Emissions puzzle

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Nov 23, 2016
- I'm finally going through the process of getting my '86 FJ60 smogged in CA so I can get a street parking permit, the truck has previously been out of state, but was getting driving a couple times a week and running well (got 14-15mpg driving 750 miles across NV/CA this past weekend)
- Under the hood the truck is all stock, its originally a NM truck and passed emissions there over the years
- The only tinkering that's been done to the emissions components has been swapping in 2 new VCVs a couple months ago, carb was last tuned in SLC (~4,400 ft); Mudrak also helped fix a leak in the intake manifold ~2 years ago

- I drive ~30mins on the freeway (~2500-3000 rpms for a solid 15-29mins) to the smog shop, get tested... pass with pretty good numbers on emissions, but fail the visual because there is a crack in the hot air pipe that helps feed warm air to the carb when its cold out
- The smog shop agrees to give me a free re-test so I go next door to Napa get a replacement hot air pipe, install that and go back to get retested
- The truck probably sits for ~45 mins while I'm finding a pipe that fits; I also have to disconnect the hose that goes into the bottom of the EGR modulator and pop it off to get access to underneath the air cleaner. I put everything back on and head back to get retested
- During the retest I now pass the visual but fail emissions
+ CO @15mpg/25mpg went from .08/.06 on first test to 1.35/1.28 on second test (fail; max allowed is .79 /1.00)
+ NO jumped from 604/620 to 1580/1501 (fail; max is 1062/1073)
+ HC also jumped from 22/12 to 97/56 (pass; max is 125/96)
+ C02 decreased from 16.2/15.9 to 14.5/14.6

- Is this symptomatic of the EGR not kicking in during the second test? (High CO means its running rich? High NOx means EGR isn't working?)
- Could I have knocked some soot in the EGR modulator loose when I moved it around while installing the hot air pipe (which shouldn't impact emissions)?
- Would the ~45mins of cooling off have made this much of a difference in the test?

I'm honestly a bit stumped as to why the results from 2 tests within ~1hr could vary so much, but I'm tempted to replace the EGR modulator and get it nice and hot before trying to test again this weekend (will be ~$30 for another retest). I am also planning to get a t-case rebuild done at Valley Hybrids in two weeks, so can probably get some help from @orangefj45 if all else fails


Supporting Vendor
Mar 14, 2003
Sticky EGR valves are a very, VERY, common issue ……….

If you take it back, make sure you let it warm up well, then drive it at least 15 minutes, preferably at higher RPMs to get the cat "good and hot".


Valley Hybrids & Cruiser Brothers
Mar 21, 2019
Seems to me the decrease in CO2 and rise in all other values would indicate the cat had cooled down. Mine did the same thing and the smog shop I went to was able to get it to pass after getting the cat really hot. I’m in NV and not CA so the shop I went to was able to check tailpipe emissions before they ran the official test.


Jun 30, 2017
You can exercise the EGR valve to make sure it's opening ok by running the engine at faster idle with the choke knob pulled, then attaching a piece of vacuum hose to the top of the EGR valve and sucking on it with your mouth (no you won't suck crap up through the hose). The engine will begin to stumble as the EGR valve opens, and should return to normal when you stop sucking.

More detailed testing info for the EGR modulator is described in the emissions manual. You should definitely have a copy of that.

But I think your second fail was due to a cold catalytic converter. Always drive for 20 minutes or so on the freeway before pulling into a smog test shop and don't turn off the engine until you're tested. If your cat is old, it might be barely sufficient

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