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Old 02-19-2021, 08:49 PM   #1
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Default Slightly High CO Emissions? Where to Start?

Hello Everyone,


I took the 87 V6 4x4 in for emissions testing today and it failed, but barely. CO readings came in at 30.4715, limit is 29.9999 in my county. HC and NOx were at about 50% or below.


My understanding is that high CO is burning rich. My air filter is somewhat dirty, but not caked. Spark plugs have maybe 10k on them (I didn't pull any to check), distributor cap was replaced with the last plugs and the ignition has maybe 20k on it.


The truck runs fairly well, though it stumbles a little if you floor it and it seems to just cut power when it stumbles. It doesn't like to redline, but it gets there eventually (it revs really well to about 4500rpm). I have not checked fuel economy, but it seems to be pretty usual.



It has a new exhaust less than 1000 miles ago.


I run the truck pretty hard, it hauls and tows a lot through the mountains so I doubt anything is dirty, but it is possible there is some carbon build up within the engine.
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Old 02-19-2021, 09:07 PM   #2
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Hello Everyone,

<snip>

It has a new exhaust less than 1000 miles ago.
Did they replace or reuse the old CAT when the exhaust was redone?
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Old 02-19-2021, 09:11 PM   #3
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Did they replace or reuse the old CAT when the exhaust was redone?

The cat was reused. They said it was in good shape.
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Old 02-19-2021, 11:00 PM   #4
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Obviously, replace the air filter, and with a quality one. Not sure if it would affect it, but do you also have the second air filter in the canister mounted low on the inner fender? That filter is often unknown/unchanged.



If a gas engine, has the upstream O2 sensor been replaced?
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Old 02-19-2021, 11:18 PM   #5
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Obviously, replace the air filter, and with a quality one. Not sure if it would affect it, but do you also have the second air filter in the canister mounted low on the inner fender? That filter is often unknown/unchanged.



If a gas engine, has the upstream O2 sensor been replaced?

I was not aware of a second air filter. I'll look for it. I have a k&n in there now so it just needs to be cleaned. It is a gas engine and I have no idea if the o2 sensor was every replaced. I have had the truck for about 8 years and never changed it myself.
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Old 02-19-2021, 11:24 PM   #6
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The cat was reused. They said it was in good shape.
How did they know if your cat con is good?
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Old 02-19-2021, 11:28 PM   #7
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How did they know if your cat con is good?
They musta put it thru a "CAT-scan"! lol
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Old 02-20-2021, 01:32 AM   #8
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I've heard from people here that have run Seafoam through their engine and it cleared up the bad emissions issues.

https://www.amazon.com/dp/B0002JN2EU...5B53Q7QYS2BDMA
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Old 02-20-2021, 02:07 AM   #9
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Quote:
Originally Posted by daskuppler View Post
Hello Everyone,


I took the 87 V6 4x4 in for emissions testing today and it failed, but barely. CO readings came in at 30.4715, limit is 29.9999 in my county. HC and NOx were at about 50% or below.


My understanding is that high CO is burning rich. My air filter is somewhat dirty, but not caked. Spark plugs have maybe 10k on them (I didn't pull any to check), distributor cap was replaced with the last plugs and the ignition has maybe 20k on it.


The truck runs fairly well, though it stumbles a little if you floor it and it seems to just cut power when it stumbles. It doesn't like to redline, but it gets there eventually (it revs really well to about 4500rpm). I have not checked fuel economy, but it seems to be pretty usual.



It has a new exhaust less than 1000 miles ago.


I run the truck pretty hard, it hauls and tows a lot through the mountains so I doubt anything is dirty, but it is possible there is some carbon build up within the engine.
Has the PCV valve been checked/changed out?
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Old 02-20-2021, 03:11 AM   #10
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A good paper filter is worth it's weigh in gold. I'm from a dusty environment so the "freer" flow from a oiled filter isn't worth the dust it lets through.



I havnt had any positive or negitive results from replacing 02 sensors in my D21.


Is your timing at 12BTDC?



Is it just high RPM that it doesn't like to rev past when in gear and going down the road or when being revved in neutral? Onload could suggest fuel delivery issues. My VG33 with VG30i injectors doesn't like above ~4200RPM under heavy load like pulling a hill at WOT in 4th passing someone.
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