Failed CA smog check 1990 300SE.
 

Unfortunately my 1990 300SE failed to pass smog today, in the past it always passed with flying colors. The technician told me it was most likely the EGR valve not functioning. I tested the EGR valve with a vacuum pump and nothing was moving, nor did it hold any vacuum. I attached the SMOG paper with the numbers. Any ideas what the numbers are telling?

See if the EGR valve moves when revving the engine and applying vacuum. An inoperable EGR valve will increase cylinder temp and then NO (nitrous oxide). Check for vacuum to the EGR also, you could have a bad valve and no signal to the valve.

Good luck!!!

Thanks, will start with that.

If you can mechanically open the valve with the engine running it should stumble with the big vacuum leak created. There is a tube from the valve around the back of the head to the bottom of the intake that clogs, if no stumbling that tube is clogged. Replace it with new if possible first, second is to try to clean it out with an old speedometer cable...not fun.

Good luck!!!

Would seafoam help to unclog it, if it's clogged?

If you could get it directly into the tube, maybe. Some have disconnected the tube at both ends and worked old speedo cables through them. One end is at the valve, the other is under the intake manifold near the center below the throttle plate.

From what I scan tell the tubes are NLA.

The EGR valve is NLA as well. What I've read it ain't easy to remove the pipe underneath the intake manifold without removing it first.

Couple of thoughts...

Perhaps a used pipe from a forum member or a junkyard would allow you to thoroughly clean it before install and study/plan on removal and install.

IIRC the connection at the bottom of the intake has a fitting between the pipe and the intake. It may be doable to remove that fitting to gain access to the inside of the pipe to clean it internally without completely removing the pipe.

Start soaking both ends of the pipe at the fittings with penetrating oil (not WD-40). Do it multiple times.

Good luck!!!

This is not discounting that anything that needs fixing should be fixed.

I think way back it was said biodiesel does not have the same emissions. With some research you might find it has less NOX.

I found this: "Effects of Biodiesel on Emissions"

https://dieselnet.com/tech/fuel_biodiesel_emissions.php

Mine is a non diesel, M103 300SE.

Fortunately to find an almost new EGR valve locally, the original one is completely toast.

Oops.

When I had the NOX issue on 2 of gasoline vehicles over they years a new but generic catalytic converter fixed the issue. The newsiest was a 92 Astro van. Note there is a number on the generic CAT. The emission test guy is going to look at that and look on his list to see if it one legal for your vehicle.

You don't have to buy the expensive CAT with the whole pipes on it but as mentioned you have to buy a CAT that the State has is OK as substitute.

https://www.smogtips.com/failed-high-NO-nitric-oxide.cfm

Premium gasoline typically had gasohol in it.

Looks like gasohol can raise you NO emissions.

"The study was prepared by a California consulting firm that has done extensive work for the governments of eight Northeastern states and California. It concludes that ''gasohol,'' or gasoline with 10 percent grain alcohol, would cut carbon monoxide by 25 percent, but that nitrogen oxides, which cause smog and acid rain, would rise by 8 to 15 percent, and hydrocarbons would rise by 50 percent. That works out to 6 percent more smog."

https://www.nytimes.com/1990/05/09/business/gasohol-may-cut-monoxide-but-raise-smog-study-asserts.html

This year 2021 my e 320 wagon egr failed too , and no longer available, i found a similiar one off a newer engine , but it didnt bolt on, so i removed the guts and they did bolt on to my valve base , it worked and passed smog , i had high
nox also, if you cant find one maybe you could do the same

https://www.eeuroparts.com/Parts/53237/EGR-Valve-0021401360/
claim to have the egr valve in stock