High NoX in exhaust B36

RonDwyer · Post by **RonDwyer** » Sun Jul 23, 2017 12:55 pm

Ok, so this basically tells me my engine is running lean. The water temp sensor is fine and I got it to pass with cobbling in a 50 ohm resistor. Where else can I look to adjust the mixture to richen it up a bit with everything apparently sealed on these cars?

Blaise · Post by **Blaise** » Mon Aug 21, 2017 11:41 am

Probably needs a new cat.

Qwodracer · Post by **Qwodracer** » Wed Aug 23, 2017 6:51 pm

The water temp sensor is an inverse function. Adding resistance, decreases fuel (more lean). The sensor is less than 30$ and should just be replaced if you have any doubts about it...

The air temp sensor (in the vane) however is a direct relationship. Adding resistance increases fuel mixture.

Also... (im unsure of California law) You can wire in a aftermarket piggyback fuel controller 200-300$ and get a good variety of adjustment, or you could figure out how to go full stand alone with say a microsquirt/megasquirt v2/v3 for about 800$ with sensor and wideband 02. But you could get it to pass a sniffer test with that method, just not sure on the visual inspection end, as its a "modification".

Also on old Bosch vanes, there is an air bypass usually there is an adjustable screw in this bypass, opening up the screw allows more air to pass the vane (lean out) closing the screw lessens the air bypassing the vane (richens) but the vane is only being read when off idle and not WOT. I just looked at my vane on the 528, its upside down, there is a hole where the screw should be. You'd have to take the vane off and look in the hole to see if there is an adjustable screw.

RonDwyer · Post by **RonDwyer** » Sun Sep 03, 2017 3:49 pm

Actually the water temp sensor is the circuit that leans the mixture as it warms up. More resistance when cold means more fuel is given. That is how I got it to pass.

Regarding the cat, that cannot be the problem because the HC levels were very low. Low HC = lean which means it is burning hotter and thus creates more NOx emissions. Don set me straight on that one.

I will take a look at the AFM, if I can adjust it that could help. Some have the bypass screw. Maybe mine got adjusted in the past.

Blaise · Post by **Blaise** » Mon Sep 04, 2017 10:36 pm

RonDwyer wrote:Regarding the cat, that cannot be the problem because the HC levels were very low. Low HC = lean which means it is burning hotter and thus creates more NOx emissions. Don set me straight on that one.

Interesting.

When I had my car with the BAR referee, I passed all except for NOX. At 15mph, I was getting 2154ppm, when you need no more than 778ppm to pass. At 25mph, I was passing. My HC levels were passing, but on the higher end at 15mph and about halfway at 25mph.

I tried fiddling with all sorts of things and could not significantly make a difference.

I then installed a new cat. It passed with flying colors.

NOX was down to 26ppm (need under 778ppm to pass) at 15mph and 46ppm (need under 718ppm to pass) at 25ppm.

Hope that helps.

If you want the exact data, shoot me an e-mail and I will send it to you.