87 5th Avenue Emission Problems

On Fri, 27 May 2005, Mr. Minnow wrote:

> I took my car(87 5th Ave with a 318(5.2L) v8) in for an emission test and it
> failed miserably
>
> Here are the results:

It's *very* hard to read your results -- the tabulation didn't come out as
you tried to make it do -- but it looks to me as if your results a

HC: 197ppm (limit 83ppm, FAIL)
CO: 0.16% (limit 0.46%, PASS)
NOx: 1220ppm (limit 893ppm, FAIL)

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.

DS

Daniel J. Stern wrote:
> On Fri, 27 May 2005, Mr. Minnow wrote:
>
> > I took my car(87 5th Ave with a 318(5.2L) v8) in for an emission test and it
> > failed miserably
> >
> > Here are the results:
>
> It's *very* hard to read your results -- the tabulation didn't come out as
> you tried to make it do -- but it looks to me as if your results a
>
> HC: 197ppm (limit 83ppm, FAIL)
> CO: 0.16% (limit 0.46%, PASS)
> NOx: 1220ppm (limit 893ppm, FAIL)


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?

> 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.

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...

> 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.

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%.

> 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.

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.

Toyota MDT in MO

On Sat, 28 May 2005, Comboverfish wrote:

> > HC: 197ppm (limit 83ppm, FAIL)
> > CO: 0.16% (limit 0.46%, PASS)
> > NOx: 1220ppm (limit 893ppm, FAIL)
>
>
> Dan, I haven't seen the whole original post; are these readings at
> idle?

Those are ASM2525 (acceleration simulation).

> The limits seem rather strict for a 1987 vehicle.

Oh, I donno...I had a '65 car that would reliably pass emission
tests with similar limits. The guy's idle results and limits are

HC: 504ppm (limit 300ppm) FAIL
CO: 6.76% (limit 1.5%) FAIL

Those are pretty standard state limits for an '87 car, and he's flunking
them very, very badly.

> 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.

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.

> > 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.
>
> 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.

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!

DS

Daniel J. Stern wrote:

> Those are ASM2525 (acceleration simulation).

OK, the limits seemed pretty tight for an idle test - that explains
things!


> HC: 504ppm (limit 300ppm) FAIL
> CO: 6.76% (limit 1.5%) FAIL

> Those are pretty standard state limits for an '87 car, and he's flunking
> them very, very badly.

No doubt. I'd go after rich-running culprits first; gross causes like
air bleed blockage in the carb, choke closed, etc...


> 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.

The converter may be toast already having to deal with this kind of
overload (at idle).

> 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 a challenge I like, but the work would be "by the hour" for
sure.

Toyota MDT in MO

On Sat, 28 May 2005, Comboverfish wrote:

> > Those are pretty standard state limits for an '87 car, and he's
> > flunking them very, very badly.
>
> No doubt. I'd go after rich-running culprits first; gross causes like
> air bleed blockage in the carb, choke closed, etc...

Air bleed, perhaps, but a stuck-closed choke doesn't jive with 0.16% CO
and 1220ppm NOx under load.

> The converter may be toast already having to deal with this kind of
> overload (at idle).

Very possibly so. I can't remember if they were still farting around with
multiple converters in '87.

> > 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 a challenge I like, but the work would be "by the hour" for sure.

Well, that's part of the challenge: matching a tech able *and* willing to
put in the time with an owner able *and* willing to pay him to do so!

Daniel J. Stern wrote:

> Air bleed, perhaps, but a stuck-closed choke doesn't jive with 0.16% CO
> and 1220ppm NOx under load.

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 ****ing without hands-on testing. Great, now I just typed
'****ing' and 'hands-on' in the same sentence.

Toyota MDT in MO

On Sat, 28 May 2005 00:48:25 -0400, "Daniel J. Stern"
> wrote:

>On Fri, 27 May 2005, Mr. Minnow wrote:
>
>> I took my car(87 5th Ave with a 318(5.2L) v8) in for an emission test and it
>> failed miserably
>>
>> Here are the results:
>
>It's *very* hard to read your results -- the tabulation didn't come out as
>you tried to make it do -- but it looks to me as if your results a
>
>HC: 197ppm (limit 83ppm, FAIL)
>CO: 0.16% (limit 0.46%, PASS)
>NOx: 1220ppm (limit 893ppm, FAIL)
>
>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.
>
>DS
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

Otherwise,Mr Stern has pretty well covered it.

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.

Thanks Mr. Minnow

On Sat, 28 May 2005, Mr. Minnow wrote:

> 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.

wrote:
> On Sat, 28 May 2005 00:48:25 -0400, "Daniel J. Stern"
> > wrote:
>
>
>>On Fri, 27 May 2005, Mr. Minnow wrote:
>>
>>
>>>I took my car(87 5th Ave with a 318(5.2L) v8) in for an emission test and it
>>>failed miserably
>>>
>>>Here are the results:
>>
>>It's *very* hard to read your results -- the tabulation didn't come out as
>>you tried to make it do -- but it looks to me as if your results a
>>
>>HC: 197ppm (limit 83ppm, FAIL)
>>CO: 0.16% (limit 0.46%, PASS)
>>NOx: 1220ppm (limit 893ppm, FAIL)
>>
>>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.
>>
>>DS
>
> 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
>
> Otherwise,Mr Stern has pretty well covered it.

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.)