Failed Emission Test - 1989 420SEL
 

My 1989 420 SEL with 255,000 KM failed the provincial emission test. There is long list of what could be the problem. Here are the ASM tailpipe emission inspection results:

ASM 2525
HC PPM limit:50, reading:101, result:fail
CO% limit .28 reading:.18 result:pass
NO ppm Limit:548, reading:241, result:pass
RPM 1414 result:valid
Dilution: 15.6, result valid

Curb idle
HC PPM limit:200, reading:72, result:pass
CO% limit 1.00 reading:.08 result:pass
NO ppm Limit:N/A, reading:N/A, result:N/A,
RPM 665 result:valid
Dilution: 15.0, result valid

Engine coolant temp 85c.

I was told the high HC during driving test or high idle causes could be:

vacuum leak
ignition system malfunction
faulty computerized engine management system and or oxygen sensor
faulty air injection system
internal engine problem
failed catalytic converter

In November 2005, I had a valve job done, new intake manifold o-rings, new chain and guides, new plugs, air filter, new head bolts, mercedes gaskets, oil change was about 1,000 KM ago, using 5w50 synthetic. o2 sensor is about 3 years old. Prior to valve job, had a rough idle. Mechanic who did valve job said definately part of the rough idle job problem was the 0-rings, they were hard`as rock, also said the my ezl was OK.

The car runs great!

Any ideas?

If your system is working properly in closed loop, I'd guess the catalyst is dying or was cold.

50 PPM is an awfully tight limit for ASM 2525. What has this limit been in the past?

I have recent California ASM results for a buddy's '87 560 SEL and it scored 42/74 on the 2525 test. In CA the 2525 test is preceeded by the 1550 test, which is the tough one. Dave's 560 was 70/100 and the best mine has been in recent tests is 73/116 on the 1550 and 47/91 on 2525. The 2525 is usually not a problem because the catalyst heats up during the 1550 test, which is the acid test if the catalyst isn't hot enough. There is no idle test in CA, but a move is on to add it.

Your limit would probably fail most KE-equipped Mercs in California as few can score much under 50.

I assume your test is only 2525 and idle? You didn't report the O2 level. Is it listed on your test report?

There's appears to be a move to tightening limits in many jurisdictions to the point where more and more cars fail.

Suggest you look at this thread and the others it links to:

http://www.peachparts.com/shopforum/showthread.php?p=833484#post833484


I don't think there's really anything wrong with your car. If the O2 is zero, the HC can't get much lower. Relatively high HC is the nature of the KE-beast, which is why "conditioning" is so important. Old cats need to be REAL HOT!

You may want to take the limit issue up with your emission test authorities.

Duke

I'll say it for the 1 000 000 time , MONEYGRAB !!!:mad:
Take all the C.A.R.B guys out back & shoot them ( ignorant S.O.B.s...everyone I've ever met). :rolleyes:

Update
 

I do not have anymore readings from the inspection, everything was posted on first post. Yes, only the ASM2525 and the curb idle test, plus the gas cap pressure test are conducted. Apparently the limits were lowered in 2005.

The car was runnning for about 45 min. with a 15 min. highway run at 100 KPH but then it sat in for 50 min. in -5c temperature. The testor was 30 min. late. I actually went out and started the car about 5 min. before the test and got the coolant temp. backup to about 85c as the guy came out to get the car.

When you say catalyst, is that the catalytic converter? and is that the part of the exhaust system, connected to the crossover pipe, where the o2 sensor is?

The HC ppm reading is double the limit. How can I get the cat. hotter and what is the probability that it will be cut in half just becuase of heat, to less than 50 from 101?

I do have a brand new complete exhaust system from timevalve, hanging on the garage wall. The existing exhaust is still in decent shape.

Should I just replace the exhaust system? Should I go for a diagnostic to determine the reason for not meeting the emission standards? If I go for a diag., should I go to the dealer or any certified repair tech. shop, like the one that did the test?

The emission report does state a repair cost limit of $450. I can get a conditional pass, if I spend at least $450 on emission related repairs (including parts, labour , diagnostics). The car cannot be sold with a conditional pass but I can get the plates renewed.

Yes, catalyst and catalytic converter are the same thing. They are the first "units" after the 02 sensor, and your engine might also have "pre-cats" just aft of the exhaust manifold.

If you read my referenced posts you should understand that lack of proper "conditioning" is an absolute recipe for FAILURE.

You must arrange that the car is tested immediately after a good warmup that includes high speed driving and brisk acceleration, and NEVER, EVER shut down the engine prior to the test. You have to "manage" your test.

Letting the car sit for 50 minutes in sub-freezing temperatures is just not going to cut it, and idling the engine to warm the coolant will not get the catalysts hot enough.

You're probably going to need to retard the timing by shorting the R16/1 resistor and disabling the vacuum advance as I discussed in the other threads.

This is a lot easier and certainly cheaper than replacing the catalysts, which won't in and of itself gurantee a pass.

Duke

Prior to 2005
 

The HC ppm limit was 58 prior to 2005 in the province of Ontario, for the ASM 2525 test. In 2005 it was lowered 50. Last time the car was tested the result was 53.

So I am hearing that I should go for a retest as soon as possible and make sure to rev. the engine for at least 10 min. at 1500 to 2000 rpm until the technician arrives to take the beast into the test. The re-test is only $20.

The last time I checked, Mercedes list for the cat was C$2,200. I hope the timevalve cat. lives up to spec.

Where is the R16/1 resister located? How do I disable the vacuum advance?

Yes you hear correctly.

I don't know where the R16/1 resistor is located on your model. Maybe someone with a 126 can help out. Remove the resistor and replace it with a home made shorting plug - like a short piece of 12-gage wire with the exposed ends folded over so they make good contact with the pin receptables.

On my car there is a short piece of rubber tubing that connects from the manifold port to the nylon line that routes to the EZL module. This can be replaced with a piece of 1/8" vacuum hose with a slug of silicone sealer that is allowed to set up.

With these temporary mods, the car will feel VERY sluggish at low revs, but the retarded timing will considerably increase EGT, which will help keep the converter hot. The substitute parts can be removed and replaced with the OE parts when you are done with the test. Once you know the drill it only take of couple of minutes to configure and de-configure for emission testing.

Duke

Question for Duke 2.6...
 

Hi there,
I have a question for you - I read on another site that running on about 50% alcohol will greatly reduce the HC emissions. What is your take on this - does it screw up some other part of the test, and is it observable to the tester?
I always retard the timing slightly and add a gallon of alcohol to a quarter tank of gas before going in, and have good results.:)

Alcohol adds oxygen to the fuel. In CA we have about 2 percent oxygen by mass (about 10 percent ethanol by volume) in our gasoline year round. The "rationale" is that it reduces HC/CO during warmup (prior to the system going into closed loop when it runs slightly rich), but the reduction is marginal and even CA has asked the EPA for a waiver, but it's turned into another federal farm subsidy program, so no dice.

During closed loop operation the system just adds more fuel to consume the onboard O2. Oxgenated fuel costs more to produce and has about 2-3 percent less energy, so it reduces fuel economy by about the same amount for no meaningful improvement in emissions, but the farm lobby is strong and has Congress in their hip pocket.

Most HC failures (assuming the test report data indicates that the fuel system is properly functioning in closed loop mode) are due to the cat bed being too cold, which reduces oxidation reactions, and it's more of a problem as catalysts age and need to be hotter to achieve close to 100 percent of potential oxidation reactions than when they were new. Retarding the ignition advance map increases EGT and helps keep the cat bed(s) hot.

Fortunately our CA emission reports show O2 content in percent, and it's an excellent diagnosic tool. You want to see that number be 0.0. If it's 0.1 or more it means the catalyst is not hot enough to consume all the available O2 in oxidation reactions, but even with O2 readouts at 0.0 KE systems can read over 50 PPM HC on the loaded tests.

Bottom line is that adding alcohol to your fuel is of little value, and 50 percent alcohol will probably push the Lambda system beyond the limits of its control authority. What you need is a REAL HOT catalyst bed. Manage your emission control test so this is achieved.

Duke

Read up on the CIS/E system:

http://mb.braingears.com/126_DISC2/program/engine_420SEL.htm

Check out 07.3 and be aware that there is a potentiometer attached to the CIS throttle plate which goes bad. They are available and can be replaced but need to be properly calibrated.

You must also keep the car HOT as much as possible. Keep the car running while waiting for the test.

My last emission test also had high HC so I'm probably going to have problems next year, emissions are tested every two years in Virginia.

Foot + Floor
Loop Until Exhaust = Glowing OR T=2min.

Test Immediately :) hehe

A lot of people around here fail emission tests so I tell them to go get their car nice and hot before they go. They still fail and I have them demonstrate "conditioning" the car...and honestly it doesn't cut it :)

Let the beast under the hood come to life :)

Passed
 

I took the car into an "emission specialist" shop to get a diagnosis done. The guy quoted $60 to $120 for the diag., then whatever is wrong needs to be fixed, and then a retest is necessary. He asked me how much I was willing to spend,before he had to call me for authorization. I told him $200 is the limit. I called him 3 hours later, the car had passed, and the bill was $170 plus tax ($80 for diagnosis, $55 for combustion flush, $35 for emission test)

Here are the passed test results:

ASM 2525
HC PPM limit:50, reading:37, result:pass
CO% limit .28 reading:.14 result:pass
NO ppm Limit:548, reading:46, result:pass
RPM 1395 result:valid
Dilution: 15.0, result valid

Curb idle
HC PPM limit:200, reading:38, result:pass
CO% limit 1.00 reading:.08 result:pass
NO ppm Limit:N/A, reading:N/A, result:N/A,
RPM 661 result:valid
Dilution: 15.0, result valid

Very sweet! I am good to go for another 2 years.

If anybody in the Toronto area wants the shop name/address, private message me.

The diagnosis fee was a bribe to the cop that pulled him over while he was doing 120MPH performing the "combustion flush".

:D :D

What diagnostics did he perform and what was the result?

What's a "combustion flush"?

I take it you didn't witness any of this?

I could have probably gotten it to pass by just driving it around the block hard a couple of times and then running the test as quickly as possible

In CA we have a "tire dry test", which the tech can run on a wet day. As an experiment, I intentionally took my car in on a rainy day in January '01 and asked the tech to run the tire dry test, which is 30-60 seconds on the rollers with no load at about 25 MPH. He did this and then went right into the first test, which is 1550 and the HC was 87 ppm versus 121 two years prior against a limit of 141. O2 dropped from 0.4% to 0.0% so all the O2 was being used for oxidation by the catalyst. I attribute the reduction directly to the tire dry test which heated up the catalyst.

The HC limit for my car dropped to 116 in '03 and after barely making the cut at 113/.1% O2, my new knowledge about the ignition map got me down to 73/0.05 O2 in '05, and I don't see how it can get any lower.

Your first test was a marginal failure and was probably just a conditioning issue, but the car still has little margin.

You're probably going to have to go through this drill every time. Or you can work on your spark advance map and properly condition the car yourself, and probably pass on the first try, which is what this guy might have done given the substantial reduction in NOx, which was exactly the response from my engine, too.

Duke