaned out when it was replaced). When it gets readings from the EGR Lift Position Sensor that do not match these ideal settings, it cuts the current to the EGR Control Solenoid.
When you replace any of the EGR System components, you have to remove the 15 Amp Fuse #2 from the underhood Relay Box for 10 seconds and reinsert it. (To reset the ECU). Then, warm the engine up (until the cooling fan comes on) and drive it for 10 minutes trying to keep it between 1700 and 2700 RPM for the ECU to reset and re-establish the new settings.
You are partially right and I thank you for your prompt reply. I replaced the O2 sensor (and removed / replaced the 7.5 amp ECU fuse for 10 seconds to reset the ECU for it too) and as soon as I replace the front strut engine mount I'm going for a retest. Will post the results when I'm done.
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Thursday, November 27th, 2008 AT 8:01 AM

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