Smog fail
Melting Slicks
Joined: Apr 2001
Posts: 2,094
Likes: 217
From: Ca.
Yup, egr needs to be checked -make sure it's functioning as it will make the biggest difference in nox then also worth a look at how old the cat is. Not sure why they put fail evap controls? Did it also fail to hold pressure in the fuel tank? Is this Kali? Put a vacuum on the line to the egr valve-the engine should stumble and want to stall if the egr valve is opening. If it looks like the valve itself is working then look at the valve that activates the vacuum to the egr if it's working.
Pro
Joined: Mar 2024
Posts: 536
Likes: 375
From: Northern California
You could have a vacuum leak going on. Not sure what the vacuum pressure for a 1990 is.. or how to test for it, but it is worth investigating. It could hurt your EGR functionality and thus give you the high NOx that's failing you.
Thread Starter
Heel & Toe
Joined: Sep 2024
Posts: 22
Likes: 0
Yup, egr needs to be checked -make sure it's functioning as it will make the biggest difference in nox then also worth a look at how old the cat is. Not sure why they put fail evap controls? Did it also fail to hold pressure in the fuel tank? Is this Kali? Put a vacuum on the line to the egr valve-the engine should stumble and want to stall if the egr valve is opening. If it looks like the valve itself is working then look at the valve that activates the vacuum to the egr if it's working.
Melting Slicks
Joined: Apr 2001
Posts: 2,094
Likes: 217
From: Ca.
If it's Kali they put a low pressure into the gas tank and check that it holds that pressure. If it's leaking it will be in the rubber vacuum lines from the tank to the charcoal can upfront under the driver side headlight. There are rubber lines up under the driver side rear wheel and under the hood that can leak.
Thread Starter
Heel & Toe
Joined: Sep 2024
Posts: 22
Likes: 0
If it's Kali they put a low pressure into the gas tank and check that it holds that pressure. If it's leaking it will be in the rubber vacuum lines from the tank to the charcoal can upfront under the driver side headlight. There are rubber lines up under the driver side rear wheel and under the hood that can leak.
