This is the 1st year I've had to get the new dynamic Smog Check II and my Sport failed miserably. Hydrocarbons almost 300, CO at 10, even after a tune-up and injector cleaning. After running a diagnostic I also replaced the thermostat (again). I had replaced it and the sending unit some time ago, but there was no change, so I assumed the gauge was busted. However, it clearly is working properly now, which was confirmed with an IR thermometer in the water lines. So apparently I had replaced one bad thermostat with another. My mechanic believes that the open thermostat and resulting cool engine temp caused the fuel mixture to be richer than it should have been, fouling the O2 sensor and catalytic converter and that both will need to be replaced. He will run his own diagnostic, but of course, a bad CC won't show up on it. However, my exhaust does have a slight rotten egg smell which he claims is characteristic of a failed CC.
The theory does make sense to me, but my knowledge of emissions systems is pretty limited. Does this make sense to those of you who are more knowledgeable about this? Also, what would reasonable replacement and labor costs be, keeping in mind that this is the SF Bay Area? I know I can't do the CC replacement myself, it requires cutting and welding, but how about the O2 sensor replacement? I also need to consider that smog check re-tests and manual checks are at no charge, so long as he does the work. A Smog Check II test runs $70, a manual check runs $45 and he's already done 1 manual, plus the original test.
Comments and suggestions welcome.
FWIW, other than the emissions problems and a noisy PS pump, it runs and looks fine.
Dan - my 91 XLT 4x4 failed last time Hydrocarbons 305, CO was 1.98 though NO
2717 Gross Polluter - Repairs included 02 sensor and ignition control module OBD code read 14 prior to repair. Post fix had hydrocarbons 56 CO .11 NO
721 - $675.00
YMMV
Rick
-- Computer recommends - Hard drinking calypso poet
SMOGSMART VIR REPORT - 1997 FORD EXPLORER 4.0 LITER ENGINE SmogSmart VIR Report #153337
Your vehicle failed for: High CO, NOx and HC at 15 and 25mph. There may be a possible rich mixture. There are potential ignition concerns. Vehicle failed CO with very high numbers. This condition is usually due to a "rich fuel mixture". CO levels of this amount in most cases automatically produce high HC. The condition which causes the high HC (due to high CO) is called a "Rich Misfire". The diagnosis for this failure should include close inspection of your vehicle's fuel management and control systems. The engine ignition system must also be diagnosed. HC faults (if not related to fuel mixture problems) are most often due to improper fuel ignition.
Some Specifics: First off your vehicle's failure will require some diagnostic time, due to the fact that we normally see vehicles with failures in more then one of the three emissions categories. When a vehicle fails all three categories (HC,CO and NOx), or at least produces high results in these categories, there is usually more then one emissions component at fault. And/or, not all of your vehicle's engine's cylinders are burning fuel at the same efficiency.
How a Rich Misfire causes high CO: CO stands for Carbon Monoxide. It is a by-product of incomplete combustion, more then often related to the presentation of too much fuel to the combustion chambers. The spark created at the sparkplug can only burn a small amount of fuel, the fuel it cannot burn is sent out the tailpipe and will normally contain high levels of partially burned fuel(CO) and raw fuel(HC). In a "Rich Fuel" condition diagnosis would begin with inspecting all possible mechanical faults which could cause excessive fuel to enter the combustion chambers. This diagnosis would include inspecting your vehicle for high fuel pressure, intake vacuum leaks, air restrictions and/or leaking fuel injectors. NOTE: A dirty air filter may restrict ample air from entering the combustion chambers. The lack of air will create a rich fuel condition and result in high CO. If your vehicle has not had a tune-up in the last 15,000 miles, we recommend a quick service from a local smog stations. A basic tune-up should run between $120.00 to $220.00.
As part of the mechanical system diagnosis, the vehicle's EVAP system would be inspected also. The EVAP system is designed to introduce gas tank and/or carburetor fuel bowl fumes into the combustion chambers. These gases(vapors) are just as combustible as the actual fuel in your gas tank. If they are not routed into the combustion chamber, the vapors build up within your engine's fuel system and eventual escape through a vent into the atmosphere. So in-order to eliminate this problem auto manufactures have designed the EVAP system to make use of this vapor. If your EVAP system is not functioning properly it can present these vapors to the combustion chamber at the wrong time and/or to often, causing a rich fuel mixture and increased CO in the exhaust.
Once the mechanical faults have been factored out, the focus would turn to the vehicle's electronic fuel control system.
Fuel distribution to your engine's combustion chambers is controlled by your vehicle's ECU(Engine Control Unit) and fuel injectors. In order for your engine to pass a smog inspection, fuel delivery must be preciously controlled to produce the least emissions. If the injectors do not present enough fuel to the combustion chambers, this would cause low CO emissions. In a situation where the injectors present too much fuel, this would causes high CO emissions. In order for the ECU to estimate the right amount of fuel to distribute, it needs to know how much fuel is currently in the system. This way it can always maintain a proper Air/Fuel ratio and keep emission levels at their lowest. The main component responsible for letting the computer know how much fuel is in the exhaust system at this moment, is the Oxygen Sensor. The Oxygen Sensor sends an electrical signal to the ECU, letting the computer determine exactly how much fuel it should continue to deliver to the combustion chambers. If for any reason the 02 sensor (oxygen sensor) does not send accurate information to the computer or it is "lazy" in sending the correct signals, the fuel delivery program can be altered. The computer may then present either too much or not enough fuel to the combustion chambers and therefore cause an emission failure.
We recommend looking into the rest of the fuel management components also. In a computer controlled engine such as this, there are several components which also play a role in determining Air/Fuel ratio. Along with the Oxygen Sensor, components such as the, TPS (Throttle Position Sensor), ECT (Engine Coolant Temperature Sensor) and the MAP (Manifold Absolute Pressure Sensor) sensors also send vital engine information to the computer which is used to determine proper air to fuel ratio. If any one of these components are defective they can alter the fuel delivery program. A smog service station can diagnose each component and report it's condition.
What does HC have to do with the High CO: There is a condition called the "Rich Misfire". This condition is created, when for any reason, the combustion chambers receive too much fuel, causing the fuel that is delivered to burn improperly and leave behind high levels of raw fuel(HC) and partially burned fuel(CO). As mentioned, fuel distribution to your engine's combustion chambers is controlled by your vehicle's ECU(Engine Control Unit) and fuel injectors. Vehicle's producing high HC for fuel management reasons usually begin producing normally HC levels once the fuel problems are corrected.
However for those vehicles suffering from high HC not related to fuel management, should have the engine ignition system closely inspected. High HC can be caused by improper spark delivery. During the combustion process any number of engine conditions can cause emissions failures. However because of the fact that out of the three systems your engine relies on to produce combustion (Air intake, Fuel Distribution, Spark Control), the Spark system has the highest likelihood of becoming defective sooner then the rest of your engine's due to the fact that sparkplugs and spark wires are constantly exposed to high temperatures and high voltages. You must insure your engines ignition system is functioning properly, by inspecting all the sparkplugs and their wires. If any of the plugs look worn out or have excessive carbon build-up replace them immediately. You may use any brand of product designed to work in your vehicle. Most of the time aftermarket parts (non-factory) will be much cheaper. More then likely you will see an instant performance increase once these corrections are made.
Why is my vehicle's NOx so high: The reason vehicles generally encounter NOx failures is usually due to one of two faults. The first may be a malfunctioning EGR valve and/or plugged up EGR ports and passages. EGR stands for exhaust gas recirculation. And that is exactly what this component does. The EGR system recirculates burned up exhaust gases back into the combustion chambers. Since these recycled exhaust gases have already been in the combustion chambers once, they have burned up most of their fuels, means there is now much less real fuel in the chambers to ignite. This keeps the chamber temperatures down and thus reduces NOx emissions. The EGR valve should be inspected to insure its proper operation. A working valve should be able to open its passage using manifold vacuum. Manifold vacuum is created during the engine's intake cycle. The high demand for air during this cycle creates a vacuum within the engine's intake manifold. This vacuum is then used to control several important functions within the vehicle, including controlling the EGR valve. Some vehicles even rely on this vacuum to control their heating and air-conditioning components. The EGR system is prone to collecting carbon build-up. Some vehicle manufacturers recommend cleaning this component an a regular basis.
High NOx may also be caused by vacuum leaks to one or more cylinders. Vacuum leaks are open passages, normally due to defective gaskets between two engine components. These leaks will allow the suction of additional and un-metered air (oxygen) into the combustion mixture or exhaust (depending on where the vacuum leak is located) disturbing pre/post fuel combustion and increasing NOx emissions. Vacuum leaks can be difficult to locate if they are present at locations not easily seen by the naked eye. Smog repair stations have special tools and methods designed to locate vacuum leaks quickly.
Final Comment: There will be a few steps involved in finding out the root cause for your vehicle's failure/s. You should consider now this will take some time and money. The emissions system/s responsible for causing high NOx, CO & HC will have to be individually diagnosed, and step-by-step eliminated as faults. Please Remember: California law only allows State Certified Smog Repair stations to conduct smog inspections and smog repairs on vehicles being driven in California. We highly recommend you search our database of SmogTips State Certified Smog Repairs stations. SmogTips Certified Stations are pre-screened for quality repairs, fast friendly service, and reasonable prices.
SMOGTIPS SMOGSMART VIR REPORTS - Save Money. Smog Smart. SmogTips.com - "California's Leading Smog Check Support Group" - 1-877-SMOG-TIPS
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