1990 300E failed emissions-need answers please - PeachParts Mercedes-Benz Forum

crs82 · #1 07-02-2011, 10:57 PM

I have looked at the "millions" of threads on failed emissions. I think I have a handle of what all to check.
Situation - passed all areas, but one, of the emissions check in Atlanta, GA.
Failed one area. 25/25, high rev, high HCs. Too much unburned fuel if not mistaken.
Question - Would a hole in the exhaust before the rear muffler affect the results? There are a few rather large holes.
I made the mistake of taking the car, which had been sitting for at least two months, without really heating it up, putting in 89 (midgrade) test fuel, and turning it off twice before the test. I know..I know.
Anything else I should try out? Going to check plugs, cap, rotor, vacuum lines, etc.
Thanks in advance.

crs82 · #2 07-03-2011, 10:06 AM

25/25 test: 50/15 TEST
Reading Allowed Reading Allowed
HC ppm 204 130 FAIL 121 134 PASS
CO% 0.35 0.83 PASS 0.13 0.75 PASS
NO ppm 449 905 PASS 301 990 PASS
RPM 1517 3000 PASS 1529 3000 PASS
CO+CO2% 13.1 6.0 min PASS 13.4 6.0 min PASS

Everything else looks pretty good. Just need those 25/25 HC numbers to come down a little...OK, a lot.

JohnM. · #3 07-03-2011, 02:04 PM

Sounds like driving it really (really) hard for a minute with the right gasoline in the tank would solve your problem.

ps2cho · #4 07-03-2011, 02:05 PM

You need to properly heat everything up, especially since it hasn't been driven recently.

Put a can of seafoam in the tank, drive it hard on the freeway in 3rd gear for 20mins then drive straight in without turning car off. Soon as you turn it off, heatsoak occurs and all emissions items will go up.

crs82 · #5 07-03-2011, 03:35 PM

I think not heating it up properly was my biggest mistake. I think I'm gonna give it a tuneup and then go back for my free re-test. I'll drive it really hard for a few minutes to get it up to passing temps.
Thanks.

ps2cho · #6 07-03-2011, 06:31 PM

Quote:

Originally Posted by crs82

I think not heating it up properly was my biggest mistake. I think I'm gonna give it a tuneup and then go back for my free re-test. I'll drive it really hard for a few minutes to get it up to passing temps.
Thanks.

It needs to be very, very hot. A few minutes won't cut it.

Like I said, freeway 70mph in 3rd gear. Hold it at ~5500 rpm for a good 15mins or so. Its the only way to heat the cat up enough to fly by emissions. A few minutes won't do anything. A new engine may be enough with all the computer adjustments, but with our older engines -- they WANT you to fail.

crs82 · #7 07-03-2011, 10:50 PM

Fair enough. Thanks for the insight.
Still curious as to whether holes in exhaust would have any bearing on emissions. Downdraft from the cat, but you never know.

ps2cho · #8 07-03-2011, 11:36 PM

After the cat -- not really unless its a huge leak causing the emissions tester to be so diluted it can't get a reading. You can always use the exhaust bandage to get you by, or have an exhaust shop fix it for you -- shouldn't be expensive. I had all my pipes backwards of the cat replaced for $180 I believe.

JohnM. · #9 07-05-2011, 01:31 AM

More holes in the exhaust the better as far as I can see. It's less emissions going into the testing machine!

ronald7410 · #10 08-07-2011, 01:09 PM

Quote:

Originally Posted by ps2cho

It needs to be very, very hot. A few minutes won't cut it.

Like I said, freeway 70mph in 3rd gear. Hold it at ~5500 rpm for a good 15mins or so. Its the only way to heat the cat up enough to fly by emissions. A few minutes won't do anything. A new engine may be enough with all the computer adjustments, but with our older engines -- they WANT you to fail.

15mins 5500rpm! can our cars handle that without overheating?

tjts1 · #11 08-07-2011, 01:13 PM

Quote:

Originally Posted by ronald7410

15mins 5500rpm! can our cars handle that without overheating?

Yes it can handle it it, no don't do that. It won't help you pass smog. Your engine is running rich. The most likely culprit is a failed or lazy O2 sensor. Relatively cheap and easy fix.

Quote:

Originally Posted by JohnM.

More holes in the exhaust the better as far as I can see. It's less emissions going into the testing machine!

The emissions test looks at HC, NO, and CO as a % percent of the total emissions so the hole is irrelevant. If there is O2 leaking into the exhaust (possible between pulses) they will fail you. Thats why the last line in his emissions test is "CO+CO2% 13.1 6.0 min PASS 13.4 6.0 min PASS". This checks for exhaust dilution with outside air.

crs82 · #12 09-20-2011, 04:07 PM

O.K. Next round. Passed on 25/25 HCs. 127 out of a possible 130, so barely. Now failed on NO ppm, 50/15 test. 1067 on a maximum of 990. Would this be the EGR? Why would it pass with flying colors on the last test (see above #s) and fail, just barely, on this test? I put in a new O2 sensor, so that helped.
Any ideas?

Here are the new numbers.
25/25 Test
Reading Allowed
127 130 HC ppm
.02 .83 CO%
792 905 NO ppm
13.0 6.0min CO+CO2%

50/15 Test
Reading Allowed
00073 00134 HC ppm
0.01 0.75 CO%
01067 00990 NO ppm
13.5 6.0 min CO+CO2%

aldedmon · #13 09-20-2011, 04:21 PM

Did you change the oil. I recommend changing the oil on all high mileage MB's the Day or THE MORNING before the test. The used oil blows by the rings and elevates the numbers. It worked for me. All my numbers were out of range early one cold morning in Texas. Car was therefore running a little rich. Changed the Oil and went back on a warmer day later in the after noon...brought 'er in HOT!....she passed with flying colors. You should have seen the techs face. He was literally like WTF! He asked what I had done and I told him.
1) 92-93 Octane (Always before the test... and add a can of that liquid Inspection Pass stuff (yeah I know its prolly just some "snake oil"
2) Fresh Oil change night before
3) Bring the car in HOT...Leave it running while you wait
Long as its not missing and you did a tune up in the last coupla years, I would worry too much about the rotors,wires or plugs.
Hope this helps and good luck!

crs82 · #14 09-20-2011, 10:23 PM

Have not changed the oil. This would be a good time (and reason)to change it, though. Thanks for the advice.
I'm just wondering about how the NO ppm went from well within specs to way high (301 ppm to 1067 ppm).

I did bring in the car HOT! I drove around town about 45 before the test.
I'm glad the HC's went down, but why the hugely elevated NO?

Hirnbeiss · #15 09-21-2011, 08:02 AM

This time the high temp may have gotcha.

What Causes High NO - Nitrous Oxide - SmogTips.com. Why did my car fail emission test high NO emissions. What is NO. My vehicle failed high nitrous oxide emissions test. Produced high NO. Common high NO failures. NO emissions. How can I lower NOx. Co