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Car Forum / Ford / Ford Cars / March 2008Failed Emissions, High HC
Okay guys... 1987 Crown Vic 5.0. Just bought it from my dad. It hasn't had to have an emissions test in 8 years or so. Where I live, it has to pass. I half expected it to fail because it had a slight miss under light throttle. I only ran it thru the test because I really wanted to hurry and get it licenced. It failed yesterday on 2 counts: CO at 15mph was double the limit. CO at 25mph was under the limit barely. HC at 15mph failed. Limit is 55ppm; I had 130something. At 25 the limit is 100, I had 140something. I took the car home and changed the Cap, Rotor, Plugs and Wires, and Air filter. The plugs, wires, cap and rotor were all the original ones. 21 years and 104k miles. The gap was supposed to be .48, but was close to .80 on all plugs. The number #8 plug was so ashed up that the gap was nearly bridged. The miss was almost completely gone afterwards, and I was very happy. Took it today to get reinspected and it failed again. This time the CO number at 15 mph was .19, just under the limit of .22. So that was improved. Unfortunately, the HC was actually WORSE! Both the 15mph and 25mph numbers were slightly up from the day before, which I don't at all understand. Today I pulled the KOEO codes and got a 34 and a 67. The 34 is an EGR error, but from my research, it doesn't appear that it should affect the HC numbers. I'll fix it obviously, but I don't think it's going to solve the problem. The only think I know of that might cause weak spark or incomplete ignition is that the coil terminal pin was corroded, but I tried to clean it up a little bit before putting the new wire on. Maybe that's it, but I seriously doubt it. The only other thing I can think of is that I noticed a few years ago that the thing doesn't like 87 octane gas. It will ping on it sometimes. In fact, I had to pull a long hill on the interstate last year and I thot it would knock itself to death. That's probably the EGR problem, but I wonder if the timing could be off enough to cause that and the HC problem. My plan at this point is to take the intake manifold off, which needs a new gasket. While I have access to everything, I'm going to replace the PCV screen, grommet, valve and hose. I'll have access to be able to see, inspect and replace, as necessary, all the vacuum hoses. I'm going to clean the plenum, take off the EGR and clean it and the ports. Okay, what next? I'm so irritated. CJB I would fix the EGR and replace the O2 sensor. Did the slight miss go away after the plugs and wires? If so I would try it again after the codes are fixed and gone... > Okay guys... > [quoted text clipped - 48 lines] > > CJB >I would fix the EGR and replace the O2 sensor. Did the slight miss go away >after the plugs and wires? If so I would try it again after the codes are [quoted text clipped - 51 lines] >> >> CJB Did you change the oil? First thing I would do with an engine with that history is decarbonize the engine (get a can of Combustion Chamber Cleaner or BG 44K and follow the instructions) then change the oil and take it for a good drive with hard accell followed by closed throttle decell to clean out the cyls (carbon) - The old "Polish tune-up". It also helps get the cat back to operational.  SignaturePosted via a free Usenet account from http://www.teranews.com > Okay guys... > [quoted text clipped - 48 lines] > > CJB I have a theory, and I want to see what you think. The O2 sensors should be sensing the high HC output and leaning out the Air/Fuel ratio, correct? That is the whole purpose of the O2 sensors, right? If the EEC is not able to lean out the mixture sufficiently, then the O2 sensors should be setting a "Too Rich" code, right? There is no "Too Rich" code, which seems to point to an O2 sensor reading wrong, and falsely believing that the mix is in compliance. Maybe the O2 sensors aren't that sensitive, but I'd think they have to be. Otherwise they'd never be able to keep the emissions numbers in compliance. What do you thing guys? I'd have thought that if the problem was anything else, there would be a "too rich" code from one of the O2 sensors. CJB >I have a theory, and I want to see what you think. > >The O2 sensors should be sensing the high HC output and leaning out the >Air/Fuel ratio, correct? That is the whole purpose of the O2 sensors, right? Except O2 sensors only measure O2 content - not HC, and high HC does NOT necessarily mean running rich. Quite the opposite sometimes. Excessively lean makes for poor combustion, which makes high HCs (and not high CO). Too rich makes high CO, and SOMETIMES high HC >If the EEC is not able to lean out the mixture sufficiently, then the O2 >sensors should be setting a "Too Rich" code, right? There is no "Too Rich" [quoted text clipped - 3 lines] >Maybe the O2 sensors aren't that sensitive, but I'd think they have to be. >Otherwise they'd never be able to keep the emissions numbers in compliance. They are VERY sensitive - to Oxygen. Absolutely NO sensitivity to Hydrocarbons. >What do you thing guys? I'd have thought that if the problem was anything >else, there would be a "too rich" code from one of the O2 sensors. > >CJB You may have a cracked PCV hose making the engine run lean, causing a lean misfire on at least one cyl - pumping raw HCs into the exhaust along with unused O2 - which makes the engine think it is ean, so it richens up the rest of the engine trying to compensate. End up with half the engine, or more, running rich to get the O2 concentration to where the engine thinks it should be, while several cyls could still be lean, pumping out unburned HCs from the lean misfire. Would show up worst at idle but not go away on the 25mph test. SignaturePosted via a free Usenet account from http://www.teranews.com > >I have a theory, and I want to see what you think. > > > >The O2 sensors should be sensing the high HC output and leaning out the > >Air/Fuel ratio, correct? That is the whole purpose of the O2 sensors, right? > > Except O2 sensors only measure O2 content - http://vehicle.me.berkeley.edu/~markw/efi/SAE920289/ > > >I have a theory, and I want to see what you think. > > > [quoted text clipped - 5 lines] > > http://vehicle.me.berkeley.edu/~markw/efi/SAE920289/ Thats right, (working) O2 sensors only report exhaust gas O2 levels to the onboard computer. As far as exhaust gases go, the onboard computer doesn't understand, or care about anything other than O2 content. It's stationary smog test gas analyzers that read HC, CO and other gases. A failed O2 sensor stops producing a signal, which the onboard computer interprets as the engine running too lean. It in turn compensates by commanding rich mixtures in response. Rich fuel air mixtures produce high HC, CO and reduced fuel mileage. Here's something to read... http://en.wikipedia.org/wiki/Oxygen_sensor Note in particular the first paragraph under 'Sensor Failures'. There is a lot of good related info and links included with in this article. Erik > Okay guys... > [quoted text clipped - 48 lines] > > CJB High HC along with high CO failures are common, and strongly suggest a bad O2 sensor/s. Other things are possible, but the O2 sensor/s should be checked first. Bad O2 sensors erroneously tell the computer it's engine is running too lean. The computer in turn (dumb and dutifully) compensates by commanding rich mixtures... driving the HC & CO high. Mileage figures suffer as well. Also,a failed coolant temperature sensor can tell the computer it's engine is running cold. The computer will run the engine rich... as in mimicking the choke function of carburetors. A bad thermostat (or one of a too cold value improperly installed) will have much the same effect. Your cylinder #8 issue is probably not O2 sensor related... hopefully just a bad plug wire or plug... Good Luck! Erik >> Okay guys... >> [quoted text clipped - 84 lines] > > Erik Just a thought I believe the catalytic converter combined with the smog pump and air diverter valve are the main components in holding down your HC, CO numbers. For what its worth > >> Okay guys... > >> [quoted text clipped - 92 lines] > > For what its worth Yes, but the HC & CO will still go high if the computer decides to run the engine rich due to erroneous inputs from a bad O2 sensor. Erik |
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