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Hi

I have a 1987 300E its just failed California Smog Emissions test

HC failed at 15 mph and 25 mph , NO failed at 15 mpg and passed at 25 mph. This vehicle does not have an EGR system.

Before I took the test I changed the plus, cap, rotor, and wires. I also changed the two idle air valve hoses and some of the vacuum hose fittings.

This time I put Bosch Platinum plugs in it. Do you think this could be the cause of the high HC? The test two years ago HC was fine.

I performed the check that this thread is based on.

I used a fluke digital volt meter and got the following results:

my vp6 was 13.5V

and my vp3 varied from first 3.8V - 4.4V then from 4V - 4.5V

I used a fluke digital voltmeter

this would give a range of of 67% to 72%

this is not right, I then tried with a Sears Craftsman analog / Volt / Dwell meter from the 80s and got the following.

according to the 6cyl scale the dwell read 33-35 degrees. Not sure if this is the same as duty cycle, but I think it is.

at idle there was very little fluctuation. as I brought the rpm up if move a bit more but not much.

I guess I should check it in the morning when it is cold.

ideas?

ok I just went out to the vehicle and did a static dwell measurement of pins 2 & 3. I turned the key to the second position (didn't start the car) and the meter read 25 on the 8 cyl scan and about 34 on the 6 cyl scale.

bear with me here I might seem to be all over the map but am converging.

On https://www.landiss.com/mixture.htm I read:
With the ignition on but the engine not running, the duty cycle tells which version of controller is installed. A 70% duty cycle indicates the standard controller with the ability to read some faults by monitoring the duty cycle. 85% indicates the California controller, which ordinarily displays the faults as a blinking LED on connector X92, although it can be programmed to display the faults as an X11-pin3 duty cycle. 100% indicates the controller does not display fault codes in this manner, or is faulty.

interesting that if you multiply my above values by 2 you get : 25 (8 cyl) x 2 - 50 and 34 (6cyl ) x2 = 68 (close to 70)?

is my meter off by a factor of 2? the meter was designed to measure the dwell of ignition points. I used it on my VW rabbits from the 70s to set the point I recall using the 8 cyl scale and then doubling it.

here is a link to the manual of my sears meter
http://kentcomputer.com/77VW/sears161.216500.pdf


I feel like I am getting close but need some clarity and direction.

Thanks!!
 

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I just read the following

"""If you have terminal 3 in your diagnositic connector then check your lambda value first. 50% is normal for most engines but the 103 engine (which I presume you have) prefers to run at 30-40% (I put it on 35% during services), they run quite well at this mixture, 50% is too lean on acceleration from experience. You can check you EHA (if fitted) for operation by watching the lambda value fluctuate +-5%.""

So I guess my readings of 33-35 is ok
ok I just went out to the vehicle and did a static dwell measurement of pins 2 & 3. I turned the key to the second position (didn't start the car) and the meter read 25 on the 8 cyl scan and about 34 on the 6 cyl scale.

bear with me here I might seem to be all over the map but am converging.

On https://www.landiss.com/mixture.htm I read:
With the ignition on but the engine not running, the duty cycle tells which version of controller is installed. A 70% duty cycle indicates the standard controller with the ability to read some faults by monitoring the duty cycle. 85% indicates the California controller, which ordinarily displays the faults as a blinking LED on connector X92, although it can be programmed to display the faults as an X11-pin3 duty cycle. 100% indicates the controller does not display fault codes in this manner, or is faulty.

interesting that if you multiply my above values by 2 you get : 25 (8 cyl) x 2 = 50 and 34 (6cyl ) x2 = 68 (close to 70)?

is my meter off by a factor of 2? the meter was designed to measure the dwell of ignition points. I used it on my VW rabbits from the 70s to set the point I recall using the 8 cyl scale and then doubling it.

here is a link to the manual of my sears meter
http://kentcomputer.com/77VW/sears161.216500.pdf


I feel like I am getting close but need some clarity and direction.

Thanks!!
 

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I just read the following

"""If you have terminal 3 in your diagnositic connector then check your lambda value first. 50% is normal for most engines but the 103 engine (which I presume you have) prefers to run at 30-40% (I put it on 35% during services), they run quite well at this mixture, 50% is too lean on acceleration from experience. You can check you EHA (if fitted) for operation by watching the lambda value fluctuate +-5%.""

So I guess my readings of 33-35 is ok
The answers to your CA emissions problems are in your other post. Your lambda readings even if they are off a little has very little to do with your car failing emissions. The spark plugs you use will not hurt or help you that much either. Been there done that... FYI The dwell meter will only give you the correct duty cycle reading in 4 cyl mode no matter how many cylinders your car has. Perhaps read post 42/46 one more time.
- Cheers!
 

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thanks, yes today I got thinking about the plugs.

I found some bosch 7978 that I am going to order, is this a good plug?

which cats did you replace? the two front cats in teh engine compartment or the rear cat under the car?
there are only the two cats side-by side right after the exhaust manifold. behind those two cats are two inline mufflers, the first one has 2 pipes in and one fatter pipe out, then the rear muffler has the one pipe in, and two exhaust pipes out.


for the diag stuff, you need a proper duty cycle measurement, I have no idea what your dwell meter with a 6 cyl vs 8 cyl scale means. use a DVM with duty cycle and subtract the reading from 100% to get the numbers given in the official mercedes documentation. any value in the middle of the scale is good enough. yes, it shifts a little when you change the throttle, as long as it doesn't peg at 0 or 100, things are working OK..
 

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The answers to your CA emissions problems are in your other post. Your lambda readings even if they are off a little has very little to do with your car failing emissions. The spark plugs you use will not hurt or help you that much either. Been there done that... FYI The dwell meter will only give you the correct duty cycle reading in 4 cyl mode no matter how many cylinders your car has. Perhaps read post 42/46 one more time.
- Cheers!
Thanks for the post. And yes, sorry I didn't initially read every post but found 42/46 to help.

To recap the vehicle is a 1987 300E the car was purchases from a MB dealership in New Jersey.

I came here as I just failed the smog / emissions test in California. HC was high at both 15 & 25 mph and NO was high only at 15 mph. I thought this test might help to indicate if my O2 sensor is working properly.
This morning after sleeping on it I decided to revisit the measurements. I used a Fluke DMM for all the DC Voltage measurements (should I have measured with the VAC setting? I used a Sears Tach / Volt/ RPM meter for the dwell.

Static (not running)
VDC DMM 6 = 11.77VDC
VDC DMM 3 = 3.60V
Dwell meter 52

The dwell of 52 does not agree with the following statement: With ignition switched on (engine not running) the duty cycle should be about 70% (California: 85%).
However does agree with the following statement:
If you’re using a voltmeter it should read 0.3 * Vp6 (California: 0.15 * Vp6.
In my case it would be .3 * 11.77 = 3.5V which is close to what I measured (3.6VDC) Actually I am measuring DC voltage the equation uses Vp (which I believe is V peak?)

Running (cold – open loop)
VDC DMM 6 = 14
VDCVDC DMM 3 = 7 VDC this would indicate a dwell of 50 = (1-(7V/14V)) X 100 = .5 X 100 = 50.
Dwell meter 44

Running (cold – closed loop)
VDC DMM 6 = 14
VDCVDC DMM 3 = 4.5-5 VDC this would indicate a dwell of 64 – 68.
Dwell meter 47-50 at idle, 47-52 slightly above idle.

I did all of this in about 3 minutes, idling from a cold start, so I didn’t drive the car or let it get up to full operating temp. I decided to come back inside and compose this.

So it seems like the system has some functionally. Perhaps the variations in values is based on VDC measurements with a Fluke DMM?

Any other ideas or should I move on and assume my CIS control system is moving properly.
 

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there are only the two cats side-by side right after the exhaust manifold. behind those two cats are two inline mufflers, the first one has 2 pipes in and one fatter pipe out, then the rear muffler has the one pipe in, and two exhaust pipes out.


for the diag stuff, you need a proper duty cycle measurement, I have no idea what your dwell meter with a 6 cyl vs 8 cyl scale means. use a DVM with duty cycle and subtract the reading from 100% to get the numbers given in the official mercedes documentation. any value in the middle of the scale is good enough. yes, it shifts a little when you change the throttle, as long as it doesn't peg at 0 or 100, things are working OK..
thanks, my car 1987 300E has a different exhaust configuration. I have the two cats right after teh exhaust manifold then I have a 3 way cat under the vehicle. that feeds into a resonator which feeds into a single muffler.
 

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I have the two cats right after teh exhaust manifold then I have a 3 way cat under the vehicle. that feeds into a resonator which feeds into a single muffler.
This is the standard 6 cylinder configuration. The two small cats in the headpipe are warmup cats meant to heat up quickly due to their close proximity to the engine. They light off quickly to reduce HC emissions from the rich mixture needed during a cold start. The large threeway catalyst located further downstream does the bulk of exhaust treatment. It contains a significant amount of platinum, palladium and rhodium which is what makes it so expensive to replace.
 

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huh, I just went through ISPPI for 2 of my cars (the M103 2.6, and my M104 3.2 cab) and they both just have the dual cat in the main exhaust lines between the headers and the pre-muffler. mercedes sells this dual cat assembly as a single part, A1244906820 for the 2.6, A1244909320 for later 3.2's.
 

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I checked on the price of that headpipe/cat assembly years ago and IIRC it was about $2500. LOL Brutal is right.
 

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I checked on the price of that headpipe/cat assembly years ago and IIRC it was about $2500. LOL Brutal is right.
and now all 3 PN's seem to be NLA.

Magnaflow makes compatible cats, including California ARB certified version, a muffler shop will cut and weld those into the existing pipes. pretty sure you can skip the front two little ones, since Mercedes did in 89+, and just use the 3-way main cat.
 
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