Hi,

I just had a second (in the last month) smog test done on a 92 honda civic 1.5, after replacing spark plugs, wires, rotor and cap, and adjusting the idle so it runs more smoothly. Last time the readings indicated a gross polluter status before doing all the checks and replacements, and while at least not GP, the readings still seem to indicate the car is running too rich:

Speed=15Mph
RPM=1600
%CO2=14.9
%O2=0.2
HC(PPM) Max=96 AVE=38 MEAS=274
CO(%) Max=0.59 AVE=0.14 MEAS=0.48
NO(PPM) Max=859 AVE=328 MEAS=1065 FAIL

Speed=25MPH
RPM=2590
%CO2=15.2
%O2=0.0
HC(PPM) Max=79 AVE=30 MEAS=79
CO(%) Max=0.51 AVE=0.11 MEAS=0.30
NO(PPM) Max=798 AVE=262 MEAS=134 PASS

Other than replacing all the electrical stuff mentioned above, I adjusted the idle switch so it runs a little more smoothly at a higher RPM. I've done a cylinder check, and the #2 cylinder seems to not be firing as much as the other cylinders (verified by pulling the spark plug wire and fuel injector wire from the cylinder). I made sure the fuel injector wasn't a problem by switching it with another cylinder, and by replacing the spark plugs and wires, of course. Not sure if this could be the problem or something else.

I replaced the O2 sensor about 25k miles back, so I don't see how this could be the problem--haven't had a CEL. I also rebuilt the cylinder head and installed a new head gasket 25-30k miles back, also, so I'm amazed I have leak in the #2 (it seems--yet to do a compression test).

So the question is, should I check the O2 sensor, and how? And would a possible cylinder leak cause the engine to run rich, and how the heck is that possible? Thanks.

 

Again, charge gas into a cylinder, it doesn't fire, raw gas goes into exhaust, gasoline is a hydrocarbon --> fail HC test.

When truly "running rich" it's prone to blow both HC and CO, but be OK on NO.

Rebuilt the head, eh? Having the valve clearance too tight will cause low compression and misfiring especially at idle. You really need a compression test.

Failing HC and NO at the same time (with an otherwise good engine) could mean a bad converter, but you have to resolve the misfiring first.

 

The first time around, before replacing plugs and wires, the NO didn't have a problem, so I'm guessing it could really well just be the misfiring. So I'd hope. How would you check/change the valve clearance? Will post compression check results soon.

 

do you have by any chance a cel?

 

Nope.

Just to make sure it worked (though I know it doesn't prove a lot), I pulled the plug from the O2 sensor and IACV and got CELs for those. Replaced the O2 a couple years ago, sp not sure how it'd go bad that fast. I doubt it really.

Also, one thing I was wondering about recently: I got the cylinder head rebuilt at a machine shop, after I took it out myself. Do machine shops normally readjust te valve clearance when rebuilding a cylinder head? I'm wondering if it's possible the valve clearances weren't changed from before the rebuild--could have actually caused the burned exhaust valve that I had to get the cylinder head rebuilt for.

 

Compression test results: ~130 pounds on #1, 3; ~90 pounds for #2.

With that low a compression, would adjusting the valves really make a difference?

 

No...

 

Adjust the valves already! Seriously. You don't have to go through the whole procedure just loosen them up a little and see if the compression comes back. Too loose they just make noise.

 

I can try it when I have myself a few free hours, probably this weekend. But really, how would valves being too tight make a 40lb difference in compression? I'm still kind of new to this area of understanding.

 

If the valve clearance is way off, it could cause cylinder compression problems. I'm assuming there is some engine damage, but it's pretty easy to do as mk has suggested. If you are lucky, he'll will be right. He does know his stuff.