Repair Topics / Smog Test

• Find out how a Emission Control System works.

• Get an online Emission Control Manual for your car

Question:

Answer:   There is no set time the monitors with complete there test cycle. Drive your car at least 20 miles, most cars will reset by then.

Question: 2002 Ford Ranger, mileage: 96,000. My truck passes all the emissions test except for NOX. I have taken it twice now to get a smog and the first time the NOX was 721 at 15 mph 1457 at 25 mph and the max is 986 at 15 mph and 846 at 25 mph. The second time I took it, it was at 15 mph 773 and at 25 mph 1283. So it passes at 15 mph every time but won't at 25. I just got a new EGR valve. So somehow I need the NOX to go down 400 ppm. If you guys could help that would be great.

Answer: You may have a partially plugged exhaust passage that feeds the EGR valve. Also try replacing the oxygen senor with a new unit.

Question: 1974 Jaguar XJ12L, miles: 78,000 My Jag failed the smog check again this year. The smog check station mechanic said that I need to have a Jaguar mechanic adjust the carburetors (4 carburetors) because the idle HC was 1405 the normal is 550. Does the Jag need carburetor repair/overhaul or just need adjustment of the 4 carburetors gas/air mixture? I can smell a strong odor of gas when I pop the trunk open.

Answer:   Adjusting the carburetors may bring the hydrocarbons down to an acceptable level. Make sure the carburetors are evenly balanced so that each one draws the same amount of air. Also, check for vacuum leaks. The strong gas odor when you pop the trunk is definitely something to look at. You may have a rubber hose on the fuel line that is leaking.

Question: 2002 Isuzu Rodeo mileage: 88,000. Can't pass Calif. smog test. H/C is way high, even at idle (in Calif. they call this a 'gross polluter'), l everything else is OK - car runs fine. Had tune up done - plugs, wires, filters, oil, adjust timing, etc. Still way high on H/C levels. Mechanic replaced throttle body gasket, which was worn. I've had most of the general upkeep on the car done, major tune-ups and a few minor ones. Oil changes, by and large. Use 'regular' gas though. Mechanic says there is carbon buildup in the cylinders, and compression for each cylinder reads: 1 - 165; 2 - 205; 3 - 185; 4 - 195; 5 - 205; 6 - 130. Mechanic wants to re-build engine - says it's the only way. Cost is about $5200. (Does that seem high?) Says he can't get a re-built anywhere locally and needs to have my motor re-built. Says new motor from Isuzu would cost more than $6200 to buy and install. Engine SEEMS to run basically fine. Idles great, runs fine. Never any trouble. Doesn't shoot out dark smoke or anything when I start it or drive it, although you can see from tailpipe that there is a fair amount of carbon buildup there. Had trouble passing smog test twice before. Should I pay to replace the cat and O2 sensor, betting that this might fix the problem? Or will the carbon deposits and bad compression force me to need a new motor regardless?

Answer:  Before you spend money on a rebuilt engine, we would suggest scanning the computer for fault codes. Replacing the mass air flow sensor and the oxygen sensor would be a good idea. The compression numbers, although not ideal, are not that bad.

Question: 1999 Subaru Outback, mileage: 117,000. Runs really good, but won't pass Calif. smog. Any pointers for things to replace, where to buy and list in the order of highest probability of causing smog check failure. I replaced, oil filer, air filter, PCV, wires, spark plugs, I don't know too much about the EGR Valve, Anti-After burn Valve, and ECS canister...novice mechanic but can follow directions...any advice appreciated. Also, I need a driver's seat and have been unable to locate one.

Answer:   Its sounds like your catalytic converter or oxygen sensor has failed. Test to replace as needed, recheck system.

Answer: Scan the PCM for trouble codes, It sounds like you have a mass air flow sensor that is weak. If no codes are present try replacing it with a new unit to recheck system.

Answer:   Check the operation of the EGR valve. If it is okay, you may have to replace the catalytic converter.

Question: 2001 Toyota Pickup Tundra mileage: 50,000. I cannot get this truck through smog. The readings are great at Idle, but at 2500 rpm there is 2% CO 30 ppm HC 1% O2 and 13.5% CO2. I know this is a rich running condition. I have changed the 02 sensor, and nothing. Before I replace the injectors, I wanted to ask you guys. Thanks

Answer: Your mass air flow sensor or oxygen sensor may be the problem, scan your PCM for trouble codes to repair as needed.

Question: 1999 Ford Explorer mileage: 106,000. My Explorer will not pass inspection because emissions are too high. A friend told me that one of the cylinders is not firing. He checked the compression and the reason is that the valves are not operating properly. There are no valve adjustments for this year. What other options do I have?

Answer:   Check for a flat camshaft. If okay, perform a cylinder leak down test, which will pinpoint which valve is causing the problems. You may have to remove and repair the cylinder head to correct this.

Question: 1999 Pontiac Grand Prix mileage: 90,000. My car failed emissions testing with a high HC rating at high speed and idle. I changed the spark plugs, air filter, oil, and oil filter. When I returned for a retest, the high-speed passed with HC well below the standard. However, the HC rose from 363 ppm to 426 at idle, so it failed the second time as well. I've also noticed that sometimes when it starts, the engine will almost die, but then the choke kicks in and shoots the RPM up. It then seems to idle fine. Sometimes as well, when the transmission is in gear, the engine will oscillate and almost die, then speed back up to idle, then almost die, and so forth. Any ideas?

Answer:   Scan the PCM for fault codes and also check the oxygen sensor and mass air flow sensor.

Question: 1999 Pontiac Firebird Formula mileage: 90,000.  We recently acquired a Firebird Formula with a fuel injection engine. It has high mileage but ran extremely well with a smooth idle and great pickup until last week when we had a diagnostic done on it because it failed emissions testing.  The diagnostic supposedly revealed a leaking intake manifold gasket and the need for a new spark plugs and plug wires.  This car was running fine when we took it in and barely running when we picked it up.  It is difficult to start, idles so low that it dies whenever you slow down or stop, and sounds like it is missing very badly when it's just sitting and idling.  The place that did the diagnostic had no idea of a cause for the instant change in the way the car was running and no suggestions as to how to restore it to how it was, just that nothing they did would have caused it.  We put on the new gasket (which by the way didn't look bad at all to us) as well as a couple other inexpensive parts like a thermostat and PCV valve while we had it all apart, and also put a new distributor cap, rotor, plugs, and plug wires on it as advised.  Unfortunately, it is still the same as it was when we picked it up.  It seems like we have checked everything but can't find anything disconnected or any cause for the low idle.  We also do not understand why the computer module won't compensate for the idle because it appears to adjust other things when they are changed.  Could something simple have happened when the diagnostic was done to cause this drastic change, or could it have caused a problem we can't figure out?  Our inclination is to have another diagnostic done somewhere else to see what shows up but any other suggestions would be greatly appreciated. 

Answer: It sounds like you have a failed injector on one or more of the cylinders. Inspect injector to replace as needed, recheck system.

Question: 2001 Cadillac Seville STS mileage: 80,000.  Could not pass California smog, all readings with the exception of NOx were way below minimum.  NOx was ok at idle and 15 mph after that item went off scale.   What should I look at first EGR or catalytic converter (its the original)?  Any other hints would be more than helpful.  Thanks

Answer: Try the EGR first as the passages may be plugged or the valve not opening properly.  It is also the easiest solution, next check the catalytic converter.

Question: 1997 Mercury Grand Marquis mileage: 132,000.  I cannot pass emissions testing.  I first brought my car in and failed on HC and CO.  About a week later I tried again burning premium fuel and after adding some emission system cleaner.  I was still high on CO and HC.  So then, I changed the air filter spark plugs and ignition wires.  I then went back and tested again.  I added some rubbing alcohol to my fuel tank to try to get it to burn a bit cleaner.  My CO and HC jumped about 50% each.  I do not want to sink too much money into this car.  What should I do?  Oxygen Sensor?  Get the computer checked?

Answer:   Scan your PCM for trouble codes, if no codes present try replacing the oxygen sensor, mass air flow sensor.

Question: 1999 Dodge 1500 Van mileage: 120,000.  Where we live at we have an annual Emission Test for our vehicles.  This year my van did not pass.  I changed the spark plugs, wires, but would not pass any ideas?

Answer: Make sure it has been tuned up and that the fuel injection is clean. Then check your catalytic converter performance, replace as needed.

Question: 2000 Ford Ranger mileage: 83,500.  When I took it in to get it inspected, the guy told me that it was very close, but not quite passing on the low end.  I had new plugs and plug wires put in approximately 3 months before, and since I took it in, I put in a new air filter and new PCV valve.  I have always run mid-grade gas in it.  Could you give me any more suggestions?

Answer: Scan the PCM for trouble codes, if no codes are present try replacing the mass air flow sensor and primary oxygen sensors.

Question: 1998 Buick Le Sabre mileage: 126,000.  I inherited this car and it fails emissions test.  There are no fault codes, car runs well except for a loping idle and sometimes a spit and die at idle.  HC and CO are way out of range.  O2 reads .8v at idle.  Exhaust smells very rich.  I have replaced the ECT and TP sensors, plugs, wires and filters.  Fuel pressure is 40 psi.  I need voltage specs for the TP and MAF sensors.

Answer:  Reference voltage is 5 volts at the sensor.  Fuel pressure should be 35 pounds.  Check compression and check for vacuum leaks also check that the EGR valve is not hanging up.  Replace Oxygen sensor.

Question: 1988 Nissan Sentra 1.6 tbi,_mileage: 200,000. I can’t pass emissions. Limits are HC 220, CO 1.20. I read HC 318, CO 5.63. Airflow meter & ISC read ok. Timing is ok. Valve job two yrs ago (broken belt). O� sensor 1 yr ago. Car runs ok. HELP!

Answer: The reasons for the high emission are numerous. The list starts with a malfunctioning catalytic converter, a faulty engine management computer system to a "tired" engine with excessive blow by and using oil.
 

Question: 1982 Toyota Pickup mileage: 135,000 My 2 wheel drive, 3 speed manual, recently didn't pass smog here in California for an exhaust leak and missing a vacuum hose from what looks like the EGR valve, but there are no hoses that are not hanging anywhere that aren't hooked up. So where do I start? The catalytic converter and muffler and O2 sensor have been replaced recently and are they all good? Help Please!

Answer: You can fabricate a doctor's ear and start at the exhaust manifold all the way to the end side of the C/Converter. You are probably leaking ahead of the converter and not being scrubbed/cleaned and polluting the air. You failed on this one.
The EGR prevents NOx to formed-it is operated by a ported vacuum thru a TVSV/VSV/Transducer, you need to confirm this with the VECI on the hood as per its routing.

Repair Topics / Smog Test