Thanks

I'll consider jumping the resistor and plugging the vac line.

I was away out of town for a while.

I just measured the O2 sensor voltage. Started the car it was already warmed up. Voltage measured around 440mV, let it run for a while and reved it a bit and it reading on the digital meter jumped around between 100mV and 700mV

According to what I have read this is the typical behavior.

I was surprised that it jumped around that much at idle and also when I would hold to rpm up around 2k rpm.


I also confirmed that 13.5VDC was going to the heater part of the O2 sensor.

I guess my O2 sensor is fine?

another detail I left out, the smog tech ran the test with the hood up. I believe the hood should stay down, he also put a external fan in front of the radiator, it was only around 70 degrees that day.

Over the years during past tests I recall the temp creeping way up to 105 and above and the fan on. When I looked at the temp gauge when the test was over it was only around 100C.

Sounds like it didn't get hot enough?

The guy I go to always leaves the hood open and places a fan in front of the car to blow out the fumes.

Change the O2 sensor, do an oil change, fill it up 3/4 of a tank with high octane quality fuel and take it for a 30 minute high revving ride, don't turn the engine off and if you have to wait go around the block again. I'm almost certain it will pass.

Both my cars with the same engine passed doing so and both were in really bad shape when I got it smogged.

so to confirm short R16/1 which will yield 12 degrees of retard. I read lots of posts about people removing the resistor and leaving it open which is no retard.

Shorting the R16/1 resistor does not retard maximum advance with engine revs, which is 32 degrees. (Initial timing is fixed at nine degrees and is not adjustable.) It merely slows the rate of advance with engine revs, so maximum advance doesn't occur until higher in the rev range. That means that during emission testing, which is done at fairly low revs, there is less advance, which cools peak combustion temperature for less engine out NOx and the higher EGR heats up the cat bed, which helps an "aged catalyst" operate closer to peak efficiency in both oxidation and reduction modes.

Blocking the vacuum signal line to the EZL MUST also be done in conjunction with shorting the R16/1 resistor socket to minimize advance under emission test conditions in order to yield the lowest recorded emissions.


As I have previously reported, removing the R16/1 resistor creates the most aggressive increase in advance with engine revs, and it allows me to use fifth gear as low as 30 MPH. With the original 750K ohm resistor installed it had so little low end torque that fifth was not useable below 45 MPH. Also, around town fuel economy increased from18-22 to 22-24. It easily keeps up with traffic shifting at 2000-2500 revs.

In your last post where you quoted my last post, I asked for your car's total mileage. I even underlined the question, but you didn't answer. I still want to know.

I hope you searched and read the threads started by me, Duke2.6, to see the testing (advance with revs and cat inlet temperature) and analysis I did over ten years ago with both the OE resistor, no resistor, and shorting the resistor socket.

It sounds like your O2 sensor is okay. Voltage should flip about two times per second at idle speed. As O2 sensors age, response time slows, and that can increase emissions. Again, how many miles does your car have and do you believe that the O2 sensor and catalyst are original???


The Mercedes maintenance schedule for my '88 calls for replacing the O2 sensor every 60K miles. I now have 85K, but have not replaced it because I have no reason to believe the O2 sensor has degraded enough to need replacement.

As far as engine temp and EGT is concerned I can pretty much guarantee that by the end of the test with the R16/1 socket shorted and vacuum advance blocked the aux. electric fan will engage before the end of the tests because coolant temp has hit 105C. That's because the higher EGT throws a lot more heat into the cooling system as it passes through the exhaust ports, and that's necessary with an aged catalyst to get it hot enough to operate at or near peak efficiency.

You will also probably notice that engine response is sluggish around town due to the severely retarded spark advance map. It's very noticeable on my five-speed because I can load up the engine at very low revs. With an automatic it may be less noticeable, because when you load the engine, revs will always jump to at least converter stall speed that I expect is about 2000 revs. You can check by firmly applying the brake and briefly floor the throttle. Revs will freeze at converter stall speed within about a second. If you do the test I'd like to know the result.


Duke

Thanks for the additional info.

The car has 233K miles. I bought it from the original owner in 2001 with 150K miles.

I just spent about an hour reviewing all the records from the original owner. In March of 1997 the car was brought to the dealer with an engine that was very hard to start at times and would die on acceleration at times. They replaced the Ignition Coil and O2 sensor then. March 1997 with 107K miles.

So it looks like the O2 sensor is 22 years old and has 126K miles. That being said I attached a volt meter to it yesterday and it seems to be working fine.

I found the original receipt for the purchase of the vehicle, the original owner paid $38,187.50 for the car on Feb 17, 1987!!!!!!!!



Thanks!!

https://www.bls.gov/data/inflation_calculator.htm

$87,793.95

126K is a pretty good service life for an O2 sensor, so I expect the issue is catalyst aging - but at 233K miles the cat is probably living on borrowed time.

At this point I think you should short the R16/1 socket, block the vacuum advance, and retest. I'll give 50/50 odds that it will pass, and start shopping for a replacement main three-way cat.

I made a shorting plug out of a short piece of 12-gage wire, stripped the ends and folded back the wire strands over the insulation, bent it into a "U" and stick it into the socket. Then I rewrap it in electrical tape, like Mercedes did at the plant. No one will ever know...

To disable the vacuum advance I cut about a 2" piece of generic 1/8" vacuum tubing, plugged it with a slug of silicone sealer and use it to replace the short molded rubber tubing at the inlet manifold end of the vacuum line to the EZL. Most of that vacuum signal line to the EZL is 3mm nylon tubing with molded rubber adaptors at the manifold and EZL ends. I usually install it at the manifold end, but I need to take the air cleaner off. The EZL end will work too, but I guess I'm paranoid enough to not have a non-OE part at that end, which is visible. If attached at the manifold, it can't be seen.

I keep the shorting plug, piece of plugged vacuum tubing, and OE 750K ohm resistor in a small ziplock bag in the glovebox. It takes about ten minutes to make the change, including removing the battery to easily access the R16/1 resistor socket.

Did you find the R16/1 resistor socket on your 300E? On my 190E 2.6 it's visible on the inside battery compartment plastic trim panel secured with a wire tie. I think it's in a different location on both the 124 and 126 models - maybe underneath the master cylinder. Where is it on your 300E?

The inflation adjusted MSRP on your car is interesting. Back then Mercedes' marketing slogan was "engineered like no other car in the world", and I think that was mostly true although they seemed more complicated than necessary. The throttle linkage on the M103 engines is one example.

Then Lexus brings out the LS400 in 1989, which was equivalent to a V-8 S-class for the price of a 300E. It became a whole new ballgame.

Mercedes made a ton of money in the American market that they used in the late eighties to buy into the German aerospace industry. Then the Soviet Union fell, defense spending plummeted, and all that money evaporated.

I'll never buy another Mercedes, but I may want to be buried in my 190E 2.6 special order five-speed instead of a coffin. ;)

BTW, if you pass the test, re-enable vacuum advance, but don't reinstall the original R16/1 resistor. Leave the socket open, and let us know if you feel better around town throttle response/low rev power and better fuel economy.

Duke

Thanks!

So do you think the O2 sensor should be replaced? I just ordered one today and it should be here next week.

If it passes why should I shop for a 3 way cat?

I believe I am burning a good amount of oil. I believe this is contributing to the high HC readings.

The R16/1 resistor is near the master cyl, access is easy. So I remove the resistor and inset the U shaped wire jumper, or leave the resistor in and short the resistor?

From your test results I think the O2 sensor is okay.

My hunch is that the main cat is aged to the point where it no longer operates efficiently enough to pass emissions testing, and high oil consumption certainly accelerates catalyst aging. How many miles per quart is it doing?

I suggest before you start replacing parts, do the temporary R16/1 mod and disable the vacuum advance as I previously described and then retest. Emissions should be much lower, maybe enough to pass. I assume the test station offers one free retest, so this approach costs nothing. If it fails the new test results may help determine if the O2 sensor is bad, the cat, or both.

If it does pass, especially with little margin, then you will be facing similar issues in two years.

Remove the R16/1 resistor and short the connector with a jumper wire as I previously described. Put the resistor in the glove box or a safe place were it won't be lost or damaged.

There have been threads over the years about replacement cats. I don't know if you can buy one from MBZ anymore, but if they are available they will no doubt be very expensive. Generic three-way aftermarket cats can be welded on by exhaust shops, but some reports say they have short life.

After the emission test remove the shorting wire from the R16/1 connector (and enable vacuum advance), but don't reinstall the resistor. I expect you will detect better performance and fuel economy due to the more aggressive spark advance map than with the OE resistor installed.

Duke

Cats from MBZ are no longer available for my vehicle. When they were they were $1800.

I orderd an O2 sensor it will arrive next week. I plan to install it an also get a cat before the next test. I figure the O2 sensor is 22 years old with 126k miles and is most likely covered in soot.

when I got home from work today I connected a voltmeter Fluke DMM to my O2 sensor.

It jumped around from around .100 V to .700 V. I counted the times the meter changed or updated the voltage reading value in a minute and was close to 140 counts.

I always though the life span of a o2 sensor was 50k-60k miles

It's flipping a little more than twice per second or a little under 0.5 Hz. Sounds okay to me. O2 sensor aging can be indicated by slow response time, but flipping a couple of times per second at idle is about what I recall when I tested mine over ten years ago.

On my '84 190E 2.3 there was a dash light "O2 sensor" that switched on at 30K miles to indicate that it needed to be replaced. I asked the dealer how they turned out the light and they said "remove the bulb". So that's what I did and left the O2 sensor alone.

I figured that since O2 sensor technology was fairly new back then Mercedes simply "programmed" a replacement requirement, so they didn't have to replace any on warranty.

When I sold the 2.3 at 50K miles to buy the '88 2.6 it passed emissions with plenty of margin.

The '88 maintenance schedule calls for replacement at 60K miles. Mine now has 85K and appears to be in proper working order.

I'm not sure what the nominal life of an O2 sensor is or what the statistical failure distribution is, but if it's not working properly, it will usually result in high emissions during testing, and those cars with diagnostics will show a "check engine" light and O2 sensor code, if it is not performing properly.

Remember the old adage: "If it works don't fix it."

Duke

I'm glad you FINALLY bought an O2 sensor. Yes, 80-100K is about right. And you have 233K on the ORIGINAL muffler? Magnaflow makes Kaliforniastan approved mufflers. I replaced BOTH of mine on my '97 CL600 with only 67K. My first Benz was an '87 300E. Had little trouble with it and sold it with about 180K. It is still in the area, now has over 300K with the ORIGINAL engine and transmission. Folks, if you take care of them they run forever, well at least a LONG time. Follow the factory recommended maintenance or buy a Toyoter or a Honder!
Anziani
'97 Cl600 69K