YJ fails new Massachusetts dyno - but I know why. - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 12-28-2000, 07:35 AM Thread Starter
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YJ fails new Massachusetts dyno - but I know why.

Hi all,
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.
Pete [img]/wwwthreads_images/icons/smile.gif[/img]

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post #2 of (permalink) Old 12-28-2000, 07:39 AM Thread Starter
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Re: YJ fails new Massachusetts dyno - but I know why.

Sorry, forgot to add that I've got the weber 32/36 also. (It's early morning here, and I'm kinda moving slow this morning. [img]/wwwthreads_images/icons/smile.gif[/img])

And they check the gas cap by putting it on a pressure-checking thingy - mine failed. [img]/wwwthreads_images/icons/crazy.gif[/img]

Pete


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post #3 of (permalink) Old 12-28-2000, 08:04 AM
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Re: YJ fails new Massachusetts dyno - but I know why.

My first guess would be the EGR valve is malfunctioning. I think I heard someone on here say Napa has them for pretty cheap. Your other readings look ok. We have the same dyno test here in AZ. I also removed the pulse air crap. But I changed the cat-con and O2 sensor before I tested. And made sure my EGR valve was working. Check the vacuum line to the EGR. Make sure there is plenty of vacuum when you rev the engine. They couldn't check my gas cap because I have the locking type, so I passed without it even being checked.[img]/wwwthreads_images/icons/smile.gif[/img]

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post #4 of (permalink) Old 12-28-2000, 12:26 PM
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Re: YJ fails new Massachusetts dyno - but I know why.

I also think that you my need fresh air going to you cat. Check to see if your cat has an air tube out the side. If it does this air tube is needed to bring in air so that the cat can do it emissions reductions. The original pulse air system was designed for just that. I need to get my emissions book.

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post #5 of (permalink) Old 12-28-2000, 01:35 PM
 
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Re: YJ fails new Massachusetts dyno - but I know why.

We have the same test here in Illinois now too and I actually somehow managed to pass everything except the gas cap. Picked up a new cap while I was X-mas shopping on Friday and swung back by the place for them to test the new cap. What happens is that the rubber seal dries out. Interesting thing to note is that the air tube to my cat is virtually non-existant...I've got one of those stupid grenn hi-temp hose sections that only lasts about a year and I'm about a year and a half into it and it's basically disintegrated at this point. I think the only thing that saved me was a fresh rebuild on the Carter by an old small town Jeep dealer. It was kinda funny watching the 5' tall woman who ran my test climbing in & out of the Jeep.

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