1987 300E just failed California Smog Test

[murphysf]

Hello

I just failed smog. See the results below. 4 or 6 years ago I failed and replaced the cat and have passed till today. In California we must run a emissions smog check every 2 years.



15 mph results 1772 rpm
%CO2 13.9
%O2 1.6

HC
111 failed max is 110

CO
.19 passed

NO
403 passed


25 mph results 1770 rpm
%CO2 13.8
%O2 1.5

HC
73 passed max is 77

CO
.16

NO
239


I am thinking of shorting the R16/1 reference resistor. This will retard the timing, will also plug the EZL vacuum line. Maybe also do an oil change as I know the car burns alot of oil. And then go for a retest.

Ideas or suggestions?

Thanks!

[Sugar Bear]

If it burns a lot of oil put valve seals and fresh spark plugs in it. Get the cat fully warm before the test so it works well by keeping it in a lower gear and the RPM's around 4500 for a few minutes.

[Duke2.6]

Originally Posted by murphysf

I am thinking of shorting the R16/1 reference resistor. This will retard the timing, will also plug the EZL vacuum line. Maybe also do an oil change as I know the car burns alot of oil. And then go for a retest.



Thanks!

Yep! That should do it. I figured this out over 15 years ago and documented all the testing I did.

Successful CA ASM emission test (KE fuel system)

Failing the whole test because HC was 1 ppm over the cutpoint is a crock. The problem is likely catalyst aging. Go to a place where you can get on the dyno ASAP, don't shut off the engine. Open the windows and turn the AC to max to put some load on the engine. Retarding the spark advance map by shorting the R16/1 resistor and blocking vacuum to the EZL will significantly retard the spark advance map, which increases EGT that will get the catalyst hotter early in the test. This will reduce HC by 20 to 30 percent, and dramatically reduce NOx due to lower peak combustion temperature from the retarded spark advance.

You should also see a reduction in O2. If it gets to zero it means the catalyst is enabling essentially all possible oxidation and reduction reactions.

I made a shorting plug with a short piece of wire stripped on both and bent into a "U", and used a short piece of 1/8" vacuum tubing that I plugged with a slug of silicone sealer to temporarily replace the short piece of molded vacuum tubing from the inlet manifold nipple to the clear nylon tubing.

Let us know how the retest turns out.

Duke

[murphysf]

Duke - thanks for the post and the link.

If I take the resistor out and short the connector do I still need to plug the vacuum line?

What happens if I just short out the resistor will it still retard the timing 6 degrees?

[murphysf]

Originally Posted by Duke2.6

Yep! That should do it. I figured this out over 15 years ago and documented all the testing I did.

Successful CA ASM emission test (KE fuel system)

Failing the whole test because HC was 1 ppm over the cutpoint is a crock. The problem is likely catalyst aging. Go to a place where you can get on the dyno ASAP, don't shut off the engine. Open the windows and turn the AC to max to put some load on the engine. Retarding the spark advance map by shorting the R16/1 resistor and blocking vacuum to the EZL will significantly retard the spark advance map, which increases EGT that will get the catalyst hotter early in the test. This will reduce HC by 20 to 30 percent, and dramatically reduce NOx due to lower peak combustion temperature from the retarded spark advance.

You should also see a reduction in O2. If it gets to zero it means the catalyst is enabling essentially all possible oxidation and reduction reactions.

I made a shorting plug with a short piece of wire stripped on both and bent into a "U", and used a short piece of 1/8" vacuum tubing that I plugged with a slug of silicone sealer to temporarily replace the short piece of molded vacuum tubing from the inlet manifold nipple to the clear nylon tubing.

Let us know how the retest turns out.

Duke

does the R16/1 mod and plugged vacuum tubing affect timing at an idle? I ask as part of the test is fo the tech to check the timing.

[Duke2.6]

Shorting the R16/1 resistor reduces the rate of spark advance with revs, but I believe full advance (IIRC 32 degrees) is achieved at 3200 regardless of resistor value including zero.

Your test speeds were just under 1800, so the advance due to revs with the resistor shorted is less than with the OE 750 Ohm resistor.

Plugging the vacuum advance signal line to the EZL will further retard spark advance at the test speeds and loads, and the more you can retard spark advance at the test speeds and loads the lower the peak combustion temperature, which reduces engine out NOx, and the greater the EGT increase to kept the catalyst hot enough to maximize oxidation and reduction reactions.

I don't know the effect of doing only one of the above because I have never tested those conditions and it's so easy to make the temporary modifications that I do both.

There is no effect on initial timing because it is fixed by the EZL and is not adjustable, which is written on the emission control data sticker. Because of this the tech is NOT required to check initial timing. This is stated in the emission test manual that you can download from the BAR Web site.

Most of the time when I inform the tech that they don't need to check initial timing because it is fixed they just sarcastically reply:"We check them all". Most of these guys are jerks who think I'm just another dumb consumer. I very likely know more about emission control than they do.

Back in the late sixties I did a MSME at the U. of Wisconsin Engine Research Center and did emission related research on a GM fellowship. Back then we pretty much knew how emissions were created and how to control them, but we didn't have the engine management technology with sufficient granularity to control fuel flow and spark advance to the necessary very tight tolerances under all operating conditions, and it took a decade or so to get there.

Microprocessor controlled port EFI and spark advance and development of the O2 sensor and three-way catalyst that oxidizes HC and CO2 and reduces NOx got us over the hump.


Duke

[murphysf]

Hi -

I took the resistor out and put a u shaped wire into the connector and also got another piece of vacuum hose and pluged it with some silicone.

Hopefully I will take it for a retest in the next day or two.

I will post the results.

Thanks!!!!

[Duke2.6]

Looking forward to the results. I hate driving my car in the emission test configuration because it won't get out of it's own way below about 2000 due to so little torque/power.

If you have an automatic it will probably not be as noticeable because the converter stall speed is probably about 2000.

I keep the shorting wire and short piece of plugged vacuum hose in the glove box. I install them the night before emission testing and remove them the moment I get home. It only takes a few minutes.

If you leave the OE resistor off the spark advance with engine revs will be the most aggressive. There is so much more low end torque that I can shift my five-speed at 2000. Fifth is okay down to 30-35 MPH, and around town MPG increased a solid ten percent.

This may not be achievable with an automatic because the moment you load the engine at low revs it will jump to converter stall speed.

Duke

[murphysf]

I passed yesterday but not by much HC are still high

the only things I did was short the R16/1 resistor and plug the vacuum line. I did try to run it hard on the freeway before the test but then had do drive at slower speeds for a bout a mile or so after getting off the freeway. The car sat running for about 5 minutes at the smog test station while the tech filled out the paperwork and entered the info into the computer before he started the test.

here are the results, the values in () are the retest values when I passed. Interesting takeaway that the HC came down the least compared to CO and NO

15 mph results 1772 rpm
%CO2 13.9 (13.8)
%O2 1.6 (1.5)

HC
111 failed max is 110 (95) 14% lower

CO
.19 passed (.14) 26% lower

NO
403 passed (323) 20% lower


25 mph results 1770 rpm
%CO2 13.8 (13.8)
%O2 1.5 (1.5)

HC
73 passed max is 77 (64) about 12% lower

CO
.16 (.15)

NO
239 (189) about 21% lower


so HC are still high, two years ago I put in a new cap and rotor, plug wires and plugs. I don't drive this car much a few k miles a year.

I think the high HCs are caused by a lean misfire due to a vacuum leak where the intake manifold attaches to the head. Not sure how hard the gasket is to change.

I am going to look at my results from 2 years ago and see what my HCs were

[Duke2.6]

Congratulations and thanks for posting the results and analysis. I thought the new measurements would be a bit lower with the R16/1 and vacuum advance "adjustments".

It's tough to get these M103 engines below about 50 ppm HC, and I think it has somewhat to do with the relatively high surface area to volume ratio of the "semi-hemi with quench zone" combustion chamber.

Something I figured out at least 20 years ago is that resistor plugs can cause enough misfires to increase HC and you can feel them at idle. Bosch no longer offers non-resistor plugs, but I recall that either NGK or Denso offers a non resistor plug equivalent to the H9DC. Their websites should have cross reference data.

The fact that there is still 1.5% O2 could be an indication of catalyst aging. How many miles on the car? Zero percent O2 indicates that the catalyst is accomplishing near 100 percent of all available oxidation and reduction reactions.

Here is the most recent test of my '88 190E 2.6 five-speed with 85K miles. It has the original catalyst and O2 sensor. I checked the duty cycle about ten years ago and it was within spec... no need to adjust. The 15 MPH test was done in 2nd gear and the 25 MPH test in third.


15 mph results 1661 rpm (2nd gear)
%CO2 16.2
%O2 0.0

HC, ppm
max 116, ave. 27, meas. 54

%CO
max 0.74, ave. 0.09, meas. 0.20

NO, ppm
max. 791. ave. 255, meas. 127


25 mph results 1627 rpm (third gear)
%CO2 15.6
%O2 0.0

HC, ppm
max. 91, ave. 18, meas. 28

%CO
max. 0.62, ave. 0.07, meas. 0.17

NO, ppm
max. 791, ave. 223 meas, 42

Your cutpoints are lower because your 300E is heavier. There is a chart on the BAR Web site that explains how the cutpoints are calculated.

The "average" is the average of passing vehicles in our year group that is something like 1986-1991. As you can see we are both above average in HC and CO, but below average on NO. I have no explanation for this.

It looks like you have enough margin to pass the next test or two with good conditioning, like you did. Let us know the mileage and whether the cat and O2 sensor are original and the type of installed spark plugs.

Up until my last two or three emission tests I was directed to a STAR (test only station) due to my car being tagged as "high emitter profile", but this is no longer the case, but I don't now the reason.

Duke

[murphysf]

The vehicle has 246k miles and burns alot of oil.

I changed the cat 4 years ago as I failed smog with my NO through the roof.


I purchased the vehicle in 2001.

The O2 sensor might be original. 4 years ago when I was failing smog I monitored the voltage and duty cycle with a dwell meter and it was operating fine according to the tech notes I found on O2 behavior.

I did get some factory non resistor plugs from another member on I believe a different forum that happened to live in my neighborhood. I Bout a large supply had extra stock and some me 12 plugs. I am still on the first set. These were installed along with a new cap and rotor and wires 4 years ago when I was failing smog.

Four years ago when I looked into non resistor plugs I recall hearing similar but also found the the dealers either had them or could get them and they were very affordable.


In the next day or two I am going to dig out the test results for the last 2-3 tests and see what my HC was. One interesting exercise would be to plot the results for each reading of all tests to see how things change every 2 years.

It doesn't start super easy like it use to , need to crank it a bit and the idle isn't as smooth as it use to be. I replaced the injector seals and 4 or 5 larger air / vacuum hoses. I do know that I have a leak at my intake gasket as I verified it by spraying carb cleaner on it as having the idle go up.



Thanks

[Duke2.6]

That's a lot of miles, and I think high oil consumption may be the cause of your relatively high HC. The longer chain molecules in oil don't oxidize as readily as lighter gasoline molecules and the phosphorous in the ZDDP anti-wear additive is believed to accelerate catalyst aging.

I've got a summary sheet of all my emission tests going back to the first one in 1991. The results are pretty consistent ever since I did the R16/1 and vacuum advance mod for the '05 test relative to '03, and since that time my annual mileage has dropped from about 1500 to 500 per year.

My 190 should outlive me, and I already know of one guy waiting for me to keel over.

Duke

[murphysf]

thanks for the insight about oil consumption

I do know that I have a large vacuum leak at the intake manifold..

does anyone kow how hard it is to change on a 1987. I saw a "how to" for a 300E on Peach Parts, but it is for a different setup as there are fuel rails and other stuff.

also I have been out of the look for about 4 years, what are the other forums that have alot of tech and DIY posts, I think I will give the gasket a go but would like to first read some how to diy posts if they exist.

thanks

[murphysf]

i pulled the last two smog reports

the HC readings have been high

2019
HC 87

2021
HC 92

2023
HC 111 failed
HC 95 passed after shorting R16/1 and plugging vacuum line


lets see what happens in 2025