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Failed Emissions Test, Looking for Ideas
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=93103		 Page 1 of 1
Author:  Steve777 [ Wed Sep 24, 2025 11:59 pm ]
Post subject:  Failed Emissions Test, Looking for Ideas
So one of my CRDs just failed its Colorado emissions test. This test basically just tests the exhaust opacity (eg smoke), after the usual check for no engine lite and emissions equipment being there. It's usually not that hard to pass, and in fact this CRD had passed in prior years with pretty good numbers. This year it failed due to too much smoke, over 40% in the 60mph test. Last year was like 16%. I must admit, I have noticed a bit more smoke in the rear view at the exhaust lately, but nothing that major, or so I thought. The jeep is running well otherwise.

So I am putting my list together of things to do before I take it in for a retest to help it pass. Usually I run on 100% biodiesel for the test, but it had been getting cold at night so I had 30% or so petro in the tank (not smart I know). I will run this tank down and put in 100% bio before the next test. Additionally, I plan on changing the fuel and air filters, changing the oil, and doing a thorough check of all the vacuum lines for cracks and leaks.

Just wondering if there is anything else I should be checking/cleaning/replacing before heading in for a retest. Suggestions?
Author:  03black [ Thu Sep 25, 2025 11:25 am ]
Post subject:  Re: Failed Emissions Test, Looking for Ideas
Black smoke is an indicator of poor fuel to air ratio, in this case to much fuel not enough air. I would look at your CAC hoses for cracks and holes. The common one being the rubber tube that feeds the turbo as that one usually gets oil from the "PCV hockey" puck and the oil eats the rubber. The other would be the turbo variable vanes. If the vanes don't open or close fully it will cause poor performance.

You can check for actuator movement by putting a hand vacuum pump on and see if the arm moves up/down a little over and 1". If not then the vanes are probably caked in soot preventing full movement. Easy to fix, just remove the turbo, split the turbo in half and on the exhaust side remove the 3 bolts to get to the unison ring (vanes) and give it a good cleaning with brake clean and a toothbrush. Be careful of vane tips to not chip/break/bend them. Reassemble and go for a drive.
Author:  WWDiesel [ Thu Sep 25, 2025 3:23 pm ]
Post subject:  Re: Failed Emissions Test, Looking for Ideas
Low boost pressure is the no. 1 cause of excess black smoke out the tailpipe when accelerating.
As 03Black said, check all the boost hoses for any cracks or leaks. Check all the vacuum hoses, especially the one that runs from the vacuum modulator valve over to the turbo vane actuator diaphragm on top of the turbo. Check turbo vanes for ease of operation by manually stroking the vanes by hand. The vanes can get sticky at times.
Is your EGR still in operation? If so the EGR valve can fail and allow boost to leak backwards through it and dump into the exhaust manifold. Or the FCV can stick partly shut due to its little metal gears in its operator failing. Very common problem.
Installing a mechanical boost gauge will help greatly in diagnosing the problem.
Report back what you find to help others. :wink:
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