348 Emissions

As a general rule of thumb, if your hydrocarbons (HC) are too high, then you are running too rich. So just lean back your A/F mixture via the screw under the blue cap on each MAF.

If your NOx are too high, then you are running too lean, so the solution is usually to enrichen your A/F mixture via the screws under the blue caps on your MAFs.

 

http://ferrarichat.com/forum/showthread.php?t=44093&highlight=348+blows

Clean 'nuff for down South, y'all

 

If you don't have a closed loop issue (348's can run in a "guessing" open loop mode or in a precisely tuned by O2 sensor and MAF feedback "closed loop" mode), then speaking generically, the most common reasons for emission test failures include: a malfunction in the components of the vehicle that regulate the fuel/air ratio such as the oxygen sensor; a dirty air filter; misfiring spark plugs; leaks in the vacuum system; or a poor-fitting fuel cap.

Oh, about that fuel cap...don't go get tested with a recently gassed-up car. The small amount of gas that drips into your fill area can fail your emissions test. You want a tight-fitting gas cap on a half-tank of long-ago-filled-up gasoline.

You also want your spark plugs gapped down to almost the lowest factory width (this prevents any "misses," the kiss of death for emissions testing).

De-tuning. De-tuning isn't always good for emissions tests. You de-tune, or lean out your fuel-air mixture ONLY IF YOU ARE HIGH ON THE "HC" (hydrocarbons) count...otherwise, you actually want to **enrich** your mixture prior to the test IF YOU ARE HIGH ON THE "NOx" count. A richer mixture will lower your NOx count, after all.

So you need to know if your car was failing because of excessive HC's (solution = lean out mixture), or failing because of excessive NOx (solution = enrich mixture) because the solution is radically different based upon an HC or NOx cause.


Have your car well-warmed-up before you arrive for testing, but not overly hot.

Your state may suggest to the testing center what transmission gear to test in at different speeds on the shop's dyno...make certain that those gears/speeds are realistic for your car. You don't want to get tested at 10 mph in 2nd gear instead of 1st!

Change your oil. Do NOT overfill! For emissions testing, the lighter weight your oil, the better. Make certain you have no obvious exhaust leaks. Make certain that you see no smoke.

For extreme cases, there is a product called Guaranteed to Pass (G2P), a fuel additive. ***You actually dont run the emmissions test with this stuff in your fuel***, rather it is billed as a "special" cleanser via the gas tank prior to the fuel used during your actual test (http://www.autobarn.net/ch05063.html ). So you run it through one tank (your emissions will be TERRIBLE during this whole tank of gas), fill up *again*, and then you may even want to add an Octane Booster to your 2nd tank of gas (to help prevent misses/knocking). Drive that 2nd tank of gas down to 3/4 or 1/2 full, then go get your emissions tested.

In summary, verify that your car is running open or closed loop when warm. However, if you are correctly running closed loop when warm, then go through my suggestions above.

 

I've mentioned this several times in the past, and No Doubt just mentioned it again, but it's really important to have the car warmed up when you get the emission test done. And I don't mean "warmed up" by sitting at idle in the shop until the fans come on, I mean warmed up by driving the car at highway speeds for at least 20-30 minutes before doing the check.

My 348 failed its emission test on the first try, when I drove it for about 15 minutes into town to the test center. I took it out on the freeway for about 30 minutes, took it back to the same center, same machine, same tester, same day, and it passed easily. No other changes done.

If the engine has vacuum leaks, sensor problems, bad plugs, whatever, then those items naturally need to be addressed first, but a properly set up and warmed up 348 should be able to pass without any magic.

 

Those are d*mn tight test limits (even the MA ones)!

Assuming that the engine is running correctly in a closed-loop fashion, you would have two areas to attack:

1. If the upstream HC & CO (the gas entering the cat) are much higher than the downstream HC & CO (the gas leaving the cat) -- indicating the cats are actually quasi-working -- fresh O2 sensors might help;

2. If the ... are about the same as the ... -- indicating the cats are ineffective -- fresh cats might help.

I sure wouldn't call 0.45% CO and 103ppm HC "bad" in any way. Does anyone have the "typical" HC & CO numbers for upstream and downstream from the 348 WSM? Just wondering what the available margin (if any ) is from what F says is "normal" and those test limits.

 

Is there an easy way to tell if a 348 is in open or closed loop mode? A signal from the exhaust ECU's, possibly??

 

i went to emmisions , got in line and they pointed me offto the office. the guy yelled in , i cant do him, hes to low , i wont be responsible for damages... , iwas given an exempt sign off... .

 

When I got my 348 spider, the cats had been punched. First smog check failed, HC 222 at 15mph; 177 at 25mph against limits of 85 and 50 PPM, respectively. New Hyperflow cats, HC was 0 PPM at 15 mph, 1 PPM at 25 MPH - not a typo.

Cheers
Kevin

 

Best way that I know of to confirm it's running closed-loop is to measure the voltage coming from the O2 sensor itself (with everything plugged in). If it's running closed-loop, the O2 sensor voltage will be swinging from ~0.1V to ~0.9V in a quasi-sinusoidal way with a period of a second or two.

 

Thanks. How different will that voltage be from the open loop values?

 

according to most service manauls I have seen they indirectly state closed loop happens via the engine temp, could vary according to engine map. What keeps it in closed loop vs. open loop would be properly functioning sensors that send the engine management system correct info and of course at operating engine temp. How to tell if its in closed loop would be, generally speaking, your CEL(s)not on. My Duc 749 is a FI engine but is somewhat of an open loop concept, there are no O2 sensors that fine tune the mixture and engine management uses different sensors as its primary information source. You can piggy back these management systems easily. The engine map does not reguire/call for the fine tune of an O2 sensor. The motronic 2.7 and 5.2 systems primarily use the air flow meter(s) as its source and the O2 to fine tune the air fuel ratio after the car is warm and running.

 

Those systems are designed to assign authority over mixture to different components during different operating modes. During warm up authority is given to the temp sensor. At idle and steady state cruise it is the O2 sensor. During periods of a high level of throttle fluxuations the MAF has primary authority.

As to TA Tech's problem the ex should be checked precat. The HC should be around 250-300 PPM, O2 below 2%, CO below 2%, CO2 above 12% at a hot idle. If your car does not conform to this you have a problem. If it does conform to this you need cats.


BTW HC goes up when too rich or too lean. HC cannot be an indicator of mixture except to confirm it is close to correct.

 

Depends what else is going on. Usually when "cold" (defined by some thermal gizmo), the air injection system is running so the O2 sensor would report a very lean condition (~0V) regardless of the true A/F ratio and the system runs open-loop per how the manual tweak is set plus probably a small fixed enrichement (in addition to the fact that a very cold O2 sensor doesn't give a meaningful output anyway). As Brian said, in other modes, like WOT, even if warm, it goes back to open-loop and dumps enough extra fuel in to get a "best power" 12~13:1 A/F -- if you measured the O2 sensor output in this condition it would just be pegged at ~1V. If you're at warm idle with the O2 sensor outout showing that it's running closed-loop, and then unplugged the O2 sensor, it would probably just read a steady ~0.8V or so.

 

I fully agree with all of what you said above except that last sentence. Hydrocarbons, essentially unburnt fuel, go **up** when too lean??

You may be right, but you've got me shakin' ma poor widdle head on that one...

 

It's called "Lean misfire". Happens long before you can hear it. Fire goes out before all the fuel has burned. Engineers have been fighting it since the era of emission control began.

O2 systems are designed to keep the mix just above it. In the brief times that a slow O2 sensor lets the motor enter it the cat cleans it up. Listen to a 328 idle some time.

 

That makes sense. Thanks for teaching me about that effect.

So would it be fair to say that in a properly tuned Ferrari that leaning the mixture **some** should reduce HC's and increase NOx's, but that leaning "too much" could trigger a "lean misfire" condition that actually increased HC's?

Likewise, is it still fair to say that in a properly tuned Ferrari that enriching the mixture somewhat will reduce NOx's?

 

Part 2, yes. Part one, maybe. The car is designed to run on the ragged edge of lean misfire. It of course makes for cleaner air but also makes the most power at that point. Thats is why modern motors make such great power with such clean exhaust and low fuel consumption. Drag motors and at Bonneville we are always trying to get the mixture to that exact point to make the most power. Exceed it and the motor will find something to burn and with all that heat available it is usually aluminum.

 

Ha! For a minute there I thought that you were going to say "my wallet."


(oh wait...)

 

If the converters are OK the exhaust gas should have

CO: 0.0-0.2 %

HC: 50 +- 20 ppm


High HC is usualy burned oil.

CO is more often close to 0.0 than beeing on the high side.

Your car should pass the test with a oil change and a fast blast to clean it internaly. Try the test on the other exhaust pipe. I even passed a test with one converter removed using the right side of the exhaust...

 

I found one source on-line with that story, or close to it. Here's what they say:

HOW IT WORKS
"The Closed Loop Monitor watches the output of the oxygen sensor, which in most cars is a voltage that varies from about 0-1 volt. When the car is in open loop, the voltage out of the sensor is normally above 600mV (ie 0.6 volts) while in closed loop, the voltage rapidly jumps back and forth in the 400 - 600mV range. When the ECU switches off the injectors completely, the oxygen sensor output voltage drops to zero."

http://www.autospeed.com/cms/A_1716/article.html?popularArticle

 

I just tested my car for emission after importing it to Sweden from Germany. The results were;

CO 1000 rpm: 1,2 Limit: 0,5
CO 2500 rpm: 0,8 Limit: 0,3
HC: 408 Limit: 100
Lambda: 0,99 Limit: 0,97-1,03

The HC is WAY too high.. The car runs fine, but at idle it is not 100% steady.. Also when I have pushed the car some at the freeway and then stops and let it run at idle, it goes up 500-800rpms before it idles.

Could I have bad cats?

Sincerely,

Simon Bring

 

I have just ordered the Hyper-flow Cats from Ricambi. I hope that they will decrease the HC, I'll have a new test after I mounted them. About the CO it is worse I guess. Could it be so that the a/f mixture is to rich and the cats is burnt out because of that?

/simon

 

Simon -- What model/version F?

 

It is a '95 348 GTS. I just measured the A/F resistance today. IT shows 390 Ohms for left and 384 Ohms for right.