I have a 90 accord EX with 187,310 miles on it. I took it to a smog only test station and it failed miserably. We replaced the catalytic converter and it failed again. The HC's and CO were through the roof at 25mph. the max for the HC was 93 and mine was 1064. The max for the CO was.63 and mine was 1.37. Anyone have any idea what the heck the problem is? We have checked the plugs and they look ok. I am thinkng that this may be an o2 sensor porblem. And advise would be greatly appreciated.

duanem

 

Post your emission results. I recently had problem w/ 94 Accord EX and had high CO and high NOx. Problem was fully-blocked EGR ports.

Yes, O2 sensor can cause high HC's if it's erroneously indicating lean (high O2)mixture. This will cause engine controller to enrich mixture to try to achieve optimum readings, however since the O2 sensor is bad you just get a rich mixture and high HC's. If you have a high impedance (1 megaohm/volt) VOM , you can measure the voltage fluctuations. A good O2 sensor should switch from 0.2-0.8V rapidly, several times per second w/ engine fully warmed and running at 2K rpms. If the O2 sensor voltage stays low (0.2 or lower) all the time, you need a new sensor. It might switch, but switch too slowly, staying low most of the time and cause similar over-rich condition.

If you've never cleaned your EGR ports, you might want to perform that maintenance. See following link. I have a 90 Accord EX w/ 265K and have never done this maintenance, but it's on my list now. There is a TSB for this maintenance that provides some good guidance. If you'll IM me w/ your email address I'll forward the pdf file I picked up somewhere.

https://honda-tech.com/zerothread?id=1011034

good luck

 

HC (hydro carbon) is raw fuel
CO (Carbon Monoxide) results from incomplete combustion.

The condition you described is definitely rich mixture.

O2 sensor giving wrong reading most likely is the cause, but have it checked.

The other thing causing high HC is a misfire. If your HC is that high, your CAT will get damaged (too much fuel to burn)

hope this helps

 

So if the o2 sensor is giving the wrong reading then it needs to be replaced correct? My Dad pulled it out and checked it with a propane torch and thinks that it is functioning. IS there any other test that i could perform on it to find out if it is working properly? We tried using a voltmeter on the o2 sensor but could not get any descent readings. Which we initially thought meant it was bad but when we checked other cars got the same result. Could this be from not warming the car up properly? Anyone know how long it takes to properly warm up a 90 accord?
So i went and got new plugs and new wires last night in hopes that will help. Are there any other suggestions?
here are my complete readings:
15 mph:

hc max: 118 measure 115 co max: .75 measure .25 no max: 799 meas 25

25 mph:

hc max: 93 measure 1064 co max: .63 measure 1.37 no max: 738 meas 72

anyone??????

 

anyone????

 

Bench testing O2 sensor requires a high impedance VOM also, but it may be easier to interpret, however I've always found the in-place test easier. You cannot test an O2 sensor w/ a cheap, needle-movement VOM.

With blue tip of flame directly on sensor it should jump to 0.6V or higher w/i 15-20 secs or sooner. Voltage should drop to 0.1V or less in less than 4 secs when flame is removed from sensor. If O2 sensor responds quickly and correctly under both these tests, the problem is something other than O2 sensor.

Other things to check. Check PCV valve. Valve should rattle and hose should be clear. If you pinch the PCV engine-Throttle body hose while engine is running, you should hear a sharp click as the check valve catches.

Check fuel pressure regulator by pulling the vacuum line to the regulator and checking for strong fuel smell in the line. If yes, the regulator diaphragm has ruptured and will allow raw fuel to be pulled into engine.

A new inlet air filter may help, but probably won't fix problem unless yours is incredibly dirty. If you're using one of those CAI's, they can cause problems sometimes.

Is your engine fully warming to 195F operating temperature. A cold engine will cause emissions problems. Install an OEM thermostat if there's any question. A good thermostat will warm the engine from dead cold to operating temperature in less than 5 minutes, if driven.

Has CEL ever lit? If yes, you need to extract the code/s and post them.

good luck

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by KatyHonda &raquo;</TD></TR><TR><TD CLASS="quote"> Voltage should drop to 0.1V or less in less than 4 secs when flame is removed from sensor.</TD></TR></TABLE>


4 seconds I would call that almost a dead O2 sensor, rise and fall for a good working O2 sensor is 100ms or less anything higher than that would be considered slow. best way to check it is with digital O-scope such as the Snap-On Vantage.

 

In a bench test, you are starting w/ a cold sensor and have to warm to operating temperature.

I agree that an oscilloscope is best way, but few have them.

regards

 

UPDATE!!!

So after changing the o2 sensor and the PCV valve. I went and got it tested again and this time it passsed!! So all in all i changed the o2 sensor, PCV vavle, spark plugs, spark plug wires, and the catalytic converter. Good times!!
Thank you guys for all of your help, expecially you KAtyhonda for all the information that you provided.

Thanks!

 

thanks for the feedback.

Did you replace w/ OEM catalytic converter or aftermarket? If aftermarket, what brand did you purchase and cost?

thanks

 

It was aftermarket. Made by a company called CATCO. Got it at a parts store here in San Diego called World Wide Autoparts. They ususally have pretty good pricing. Anyway it ran $117 plus tax.....