Re: CJ7 barely failed emissions
 

In message <3F308C26.20BCB15@sympatico.ca>, "Mike Romain" wrote:

>You are right, but blocked idle tubes can 'easily' make the mix go out
>of the computer controlled stepper motor's pins travel range.

Blocked idle tubes cause a lean condition. The computer will try to correct.
If the mix is so lean it's out of the stepper motor's ability to correct the
mix, it's still too lean.

In the post I replied to, you said "Too rich can be caused from partially
blocked idle tubes." That's not true.

>
>They adjust the air flow only, the mix screws are set at factory rich
>and plugged off.
>

The idle mixture screws are set correctly when the stepper motor is moving in
and out near the middle of it's range.

>When the tubes really crap out, you have to remove the spring from the
>idle speed screw in order to get any idle at all. It goes out of
>range....

That's because it's so lean you have to open the throttle to keep it running.

>
>When I see a carb with the idle speed screw compressed tight, I
>immediately suspect partially blocked idle tubes.
>

Yes, because it's too lean and they're trying to keep it running.

>Clean tubes and the mix screw spring is about 5/8" long, plugged tubes
>and the spring is compressed or about 3/8" long.
>
>If you can get at the mix screws, you can force the carb lean with
>them, That can pass emissions usually but doesn't address why it is
>running rich, just the symptoms.

There aren't many Jeeps with carbs running around that still have sealed mixture
screws. By now they've all been cut, drilled or whatever. It's probably too
rich because somebody's been f*ing with it and don't know what they're doing.

>
>Mike
>
>bllsht wrote:
>>
>> In message <3F2FD37B.CE04B6CC@sympatico.ca>, "Mike Romain" wrote:
>>
>> >Too rich can be caused from partially blocked idle tubes. The computer
>> >will set the stepper motor rich.
>>
>> It doesn't work that way. The computer will correct the mixture (lean or rich)
>> to achieve the "proper" amount of O2 in the exhaust.
>>
>> >
>> >See this link:
>> >
>> >http://www.off-road.com/jeep/tech/engine/carter.html
>> >
>> >A bad charcoal canister can also cause that, but with a bad canister,
>> >the idle will 'usually' surge up and down a little and you will get
>> >spits of oil coming into the air filter from the valve cover vent.
>> >
>> >Mike
>> >86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
>> >88 Cherokee 235 BFG AT's
>> >
>> >bllsht wrote:
>> >>
>> >> High CO = too rich. Lean out the idle mixture a bit. You didn't fail by much,
>> >> so it shouldn't take a big adjustment.
>> >>
>> >> In message <BB542759.1BE22%nospam@thanksImFull.spam>, "KurtS" wrote:
>> >>
>> >> >'85 C7 258 - computer in the loop - stock everything
>> >> >Damnit. I should have know better than to take my Jeep in for testing on a
>> >> >rainy day but I did it anyway (it's a bit sluggish in wet weather). So here
>> >> >are my results:
>> >> >
>> >> >HC PPM Idle - 223/300 -- Pass
>> >> >HC PPM 2500 RPM - 103/300 -- Pass
>> >> >CO % idle - 2.10/2.00 -- fail
>> >> >CO % 2500 RPM - 1.58/2.00 -- pass
>> >> >
>> >> >I barely failed CO at idle -- seems all my idle readings are much higher by
>> >> >ratio. I have been doing mostly city driving for a couple months. Would an
>> >> >hour or so on the highway take care of the high CO? Any other hints? I
>> >> >replaced the EGR and O2 sensor about 3000 miles ago.

Re: CJ7 barely failed emissions
 

In message <3F308E5F.CF4717CD@sympatico.ca>, "Mike Romain" wrote:

>bllsht wrote:
>>
>> In message <BB557AAA.1BF03%nospam@thanksImFull.spam>, "KurtS" wrote:
>>
>> >That's what I thought. It has been running a little rich lately (black tail
>> >pipe recently). Since the canister is new from the dealer a few months ago,
>> >I'll give the tubes a ream. It's been about 9 months since the last time.
>> >Tnx guys!
>>
>> Plugged idle tubes can cause it to run too lean(not enough fuel). Yours is too
>> rich(too much fuel). You could probably give each of the idle mixture screws
>> about 1/2 to 1 turn in (clockwise) and be fine. If the tubes are plugged,
>> cleaning them will only add more fuel. Not the direction you need to go.
>>
>> >
>> >> From: bllsht <nospam@invaliddot.net>
>> >> Reply-To: nospam@invaliddot.net
>> >> Newsgroups: rec.autos.makers.jeep+willys
>> >> Date: Tue, 05 Aug 2003 06:43:56 GMT
>> >> Subject: Re: CJ7 barely failed emissions
>> >>
>> >> High CO = too rich. Lean out the idle mixture a bit. You didn't fail by
>> >> much,
>> >> so it shouldn't take a big adjustment.
>
>Other way around bllsht.
>
>The computer sees a lean condition because of blocked tubes and goes
>into full rich mode.

It goes as rich as it needs to go, to correct the mixture. Remember that it's
looking for oxygen content in the exhaust, as reported by the O2 sensor. If O2
content gets too low, it will back out the stepper motor to lean it out.

>
>When anything gets out of the computer's range, like blocked tubes will
>do, it goes into 'limp home' mode and sets the carb rich and clamps down
>on the timing advance.

Nope. When the mixture gets out of range, it moves the stepper as far as it
can, in the desired direction, in an attempt to correct the situation.

>The mix screws on a computer controlled Carter BBD are blocked by a 1/4"
>deep and 1/4" round metal plug that has to be drilled or cut out to
>adjust them.

I bet there aren't many around that still have the plugs in them. I haven't
seen one with the plugs in years. That means there's a lot of mixture screws
out there that anyone who knows which end of a screwdriver to hold can, and
will, turn. Usually in the rich direction.

>
>Mike
>86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
>88 Cherokee 235 BFG AT's

Re: CJ7 barely failed emissions
 

On Wed, 06 Aug 2003 01:13:03 -0400 in rec.autos.makers.jeep+willys,
Mike Romain <romainm@sympatico.ca> wrote:

>When anything gets out of the computer's range, like blocked tubes will
>do, it goes into 'limp home' mode and sets the carb rich and clamps down
>on the timing advance.

Could a Jeep possibly have been that close to passing smog in "limp
home" mode?

Re: CJ7 barely failed emissions
 

Before this gets ugly, bllsht is right on the money. Thinking back to the
last rebuild, I remember backing the idle screws out a little mit - not
much. I had heard it's best to get them out of the way as far as possible
when the computer is still in charge. Apparently my source was sadly
mistaken.

> From: bllsht <nospam@invaliddot.net>
> Reply-To: nospam@invaliddot.net
> Newsgroups: rec.autos.makers.jeep+willys
> Date: Wed, 06 Aug 2003 06:39:05 GMT
> Subject: Re: CJ7 barely failed emissions
>
> I bet there aren't many around that still have the plugs in them. I haven't
> seen one with the plugs in years. That means there's a lot of mixture screws
> out there that anyone who knows which end of a screwdriver to hold can, and
> will, turn. Usually in the rich direction.

Re: CJ7 barely failed emissions
 

I guess as bllsht says, there aren't many if any perfect' setups left so
the mix screws are now in play on most...

Mike

KurtS wrote:
>
> Before this gets ugly, bllsht is right on the money. Thinking back to the
> last rebuild, I remember backing the idle screws out a little mit - not
> much. I had heard it's best to get them out of the way as far as possible
> when the computer is still in charge. Apparently my source was sadly
> mistaken.
>
> > From: bllsht <nospam@invaliddot.net>
> > Reply-To: nospam@invaliddot.net
> > Newsgroups: rec.autos.makers.jeep+willys
> > Date: Wed, 06 Aug 2003 06:39:05 GMT
> > Subject: Re: CJ7 barely failed emissions
> >
> > I bet there aren't many around that still have the plugs in them. I haven't
> > seen one with the plugs in years. That means there's a lot of mixture screws
> > out there that anyone who knows which end of a screwdriver to hold can, and
> > will, turn. Usually in the rich direction.

Re: CJ7 barely failed emissions
 

David Harmon wrote:
>
> On Wed, 06 Aug 2003 01:13:03 -0400 in rec.autos.makers.jeep+willys,
> Mike Romain <romainm@sympatico.ca> wrote:
>
> >When anything gets out of the computer's range, like blocked tubes will
> >do, it goes into 'limp home' mode and sets the carb rich and clamps down
> >on the timing advance.
>
> Could a Jeep possibly have been that close to passing smog in "limp
> home" mode?

Not likely, more likely his air filter is dirty or something.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Re: CJ7 barely failed emissions
 

I don't think the computer is that smart.

I think when it sees a lean it can overcompensate.

The OP was only slightly over on CO.

The stepper motor only has so many steps. The proper mix could be a
half a step leaner than the computer sets it.

Mike

bllsht wrote:
>
> In message <3F308C26.20BCB15@sympatico.ca>, "Mike Romain" wrote:
>
> >You are right, but blocked idle tubes can 'easily' make the mix go out
> >of the computer controlled stepper motor's pins travel range.
>
> Blocked idle tubes cause a lean condition. The computer will try to correct.
> If the mix is so lean it's out of the stepper motor's ability to correct the
> mix, it's still too lean.
>
> In the post I replied to, you said "Too rich can be caused from partially
> blocked idle tubes." That's not true.
>
> >
> >They adjust the air flow only, the mix screws are set at factory rich
> >and plugged off.
> >
>
> The idle mixture screws are set correctly when the stepper motor is moving in
> and out near the middle of it's range.
>
> >When the tubes really crap out, you have to remove the spring from the
> >idle speed screw in order to get any idle at all. It goes out of
> >range....
>
> That's because it's so lean you have to open the throttle to keep it running.
>
> >
> >When I see a carb with the idle speed screw compressed tight, I
> >immediately suspect partially blocked idle tubes.
> >
>
> Yes, because it's too lean and they're trying to keep it running.
>
> >Clean tubes and the mix screw spring is about 5/8" long, plugged tubes
> >and the spring is compressed or about 3/8" long.
> >
> >If you can get at the mix screws, you can force the carb lean with
> >them, That can pass emissions usually but doesn't address why it is
> >running rich, just the symptoms.
>
> There aren't many Jeeps with carbs running around that still have sealed mixture
> screws. By now they've all been cut, drilled or whatever. It's probably too
> rich because somebody's been f*ing with it and don't know what they're doing.
>
> >
> >Mike
> >
> >bllsht wrote:
> >>
> >> In message <3F2FD37B.CE04B6CC@sympatico.ca>, "Mike Romain" wrote:
> >>
> >> >Too rich can be caused from partially blocked idle tubes. The computer
> >> >will set the stepper motor rich.
> >>
> >> It doesn't work that way. The computer will correct the mixture (lean or rich)
> >> to achieve the "proper" amount of O2 in the exhaust.
> >>
> >> >
> >> >See this link:
> >> >
> >> >http://www.off-road.com/jeep/tech/engine/carter.html
> >> >
> >> >A bad charcoal canister can also cause that, but with a bad canister,
> >> >the idle will 'usually' surge up and down a little and you will get
> >> >spits of oil coming into the air filter from the valve cover vent.
> >> >
> >> >Mike
> >> >86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> >> >88 Cherokee 235 BFG AT's
> >> >
> >> >bllsht wrote:
> >> >>
> >> >> High CO = too rich. Lean out the idle mixture a bit. You didn't fail by much,
> >> >> so it shouldn't take a big adjustment.
> >> >>
> >> >> In message <BB542759.1BE22%nospam@thanksImFull.spam>, "KurtS" wrote:
> >> >>
> >> >> >'85 C7 258 - computer in the loop - stock everything
> >> >> >Damnit. I should have know better than to take my Jeep in for testing on a
> >> >> >rainy day but I did it anyway (it's a bit sluggish in wet weather). So here
> >> >> >are my results:
> >> >> >
> >> >> >HC PPM Idle - 223/300 -- Pass
> >> >> >HC PPM 2500 RPM - 103/300 -- Pass
> >> >> >CO % idle - 2.10/2.00 -- fail
> >> >> >CO % 2500 RPM - 1.58/2.00 -- pass
> >> >> >
> >> >> >I barely failed CO at idle -- seems all my idle readings are much higher by
> >> >> >ratio. I have been doing mostly city driving for a couple months. Would an
> >> >> >hour or so on the highway take care of the high CO? Any other hints? I
> >> >> >replaced the EGR and O2 sensor about 3000 miles ago.

Re: CJ7 barely failed emissions
 

In message <3F315E76.96E87105@sympatico.ca>, "Mike Romain" wrote:

>I don't think the computer is that smart.
>
>I think when it sees a lean it can overcompensate.

I hope you're kidding...

The computer monitors O2 content of the exhaust. It alters the mix to achieve
it's desired O2 level. That's what it's designed to do, and yes, it is that
smart.

>
>The OP was only slightly over on CO.

Right. Too rich. Too much fuel. Not enough O2. That's what I said.

>
>The stepper motor only has so many steps. The proper mix could be a
>half a step leaner than the computer sets it.

Which is why I said the mixture screws are probably too rich. If the stepper
motor has reached it's lean limit, then the mixture screws are set too rich, or
something else has gone wrong in the carb to cause a rich condition. The
computer will not cause it to be too rich.

>
>Mike
>
>bllsht wrote:
>>
>> In message <3F308C26.20BCB15@sympatico.ca>, "Mike Romain" wrote:
>>
>> >You are right, but blocked idle tubes can 'easily' make the mix go out
>> >of the computer controlled stepper motor's pins travel range.
>>
>> Blocked idle tubes cause a lean condition. The computer will try to correct.
>> If the mix is so lean it's out of the stepper motor's ability to correct the
>> mix, it's still too lean.
>>
>> In the post I replied to, you said "Too rich can be caused from partially
>> blocked idle tubes." That's not true.
>>
>> >
>> >They adjust the air flow only, the mix screws are set at factory rich
>> >and plugged off.
>> >
>>
>> The idle mixture screws are set correctly when the stepper motor is moving in
>> and out near the middle of it's range.
>>
>> >When the tubes really crap out, you have to remove the spring from the
>> >idle speed screw in order to get any idle at all. It goes out of
>> >range....
>>
>> That's because it's so lean you have to open the throttle to keep it running.
>>
>> >
>> >When I see a carb with the idle speed screw compressed tight, I
>> >immediately suspect partially blocked idle tubes.
>> >
>>
>> Yes, because it's too lean and they're trying to keep it running.
>>
>> >Clean tubes and the mix screw spring is about 5/8" long, plugged tubes
>> >and the spring is compressed or about 3/8" long.
>> >
>> >If you can get at the mix screws, you can force the carb lean with
>> >them, That can pass emissions usually but doesn't address why it is
>> >running rich, just the symptoms.
>>
>> There aren't many Jeeps with carbs running around that still have sealed mixture
>> screws. By now they've all been cut, drilled or whatever. It's probably too
>> rich because somebody's been f*ing with it and don't know what they're doing.
>>
>> >
>> >Mike
>> >
>> >bllsht wrote:
>> >>
>> >> In message <3F2FD37B.CE04B6CC@sympatico.ca>, "Mike Romain" wrote:
>> >>
>> >> >Too rich can be caused from partially blocked idle tubes. The computer
>> >> >will set the stepper motor rich.
>> >>
>> >> It doesn't work that way. The computer will correct the mixture (lean or rich)
>> >> to achieve the "proper" amount of O2 in the exhaust.
>> >>
>> >> >
>> >> >See this link:
>> >> >
>> >> >http://www.off-road.com/jeep/tech/engine/carter.html
>> >> >
>> >> >A bad charcoal canister can also cause that, but with a bad canister,
>> >> >the idle will 'usually' surge up and down a little and you will get
>> >> >spits of oil coming into the air filter from the valve cover vent.
>> >> >
>> >> >Mike
>> >> >86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
>> >> >88 Cherokee 235 BFG AT's
>> >> >
>> >> >bllsht wrote:
>> >> >>
>> >> >> High CO = too rich. Lean out the idle mixture a bit. You didn't fail by much,
>> >> >> so it shouldn't take a big adjustment.
>> >> >>
>> >> >> In message <BB542759.1BE22%nospam@thanksImFull.spam>, "KurtS" wrote:
>> >> >>
>> >> >> >'85 C7 258 - computer in the loop - stock everything
>> >> >> >Damnit. I should have know better than to take my Jeep in for testing on a
>> >> >> >rainy day but I did it anyway (it's a bit sluggish in wet weather). So here
>> >> >> >are my results:
>> >> >> >
>> >> >> >HC PPM Idle - 223/300 -- Pass
>> >> >> >HC PPM 2500 RPM - 103/300 -- Pass
>> >> >> >CO % idle - 2.10/2.00 -- fail
>> >> >> >CO % 2500 RPM - 1.58/2.00 -- pass
>> >> >> >
>> >> >> >I barely failed CO at idle -- seems all my idle readings are much higher by
>> >> >> >ratio. I have been doing mostly city driving for a couple months. Would an
>> >> >> >hour or so on the highway take care of the high CO? Any other hints? I
>> >> >> >replaced the EGR and O2 sensor about 3000 miles ago.

Re: CJ7 barely failed emissions
 

Not kidding, really....

Here is how I see it working. If I am mistaken, I would appreciate the
feedback.

The OP stated he has a 'stock everything' 85.

I therefore do not assume that the carb has been drilled or cut up to
access the idle mix screws.

The stepper motor has (for easy numbers) 'say' 5 steps from full rich to
full lean.

The carb if manually set up has 'say' 5 turns on the mix screws from
full rich to full lean.

With a perfectly working system, either the stepper or the mix screws if
a manual BBD operate approximately in the middle of the range or at 2.5
turns out for the screws or jumping from step 2 to step 3 to get the O2
sensor to read correctly with the computer.

Now we toss in a partially plugged idle tube or something else gummed up
forcing a lean to 'some' extent.

If I am manually setting the mix, I then need to open the mix screws to
'say' 3 1/4 turns out to get it stable.

In comes the stepper motor on the computer BBD. It has a choice of
either the 3rd step or the 4th step.

It tries step 3, nope, too lean. 1/4 turn too lean if manual. It then
tries step 4, nope again, too rich. 3/4 a turn if manual too rich.

It keeps jumping back and forth between step 3 and 4. Every time it
hits step 4, it goes rich, a lot more rich than it goes lean when on
step 3.

Bingo, a carb that 'just' fails emissions by being slightly rich.

I also believe this is one of the main reasons you see the mix screws
cut open. Forcing a mix change via the manual mix screws can make the
O2 tell the stepper motor to 'see' it as 'say' 2.5 steps exact like it
was from the factory so when it samples it is an even 2 step to 3 step
pulse which puts the mix back into emissions range.

This is just fixing the symptoms, that blocked idle tube is still
there...

Mike

bllsht wrote:
>
> In message <3F315E76.96E87105@sympatico.ca>, "Mike Romain" wrote:
>
> >I don't think the computer is that smart.
> >
> >I think when it sees a lean it can overcompensate.
>
> I hope you're kidding...
>
> The computer monitors O2 content of the exhaust. It alters the mix to achieve
> it's desired O2 level. That's what it's designed to do, and yes, it is that
> smart.
>
> >
> >The OP was only slightly over on CO.
>
> Right. Too rich. Too much fuel. Not enough O2. That's what I said.
>
> >
> >The stepper motor only has so many steps. The proper mix could be a
> >half a step leaner than the computer sets it.
>
> Which is why I said the mixture screws are probably too rich. If the stepper
> motor has reached it's lean limit, then the mixture screws are set too rich, or
> something else has gone wrong in the carb to cause a rich condition. The
> computer will not cause it to be too rich.
>
> >
> >Mike
> >
> >bllsht wrote:
> >>
> >> In message <3F308C26.20BCB15@sympatico.ca>, "Mike Romain" wrote:
> >>
> >> >You are right, but blocked idle tubes can 'easily' make the mix go out
> >> >of the computer controlled stepper motor's pins travel range.
> >>
> >> Blocked idle tubes cause a lean condition. The computer will try to correct.
> >> If the mix is so lean it's out of the stepper motor's ability to correct the
> >> mix, it's still too lean.
> >>
> >> In the post I replied to, you said "Too rich can be caused from partially
> >> blocked idle tubes." That's not true.
> >>
> >> >
> >> >They adjust the air flow only, the mix screws are set at factory rich
> >> >and plugged off.
> >> >
> >>
> >> The idle mixture screws are set correctly when the stepper motor is moving in
> >> and out near the middle of it's range.
> >>
> >> >When the tubes really crap out, you have to remove the spring from the
> >> >idle speed screw in order to get any idle at all. It goes out of
> >> >range....
> >>
> >> That's because it's so lean you have to open the throttle to keep it running.
> >>
> >> >
> >> >When I see a carb with the idle speed screw compressed tight, I
> >> >immediately suspect partially blocked idle tubes.
> >> >
> >>
> >> Yes, because it's too lean and they're trying to keep it running.
> >>
> >> >Clean tubes and the mix screw spring is about 5/8" long, plugged tubes
> >> >and the spring is compressed or about 3/8" long.
> >> >
> >> >If you can get at the mix screws, you can force the carb lean with
> >> >them, That can pass emissions usually but doesn't address why it is
> >> >running rich, just the symptoms.
> >>
> >> There aren't many Jeeps with carbs running around that still have sealed mixture
> >> screws. By now they've all been cut, drilled or whatever. It's probably too
> >> rich because somebody's been f*ing with it and don't know what they're doing.
> >>
> >> >
> >> >Mike
> >> >
> >> >bllsht wrote:
> >> >>
> >> >> In message <3F2FD37B.CE04B6CC@sympatico.ca>, "Mike Romain" wrote:
> >> >>
> >> >> >Too rich can be caused from partially blocked idle tubes. The computer
> >> >> >will set the stepper motor rich.
> >> >>
> >> >> It doesn't work that way. The computer will correct the mixture (lean or rich)
> >> >> to achieve the "proper" amount of O2 in the exhaust.
> >> >>
> >> >> >
> >> >> >See this link:
> >> >> >
> >> >> >http://www.off-road.com/jeep/tech/engine/carter.html
> >> >> >
> >> >> >A bad charcoal canister can also cause that, but with a bad canister,
> >> >> >the idle will 'usually' surge up and down a little and you will get
> >> >> >spits of oil coming into the air filter from the valve cover vent.
> >> >> >
> >> >> >Mike
> >> >> >86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> >> >> >88 Cherokee 235 BFG AT's
> >> >> >
> >> >> >bllsht wrote:
> >> >> >>
> >> >> >> High CO = too rich. Lean out the idle mixture a bit. You didn't fail by much,
> >> >> >> so it shouldn't take a big adjustment.
> >> >> >>
> >> >> >> In message <BB542759.1BE22%nospam@thanksImFull.spam>, "KurtS" wrote:
> >> >> >>
> >> >> >> >'85 C7 258 - computer in the loop - stock everything
> >> >> >> >Damnit. I should have know better than to take my Jeep in for testing on a
> >> >> >> >rainy day but I did it anyway (it's a bit sluggish in wet weather). So here
> >> >> >> >are my results:
> >> >> >> >
> >> >> >> >HC PPM Idle - 223/300 -- Pass
> >> >> >> >HC PPM 2500 RPM - 103/300 -- Pass
> >> >> >> >CO % idle - 2.10/2.00 -- fail
> >> >> >> >CO % 2500 RPM - 1.58/2.00 -- pass
> >> >> >> >
> >> >> >> >I barely failed CO at idle -- seems all my idle readings are much higher by
> >> >> >> >ratio. I have been doing mostly city driving for a couple months. Would an
> >> >> >> >hour or so on the highway take care of the high CO? Any other hints? I
> >> >> >> >replaced the EGR and O2 sensor about 3000 miles ago.

Re: CJ7 barely failed emissions
 

OK. So Factory Settings should be in the neighborhood of 2.5 turns out from
full travel in, correct?

> From: Mike Romain <romainm@sympatico.ca>
> Organization: Bell Sympatico
> Newsgroups: rec.autos.makers.jeep+willys
> Date: Thu, 07 Aug 2003 12:23:31 -0400
> Subject: Re: CJ7 barely failed emissions
>
> Not kidding, really....
>
> Here is how I see it working. If I am mistaken, I would appreciate the
> feedback.
>
> The OP stated he has a 'stock everything' 85.
>
> I therefore do not assume that the carb has been drilled or cut up to
> access the idle mix screws.
>
> The stepper motor has (for easy numbers) 'say' 5 steps from full rich to
> full lean.
>
> The carb if manually set up has 'say' 5 turns on the mix screws from
> full rich to full lean.
>
> With a perfectly working system, either the stepper or the mix screws if
> a manual BBD operate approximately in the middle of the range or at 2.5
> turns out for the screws or jumping from step 2 to step 3 to get the O2
> sensor to read correctly with the computer.
>
> Now we toss in a partially plugged idle tube or something else gummed up
> forcing a lean to 'some' extent.
>
> If I am manually setting the mix, I then need to open the mix screws to
> 'say' 3 1/4 turns out to get it stable.
>
> In comes the stepper motor on the computer BBD. It has a choice of
> either the 3rd step or the 4th step.
>
> It tries step 3, nope, too lean. 1/4 turn too lean if manual. It then
> tries step 4, nope again, too rich. 3/4 a turn if manual too rich.
>
> It keeps jumping back and forth between step 3 and 4. Every time it
> hits step 4, it goes rich, a lot more rich than it goes lean when on
> step 3.
>
> Bingo, a carb that 'just' fails emissions by being slightly rich.
>
> I also believe this is one of the main reasons you see the mix screws
> cut open. Forcing a mix change via the manual mix screws can make the
> O2 tell the stepper motor to 'see' it as 'say' 2.5 steps exact like it
> was from the factory so when it samples it is an even 2 step to 3 step
> pulse which puts the mix back into emissions range.
>
> This is just fixing the symptoms, that blocked idle tube is still
> there...
>
> Mike
>
> bllsht wrote:
>>
>> In message <3F315E76.96E87105@sympatico.ca>, "Mike Romain" wrote:
>>
>>> I don't think the computer is that smart.
>>>
>>> I think when it sees a lean it can overcompensate.
>>
>> I hope you're kidding...
>>
>> The computer monitors O2 content of the exhaust. It alters the mix to
>> achieve
>> it's desired O2 level. That's what it's designed to do, and yes, it is that
>> smart.
>>
>>>
>>> The OP was only slightly over on CO.
>>
>> Right. Too rich. Too much fuel. Not enough O2. That's what I said.
>>
>>>
>>> The stepper motor only has so many steps. The proper mix could be a
>>> half a step leaner than the computer sets it.
>>
>> Which is why I said the mixture screws are probably too rich. If the stepper
>> motor has reached it's lean limit, then the mixture screws are set too rich,
>> or
>> something else has gone wrong in the carb to cause a rich condition. The
>> computer will not cause it to be too rich.
>>
>>>
>>> Mike
>>>
>>> bllsht wrote:
>>>>
>>>> In message <3F308C26.20BCB15@sympatico.ca>, "Mike Romain" wrote:
>>>>
>>>>> You are right, but blocked idle tubes can 'easily' make the mix go out
>>>>> of the computer controlled stepper motor's pins travel range.
>>>>
>>>> Blocked idle tubes cause a lean condition. The computer will try to
>>>> correct.
>>>> If the mix is so lean it's out of the stepper motor's ability to correct
>>>> the
>>>> mix, it's still too lean.
>>>>
>>>> In the post I replied to, you said "Too rich can be caused from partially
>>>> blocked idle tubes." That's not true.
>>>>
>>>>>
>>>>> They adjust the air flow only, the mix screws are set at factory rich
>>>>> and plugged off.
>>>>>
>>>>
>>>> The idle mixture screws are set correctly when the stepper motor is moving
>>>> in
>>>> and out near the middle of it's range.
>>>>
>>>>> When the tubes really crap out, you have to remove the spring from the
>>>>> idle speed screw in order to get any idle at all. It goes out of
>>>>> range....
>>>>
>>>> That's because it's so lean you have to open the throttle to keep it
>>>> running.
>>>>
>>>>>
>>>>> When I see a carb with the idle speed screw compressed tight, I
>>>>> immediately suspect partially blocked idle tubes.
>>>>>
>>>>
>>>> Yes, because it's too lean and they're trying to keep it running.
>>>>
>>>>> Clean tubes and the mix screw spring is about 5/8" long, plugged tubes
>>>>> and the spring is compressed or about 3/8" long.
>>>>>
>>>>> If you can get at the mix screws, you can force the carb lean with
>>>>> them, That can pass emissions usually but doesn't address why it is
>>>>> running rich, just the symptoms.
>>>>
>>>> There aren't many Jeeps with carbs running around that still have sealed
>>>> mixture
>>>> screws. By now they've all been cut, drilled or whatever. It's probably
>>>> too
>>>> rich because somebody's been f*ing with it and don't know what they're
>>>> doing.
>>>>
>>>>>
>>>>> Mike
>>>>>
>>>>> bllsht wrote:
>>>>>>
>>>>>> In message <3F2FD37B.CE04B6CC@sympatico.ca>, "Mike Romain" wrote:
>>>>>>
>>>>>>> Too rich can be caused from partially blocked idle tubes. The computer
>>>>>>> will set the stepper motor rich.
>>>>>>
>>>>>> It doesn't work that way. The computer will correct the mixture (lean or
>>>>>> rich)
>>>>>> to achieve the "proper" amount of O2 in the exhaust.
>>>>>>
>>>>>>>
>>>>>>> See this link:
>>>>>>>
>>>>>>> http://www.off-road.com/jeep/tech/engine/carter.html
>>>>>>>
>>>>>>> A bad charcoal canister can also cause that, but with a bad canister,
>>>>>>> the idle will 'usually' surge up and down a little and you will get
>>>>>>> spits of oil coming into the air filter from the valve cover vent.
>>>>>>>
>>>>>>> Mike
>>>>>>> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
>>>>>>> 88 Cherokee 235 BFG AT's
>>>>>>>
>>>>>>> bllsht wrote:
>>>>>>>>
>>>>>>>> High CO = too rich. Lean out the idle mixture a bit. You didn't fail
>>>>>>>> by much,
>>>>>>>> so it shouldn't take a big adjustment.
>>>>>>>>
>>>>>>>> In message <BB542759.1BE22%nospam@thanksImFull.spam>, "KurtS" wrote:
>>>>>>>>
>>>>>>>>> '85 C7 258 - computer in the loop - stock everything
>>>>>>>>> Damnit. I should have know better than to take my Jeep in for testing
>>>>>>>>> on a
>>>>>>>>> rainy day but I did it anyway (it's a bit sluggish in wet weather). So
>>>>>>>>> here
>>>>>>>>> are my results:
>>>>>>>>>
>>>>>>>>> HC PPM Idle - 223/300 -- Pass
>>>>>>>>> HC PPM 2500 RPM - 103/300 -- Pass
>>>>>>>>> CO % idle - 2.10/2.00 -- fail
>>>>>>>>> CO % 2500 RPM - 1.58/2.00 -- pass
>>>>>>>>>
>>>>>>>>> I barely failed CO at idle -- seems all my idle readings are much
>>>>>>>>> higher by
>>>>>>>>> ratio. I have been doing mostly city driving for a couple months.
>>>>>>>>> Would an
>>>>>>>>> hour or so on the highway take care of the high CO? Any other hints? I
>>>>>>>>> replaced the EGR and O2 sensor about 3000 miles ago.