Hello,

My '97 Civic HX seems to be having a problem maintaining the proper fuel to air ratio in the combustion chamber. I am experiencing fouled oxygen sensors and clogged EGR valves (lift sensor malfunction code). Thus, I'm thinking that the exhaust is full of hydrocarbons that probably clogs things up in the EGR system and in the exhaust manifold.

Does anyone else have experience with this problem? If so, I'd love to hear any advice about how to correct this problem because oxygen sensors are really expensive!

(FYI - I have replaced spark plugs, flushed fuel system, new rotor, new plug wires already)

Thanks for any advice!

 

Does the CEL work (when key is turned to ON(II), the CEL turns ON for 2 seconds and then OFF). Or does the CEL instead remain ON?

Any known engine performance problems?

 

Yes, the CEL remains on all the time.

 

Retrieve the CEL code(s) from the ECU. This can be done at home using the jumper wire method described at the link in my signature. Post the retrieved codes if you want more feedback. Afterward, clear the codes from the ECU (remove 7.5A BACKUP fuse under the hood for about 1 minute). If later the CEL returns, retrieve the codes again. Repeated codes are worth troubleshooting.

 

I pulled the engine codes already and I have the following problems:

2 O2B - Oxygen sensor #2 (possibly fouled due to high hydrocarbon exhaust content?)
80 EGR Valve/Line - Lift error (possibly associated with clogged EGR system?)
71 random misfire cylinder 1 (the misfire codes are probably due to the above problems)
72 random misfire cylinder 2
73 random misfire cylinder 3
74 random misfire cylinder 4

 

My guess is that random misfiring on all four cylinders is the root cause of your problem. Is the CEL blinking while you drive? If so, the misfiring is severe enough to destroy the catalytic converter. Don't drive the car in this condition. A new cat is very expensive.

Unfortunately, there are many possible causes for random misfiring like this. Start by checking whether the fuel pressure is low and whether the coil or ICM inside the distributor is bad (take them to local auto parts store for testing). Also clean the IACV on the throttle body.

 

Thanks for the reply! Can you expand on the abbreviations in your last post? I'm not sure what ICM, IACV mean.

-Dan

 

Actually, a faulty EGR valve or line could also cause the type of misfiring you are experiencing. Clean the EGR port and valve as mentioned in the diagram below. If this does not clear the EGR system and misfiring CEL codes, then replace the valve. Then go from there.

IACV = idle air control valve (located on throttle body -- two coolant lines attached)
ICM = ignition control module

Also be sure to download the 96-98 Civic manual at the link in my signature. It's a great resource.

 

Also check the fuel pressure. Too much fuel pressure will make it run rich.

The second O2 sensor does not control fuel mixture, the first one does. The second one confirms the performance of the catalytic converter. You could be getting "sensor" codes because the converter is bad.

If you force the EGR valve to open with the engine idling, it should stumble or stall. Do this by disconnecting the hose and applying vacuum to the valve port. This will also check that the valve diaphragm is good.

 

All,

Thank you for your extremely helpful tips. I spent some quality time with the Civic service manual and I feel as though I have pin-pointed my problem - the idle control system seems to be malfunctioning. This is confirmed by the engine misfire at low RPM and low load. This is causing misfires, EGR codes and secondary O2 sensor codes as well. I'll try cleaning the IAC valve and move on from there.

Thanks again for all of your help and the service manual!

*Dan