Rep Power: 0

Looking for help diagnosing the engine on my friends %u201998 Civic LX. She%u2019s been driving it with the check engine light on and wants to get it to go off so she can take it for the Ontario emissions test. I%u2019ve been helping but I drive an older car with a carbureted pre-OBDI engine and don%u2019t understand her OBDII fuel injected engine. Here%u2019s what we%u2019ve learned so far%u2026

1. Blow by- Removing the oil filler cap on the valve cover with the engine running shows pressure buildup, air blowing out the filler hole. I think that%u2019s a problem because on my car there is a slight sucking, or vacuum, at the oil filler hole.

2. Compression. I did a compression test and got nice even compression across all 4 cylinders of 190 dry. Wet it was an even 210. Is that a problem?

3. Vacuum. I have a vacuum guage and would like to measure the intake vacuum but don%u2019t know a safe place to pull a hose and insert the guage. Can anyone tell me, and preferably show a photo, of a hose? I looked for the PCV hose but apparently it%u2019s under the engine somewhere on this model. On my car it%u2019s conveniently located on top of the valve cover although I use the distributor vacuum advance hose instead.

3. Check engine light. We read the code and got one flash which the Haynes manual says if an out-of-bounds reading on the upstream oxygen sensor. We got a decent looking sensor from a junk yard but haven%u2019t tried it yet. What we did is remove the existing sensor and clean it with a propane torch. The reading on the voltmeter looked good during the cleaning, like the one on the YouTube video where we got the idea for cleaning. We put the sensor back on the car and cleared the codes. The light came on after a couple of days. She took it to an auto parts store which reads codes for free and they told her it was a 420(?) code and that the problem was ahead of the catalytic converter. I then looked at the voltages on the two oxygen sensors while the engine was running by slipping a sewing needle under the insulation on the white wire and grounding the meter on the -ive battery post. The downstream sensor looked okay with the voltage varying rapidly between 300-400 millivolts. The upstream sensor voltage was changing slowly and not going over 20 millivolts. We read the codes again and now the one flash code was set again and the 420 code was gone.

4. What to do now? I don%u2019t know how to proceed. She could take it for an electronic engine diagnosis. Would that likely tell us what is wrong with the engine? What else can we do to try and turn off the check engine light.

Background. She has owned the car for 4 years. Ontario requires cars to pass an emissions test every 2 years. She got it to pass the test a year and a half ago by putting in a new catalytic converter and oxygen sensors at a cost of just under $1,000. We went over her repair and maintenance records and noticed she has not been very good at having the oil changed. The engine burns oil but she has not kept track of how much she has been adding. I%u2019m trying to help her now when the weather is warm rather than waiting until the winter deadline for the test as I can%u2019t work on the car in freezing winter temperatures. An Ontario emission pass is good for a year so if we can get it to pass now that will still be good when her test is due in January. Oh yes, I did suggest she start using xxW40 oil or an oil formulated for older engines. I suspect worn valves or rings but don%u2019t know exactly how that effects emissions or how to prove that%u2019s what%u2019s making the check engine light go on.

Thanks for any help.

PS Forgot to mention I had the spark plugs out. The electrodes look fine, clean with bit of whte coating. The isulator has what looks like black soot on it. No oily deposits or carbon buildup.

 
Rep Power: 518

Not a valid test.

Sounds great to me.

Don't use blinks if you have access to a code reader.

Wow.

That's a rather narrow range for a downstream (I would have blipped the throttle a several times to check the voltage range ability of the downstream sensor) and a downstream sensor should be very slow to swing if the cat is working well.

It needs to be much slower than the front sensor swing, and that may be the issue. Front sensor may be close to dead.


I'd probably start with a NEW front O2 sensor of the correct brand, NTK or DENSO whichever was equipped when the car was built.

Then drive it and see what happens next.

(Or install your used sensor and see what happens.)


I would never willingly put a Bosch O2 sensor in a Honda.



What does the oil cap say?

I'd never run xxw40 in one of those cars, especially not up there where the cold winds blow.

I personally would not be scared to run even thinner oil in it (5w20 or 0w20) and it would be much higher quality.
Better quality oil can slowly clean the ring grooves and slowly reduce oil consumption, and the thinner oil can help it start easier in the subzero cold.