General engine questions/issues that aren't specific to the other categories
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By suspendedHatch
#59785 **2016 edit ALL THE HELP I CAN PROVIDE IS NOW CONTAINED IN THIS FIRST POST


Here is a very basic rundown of smog failures and how you should address them on an OBD1 Honda. Essentially if you fail smog, you are not getting the most from your engine. Every effort should be made to pass smog legitimately because the end result is better performance, better fuel economy, better reliability, and less stress on the environment.

I am a certified I/M and Safety tech in the state of Utah where the ASM (dyno) test is required for OBD1 cars. I'm also very familiar with CA smog having lived there until recently.

Diagnosing an emissions issue requires looking at ALL of your gasses, not just the regulated gasses. Without analyzing CO2 and O2 readings, you cannot tell why the engine is running incorrectly.

CO Fail
High CO (above .1%) is caused by running rich. Besides failing smog, running rich reduces power and fuel economy, wears out your cat converter, and harms your O2 sensor. Running rich is commonly caused by a bad fuel pressure regulator (check vacuum and return line), aftermarket fpr, bad, clogged, or incorrect injectors for the application, bad O2 sensor, bad, missing, or tampered thermostat causing you to run cold, clogged air filter, chipped ECU, altered or tampered sensor wiring, etc.

HC Fail
There are two main causes of HC fails: air fuel ratio off, or weak ignition. %O2 and %CO will indicate a problem with air fuel ratio. %O2 above a couple % indicates you're running lean. If the idle speed is high, you have a vacuum leak. Check hoses and gaskets. If Idle is normal, check your fuel filter and O2 sensor. If %O2 is 0 and CO is high (.5 or higher), then you're running rich. Check your fpr, air filter, O2 sensor. Note that the O2 sensor can be weak and not throw a code. Remove it and clean it with a torch, wire brush, and compressed air. If it's old, just replace it.
If %O2 is near 0 and CO% is .0x or lower, then your problem is most likely a weak ignition system. Less commonly it could be low or uneven compression. Check your ignition rotor, distributor cap, spark plugs, ignition timing. Mist water over the spark plug wires with the engine running in the dark. If they're bad, you'll see sparks. If all these check out, get a multimeter and check the ignition coil and ignitor inside the distributor. If those are within spec, do a compression test. You can sometimes improve compression with a valve adjustment. Sometimes you have a burnt valve or worn piston rings.
Also make sure you are running the correct octane for the engine. SOHC Honda engines run best on 87 octane but have trouble burning 91. B Series VTEC motors have higher compression ratios and benefit from 91 octane.

NOx Fail
High NOx is caused by very hot combustion (1800-2500 F). Most Hondas do not have EGR (EGR cools the combustion chamber) except for Accords, the VTEC-E motors and 99 and later motors ie D17A, late D16Y8. When the EGR fails it most often is clogged on the intake side.

High coolant temps are often times the cause of high NOx for us. The gauge may indicate a normal temperature however I have found that it will give the same reading from 180-220 degrees F! A better indicator is that your radiator fan comes on often and stays on for a long period of time. An even better indicator is a pyrometer. Make sure the smog tech is using the dyno fan. Try flushing your coolant system at both the radiator and through the thermostat housing. One way to artificially increase the efficiency of your coolant system is to install a higher pressure radiator cap (stay within a few PSI of the stock rating). Just be aware that doing so will cause all your old hoses to blow. Silicon hoses are a very nice upgrade. Another option in non freezing climates is to run a slightly higher water concentration than the recommended 50/50 mix. Many people choose to run bigger and thicker radiators but this is usually overkill for non turbo applications.

JDM motors tend to have higher NOx emissions possibly due to their slightly higher compression. Retard the ignition timing to the low side of spec and run high octane. Seafoam the combustion chamber and make sure the coolant system is operating at its best. High NOx are also caused by lean mixtures (up to about 16.5:1 after which NOx levels tend to fall off). Check the O2 sensor, fuel filter, fuel pump strainer, and fuel pump.

NOx feeds back on itself meaning the NOx causes runaway NOx, often resulting in readings of 2000+. If your readings are this high it's a good indication that simply replacing the cat converter isn't going to be enough.

Catalytic Converter
Catalytic converters are the 2nd highest oversold item (meaning that good cat converters are often times replaced w/out cause). Repair shops love to replace catalytic converters because they are a high price item so there's a big margin. Often times a fresh cat converter will mask an engine problem and get you to pass smog, but the underlying problem will then destroy the cat converter so that you need to replace it again at your next smog check. Federal law requires that they are warrantied not to fail for at least 8 years or 80,000 miles (on a properly running engine). For this reason I recommend doing a complete tune-up and replacing the cat converter only as a last resort.

Catalytic converters should never wear out. Some things that kill cat converters or cause it not to work properly are 1) dropping it/scraping it, 2) running rich (overheats it and melts the precious metals inside) 3) Silicone (gives off a gas when hot which will temporarily coat the precious metals but will later burn off) 4) Phosphorus (from crappy oil or gas and from not changing the oil regularly).

Many times when your cat converter is not working efficiently you can remove it and blast the insides with a torch. It will give off some bright green and blue flames.

If your cat converter turns out to be bad, you can recycle it for about $20-30.

Properly Diagnosing the Cat Converter
The best way to test your cat converter is to first test your tail pipe emissions. Then drill a 3/16 hole in your exhaust pipe before the cat. Install the auxilliary adapter to the smog test probe and insert it in the hole. Measure the emissions and compare them to your previous reading. Comparing the pre and post cat readings will tell you its efficiency. OBD2 cars have an O2 sensor before an after the cat for this purpose.

O2 Sensor
O2 sensors greatly affect your AFR ratio because they are used for AFR feedback. A bad O2 sensor causing you to run rich will hurt your power in the driving range (WOT is unaffected unless you're in limp mode from a catastrophic O2 sensor failure). A bad O2 sensor causing you to run overly lean can cause additional stress on your engine. The most common symptom of a bad or lazy O2 sensor is hesitation, loss of power, and loss of fuel economy.

Note that under heavy load conditions (heavy and wide open throttle), O2 feedback is ignored and the ECU reads from a fuel table. This is why having your car dyno tuned can result in a significant power increase.

O2 Sensors are a maintenance part and will wear out and "get lazy" over time. Most times it will not cause a check engine light unless it's a catastrophic failure. You can test O2 sensors for laziness using a digital multimeter. The procedure can be found in the repair manual. Do not replace the O2 sensor w/out first verifying that it is bad. If your O2 sensor fails prematurely it's probably due to a blown headgasket (burning coolant), bad piston rings (burning oil), or running rich. Some types of engine cleaners and liquid gaskets can harm O2 sensors as well.

O2 and CO2 as Indicators
A good running engine will have low O2 (near zero) and high CO2 (near 14.9). There should be almost no O2 reading unless you have an air injected cat converter (S2000?). If you have a lot of O2, you're running lean. O2 can sometimes be caused by an exhaust leak.

Full Tune-Up
Besides the regular tune up items (distributor cap, rotor, spark plugs, synthetic oil change, base ignition timing, tire pressure, air filter, PCV) you should also perform the following according to the maintenance schedule: fuel filter, fuel pump strainer (inside fuel tank), have your injectors balanced/blueprinted (especially on JDM imports), remove and clean out your throttle body, IACV, and intake manifold. Adjust the slack in the throttle cable and a/t cable. Seafoam the motor a few dozen miles before you change the oil and filter spark plugs and O2 sensor if applicable. Check plug wires. Test O2 sensor with a multimeter. Some states have begun testing charcoal canisters. Your fuel cap may need to be replaced if it fails the test.

Effect on the Environment
NOx
Oxides of Nitrogen cause a nasty haze above cities that carries over into many famous wilderness areas ie the Grand Canyon. It combines with industrial emissions and hydrocarbons from cars to cause acid rain. It causes eutrophication which kills fish and degrades water quality. It creates particulate matter small enough to bypass the tiny hair follicles in your throat and embed directly into your lung tissue causing cancer. Most NOx emissions come from power plants and diesel engines.

CO2
Carbon Dioxide is a greenhouse gas and a cause of climate change. Plants convert CO2 into sugar and O2 but cannot keep up with the amount we are generating. An effort needs to be made to limit the amount of CO2 emitted in the atmosphere so that the plants and plankton in the ocean can handle it so the world is still livable for puppies and children.

CO
Carbon Monoxide is clear, odorless, and poisonous. It gets into your blood displacing the oxygen and stays there until the blood cells die. Over time, CO accumulates in your system causing you to be forgetful, feel lazy, and have headaches. It also contributes to global warming.


Interestingly, the most effective regulation to reduce air pollution has been the requirement to test gas caps. A bad gas cap will cause many times as much pollution as a car that failed on HC's. The worst part about a bad gas cap is that the car doesn't even have to be running to emit pollution.




2014 edit (taken from page 4)
So for background info I posted this thread in 2008 and haven't worked in safety/emissions in over 4 years. Honestly, when I have an emissions problem I'll often reference this thread, as I often reference some of my other threads on other sites for other info and of course my own damn website :lol: I never imagined I would still be messing with Hondas and answering questions on forums 6 years later (got into the game in 2002 actually) but I just bought another VX winter 2013 and this is a great little community so here goes:

EVERYONE IN THIS THREAD SHOULD READ THIS

These cars are all over 20 years old and in the hundreds of thousands of miles. A simple tune up (oil, spark plugs, rotor, cap, PCV, check wires, ignition timing, fuel filter, check O2 sensor, check idle speed) just doesn't cut it anymore. If you haven't even gotten this far, put away your smart phone and come back when you have.

(On your VX make sure you have the right spark plugs in there and only use NGK or dealer plugs. Most VXs have the wrong ones since the application is often incorrect and most parts stores stopped carrying the correct plugs (try amazon).)

After the basics, you still need to do some reconditioning before you can even get a baseline for diagnosis.

All VX's and most other models need the intake manifold removed and thoroughly cleaned, especially around the EGR ports. Remove the MAP sensor as it is sensitive to cleaners and solvents. You'll need a new throttle body gasket and intake manifold gasket and you can't count on the bigger auto parts chain stores having them anymore. Oven cleaner works reasonably well for cleaning baked on gunk, but it will still require a lot of soaking and brushing. Aircraft remover helps get the old gasket off along with a razorblade scraper and a fine grit sand paper on a grinder. Also clean the head ports and injector holes a bit but don't get a bunch of gunk into the cylinders and don't spray too much throttle body cleaner in there or you'll have a fun time drying it out so it can start again. While you have the manifold off, pull the breather box off, clean it out and replace the O ring to the block. You'll need the exact right size O ring.

All EGs need fuel injector service. I like Injector Rehab. VXs and CXs have smaller injectors than all other D and B series (which are all 240CC) so keep this in mind if you plan to send junkyard injectors in to minimize downtime.

All EGs need valve adjustments (see my other thread). You will find that each valve is inconsistent with the next and that the intake side is often too tight and the exhaust side too loose. This is wasted power potential, wasted gas, preventable emissions, premature death for your O2 sensor and cat converter, and it's hard on your engine because some cylinders are running rich and others lean.

Put 1/3rd can of Seafoam in the fuel tank, oil, and suck the other 1/3rd in the brake hose. Before you do the latter, remove your O2 sensor and put a spark plug in it's place to plug the hole. PS, have fun getting that O2 sensor out w/out stripping it. Get yourself an O2 sensor wrench (not socket) and a thread chaser.


Now get your car tested, note which gas failed and refer to page one. Honestly I would be VERY surprised if you failed after this and if you did, there's not a whole lot else you can do. All you're left with is an intermittent fault ie coil, ignitor or the piston rings are shot and you need an engine swap :?
Last edited by suspendedHatch on Thu Oct 09, 2014 5:41 pm, edited 6 times in total.
User avatar
By biretsu89
#59829 :thumb: :thumb: :thumb:

Holy crap... This is very useful... Ima actually save it to my computer for future assistance. Thanks... oh and quick question....

How long does a high flow cat last compared to a oem cat from the dealer? Yeah I know the dealer oem cat would be the best... just curious to find out if there is a HUGE difference.
User avatar
By suspendedHatch
#59906 The US federal government requires manufacturers to warranty cat converters for at least eight years. If your cat converter fails within that time period, and it's not due to an engine malfunction ie rich mixture, burning oil, burning coolant, or tampering, then they have to give you a free cat converter. The exact details of this warranty are included in the box with your new cat converter.

It should be noted that the air restriction of any cat converter is very small. Hollowing a cat converter actually makes them flow worse because it creates an open chamber that causes the exhaust flow to slow down and expand. The slight restriction from a cat converter actually improves scavenging at low to mid RPM. Test pipes are for high revving motors or extreme boost and have no place on a daily driver.
Last edited by suspendedHatch on Wed Oct 15, 2008 10:45 pm, edited 1 time in total.
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By biretsu89
#59916 :o ... you are smart... hahaha... I shall come to you when I need a question answered... I have a magnaflow muffler... Now ima buy a cat from them... freakin sweeet... well I guess I would have found all this out by just looking up more stuff of magnaflow... but I didnt even know they sold cats... Thanks.. I will now be purchasing a cat from magnaflow :thumb: :thumb:
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By teal_dx
#74483 Magnaflow is a reputable company, but stay away from no name high flow cats on ebay, as they are junk and do a poor job, if they even have anything inside of them.

Thanks for taking the time to post this, I'll definitely add this to the FAQ list :woot:
By sdots
#74538 Nice write up :thumb:
By blind monkey
#78887 how about combinations of high numbers? my '92 VX with 438,xxx km(263,xxx miles) is currently failing for high NOX but the CO is also quite high.

the readings I am getting during the simulated driving test is
HC: 0.1957 g/km max is 0.5 and average passing for the region is 0.2668

CO: 7.0336 g/km max 9.32 average passing for the region is 5.0605

NOX: 1.7032 g/km max 1.24 average passing for the region is 0.8169


EGR is functioning correctly, I personally am thinking the cat has expired. aircare here archives all test results online so I was able to look up my car and get all previos test results with odometre reading at that time and it looks like it has been running high CO(8.39g/km) for 4-5 years and 100,000-150,000 km(60-90k miles) as well as moderate to high HC of .3g/km. the car had a bad dizzy bearing and crank angle sensor when I bought it(all trigger wheels were hitting there respective sensors in the dizzy).

is it likely that the dizzy which had obviosly been bad for so long caused poor timing and killed my cat?
By Imptuner
#298851 I went to smog my car the other day, it failed because the timing was off.
I go the second time and it turned out to be a Gross Polluter now.

CO2%
Meas :15.0


O2%
MEAS: 0.4



HC (PPM)
MAX: 68
GP : 288
MEAS : 115

CO %

MAX: 0.59
GP: 2.09
MEAS: .21

NO (PPM)

MAX: 731
GP : 1992
MEAS : 2055

I talked to the guy he said it could be the catalytic converter :x
Any help or input will be appreciated :) I just don't want to spend $300+ on a new cat, and fail the test again :thumbdown:
User avatar
By suspendedHatch
#299608 They ALWAYS say cat converter. That doesn't make sense for your readings.

Cat converters never wear out btw. They're ruined by poorly running engines.

Your engine is running insanely rich. First take off any fuel mods you've done. Get your injectors professionally cleaned (don't waste your money on "injector cleaner").

Your high reading for unburned fuel could also be caused by weak or poorly timed spark. Did you jumper the ECU when adjusting the timing? Did you reset the ECU afterward? If the answer is no to either question, then you didn't actually change your base ignition timing and you'll have to redo it properly. I'm assuming you set it to the red center mark between the two white marks on the crank pulley.

Fix that problem and that should bring your NOx way down.

The good news is that your car is going to make more power after you've fixed the problem with it running so rich.
User avatar
By suspendedHatch
#299609 To the guy with the VX that posted in 2008 LOL, take off your intake manifold and clean it thoroughly, especially the EGR ports. EGR may be functioning but I guarantee you the port is choked with exhaust crap.

With that high of miles, it may be time to pull the head, clean / check all the valves and pistons etc etc etc.

If anyone asks why I bother answering this, try this thing called Google. It regularly returns results from 2002. I hate finding my exact question unanswered in some forum.
By Gkaiho
#300745 Hello.
I own a 1993 Civic Hatchback, and Im having an Emission issues. Its failing the inspection with very high Nox readings.

When I first had it inspected, it failed both on HC and Nox miserably.
So I have replaced the whole Exhaust system (Exhaust mani, Magnaflow Cat, Mid pipe, and muffler) and tested again.

However, I still failed with high Nox reading.

HC Standard 153 / Reading 56 PASS
CO Standard 0.86 / Reading 0.02 PASS
NOx Standard 1123 / Reading 3038 FAIL

1993 Honda Civic, B16A DOHC engine
The Cat I bought was 49 State legal (I live in Texas)
I put high octane gasoline almost every time
Changed Engine oil, filter, transmission oil less than 1month ago
Spark plug is less than 1year old (Plug cord is older, haven't touched the ignition timing so I don't know if the timing is correct)
Air Intake is not in good shape (currently working on it)

A guy from a shop told me that it could be an air leak on intake, so I am replacing the air filter right now.

Sorry for a long post,
but is there any other place I should look for rather than the intake?
User avatar
By suspendedHatch
#300879 Honda uses a MAP sensor so anything between the throttle body and air filter can leak all it wants. Worse that will happen is the unfiltered air will wear out your piston rings over time. But it will run fine, unlike with a MAF. Neither will an air filter fix a leak in an air pipe.

Magnaflow cats are trash. Absolute crap. Everything else made by Magnaflow is good, but their cat converters are made by Carsound and they're garbage. Brand new Magnaflows right out of the box will fail a smog test. Recycle that junk and get any old generic cat that they sell at the exhaust shop.

Furthermore, "high flow" cats are a gimmick. There is nothing to be gained by using a "high flow" cat or deleting a cat converter. The only thing that matters performance-wise on a cat converter is diameter, and to a lesser extent the smoothness of the transition on the piping going in and coming out.

Replacing the rest of the exhaust was a waste of money unless you had an exhaust leak before or in the vicinity of the O2 sensor. Try to avoid wasting money on parts w/out diagnosing the problem. Some guy's guess is never a diagnosis.

Your HC is high eventhough it passes. You are not burning as much of the fuel as you should be. That's wasted power. But what concerns me is that you didn't check the timing. Timing is absolutely critical to emissions and to NOx especially. Set your base ignition timing properly (jumper the ECU, reset it afterward).

Without O2 and CO2 readings I can't be of much help. It's unfortunate that in many states they don't measure it. But I recommend replacing the cat and setting the ignition timing. Search for how to read plugs and see if you can spot anything obvious.
By Gkaiho
#301037 Thank you very much for the reply.
I will focus on getting a better Cat and fixing the Ignition timing.

My old exhaust was very poorly done and they were in bad shape, I changed the whole exhaust so that I could simply un-bolt to change parts rather than taking it to muffler shop every time to have them cut and weld.

Here were my other readings from the past inspection.

CO (%) Standard 0.86 / Reading 0.02
CO2 (%) Reading 14.3
O2 (%) Reading 2.7
DILUTION (%) Standard >6 / Reading 14.3

suspendedHatch wrote:Honda uses a MAP sensor so anything between the throttle body and air filter can leak all it wants. Worse that will happen is the unfiltered air will wear out your piston rings over time. But it will run fine, unlike with a MAF. Neither will an air filter fix a leak in an air pipe.

Magnaflow cats are trash. Absolute crap. Everything else made by Magnaflow is good, but their cat converters are made by Carsound and they're garbage. Brand new Magnaflows right out of the box will fail a smog test. Recycle that junk and get any old generic cat that they sell at the exhaust shop.

Furthermore, "high flow" cats are a gimmick. There is nothing to be gained by using a "high flow" cat or deleting a cat converter. The only thing that matters performance-wise on a cat converter is diameter, and to a lesser extent the smoothness of the transition on the piping going in and coming out.

Replacing the rest of the exhaust was a waste of money unless you had an exhaust leak before or in the vicinity of the O2 sensor. Try to avoid wasting money on parts w/out diagnosing the problem. Some guy's guess is never a diagnosis.

Your HC is high eventhough it passes. You are not burning as much of the fuel as you should be. That's wasted power. But what concerns me is that you didn't check the timing. Timing is absolutely critical to emissions and to NOx especially. Set your base ignition timing properly (jumper the ECU, reset it afterward).

Without O2 and CO2 readings I can't be of much help. It's unfortunate that in many states they don't measure it. But I recommend replacing the cat and setting the ignition timing. Search for how to read plugs and see if you can spot anything obvious.
User avatar
By suspendedHatch
#301184 Okay, those readings change the story a little. High CO2 (around 15) and low 02 (ideally 0%) indicate it's burning all the fuel.

Properly set the ignition timing (jumper the ECU, reset it afterward), change the cat, and run the 91 or 93 octane if you can get it, and that should get you to pass on NOx.

JDM engines; particularly the B16, are prone to NOx due to the higher compression.
By kingkong559
#320173 Hey I would like some help if possible. After 5 years of non op, i decided to get my 92 civic si (all stock) out of non op. Before i can get my tags, i needed to take my car to a test only center. It failed 2 smog tests in california.

Smog test 1. Timing 16btdc

No tune up done except for air filter change. Pumped 87 octance from chevron and went to get it smog (10 minute drive to smog station)

Results:
15 mph failed
% CO2: 14.6
% 02: .2

Max/meas (PPM)
HC 108/101
CO% .57/.34
NO 835/1640

25 MPH failed

% CO2: 14.7
% O2: .1

Max/meas (PPM)
HC: 73/91
CO% .48/.27
NO: 542/1386

I talked my friend who is a tech. He said I failed because I didnt let my cat heat up to normal operating temperature. So the next day after I failed my 1st smog test, I started my car and let it idle for 45 mins then drove to a different smog station. My car was on and running for 1 hour before the 2nd smog test.

Smog test 2 failed both speeds. Timing 17btdc

15MPH
CO2%: 14.5
O2%: .3

Max/meas (PPM)
HC:108/118
CO%: .57/.39
NO: 835/1908

25MPH

CO2%: 14.6
O2%: .2

MAX/MEAS
HC: 73/98
CO%: .48/.30
NO: 542/1547

Note: my car has been sitting in my garage for about 5 years and I didnt start it and let it run weekly. No tune up was done either before the tests.

Any help would be greatly appreciated.

Smog tech for test 1 said it could be my cat. My friend who is a tech said it might be my cat too. Before I go and throw money away on a new cat I'd like some help first. After 2nd test I finally got paid and did some tune up. I did timing belt, water pump, timing tensioner, valve cover gaskets, crank/cam seals, thermostat/gasket remove and replace the coolant. Once I replace my oil pan gasket, I'm going to change my oil and oil filter. Then replace my clutch and tranny fluid.

If I need to change my spark plug dist cap and rotor before smogging, let me know and I'll do that.