failed emissions
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New User
Joined: Oct 2007
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failed emissions
95 F-150 with 130,000 miles. Went to get my emissions test and failed. The nox was high and that was it. Everything else was well within the limits. Guy at the place said it could be the EGR, or Catalytic converter. My mechanic said he thinks all I need is a tune up, my last tune up was at 100,000 so I am due. Truck runs well and gas mileage is is stable. Anyone have any ideas as to what may be causing it to fail?
Super Moderator
Joined: Apr 2004
Posts: 34,507
Likes: 2,823
Nox is caused by high combustion temps.
--lean condition (vacuum leaks?)
--ignition timing out of spec (although smog usually checks this, if so, your report should show it)
--egr problem--check that plumbing
--overheated cat (?? as you don't have a miss for example)
As per prior post, check the plugs and see if there is any evidence of any of the above.
Good luck.
--lean condition (vacuum leaks?)
--ignition timing out of spec (although smog usually checks this, if so, your report should show it)
--egr problem--check that plumbing
--overheated cat (?? as you don't have a miss for example)
As per prior post, check the plugs and see if there is any evidence of any of the above.
Good luck.
Elder User
Joined: May 2007
Posts: 754
Likes: 1
From: Solon, Ohio
We could help you better if we knew your readings for both NOx and HC, and the acceptable limits in your area.
Usually when NO's are high, HC is low (lean)
If you just missed your NO limits by a small amount and you aren't throwing any codes, I would just run the gas down to almost empty, then put in ten gallons of high octane gas.
Run off a couple of gallons of that ten, then add a couple quarts of denatured alcohol (shellac thinner) and take it back for retesting. The above should drop your NO about 10%.
Usually when NO's are high, HC is low (lean)
If you just missed your NO limits by a small amount and you aren't throwing any codes, I would just run the gas down to almost empty, then put in ten gallons of high octane gas.
Run off a couple of gallons of that ten, then add a couple quarts of denatured alcohol (shellac thinner) and take it back for retesting. The above should drop your NO about 10%.
