Emissions Guys...step in
Thread Starter
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Emissions Guys...step in
My daughters car failed emissions it's a 1990 Pathfinder V6. Her HC (PPM)
Idle Limit 220
Idle Emissions 535-this is where she failed
She's a great kid, any help would be appreciated.
225832 on the mileage.
Idle Limit 220
Idle Emissions 535-this is where she failed
She's a great kid, any help would be appreciated.
225832 on the mileage.
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
It needs to be checked... for sure...
What is the maintenance history?
When was the last complete tune up? Any engine codes? What about O2 sensors?
My first thought would be that the cat(s) is/are dead. This happened to a friend of mine with his similar vintage Nissan puckup.
You can get generic high flow cats pretty cheap.
What is the maintenance history?
When was the last complete tune up? Any engine codes? What about O2 sensors?
My first thought would be that the cat(s) is/are dead. This happened to a friend of mine with his similar vintage Nissan puckup.
You can get generic high flow cats pretty cheap.
Thread Starter
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Thanks Bogus, the cats fairly new 1-2 years, tune up and 02 about 1 year old, past due on oil change, PVC about 1 year old. What I was kinda wondering about is the air duct between the MAF and TB, it's got 2 big cracks. Been ideling an running ruff..low on power.
Le Mans Master
Joined: Jan 2006
Posts: 6,564
Likes: 6
From: Woodstock Georgia
Did she drive it around and get it to operating temp, or drive it down the block and right into the test center? Just reread the post. Cracked duct between the MAF and the TB would cause added air, plus sucking in dirt.
Fix that soon and retest, I suggest.
Fix that soon and retest, I suggest.
Last edited by aminnich; Oct 14, 2006 at 09:53 PM.
Thread Starter
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Thanks Guys, I'm gonna help her repair the duct. She's got a Chiltons POS, but I'm also gonna check for codes, check the plugs and have her get her oil changed.
Yeah it's high HCs at idle.
Yeah it's high HCs at idle.
Pro
Joined: Jul 2001
Posts: 650
Likes: 0
From: Flushing NY
make sure you put fresh oil in her, before you test also I sometimes add some denatured alcohol to the tank or some cleaners few days before also to clean her out .....and check the plugs if its not a pain to get at not in this order though
Alan
Alan
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Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
HCs (hydro carbons) are unburned gasoline. A rich mixture causes high CO. The HCs can be high, too if not all the extra gasoline is burned. A too lean mixture, can cause a "lean misfire" that will leave unburned (HCs) gasoline.
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RACE ON!!!
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Rick, I'm no emissions guy, but from what I have read in some of my books, the web, and here..it is running rich. We don't have emmissions testing here but my Dodge with 255,xxx miles I'm sure would fail even though it runs good. You know what things could make them run rich and the cracks in the air duct would be a first fix. As you know the "running ruff and low on power" could be a cylinder misfire (unburn fuel), leaky injector(s), or O2 sensor..to name a few. I'd be nice if you could plug it up to your scanner.
Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by RRT vette
Rick, I'm no emissions guy, but from what I have read in some of my books, the web, and here..it is running rich.
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Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
You catch on quickly. HCs are the unburned gasoline molecules. If the mixture is too lean to burn, the unburned molecules show up in the exhaust and are measured by a smog machine as HCs, because gasoline is a hydro carbon. That is why changing your oil before a smog test, helps. If there is gasoline diluted in your oil, it may not all burn, and cause you to fail for excess HCs. I once failed on HCs because an overactive EGR valve leaned the mixture and caused a lean misfire resulting in high HCs.
You bet your sweet... The A/F ratio as to be in the proper range to ignite. But it doesn't take much unburned fuel to screw up a smog test.
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Originally Posted by bogus
Lean misfire - not enough fuel to burn, but enough fuel to raise the HC's?
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Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
Lean misfire can really get tricky from the diagnostic standpoint since a misfire also introduces a large amount of oxygen into the exhaust, when the O2 sensor "sees" the high oxygen content it commands wider pulse width.
One key as CFI-EFI pointed out is that high HC indicates incomplete combustion or misfire, high CO indicates a rich mixture. 5 gas analyzers can help diagnosis by reading O2 and CO2 at the tailpipe, the lean misfire condition would have high O2 and low CO2.
Stuck open or overactive EGR as CFI-EFI said, plugged or inoperative injector are possible causes of lean misfire.
One key as CFI-EFI pointed out is that high HC indicates incomplete combustion or misfire, high CO indicates a rich mixture. 5 gas analyzers can help diagnosis by reading O2 and CO2 at the tailpipe, the lean misfire condition would have high O2 and low CO2.
Stuck open or overactive EGR as CFI-EFI said, plugged or inoperative injector are possible causes of lean misfire.
Thread Starter
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Thanks guys 
this comming weekend we'll get it in my garage..fix the duct work, pull the plugs (with this many miles) they may be foulded, check the 02 sensor and change the oil. I'm gonna check the fuel pressure and see if there's any stored codes.Clean the MAF sensor connections and see what happens.Thanks again. 
this comming weekend we'll get it in my garage..fix the duct work, pull the plugs (with this many miles) they may be foulded, check the 02 sensor and change the oil. I'm gonna check the fuel pressure and see if there's any stored codes.Clean the MAF sensor connections and see what happens.Thanks again.