So I took the dakota into emissions knowing it would fail, since you can tell it runs rich just by standing near it.
Now, it barely failed and the only thing that was bad was the CO and it was slightly off of what the Democratic People's Republic of Maryland finds acceptable.
Any suggestions on how to either lean it out or lower that particular emission without screwing everything else?
Gapping the plugs out works well. Check your rules as many states will give you a hall pass on the second try if you show an improvement and have receipts for recent repairs. In Ohio they used to now even charge you for the second time. The trick used to be to buy the requisite tuneup but keep in in the truck and just show the receipt. Gap out the stock plugs to lean it out and a viola you have passed.
Yeah md you have to keep all receipts as far as I know
I've got until may so I can at least wait until it warms up a bit more. And I suppose I can fix the headlights at about the same time.
If it's running in closed loop, anything you do to "fake it leaner" would not do anything. Meaning, the way you have to make it run leaner is to fix whatever is wrong.
If it's not running in closed loop, the easiest way to fix it is to allow it to run in closed loop.
Sory to burst your bubble but it seems that the way to make your truck pass emissions is to fix it so that it's running correctly 
Do you have exhaust manifold gasket leaks? Those are notorious for making a car run rich when in closed loop.
No leaks as far as I can tell, runs great.
It's just a 26 year old 3.9, so lord knows what the hell is wrong with it. I mean, the motor has given me literally zero issues that would indicate anything is off, it's just a bit stinky.
I'm not trying to fake the test, since I'm not going to bother putting historic tags since md got a stick up their ass about it I'd rather it just pass everything fine and dandy.
E: also it wasn't that long ago that it was inspected, and they didn't say anything about the motor, just a bunch of suspension and brakes crap.
Is Maryland as convoluted as pa? Could you just register it to an address in a county without eMissions? Po boxes are cheap, and the ups store counts as a physical address.
It could probably use new upstream O2 sensor(s).
I bet sensors would do it.
Alright so just replace em or is there anyway to check to see if they're still good?
They look cheap enough that I'll probably still change them. Doubt it was done in the 146 thousand miles it has, and lord knows the asshat who sold it to me didn't do it.
In reply to Grizz:
The problem with old O2 sensors is that they may still give a signal that the ecm accepts as valid, so it doesn't throw a bad sensor code, but its no longer accurate enough to keep the A/F mixture right.
Chrysler parts are cheap, at that age just replace them, its normal maintenance. You may even notice it runs better, or gets better MPG.
In reply to HappyAndy:
That's the odd part, it runs better than any 3.9 I've been in. It's hard to describe since you can't use the terms fast or even quick, but I took it up to the scrapyard in coatesville with a hair over 1000 pounds in the bed and the only issue it had was the drums in the back deciding they really hated the hills.
I can't tell if it's just the first good example of a motor I typically hated or if it's hotted up somehow.
When you get a lot of miles on an O2 sensor it starts to drift out of spec and report leaner than reality, so the ECU compensates by adding fuel that it doesn't need to add. On an OBD2 vehicle you can just look at the long term trim numbers in the live data, with old O2s they'll be high, like +8% or more, at that rate you recuperate the cost in saved fuel pretty quickly. Just be careful handling the new ones, they're rather delicate for something that lives for years in a hot exhaust stream, hand tools only.
My last truck was incapacitated because of morons using tools they shouldn't have on it, I very rarely use anything but hand tools because of it.
Snapped a valve cover bolt, right at the start of winter. Head would not come off without breaking more stuff. Then they berkeleyed off to prison on murder charges(that was lovely to find out about). On the upside it let me figure out that there was no way in hell my 400 dollar ram was passing state inspection with as bad as the rust turned out to be, and at that price it really wasn't worth bothering with.
Grizz wrote: No leaks as far as I can tell, runs great.
If it's blowing high CO to the point where you can smell the exhaust, no, it is not running great.
Temperature sensors are always overlooked
"Move" too a p.o. box in west virginia like all my friends in maryland did.
High CO means it's running rich. So figure out why it would run rich.
O2 sensors,as mentioned, are used to adjust fuel mixture based off reading the exhaust.
(These can be lazy or biased because of age and effect fuel trims and not be noticeable on performance)
MAP\MAF sensors decide how much fuel to dump in based on load or volume of air intake.
(Usually if these are bad you'll get driveability issues)
Engine Coolant/Air Temperature (ECT/IAT) sensors adjust mixture based on engine temperature and intake air temperature.
(These sensors fine tune mixture and could give rich/lean conditions without noticeable driveability isues)
Then you have the catalysts. They could be worn out and no longer catalyzing the unburnt fuel. The motor may be running just fine, but the emissions increase because they aren't being cleaned up on the way out. A newer OBD II system with inlet and outlet O2 sensors usually pick up a failing catalyst before it's noticeable to us.
My wife accuses me of producing random emissions quite frequently. Oh, wait...
Hey Grizz, next time you're making a scrap run to Coatesville take a quick trip over to Downingtown. My shop is 10 - 15 minutes from the scrappers.
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