honda.lioness

My 91 Honda Civic LX (all stock, 208k miles, I am original owner) failed idle emissions yesterday as follows:

HC = 330 ppm (180 allowed)
CO = 2.7% (1.2% allowed)

This tells me the car is running rich--too much fuel--at idle. It passed high speed emissions. I do not have the high speed numbers with me.

The O2 sensor is Denso OEM, 4.5 years and 55k miles old. All ignition parts (wires, dizzy cap & rotor) are OEM and under four years old. NGK Plugs are 2 years and 20k miles old. Air Filter was changed one year and 5k miles ago. Timing was checked in September of 2008. Fuel mileage seems a little down, from maybe 40 mpg to 38 mpg.

For the test, the car was warmed up 15 minutes in about 40 degree F weather, which I think could be the problem.

I went looking for exhaust leaks and found that the first two flanges downstream of the catalytic converter were leaking. Even though these seem far away from the oxygen sensor, could enough air be leaking in and travel upstream to the oxygen sensor at idle to throw the O2 sensor off?

If you have any experience at all with finding an exhaust leak to be the cause of a failed emissions test, please post back a.s.a.p.

thesmogman

Anything after the cat is not going to affect emissions. Unless there is so much air getting in that it causes a sample dilution. (Not enough exhaust to test) Just make sure you don't have any leaks before the cat.

I think it is time for a full tune-up. And if you suspect the O2 sensor have it checked. At 208K it is normal to burn a bit of oil. This over time will plug up either the O2 sensor or the cat. Plus create deposits on the plugs causing resistance to the spark.

CO and HC suggests poor combustion/ignition. Bad enough to cause a mis-fire. This could be just one cylinder doing this to you. What RPM is your idle at? Might need to raise it to 800rpm. If your at 700 or below. Spec is 750 + or - 50rpm. This will help a little bit. Might want to try the test when it is warmer too.

honda.lioness

Smogman, thank you for the quick response. I battled getting this car to pass emissions for some five days and am now taking a break.

To be precise: air filter, OEM ignition wires, dizzy cap and rotor are 1 year old. The OEM PCV valve is 8 months old. Since I last posted, I checked the oxygen sensor voltage; it seemed fine, but I swapped it with an old OEM one that I had replaced a few years ago pre-emptively, anyway. I checked the MAP sensor line per Honda TSB 92-041; it is fine. The idle RPM seems to be about 800 (I do not have a tach; just using the cluster tach). I put in new NGK plugs (the ones specified in the owner's manual). The old plugs did not look abnormal for two years and 20k miles of use. I checked the timing; it was fine. I checked the air filter; fine. I replaced the exhaust downpipe gasket (inches from the O2 sensor) even though there were no signs of leakage. For my most recent emissions test, I retarded the timing, filled up with 88 Octane, and added a yellow bottle of Heet (on others' suggestion, in the archives). I warmed it up at highway speed for 30 minutes. It sat only a few minutes before the test was done. It still failed HCs on idle by a factor of about 2. I asked the tester to let me rev the car to 3500 RPM and then release, per Honda TSB 92-041; no joy. The tester did not test beyond this.

At this point I have added a bottle of Chevron Techron. I am going to adjust the valves today. Then I am going to adjust the timing to maximum retard and try again. If it fails again, then I am going to keep adding Chevron Techron at every tank of gas for a total of four tanks. Lastly, I will consider purchasing the purge control kit, Part # 04103-sh3-k30, suggested in Honda TSB 93-009. It costs around $150 from Majestic. From http://www.hondacarforum.com/honda-2...ivic-88-a.html :

<quote>THE CAUSE
Apparently the injectors start leaking in the throttle body and let fuel
come in around the injector base o-rings. The key here is that the car is
getting way too much fuel, yet the Pulse Width is normal. When this happens the car
will run rich most all the time. The engine control module (ECM) tries to
maintain control by cutting the PW back, but it still runs way too rich.</quote>

I want to stay away from additives like Sea Foam and "Guaranteed to Pass."

The two TSBs mentioned above are the only ones that treat emissions that I found for my 91 Civic. I am pretty sure that on the second test the danged tester (a trainee, which is the price of a free re-test) hot soaked my Civic (turned it off after it had been run a long time, then turned it on again after a few minutes, so that sensors absorbed engine heat while the car was off and hence were all messed up), causing ridiculously high readings for HC and CO; like factors of 3 or more higher than allowed for all four checks (HC and CO at idle and high speed). I will take some blame for not knowing my Civic is susceptible to this. The two tests after this, where I directed the car not be turned off, had far better readings, like factors of 2 or less and only for two of the four checks.

From reading the archives this problem is pretty common for older Hondas. I am going on the theory that either I have not been using Chevron Techron enough (was using it about once a year for the last few years); the car has been sitting a lot in the last six months (only about 3k miles in six months); or the o-rings on the injectors have failed and I really need that purge control kit.

If you or anyone else has other ideas, I am all eyes. Thanks in advance.

jb2wheels

When my 90 failed last summer, it failed for high HC at idle only. Everything else was fine. Turns out, my cat was done. New cat dropped HC and CO numbers.

link if you're interested:
http://www.hondacivicwagon.com/bb/vi...php?f=7&t=4074

before numbers:
At 800 RPM (idle?):
HC 401 actual 220 limit (fail)
CO 0.43% actual 1.20% limit (pass)
CO2 13.1% actual no limit specified
O2 1.7% actual no limit specified
Dilution 13.53 actual >6.0 required (pass)

At 2700 RPM:
HC 89 actual 220 limit (pass)
CO 0.67% actual 1.20% limit (pass)
CO2 13.3% actual no limit specified
O2 1.1% actual no limit specified
Dilution 14.17 actual >6.0 required (pass)

after new converter numbers:
At 892 RPM (idle?):
HC 10 actual 220 limit (pass)
CO 0.00% actual 1.20% limit (pass)
CO2 15.0% actual no limit specified
O2 0.3% actual no limit specified
Dilution 14.96 actual >6.0 required (pass)

At 2622 RPM:
HC 13 actual 220 limit (pass)
CO 0.01% actual 1.20% limit (pass)
CO2 14.8% actual no limit specified
O2 0.3% actual no limit specified
Dilution 14.81actual >6.0 required (pass)

honda.lioness

jb2wheels, I moved from one state to another, so as it happens, I had an emissions test done in August, failed it, put on a new Magnaflow direct fit Cat (almost exactly as you described in your link), and then, like your experience, passed with flying colors in September. Now it is February and my car is failing in a different state. Idle emissions seems to be the bigger problem, based on the four trips I have made so far to the emissions center.

I am curious as to whether (1) the cheap Magnaflow et al. cat converters really would have such a short life or (2) back in Aug-Sep, the other things I did were what made the difference, in particular warming up the car more and doing an "Italian tuneup" (driving up a long steep hill at high RPM). Magnaflow cat converters do have a long warranty. Unfortunately, for once in my life I am not sure I completed the warranty card on it.

Taking a cue from the one TSB, this morning for the first time ever in the car's life I pulled the injectors. They seem quite dirty from the looks of the outside, with a kind of varnish that mostly wipes off with a Q-tip but really wipes off well with ordinary carb cleaner. I am soaking them in carb cleaner right now and am off to the store to study other FI cleaners. I am also considering a fuel injector cleaner service, as many mention here and elsewhere. Gonna try to replace the FI o-rings with ones from True Value hardware, too.

Thanks for posting. The similarity of your and my situations helps.

honda.lioness

The other day my 91 stock Civic failed again but only at idle. It had terrific numbers at high speed. Since most of the failed HC and CO tests have occurred at idle, I googled. One poster elsewhere suggested looking at the evaporative system, especially the charcoal canister and its connections. I followed the troubleshooting chart in the shop manual and found that the purge cut-off solenoid valve was not working right. After warmup (rad fan has come on), this valve is supposed to send a vacuum signal to the diaphragm valve on top of the charcoal canister to purge stored fumes. I was not getting any vacuum signal. I checked the electrical signal from the ECM and PGM-FI main relay and found it was constant at battery voltage, whereas it should have changed from battery voltage when cold to 0 volts when warmed up. When warmed up, it is supposed to change via the ECM opening the ground.

Right now my theory is that I have an air leak to the throttle body via the purge cut-off solenoid valve staying open at all times--cold and warmed up--when running. This messes up the engine control system so that my Civic runs rich.

I figure either there is a short in the wire between the 2P connector (the one attaching to the purge cut-off solenoid valve) and the ECM, or a sensor is not sending the correct signal, perhaps because it is just too cold here and, even with the rad fan coming on, the ECM does not see the engine as being warmed up. I am leaning towards the sensors being sluggish and not dealing with the cold here well. In September when my Civic passed emissions it was much warmer and I was very careful to warm up the car well before the test.

I checked the ECT sensor's resistance per the shop manual and it is 292 ohms. Spec is 200-400. So it seems fine. Still I am suspicious of it.

No codes are being thrown.

If anyone knows what sensor(s) in particular trigger the ECM to open the ground discussed above, or if anyone has other suggestions, please post back.

Edit:
Fortunately for my wallet, and unfortunately for my automotive
education, I sold my 91 Civic LX yesterday for a little less
than KBB "good condition" price, to a family who lives in the next
town over where emissions testing is not required and so they said they did not care. Selling the car has been my goal for a few weeks now, before I even learned it would not pass emissions where I was.

I did not like the readings I was getting for the O2 sensor (Denso, 55k miles, 4.5 years old), so next I was going to replace it. Other things I was considering were checking compression (worn rings could be the problem); replacing the ECT sensor; replacing the o-rings on the injectors; continuing with Chevron Techron for at least four tanks of gas; drive the car daily and try to do higher RPMs under load, to help burn off carbon on valves, cyl walls, etc.