Your CO is about 1/3 of the allowable limit, and is an excellent reading for a carbureted car -- but your HCs are more than double the allowed limit, and your NOx is 1/3 higher than allowed. This combination of results suggests your engine is running so lean that it is misfiring. Those cylinders that do fire produce a great deal of NOx due to the lean mixture, while those that do not fire produce a great deal of HC due to noncombustion.
(These '85-'89 civilian M-body cars with the Holley 2bbl don't generally run very well in stock form, even when everything is set by the book. Lean surge under steady throttle is the rule, rather than the exception. Not that this helps you -- just saying.)
So, what's causing your misfiring? Could be any number of things. A faulty Oxygen sensor in the driver side exhaust manifold (how long since you replaced it?). A faulty carburetor, a faulty Lean Burn computer, a plugged fuel filter...it might not even be a lean misfire at all; your readings could also be caused by the reduction portion of the exhaust catalyst system having reached the end of its life, resulting in very high NOx tailpipe readings and insufficient free Oxygen in the exhaust stream to allow the oxidation section of the catalyst to clean up the HC.
Time for some systematic diagnosis by someone who has considerable experience with the carbureted Mopars of the mid '70s through late '80s. Just throwing parts at it will get very expensive long before the problem is solved.
Dan, I haven't seen the whole original post; are these readings at idle? The limits seem rather strict for a 1987 vehicle. What state is this guy in?
I would say that a lean burn 318 that met these failure limits is a decent running engine. That doesn't help the car owner, but it sounds like his state is trying to get rid of carbureted cars in one swoop...
Lean misfire (very minor) is my immediate guess. I'm sceptical that the converter has failed to reduce NOx while still oxidizing CO like a champ. I mean, if his typical engine is producing typical CO, this converter is doing quite a job to get it down to .16%.
Hear, hear! Some research in his yellow pages for a shop that doesn't wince when he mentions his problem would be a good start.
Is this vehicle still 100% stock, or has somebody screwed around with the lean-burn?I've seen these engines "converted" to standard carbs (remove the lean-burn) not have a chance of passing E-Test
Those are pretty standard state limits for an '87 car, and he's flunking them very, very badly.
If he's running lean enough to cause those readings, there won't be much CO off the manifold in the first place, so the catcon won't have a big job getting rid of it.
He might be on the phone awhile. There weren't all that many techs who could do a good job with these Lean Burn systems when they were current and new!
That's the problem here... there are surely multiple problems which will all need to be corrected before all three gasses are within the allowable limits.
We're theory pissing without hands-on testing. Great, now I just typed 'pissing' and 'hands-on' in the same sentence.
I'm From Canada (ONT.) And I forgot to mention a stubborn oil leak from your guess is as good as mine(I just can't pin point it.) I know it's not the EGR or Cat Con (Replaced in '01 car drove it to Nov 2002 then it sat for 2003 &
2004). I don't know if the oxygen sensor was replaced but more than likely it was.
You really can't say the EGR and catcon are good just because they were replaced. With your HC as high as it is, the catcon could easily be cooked. And the EGR valve is only one part of the system; the crossover passage and ports (in the intake manifold and the heads, respectively) could well be clogged with carbon.
Don't know where in Ontario you are, but I can recommend a couple of good shops in the Toronto area. Canadian Tire does not count as a good shop.
Actually, a converted car WITH a working set of catalysts and correctly tuned SHOULD pass with flying colors. But what usually happens is that someone replaces the ignition system, disconnects the lean-burn computer, and leaves the lean-burn carb in place. That doesn't work so good, because the lean-burn carb NEEDS computer control to work right.
There are two ways to do the conversion:
1) replace both the carb AND the ignition and do away with the computer,
2) Replace the ignition, but let the computer continue to control the carb. It doesn't "know" that its not still controlling the ignition, and will merrily hum along (assuming that the computer is working, the O2 sensor is working, and the carburetor's VDC solenoid is working.)
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