Duke,
The 02 sensor has one long, thin connector and a separate 2-prong connector. Could you please explain how the probes of the digital multimeter set to DC voltage should be applied in order to properly take the measurement.
Thanks

The two pin connector is the O2 sensor heater. Disconnect this connector and measure the O2 sensor heater for continuity. It should measure a few ohms. With the engine running there should be 12V on the chassis harness side. Continuity of the heater and 12V on the input harness means the O2 heater and power supply are okay. On my '88 the heater is on all the time, but on some heated O2 sensor systems the heater may only be on during warmup.

The single pin connector is the O2 sensor signal. If you pull the connector apart just enough to attach a small test lead or probe from your voltmeter or scope to the pin, you can eavesdrop on the O2 sensor. Connect the meter or scope ground wire to any convenient chassis ground or the battery negative terminal to be absolutely certain that you have a good ground. A DC voltmeter should show about 450 millivolts.

If you have a scope you can juggle the time and voltage scales until you get a good image of the voltage waveform, which should jump between 0.2V and 0.8V several times per second.

If the readings are not as above, then you have either a bad O2 sensor or there is a problem somewhere in the control system. For example, if you disconnect the EHA connector, the system will default to "open loop" operation, which should be a bit rich if the basic mechanical mixture adjustment on the air meter is in the proper range. This will cause a high voltage reading on the O2 sensor or a constant high voltage reading on a scope.

Duke

Thanks Duke. You made it pretty clear. One follow-up: Are any special tools needed to remove the sensor from the exhaust pipe? I've seen something advertised on Ebay as such a tool.

I've never removed the O2 sensor from my 190. They usually have a big hex, but sometimes access can be tight. Also, they tend to seize, so be sure to use a good high temp antiseize compound when installing a new one and don't overtorque it.

Duke

CO2 readings are a funtion of the fuel blend. In my test last February my car was over 15 percent, but with the new CA fuel that substitures ethanol for MTBE CO2 levels are lower because of the lower carbon/hydrogen average ratio of the fuel. For example, straight run gasolines averages C8H18, but methane (natural gas) is CH4, so methane will produce less CO2 and more water vapor than straight run gasoline.

The equation %C02 + %CO = xx, where xx is the percent CO2 with complete combustion (zero CO), and this will vary with fuel blend.

NOx is created in the flame front, which reaches about 4500 degrees F. There are two practical ways to control the amount produced during combustion. One is to retard timing from optimum and the other is to dilute the fresh charge with an inert gas, which is what EGR does. Both of these strategies reduce peak flame temperature, but this reduces thermal efficiency, which reduces fuel economy. Rich mixtures, such as what occurs at WOT will also reduce NOx to very low levels, and there is little at idle. Most NOx formation occurs during steady state cruise.

Heavier cars are more likely to require EGR than lighter cars. In order to meet the absolute certification standards in grams per mile, which are the same for all cars, a heavy car will have to have lower proportion emissions than a light car. Final NOx values after the converter depend on having the correct exhaust gas composition and converter efficiency. I don't have a good feel for how much reduction of NOx occurs in the converter. In the several ASM tests I have had on my two modern cars with three way catalysts, the NOx measurements and limits are all over the place. This is why I think the CARB is still trying to figure out what they are actually measuring.

Duke

Well, with a tune and a new cat I'm almost there. Here's the new #'s

15 MPH

CO2 - 14.2
HC - 132 (126 max) failed
CO - 0.9 (0.79 max) failed
NO - 305 (1316 max)


25 MPH

CO2 - 14.5
HC - 72 (101 max)
CO - 0.4 (0.59 max)
NO - 366 (1112 max)


Like I said earlier, we've gone from 72 shops to 8 so I have a MB tech comming to the dyno shop after hours next week to do a 'tweak' and get those 15 MPH #'s down. Thanks all for your help and explainations, especially Duke! After this experience I don't think I'll ever sell my smog exempt fords.

__________________
E55, 300E, 65 Hipo Mustang, 66 Shelby GT-350, 69 Mach I, 66 Fairlane GT Conv., etc

John - Did you ever run your Shelby with COCOA at Willow Springs? I used to run my Cosworth Vega with them in the eighties until Lynn Park got so many entries that he limited it to Ford powered cars only.

Duke

Richard,

Not sure if your car takes the same O2 sensor as the 560, but the 560 only required a 22mm box wrench. Many folks will simply cut the wire to the old sensor, remove then feed the wire to the new sensor through the box wrench to install. I found it easy enough to feed the wire through the wrench prior to removal, allowing me to bring it out in one piece.

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

This is about cars that pass loaded mode smog checks. Being a former bay area smog tech,now so cal. area. San diego. i find that test results on cars that pass do not reflect that cars best smog numbers.The old test ran the car for the full test then gave it a second chance to pass if the car was failing. This new test will only test long enough to get passing numbers, then switch to the next part of the test. this will give passing numbers but will not give the best numbers that the cat can produce with a full time test. also german gas caps almost always fail.even on 5 year old cars.I test these caps twice and they will pass most of the time.ask the smog tech. GREAT FORUM

Duke

The shelby is an ex-drag car (tubbed, no-shock towers) that I'm converting to an "open track" car to run local shelby events. Sears Point is my home track (ten minutes away) but I'd love to go to Willow Springs (and T. Hill & LS) when the car is complete.

__________________
E55, 300E, 65 Hipo Mustang, 66 Shelby GT-350, 69 Mach I, 66 Fairlane GT Conv., etc

Does any of this method of preparing the car for smog apply to a 400E?

__________________
1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500

All Merc engines with the KE systems have the same emission control technology, and analysis of test numbers and troubelshooting are basically the same. The one fly in the ointment are those models with air pumps. If they are set up to only inject air during cold mode, then analysis of the emission numbers is that same as what has been discussed here.

If they inject air all the time - including normal warmed up operation, the O2 content in the exhaust cannot be used to analyse converter efficiency. My car predates the adding of air pumps, so I'm not sure what modes they are active, but maybe someone else can chime in.

Three way catalysts work best with the native exhaust consituency that occurs with a stoichiometric air fuel ratio, which has a faction of a percent of oxygen, so air pumps on modern cars usually only inject air to reduce CO and HC during warmup. Once the O2 sensor heats up enough to allow closed loop operation supplemental air injection is suspended, and for this reason, many air pumps on modern cars are electically driven rather than engine driven.

Duke

Hi John

Looks like you are almost there.

Your new numbers indicate a marginal improvement which would indicate to me that the "Cause" has yet to be addressed.


I am curious about the following items: 1) How is the "idle quality" on your car? 2) Have you had the "CO adjusted" yet? 3) Have you installed a new "O2 Sensor?" 4) Did you install an "OE cat?" 5) If “No” did the replacement Cat come with "Pre-Cats?" 6) Have you replaced the distributor cap and rotor in the last two years? 7) And is your “intake system” sealed well? (IE: injector seals, pcv hoses, idle valve hoses, and rubber boot under the fuel mixture housing)

Over time subtle intake leaks do develop in these areas which become masked by adjusting the CO, at some point the engine is simply too “Rich.”

Good Luck!

Hey Mr. CJ

To answer quour q's:

1) Idle quality is better than most 300e's, but like all that I've seen idle is better when the motor is cold.

2) CO will be done this week

3) Ne O2 senson two year ago

4) Aftermarket cat

5) Pre-cats are orig to the car

6) Cap/rotor/wires one year ago

7) Intake test for leaks - passed


Let me know if I'm missing anything and thanks for your input!

__________________
E55, 300E, 65 Hipo Mustang, 66 Shelby GT-350, 69 Mach I, 66 Fairlane GT Conv., etc

Duke,
excellent diagnosis,
I too work with emissions, we have the latest & greatest IM 240, results are in mass, grams pollutant/miles driven. A passing standard for an 86 would be .8 grams per mile of HC. So do the math and see how much even clean cars emit in a 20K mile year, multiple that by 1.3 million cars that are OUR test area alone, one city in one state, then muliple that by a factor of 4-700 and one gets a general idea of why cars are targeted for reducing emissions.
its all in the numbers.

Tangas,
Beautiful numbers. Obviously good maintenance and attention to the vehicle.

Manny,
CARB RULES!...(and regs) so does CDEQ!