NOx - Smog test issues

[Fox W.]

Hey guys, 

 

Wondering what from experience with these engines is my best bets other than the cat for these results attached.:

 

The HC and CO levels are fine, but I failed by a bit for NO ; I've read that high temps can cause this.  I keep everything on this car tip top as I can, I am not aware or seeing any cooling issues, or problems with the EGR.   I am using the Bosch gen3 injectors, that's the only more unusual variable I have going on.

 

Any ideas of things I could try?   What data/outputs from the CRT could I view to get some bearing on this?  Wish I had an NO meter so I could just test.

 

The O2 sensor is quite new and OEM, the fuel pressure regulator is quite new ; MAF cleaned recently.

 

My converter only has about 35k miles on it, it's a direct-fit replacement from Magnaflow.  I realize factory ones are better.   

 

Thanks.

[Bloo]

EGR is the main thing.

 

Less likely things, coolant running too hot, ignition timing too advanced (that's not possible on a Reatta is it?), one bed of the 3-way catalytic converter either missing or not working well, catalyst efficiency reduced by upstream air leaks.

 

If the car has upstream AIR injection (up at the exhaust manifold, does it?), it needs to shut completely off when the car is warm. On cars with a 3-way catalytic converter AIR injection always either shuts off completely or is diverted downstream to a hose on the catalytic converter when the car is hot. This is because the first bed in the converter, the one that deals with NOX, needs to starve for oxygen a little bit to work it's best. The other bed wants oxygen.

 

Anyhow I would ignore most of that for now and nitpick the EGR. It directly affects NOX output. It is a far more likely suspect than anything else. Passages can plug with carbon.

 

Was the car tested with the cat good and hot? When you retest I would take it for a good run down the freeway a few exits first.

 

 

[padgett]

What was the engine temperature ? I find running an engine cool, (under 190F) keeps NOX down.

[edinmass]

NOX is a result of high temperatures………unless I am not remembering correctly. A simple chemical reaction in the combustion chamber of nitrogen and oxygen. 

[Bloo]

That is correct, and with temperature being related to pressure, large amounts of NOX are usually related to detonation. Even a healthy engine puts out some NOX though. I am a bit out of the loop on this one because WA was not officially testing for it when I was in that business.

 

The whole purpose of EGR is to reduce detonation and by doing so reduce NOX. On older cars that still used vacuum and centrifugal advance, when an EGR valve was present so was about 5 degrees extra vacuum advance. You can expect to see this extra advance in ECU controlled timing as well. When the EGR plugs up, you still have this extra advance and the engine tends to detonate, making a whole bunch more NOX than a healthy engine without emission control would. The catalytic converter probably cannot clean all of it up.

 

Some state tests require lower NOX output than a healthy engine would produce without a converter (Georgia comes to mind), and so a weak catalytic converter can cause a failure even when nothing else is wrong. 

 

Edited October 14, 2022 by Bloo (see edit history)

[edinmass]

Wasn’t part of EGR operation to introduce inert gas to cool the combustion chamber? We’re are going back fifty years now…….

[Bloo]

It acts like air in brakes. It prevents a sudden rise in pressure. I suppose that keeps things cooler because pressure raises the temperature. That's why the extra timing is there, to make the firing impulse happen at the right time with the pressure rising slower. It is only used at part throttle cruise, so there's no effect on maximum power.

 

NOX is produced above some certain temperature (I don't remember how many degrees). Normal engines make some, high compression makes little bit more, detonation makes great gobs of it.

 

Edited October 14, 2022 by Bloo (see edit history)

[padgett]

Yes, any of the above can cause NOx: detonation, clogged EGR, high coolant temperature, too much advance,.... If I lived in California would throw the kitchen sink at it and have my own testers. Since I live in Florida with 3000 miles of Atlantic Ocean and occasional windy spells to clean the air, we have not had inspections since the last millennia.

[Fox W.]

Thank you all,  yeah I wish I had a meter so I could just test myself and adjust what I can.  I do not know what the engine temp was the day I tested, however I do know it was extremely hot out and I had the A/C on, so I'm sure after some idling at the test station it was hitting the 213f peak where even the aux fan comes on.    Perhaps just re-testing during the cooler season would pass me.

 

I did replace the water pump myself and intake manifold gasket and such, hopefully I didn't end up causing a coolant leak.

[padgett]

One way is to use an IR gun  (note coupon) and measure the thermostat and manifold pipe temperature. If one pipe is cooler it is not firing properly. Fancy ones have a scream but never needed one, digital display is fine for me.

[Fox W.]

Great idea.  Yeah I already have the 'Klein IR5 Dual Laser 12:1 ' one ; Thank you.

[ChrisWhewell]

Let me add it could be a poisoned or otherwise iinoperative NOx catalyst in the converter.    I replaced mine with an aftermarket one about 7 yrs ago, b/c the exhaust seemed smelly when I went WOT on the hwy.   I think I only paid about $80 back in '16 for it, but kept the old one.   I wonder the value of the metals, in the 1990 Reatta convertor.  I bet there's rhodium in it.

Edited November 26, 2022 by ChrisWhewell
elim. confusion (see edit history)

[padgett]

Used to be platinum. Early catalysts had a hex plug in the bottom and could drain the pellets out because had a lot of back pressure. Modern ones are pretty good. Does require enough heat (600F) to "light off". Rotten egg smell was an over rich mixture.

[Oldhowguy]

I read you changed the injectors. NoX increases when running lean. This could be the cause if everything else is ok. Make sure the injectors are right

[wufibug]

Bought the convertible in Ohio.  Tried to get it smogged here in CA.  Most stations charge over $100 for pre 2000 cars with no re-test if it fails.  Found one that charges $30 for a "pre-test".  It failed.  Replaced the EGR. Then discovered the PO had removed the catalytic converter altogether.  I opted to install at 50 state Cat and will have it pretested.  Then just hope the tester does not look for Cat numbers for CA compliance. When the cat theft epidemic was at its height, folks were having covers welded over the cat to deter thieves. They also cover the cat numbers.  Maybe I'll have to go that route, though trapping the heat generated by the cat is an unappealing solution. 

[minor4326]

Might try a steal cover with open slats to let heat out. 

[wufibug]

Was thinking of just having it tack welded then removed after the test.  Same procedure every 2 years.