Helping a friend with emissions testing with his '99 LS1.

Everything passed except 'NO' count, which was a good amount over the limit.

What needs to be tweaked to lower the NO counts ? Timing ?

Thanks,
Rob (Bad30th)

 

NOX is usually a result of running too lean.
Richen it up a tad...but too rich will increase your HC count.

ideally, you should use a wideband 02 and some loggin tools and figure out what the issue is...

 

Retard timing. Turn off EGR. Just my $0.02

 

When I run the HPT scanner on it, it shows the LTRIMs to be right around 0 to -2, so I figured that was good to go...

I will suggest to him to drop the timing a couple of degrees in the 15mph range (where it failed the roller test). His EGR is installed but is showing "incomplete" in the readiness tests.

Thanks for the input, anyone else ?

Rob (Bad30th)

 

Change the EGR DTC to "3 - No Error Reported" and leave SES "Enabled". That'll take care of the incomplete thing.

On the other issue...I have no idear.

 

The EGR is used to reduce NOx, turning it off would not help.

 

I agree, that was the original purpose of EGR. We need to cool the combustion chamber temps and as previously suggested, EGR and retarding the timing should help reduce NOX.

 

Yep, lower combustion temps.
You can also turn your fans on a little earlier. Maybe back timing off a tad. If its closed loop you wont be able to do much to richen it up. Though you might have some luck messing with o2 switch points at the closed loop airflow mode that the test fails at.

Let us know how you go.

 

Just out of curiosity (and the fact that my 99' is getting old), what are his mods?

 

stuff the tail pipe with sos pads that should lower them some it would act as a filter.

 

Do you leave the soap in those pads

Bill

 

The EGR is used to reduce NOx emissions.

Has it even thrown an EGR code? I'd suspect if its not passing the readyness test that might be the culprit. Lowering the timing might help also.

 

Anything that raises combustion temps (cylinder pressure,
leanness) will aggravate NOx production. So will swinging
too far into the lean, with the proportional fueling action.
If you see the O2s swinging stop-to-stop there is a good
chance you are spending too much time in the bad place
(both of 'em). If you can make it swing tighter and faster
you will cut all emissions down. I'm no expert on how, but
this is where I'd study up on "what", for starts. Also may
want to be sure you do not have some sort of injector
balance problem (like one drooler makes three lean in the
bank, etc. or vice versa).

 

If he can nail down his part throttle afr he could run in Open Loop during the test to avoid rich/lean swings.

 

Thanks, sometimes I type faster than I think.

 

FWIW, spark advance makes the most difference to both heat and pressure in the chamber.
If the dyno is really loading you down in that speed range, then dropping the advance in that area of the table will do the trick.

*I learned everything I know from the intra-web, so it must be true*