Well, the YJ failed the new Massachusetts dyno emissions inspection system. [img]/wwwthreads_images/icons/frown.gif[/img].
That is quite an interesting system (along with being a major PITA). I passed with flying colors on HC and CO, but failed on NOx. They also failed my gas cap. (didn't know they checked the gas cap.) [img]/wwwthreads_images/icons/crazy.gif[/img]
I believe these are in Grams per Mile:
HC: 2.11, limit 5.72
CO: 39.02, limit 94.36
NOx: 11.92, limit 6.77
CO2: 673.17, no limit given.
They drive the Jeep on the dyno, and have to follow what look like a bell-curve on speed, up to about 30 MPH, and then back down. They give you printouts of all of the curves (HC, CO, NOx, CO2) and it looks like my NOx start being bad about 10 MPH, is worse at about 20, and goes back down at about 30 MPH.
I had the timing set pretty high (used to do that for the old idle test, to get the most efficiency out of the motor for the idle test, but I guess that's not the best thing to do for the dyno test. [img]/wwwthreads_images/icons/tongue.gif[/img] I read up on NOx, and it seems that excessively high cylinder temps lead to NOx, and advanced timing is one of the big hitters there. I also don't know if the EGR valve is working, as the Jeep sat for 4 or 5 months this summer, so it may be stuck. I will check that and go retest soon. Also have to buy a new gas cap.
So, that's my story. Also, here is my current configuration:
88 YJ, 258, GM HEI, new plugs (about .045"), cap, rotor, oil change, cat is about 2 yrs old, no pulse air system, exhaust manifold connection capped off, cat connection capped off, entire pulse air tube setup removed (no visual inspection in MA).
Anyway, I'll keep you all posted on my retest. Wish me luck. I think she'll pass no problems next time. [img]/wwwthreads_images/icons/smile.gif[/img] I was going to just retard the timing and go back, but I want to check the EGR valve and put a new vacuum hose on it - it's a bit short and could be restricting some vacuum to the valve where it loops around. They give you 60 days to retest.
Happy new year to all.