Carburetor EGR port question

In article >, jim >
wrote:

> aarcuda69062 wrote:
>
> >
> > > The signal from venturi vacuum was to weak to operate an EGR valve
> > > in a
> > > reliable way so it needed to be amplified and then the same old EGR could
> > > be used. The reason it was tied to the weaker venturi vacuum was that
> > > would allow for more accurate metering of air and fuel under a wider
> > > range of operating conditions.
> >
> > That was Chrysler's way of doing it. That's all that can be said.
>
> For someone who claims to know something that is as good as saying you
> don't.

That's hilarious coming from someone who's above statement describes the
EGR as metering air and fuel.

> I didn't say chrysler used the same engines for all those years I
> said the EGR's were all pretty much the same in that era.

Must be why they all had the same part number (not).

> The means of
> controlling the vacuum, which determined how much exhaust gas was
> delivered and when it was delivered is what changed depending on make,
> model and year.

Now you're getting it.
Did the 87 Dakota V-6 use a vacuum amplifier?

> That was the purpose of vacuum hose configurations, vacuum amplifiers or
> transducers and different vacuum ports. The difference in the valve itself
> had more to do with how they fit on the engine rather than how they
> behaved.

Sounds like something the guy at the junkyard would say.

> At any rate EGR clearly has a huge effect on NOX emissions and does
> completely change the way air and fuel burn inside an engine.

Never said otherwise.

> That mains
> the entire way the engine is tuned needs to change to accompany the
> changes that EGR creates.

Indeed.

> For the most part EGR is beneficial. It is a lot
> like getting an octane boost (at no extra cost) and does allow for better
> fuel economy as well as overall better emissions *if* the engine is tuned
> to accommodate the changes in burn characteristics. That means changing
> air/fuel ratio as well as timing.

Which is not the same as asserting that the EGR changes the air fuel
ratio.

> The modern vehicle's computer takes care
> of all of that for you so yes you can get along quite nicely with any
> knowledge of it.

Absolutely.

aarcuda69062 wrote:

>
> > The signal from venturi vacuum was to weak to operate an EGR valve in a
> > reliable way so it needed to be amplified and then the same old EGR could
> > be used. The reason it was tied to the weaker venturi vacuum was that
> > would allow for more accurate metering of air and fuel under a wider
> > range of operating conditions.
>
> That was Chrysler's way of doing it. That's all that can be said.

For someone who claims to know something that is as good as saying you
don't. I didn't say chrysler used the same engines for all those years I
said the EGR's were all pretty much the same in that era. The means of
controlling the vacuum, which determined how much exhaust gas was
delivered and when it was delivered is what changed depending on make,
model and year.
That was the purpose of vacuum hose configurations, vacuum amplifiers or
transducers and different vacuum ports. The difference in the valve itself
had more to do with how they fit on the engine rather than how they
behaved.

At any rate EGR clearly has a huge effect on NOX emissions and does
completely change the way air and fuel burn inside an engine. That mains
the entire way the engine is tuned needs to change to accompany the
changes that EGR creates. For the most part EGR is beneficial. It is a lot
like getting an octane boost (at no extra cost) and does allow for better
fuel economy as well as overall better emissions *if* the engine is tuned
to accommodate the changes in burn characteristics. That means changing
air/fuel ratio as well as timing. The modern vehicle's computer takes care
of all of that for you so yes you can get along quite nicely with any
knowledge of it.

-jim


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In article >, "Mike" >
wrote:

> > Yes it is.
> > Ever open an EGR valve at idle?
>
> Yep.
>
> > Did the engine run better or worse?
>
> Didn't run at all, they don't run well on an inert gas.

Next time, don't open it so far. Try a 10% or 20% command on your scn
tool instead of 80% .
>
> > Do you suppose HC goes up or down if you open the EGR at idle?
>
> Being the engine wouldn't stay running I would say it went down. If
> it
> would stay running it would have a lean misfire that would lead to an
> increase
> in HC.

No, it wouldn't be a lean misfire. Lean misfire comes from too much air
and not enough fuel. Opening the EGR does not add more air.
The exhaust gasses displace what would have been combustible mixture in
the combustion chamber, the actual ratio of that combustible mixture
doesn't change.
If you have an engine with a leaking EGR valve at idle, fattening up the
mixture doesn't improve how the engine will idle.
Comparing secondary spark lines on a ignition scope, a lean mixture
looks completely different than a stuck open or leaking EGR valve.

> > Air pumps tend to have a generic universal design, what if instead of a
> > 4 CFM air pump made for a 3.9 liter engine, he got a 10 CFM replacement
> > pump made for a 7.4 liter engine.
> > You -can- pump too much air into a catalytic converter and snuff out the
> > fire.
>
> Yep, I see your point here. My experience has been that aftermarket
> emission parts are junk.

Yup.

aarcuda69062 wrote:
> In article >, jim >
> wrote:

> > As for the Chrysler lean burn crap - that was easy to fix. What was so
> > incredibly stupid was it took Chrysler engineers 10 years and near
> > bankruptcy to figure out how to fix it.
>
> That's the way innovation is.

Ultradrive innovation?

Mike wrote:
> "aarcuda69062" > wrote in message
> ...
>> In article >, "Mike" >
>> wrote:
>>
>>>> Why wouldn't the HCs increase? When the exhaust gas
>>>> recirculation valve opens, what is it allowing into the intake
>>>> manifold/ combustion chamber?
>>>> CO2, CO, O2, NOx and HC.
>>> Yep, the EGR valve allows exhaust gas back into the combustion chamber,
>>> but,
>>> it is only a very small percentage of the total combution chamber volume.
>> So? If the air fuel mixture is lean to begin with, how does adding
>> exhaust gas make the flame propagate better?
>>
>>> The exhaust gas was already burnt once in the combustion chamber, how does
>>> running
>>> it through the combustion chamber a second time cause the HC to increase
>>> even
>>> further ?
>> See above.
>>
>>> Isn't the HC reading from the smog test unburned hydrocarbons ?
>> Yes it is.
>> Ever open an EGR valve at idle?
>
> Yep.
>
>> Did the engine run better or worse?
>
> Didn't run at all, they don't run well on an inert gas.
>
>> Do you suppose HC goes up or down if you open the EGR at idle?
>
> Being the engine wouldn't stay running I would say it went down. If it
> would stay running it would have a lean misfire that would lead to an increase
> in HC.
>
>
>>>> When the exhaust gas recirculation valve opens what happens to
>>>> manifold pressure?
>>>> It goes up.
>>>> What does the power valve do when manifold pressure goes up?
>>>> It opens and allows more HC (gasoline) to flow into the venturi
>>>> in the carb
>
>>> Yep, that's how the power enrichment works as well but why such a jump
>>> in
>>> HC ? This is the first time I remember seeing a NOx problem fixed were the
>>> HC reading jumped up like that.
>> Not for me.
>> It's very common on some engines to repair a non functioning EGR for a
>> NOx failure and have the car fail on HC. Typical 4 cylinder where the
>> EGR feeds into the intake ports individually (4 separate EGR passages)
>> and 2 or 3 are plugged. The 1 or 2 that do flow EGR are over fed and
>> cause a misfire. Roto-Root the passages and everything is fine...
>>
>>> Does this have anything to do with the vehicle
>>> being equiped with an air pump ?
>> The high HC? Maybe yes, maybe no. That's why there's a thing called
>> 'diagnostics.' I'd watch the reading with the air pump disabled.
>
> Yes, I'd like to see the results with the air pump disabled.
>
>> The OP has a 21 year old truck, what are the odds hat the air pump is
>> original? I couldn't get the air pump on my bought new 85 F-150 to last
>> more than three years.

The air pump is original equipment. I bought the truck new and I have
done all my own work on it, including changing the lifters and changing
a blown head gasket, two separate operations. So I know the air pump is
original. Whether it's working as it should today, I can't say. I tested
it a few years ago according to the manual and it seemed to be working then.

What has me puzzled at this point is which of the 4 operations I
performed on the fuel and ignition systems contributed to the
skyrocketing of CO emissions on the third test (test results reprinted
below). HC and NO came down significantly, as did O2, but at the expense
of CO.

Only the enrichening of the idle mixture and the widening of the
canister purge line ports in the wall of the carb throttle body could
have fattened up the mix, which would have resulted in the higher CO and
lower O2 readings. Assuming no freakishly timed breakdown of the air
pump, it's operation would have been the same for all 3 tests, whether
working or not.

If the guy who owns the smog shop will allow it, I would like to run
another pre-test and see if clamping down the canister purge hose
changes the readings mid-test.

I leaned out the idle mixture screws just a bit after the third test.
They were pretty close to lean best idle as it was. I can't imagine that
the small change that I made to the idle mix could have such a strong
affect on the emissions with the engine running at 1325 rpms. So the
enlarging of the canister purge line ports into the venturi just above
the throttle plates is the likely suspect, IMO.


%CO2 %O2 HC PPM %CO NOx PPM

15mph

1st test 10.8 5.9 34 .01 3641-FAIL
2nd test 10.4 6.7 132* .01 626
3rd test 12.2 3.6 82 1.02-FAIL 358


25mph

1st test 10.7 6.0 26 .01 3225-FAIL
2nd test 10.7 6.1 65 .04 606
3rd test 12.5 2.9 73 1.14** 191


1st test - 1. EGR run from EGR port on carb resulting in essentially
no EGR function
2. MSD ignition hooked up

2nd test - 1. EGR run from spark advance port on carb
2. MSD ignition not hooked up

3rd test - 1. EGR run from modified EGR port on carb
2. Idle mixture enriched slightly
3. The ports entering both barrels from the canister
purge hose were enlarged to correspond to those in the
original stock carb.
4. MSD ignition hooked up


* passing is 134, measured 132
** passing is 1.14, measured 1.14


>> Air pumps tend to have a generic universal design, what if instead of a
>> 4 CFM air pump made for a 3.9 liter engine, he got a 10 CFM replacement
>> pump made for a 7.4 liter engine.
>> You -can- pump too much air into a catalytic converter and snuff out the
>> fire.
>
> Yep, I see your point here. My experience has been that aftermarket
> emission parts are junk.
>
>
>>> We don't see too many air pumps on the east
>>> coast.
>> Dunno why, they were pretty common in the day that the OPs truck was
>> built.
>
> They sure were, but living in the rust belt they don't last very long and
> are long ago rusted away.
>
>> Now they're likely to be electric.
>

In article
>,
wrote:

> aarcuda69062 wrote:
> > In article >, jim >
> > wrote:
>
> > > As for the Chrysler lean burn crap - that was easy to fix. What was so
> > > incredibly stupid was it took Chrysler engineers 10 years and near
> > > bankruptcy to figure out how to fix it.
> >
> > That's the way innovation is.
>
> Ultradrive innovation?

Yes.

aarcuda69062 wrote:
>
> In article >, "Mike" >
> wrote:
>
> > > Yes it is.
> > > Ever open an EGR valve at idle?
> >
> > Yep.
> >
> > > Did the engine run better or worse?
> >
> > Didn't run at all, they don't run well on an inert gas.
>
> Next time, don't open it so far. Try a 10% or 20% command on your scn
> tool instead of 80% .
> >
> > > Do you suppose HC goes up or down if you open the EGR at idle?
> >
> > Being the engine wouldn't stay running I would say it went down. If
> > it
> > would stay running it would have a lean misfire that would lead to an
> > increase
> > in HC.
>
> No, it wouldn't be a lean misfire. Lean misfire comes from too much air
> and not enough fuel. Opening the EGR does not add more air.

It does add gas which displaces air. That would mean less air going into
the cylinders. At least that is what would happen in the first fractions
of a second. So for a very brief period of time you get a rich condition.


> The exhaust gasses displace what would have been combustible mixture in
> the combustion chamber, the actual ratio of that combustible mixture
> doesn't change.

How can the mixture not change if you just took away some of the air. Of
course in about the time it takes you to blink the dynamic system that
controls fuel, air, timing and idle speed is going to react to those
changes - so any conclusions you draw from this experiment are more than
likely to be completely wrong.


-jim


> If you have an engine with a leaking EGR valve at idle, fattening up the
> mixture doesn't improve how the engine will idle.



> Comparing secondary spark lines on a ignition scope, a lean mixture
> looks completely different than a stuck open or leaking EGR valve.




>
> > > Air pumps tend to have a generic universal design, what if instead of a
> > > 4 CFM air pump made for a 3.9 liter engine, he got a 10 CFM replacement
> > > pump made for a 7.4 liter engine.
> > > You -can- pump too much air into a catalytic converter and snuff out the
> > > fire.
> >
> > Yep, I see your point here. My experience has been that aftermarket
> > emission parts are junk.
>
> Yup.


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In article >, jim >
wrote:

> > No, it wouldn't be a lean misfire. Lean misfire comes from too much air
> > and not enough fuel. Opening the EGR does not add more air.
>
> It does add gas which displaces air.

Displaces air -and- fuel.

> That would mean less air going into
> the cylinders.

Less air -and- fuel going into the cylinder.

> At least that is what would happen in the first fractions
> of a second. So for a very brief period of time you get a rich condition.
>
>
> > The exhaust gasses displace what would have been combustible mixture in
> > the combustion chamber, the actual ratio of that combustible mixture
> > doesn't change.
>
> How can the mixture not change if you just took away some of the air.

What makes you think that EGR only takes away air.
What makes you think that EGR takes away anything?
EGR displaces a volume in a cylinder.

> Of
> course in about the time it takes you to blink the dynamic system that
> controls fuel, air, timing and idle speed is going to react to those
> changes - so any conclusions you draw from this experiment are more than
> likely to be completely wrong.

None of what I've said are mine nor are they conclusions.
IOWs, you assume wrong again
They are the physics of the internal combustion engine, documented and
published (but probably not in Popular Mechanics).

Don't take my word for it, feel free to run Simpson's non operating EGR
valve gas readings and his operating EGR valve gas readings thru a
Lambda calculator.
You'll find that the air fuel ratio changes by .01 which is well within
the expected sampling error of the type of equipment being used for his
tests.

aarcuda69062 wrote:
>
> In article >, jim >
> wrote:
>
> > > No, it wouldn't be a lean misfire. Lean misfire comes from too much air
> > > and not enough fuel. Opening the EGR does not add more air.
> >
> > It does add gas which displaces air.
>
> Displaces air -and- fuel.

One can only guess what it is you are talking about. Let's assume you were
talking about a modern car with fuel injection. Air gets displaced
meaning less will enter intake (at least for an instant). The fuel at the
same time doesn't get displaced. There is nothing physical to cause the
fuel to be displaced. If the end result is less fuel is delivered it is
only because the engine's control system delivers less fuel (but it could
deliver more air or both).
On a vehicle with carb it's different because airflow is part of the
physical process that delivers fuel. But that still doesn't mean the
air/fuel ratio will stay the same without some engineering effort to make
that happen.


>
> > That would mean less air going into
> > the cylinders.
>
> Less air -and- fuel going into the cylinder.

Maybe or maybe not. All depends how a particular system is designed.
Hopefully it's designed well enough that it won't change the air/fuel
ratio very much in your scenario since EGR failures are not rare
occurrences.



>
> > At least that is what would happen in the first fractions
> > of a second. So for a very brief period of time you get a rich condition.
> >
> >
> > > The exhaust gasses displace what would have been combustible mixture in
> > > the combustion chamber, the actual ratio of that combustible mixture
> > > doesn't change.
> >
> > How can the mixture not change if you just took away some of the air.
>
> What makes you think that EGR only takes away air.
> What makes you think that EGR takes away anything?
> EGR displaces a volume in a cylinder.

That was your terminology. Air is a gas. So is the exhaust coming from EGR
- fuel is not. If you say some of the volume of gas is displaced that
equivalent to saying some is taken away.

>
> > Of
> > course in about the time it takes you to blink the dynamic system that
> > controls fuel, air, timing and idle speed is going to react to those
> > changes - so any conclusions you draw from this experiment are more than
> > likely to be completely wrong.
>
> None of what I've said are mine nor are they conclusions.

It sounded like it was your experiment. It also sounded like your
conclusion or at least you hoped others would reach from the experiment.
The only reason your experiment would lead to that erroneous conclusion is
because that is the way it is engineered to work. If the controls are
working as they should then it won't affect air/fuel because it is
designed not to.




> IOWs, you assume wrong again
> They are the physics of the internal combustion engine, documented and
> published (but probably not in Popular Mechanics).
>
> Don't take my word for it, feel free to run Simpson's non operating EGR
> valve gas readings and his operating EGR valve gas readings thru a
> Lambda calculator.
> You'll find that the air fuel ratio changes by .01 which is well within
> the expected sampling error of the type of equipment being used for his
> tests.


I suspect that Chrysler had a good bit of data on the vacuum controls for
EGR in the 80's also. And that data is what they used to design EGR
controls so that didn't throw the air/fuel ratio out of wack. But when you
start doing your own design on an engine as the OP is doing it is
extremely unlikely that you will end up not changing air/fuel ratio if you
just slap any EGR control onto the system any which way and simply hope.


-jim


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jim > wrote in :

>
>
> aarcuda69062 wrote:
>>
>> In article >, jim >
>> wrote:
>>
>> > > No, it wouldn't be a lean misfire. Lean misfire comes from too
>> > > much air and not enough fuel. Opening the EGR does not add more
>> > > air.
>> >
>> > It does add gas which displaces air.
>>
>> Displaces air -and- fuel.
>
> One can only guess what it is you are talking about. Let's assume you
> were talking about a modern car with fuel injection. Air gets
> displaced meaning less will enter intake (at least for an instant).
> The fuel at the same time doesn't get displaced. There is nothing
> physical to cause the fuel to be displaced.



I'd think the engine's computer would sense the decrease in fresh air
intake and reduce fuel delivery accordingly.



--
Tegger