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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Hello everyone. I have used this site to look for answers to all my thirdgen questions and now after a failed smog thought to finally make a account and ask one myself.
The tech told me that the fail could be from the egr, cat, or air injection not working right. From my own reserch on other posts the egr seems to be a big part of this.
After getting home I noticed a plug that looks like goes to what I belive to be the egr solenoid was unplugged. Im not sure if this was always unplugged or I did it poking around. I got the car a while ago with 2016 tags and redid most vacuum lines when I got it. I also got a vacuum pump and when I applied vacuum to the egr cold it killed the engine. At tempture it hiccupped but still ran.
looking to seek advise on what to test and how to test it(egr and egr solenoid specifically but also air pump) .Is there any additive to lower nox? My tank was about on empty does that effect it?
Lets start with what you have. What is the car, what motor? Is the motor stock?
Your HC and CO numbers look good, so the cat is doing something. I wouldn't be looking there first. The EGR system is there to reduce NOX and if it's not working, that could cause or contribute toward your issue. Plug the connector back in to the EGR solonoid and verify all of the vacuum lines are in place. Also, see if you can push up on the EGR valve diaphragm to make sure it isn't stuck. You could still have a bad solonoid, bad valve and/or carbon plugged EGR passages, but start there anyway.
Ignition timing can make a big difference in NOX. Start with setting the timing to the stock spec according to the underhood emissions sticker. We'll assume for now that the timing mark on the crank balancer is accurate or close enough.
So, make sure all of your tune-up parts are good (plugs, wires, cap/rotor), timing set correctly, EGR system working properly and go back through the test. If it still fails, you could retard the ignition timing a little to get it through and then put it back. Retarding the timing will drop NOX, but HC and CO will go up.
I went through this with my GTA a long time ago. I was unaware at the time, but the motor had swirl port heads from the TBI 350 in the full size trucks. Everything else was stock. I replaced the cats, EGR valve, new injectors, stock timing setting and still couldn't get the NOX emissions low enough to pass (HC and CO were fine). I ended up adjusting the base ignition timing from 6 BTDC to 4 ATDC and it passed, drove it to the parking lot next to the emissions testing place and reset it to 6 BTDC (stock). That's the only way it would pass. When I tore the motor down a few years later and found that the heads were incorrect, it all made sense. The swirl port heads don't need as much ignition timing as the L98 heads, so in effect it was like I was running timing advanced from stock.
California checks the base timing, if it's not within the allowed tolerance of factory spec then they'll fail you.
The allowed range was +/- 3 degrees on my car, but I've seen some people insist it's 2. The tolerance might be different for different model years or what type of testing "region" you are in.
It think it says the allowed timing range on your printout somewhere.
If you adjust the distributor to the edges of the tolerance, you might get failed if the inspector reads it a little differently than you did.
If you can't figure out the problem, and you really want to tweak the timing, you can get away with that by using a chip. They only check the base timing, if that's set correctly then it's a pass. They don't know what the chip is doing to the final amount of advance.
06-17-2023, 02:37 AM
