300TE Failed AZ Emissions...NOx close... - PeachParts Mercedes-Benz Forum

ps2cho · #1 05-11-2011, 07:40 PM

Here are my emissions results...

300TE /// Standard (grams per mile) /// Result

HC: 0.39 /// 1.60 /// PASS
CO: 5.42 /// 15.00 /// PASS
NOx: 2.85 /// 2.50 /// FAIL

Fuel Cap: FAIL

Would the fuel cap possibly attribute to the fail?

I have all the standard tune up items done ignition-wise (rotor, cap, wires) in the last 20k, new spark plugs in the last 5k and a rebuilt fuel distributor + flow matched EHA on the fuel side last month. Duty cycle is closed-loop around 50%. O2 sensor is about 15k old. I have a new High Flow Magnaflow Cat which is 3 years old now. Precats are hollowed out (passed CA smog with it last year).

Ideas? I get a free retest within 60days so I got some time to work through this.

EDIT:

PS: No EGR on my model.

JohnM. · #2 05-11-2011, 08:10 PM

Excess NOx is usually caused by high combustion temperatures. But with your car in such good tune and the fact that NOx was close, I doubt that is the cause.

Usually when you fail only NOx, and its close, its your cat. I remember running into a lot of posts about the Magnaflow cats when I failed emissions a year back. They are good for 2-3 years tops, before they need replacement again to be effective.

Here are my smog numbers for reference (original cat):

First E-Test after Purchasing Car (2/23/2008)
HC - 1.6 (Limit 2.5)
CO - 15.6 (Limit 20)
Nox - .017 (Limit 3.5)

First E-Test Failure (2/26/2010)
HC - 3.2(Limit 1.5)
CO - 120(Limit 20)
Nox - .024 (Limit 3.5)

Latest E-Test (3/26/2010)
HC - 1.3 (Limit 1.5)
CO - 5.6 (Limit 20)
Nox - .094 (Limit 3.5)

ps2cho · #3 05-11-2011, 09:49 PM

If it is the cat, could running some bottles of isoheet or rubbing alcohol in the fuel bring it down a tad since I am so close?

Or....Richen my mixture slightly since it indicates possible lean?

JohnM. · #4 05-11-2011, 10:14 PM

Yeah. I was going to mention the really low HC's. Some octane booster / isoheet / whatever in the gas tank along with a richer mixture might bring down NOx enough.

david s poole · #5 05-13-2011, 11:27 AM

a trick i often use is to pump up the rear tires to about 45psi for the test.when car sits on dyno there are two bags created with two dyno rollers and this adds to the drag.higher tire pressures makes a measurable difference.

Duke2.6 · #6 05-13-2011, 12:43 PM

You have a very marginal failure. There may be nothing wrong with the emission control system, and it may be just a case of failing the somewhat arbitrary NOx cut point.

There are a couple of things you can do, and both involve retarding the spark advance map, which will reduce peak combustion temperature, which can dramatically lower NOx.

First, temporarily plug the vacuum advance line to the EZL.

Second, replace the R16/1 resistor with a shorting plug that you can make from short piece of wire. This will minimize the rate of advance with engine revs.

Search the archives if you don't understand what I mean by R16/1 resistor or where to find it on your model.

Retarding the spark advance map will reduce "engine out" NOx due to the cooler peak combustion temperature. It will also increase EGT, which will keep the catalyst bed hotter and more efficient.

Be prepared for a loss of performance, particularly below 2000 RPM. The above two temporary changes will reduce power so much below 2000 that it will be a real dog, but it's only temporary until you pass emissions.

BTW, if you do not replace the OE R16/1 resistor, which is probably 750 ohms - just leave the socket open, the rate of advance with engine revs will be more aggressive than OE, and the engine will have noticeably more low end torque, and probably reduced fuel consumption in around town driving, but be sure that it's not accompanied by detonation.

Duke

P.S. I have a background in automotive emission research. If you search the archives under my handle, you will find a number of threads where I explain how emissions are created and controlled, how to MANAGE your emission test, and low cost, easy ways to improve the emission performance of M103 engines based on experiments and tests I conducted on my '88 190E 2.6 five-speed that I bought new and still own.

My car (as is the case with most M103s) was always close to the HC limit in the California ASM 15 MPH test, which precedes the 25 MPH test. The primary issue is probably normal catalyst degradation due to aging. The above two changes dropped HC by about 40 percent due to the hotter catalyst, which gained me a comfortable margin. NOx was never a problem, but the lower peak combustion temperatures reduced engine out NOx so much that the tailpipe reduction was about 90 percent!!!

ps2cho · #7 05-13-2011, 10:37 PM

Thanks for the response Duke,

I am aware of the R16/1 resistor. Whats the difference between removal and shorting it in regards to timing?

When you say plug the vac line to the EZL, are we plugging the vacuum line side or the EZL side, or both?

Thanks,

I know my tire pressures were not 45psi for the test, they were probably ~28psi so that probably didn't help.

Got my 4 bottles of isoheet today also, so with everything mentioned combined, I have a feeling I will blow the test away this time

Duke2.6 · #8 05-14-2011, 01:13 PM

If you search the archives you will find detailed data on the spark advance vs. RPM (without vacuum advance) for both open circuit, shorted, and OE 750 ohm R16/1 resistor that I documented for my engine with a dial back timing light. It's also in the Mercedes service literature. Shorting is the laziest curve, and open circuit is the most aggressive.

You can always run your own test with a dial back timing light, too.

The initial timing is fixed by the EZL and cannot be changed. On my M103 it's 9 deg. BTDC.

On my M103 there is a vacuum line running from the inlet manifold to the EZL module consisting of 3 mm nylon tubing with short molded rubber hose sections at the manifold and EZL.

I cut a short piece of 1/8" generic vacuum hose, plugged it with silicone, and substitute it for the molded piece at the manifold for emission testing, but you can plug this line at any point in the circuit that you find most convenient. The point is to block the vacuum signal to the EZL, so it will not advance the timing at less than full load.

The combination of the least aggressive centrifugal spark advance curve with no vacuum advance yields lower spark advance for all speed/load conditions during the ASM and IM240 emission test procedures, which reduces peak combustion temperature (lower engine out NOx) and increases EGT to keep the catalyst bed hotter, which will result in more oxidation and reduction reactions inside the cat.

Fuel additives that claim better emission test performance are a complete waste of money. The modifications that I discussed cost about a dollar and a few minutes of time to configure.

Duke

Merkey · #9 05-14-2011, 11:52 PM

Wow!
Great Info!

Rahulio1989300E · #10 05-15-2011, 12:16 PM

Agreed, extremely useful information, bookmarked and saved in a Word document for me!

ps2cho · #11 05-20-2011, 12:49 AM

Read this BS right here....

Plug vac advance at EZL, short pins at R16/1 resistor, 4 bottles of ISOheet, 1/6 turn clockwise rich mixture...
New Air Filter, New Gas Cap, 1/2 tank of gas, 45psi rear tires, 15mins 70mph held in 3rd gear so run at 5000rpm for 15mins basically

Results

HC: 0.10 /// 1.60 /// PASS
CO: 2.11 /// 15.00 /// PASS
NOx: 2.46 /// 2.50 /// PASS

Fuel Cap: FAIL

WTF??? I still FAILED the gas cap. I was so pissed off. I went in spoke with the manager, showed her my receipt its brand new. She says ok let me test it again...I drive around and she now starts running the car on the dyno again, but the car had been sitting turned off in the parking lot for about 20mins at this point...

So...

HC: 0.28 /// 1.60 /// PASS
CO: 3.42 /// 15.00 /// PASS
NOx: 2.52 /// 2.50 /// FAIL

Fuel Cap: VISUAL PASS

WTF???? I mean really?

I knew it was gonna fail, and I told them that since the car had been sitting turned off for 20mins, she said sorry can't let you hold RPM's high because it causes contamination.

Really, really pissed off.

At this point, should I go get the cat replaced or try to get by again?
I don't understand how a brand new gas cap can fail? She said she had to override it with a visual pass.

GRRRR

2wheelsoff · #12 05-20-2011, 02:06 AM

wtf? sounds AWFUL! I would retest, since method worked the first time around. If you go with new cat - amazon had the lowest priced CA versions.

JohnM. · #13 05-20-2011, 02:28 AM

I would go back and try to pass again, also keep it in low gear all the way there to get the cat nice and hot, don't go if there is a huge line. The engine went into heatsoak which is why it failed the second time around.

Also, maybe go richen up the mixture a bit more.

benzworldrefuge · #14 05-20-2011, 09:33 AM

I've never found myself rooting for someone else to pass an emissions test as much as I am for ps2cho right now. Would the gas cap fail be due to a leak in the vapor capture system canister leak or rubber hose fracture?

Best wishes on your next try. Some great advice in this thread.

Rafi · #15 05-20-2011, 10:37 AM

The variation in the results for retests tells me that testing is unreliable and they should set the limits higher. This testing is a crap shoot. At least they are letting you retest as much as you want which is the only positive thing.
Good luck.