Hello,

My '87 420SEL just failed emissions in VA. Here's the readout:

15 MPH HC PPM Limit 65 (70) FAIL 25 MPH HC PPM Limit 119 (113) PASS
15 MPH CO% Limit 0.26 (0.20) PASS 25 MPH CO% Limit 0.38 (0.15) PASS
15 MPH NO Limit 857 (123) PASS 25 MPH NO Limit 833 (259) PASS

The actual readings are shown in ()

The only test I failed was the 15 MPH HC which was so close! Prior to the inspection I replaced the plugs, air filter, and changed the oil. What could be tweaked to bring down the HC by such a tiny amount?

The other thing I don't understand is in 2005, the allowable 15 MPH limit for HC was 134, for CO% 0.75, and for NO 990. How could the HC PPM limit be cut by more than half? If anything, the limit should either remain the same each year or even slightly increase as the car gets older to compensate for normal wear & tear on an engine. Using the 2005 limits, my car would have easily passed.

Could the attendant at the emissions station made a mistake when he setup the limits on his machine? Are the limits for other states the same or can each state set their own limits? I am really trying to figure this whole thing out. Thanks a bunch.

T.C.

I am assuming they ran two tests.

Was the engine hot (enough)?
My 260E would always fail the first test, but would pass once the engine got nice and hot.

Did you add anything to the fuel beforehand?
Fuel additives will elevate HC readings.

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2008 E350 4matic / Black/Anthracite

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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black

Did the Technician enter the correct model year, before he ran the test?
Chasing 5 parts per million hydrocarbons is nearly impossible.
You could run the same test 10 times in the row, and have hydrocarbon variations much greater than 5 ppm.
How much did it cost for the test?

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2007 C 230 Sport.

Each state definitely sets their own emissions limits. MO is moving to no emissions tests for 95 and earlier this September, for example.

Your CO is also close to the limit, which means that you should be injecting just a bit less fuel. This will probably raise NOx, but you have plenty of room there.

No, I haven't used any fuel additives. Emissions testing in VA costs $28.00 with a free re-test and is required every 2 years. It was about a 10 minute drive to the station but since there were many cars in line the engine was turned off. I waited in line for over an hour before starting the car for its inspection, so probably it was not fully hot. I would think though, that a tepid cat convertor would affect the NO readings a lot more than the HC readings but I could be wrong. However, the NO readings were well within spec so wouldn't this indicate that it was up to temperature?

Anyway, at the first opportunity, I am going to test the O2 sensor at the connector to make sure that its voltage is fluctuating between .2 and .8 volts.

If the O2 sensor checks out, I will try leaning the mixture ever so slightly since as Matt L. pointed out, there is plenty of room in the NO reading. Thanks.

T.C.

And therein lies the problem.
What a bunch of Idiots.
CO, HC, NOx , etc. is no different in Virginia than anywhere else.
Can you say stupid rip-off.
P.S. This is coming from somebody that does emissions testing every day.

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2007 C 230 Sport.

Go back for retest around the middle of this week lines are usually shorter than end of month and drive car for at least 1/2hr in reg traffic. if you can't do it than let car run while in line at least 2 cars before your turn.

All limits are set by state and mech inserts info from registration and computer
does the rest. A minor thing like incorrect tire size can throw you off.
Good luck keep us posted and welcome to Va

Before you go back, do an oil change. When your oil turns dark it is not because of engine wear, it is because before your exhaust leaves the cylinder a certain amount goes past the rings and into the oil which makes it turn color to dark. When your piston goes back up, oil gets coated on the cylinder wall and burns with the gas. With emissions laden oil burning with the gas and going out in your exhaust, your emissions will read higher for the test.

A fresh oil change is the is a must for older cars before you make any mixture adjustments or emissions test for true accuracy.

I tested the duty cycle using the X11 diag connection and it showed a rock steady 7.18 Volts. This equates to a 47% duty cycle which is on the slightly rich side. The fact that the voltage never varied pointed to the O2 sensor. I then tested the O2 sensor to see if its voltage varied between .2 and .9 volts and my meter stayed steady at .002-.003 volts (basically zero volts) so the sensor is definitely the culprit. I also checked the O2 heater circuit to make sure it wasn't at fault it showed a solid 14 volts.

I see the street price for the Bosch unit is around $135. A universal 3-wire replacement is only around $42 which is tempting. It doesn't come with the full wire harness with connectors so you simply crimp it to the existing wires. This may actually be a blessing since you don't have to reroute the new cable through the floor pan and into the interior of the car.

T.C.