The Reverend Natural Light

Greetings.

I'm working on a 1990 Jeep YJ, 4.2L I6, that won't idle. From 1200RPM
up, everything's fine. It runs smooth under power. It won't idle at
all.

The previous owner replaced the carb with an older non-computer
controlled unit. He made the decision to use the older carb because it
was cheaper and simpler and someone knowledgeable (?) told him to. I
believe it never ran right while he owned it.

I have:

1. Checked for vacuum leaks.
2. Made sure the EGR valve is completely closed.
3. Replaced spark plugs and checked cap and rotor (old plugs were worn
but tan).
4. Verified functional vacuum advance function.
5. Verified electric choke function.
6. Tried various settings of the idle bleed screws. Currently 2 turns
out.

No help.

Since it has an ECM controlling spark but no electronic carb, I figured
the computer controlled spark could be an issue. So, I picked up a new
spark control module for a non-ECM jeep and wired it up to the
distributor following the wiring diagram for an older jeep. Now there
is no computer control whatsoever.

No help with idle, but the throttle response seems a bit crisper.


It appears to be running lean at closed-throttle because it will idle
if I manually close the choke flapper. This leads me to believe that
the problem is not the common "idle tubes" issue which causes a rich
condition. It really feels like a bad vacuum leak but I can't find it.


I'm completely out of ideas. In all honesty, I'm a lot more
comfortable working on fuel injection. A grizzled Jeep veteran could
probably whack it with a hammer and it would purr like a kitten. Any
advice?

Thanks!


-rev

Joe C

If it's the original Carter check out this site.
http://www.off-road.com/jeep/tech/engine/carter.html

"The Reverend Natural Light" <reverend@fourthgen.org> wrote in message
news:1152548720.923722.28230@s13g2000cwa.googlegro ups.com...
> Greetings.
>
> I'm working on a 1990 Jeep YJ, 4.2L I6, that won't idle. From 1200RPM
> up, everything's fine. It runs smooth under power. It won't idle at
> all.
>
> The previous owner replaced the carb with an older non-computer
> controlled unit. He made the decision to use the older carb because it
> was cheaper and simpler and someone knowledgeable (?) told him to. I
> believe it never ran right while he owned it.
>
> I have:
>
> 1. Checked for vacuum leaks.
> 2. Made sure the EGR valve is completely closed.
> 3. Replaced spark plugs and checked cap and rotor (old plugs were worn
> but tan).
> 4. Verified functional vacuum advance function.
> 5. Verified electric choke function.
> 6. Tried various settings of the idle bleed screws. Currently 2 turns
> out.
>
> No help.
>
> Since it has an ECM controlling spark but no electronic carb, I figured
> the computer controlled spark could be an issue. So, I picked up a new
> spark control module for a non-ECM jeep and wired it up to the
> distributor following the wiring diagram for an older jeep. Now there
> is no computer control whatsoever.
>
> No help with idle, but the throttle response seems a bit crisper.
>
>
> It appears to be running lean at closed-throttle because it will idle
> if I manually close the choke flapper. This leads me to believe that
> the problem is not the common "idle tubes" issue which causes a rich
> condition. It really feels like a bad vacuum leak but I can't find it.
>
>
> I'm completely out of ideas. In all honesty, I'm a lot more
> comfortable working on fuel injection. A grizzled Jeep veteran could
> probably whack it with a hammer and it would purr like a kitten. Any
> advice?
>
> Thanks!
>
>
> -rev
>

Joe C

If it's the original Carter check out this site.
http://www.off-road.com/jeep/tech/engine/carter.html

"The Reverend Natural Light" <reverend@fourthgen.org> wrote in message
news:1152548720.923722.28230@s13g2000cwa.googlegro ups.com...
> Greetings.
>
> I'm working on a 1990 Jeep YJ, 4.2L I6, that won't idle. From 1200RPM
> up, everything's fine. It runs smooth under power. It won't idle at
> all.
>
> The previous owner replaced the carb with an older non-computer
> controlled unit. He made the decision to use the older carb because it
> was cheaper and simpler and someone knowledgeable (?) told him to. I
> believe it never ran right while he owned it.
>
> I have:
>
> 1. Checked for vacuum leaks.
> 2. Made sure the EGR valve is completely closed.
> 3. Replaced spark plugs and checked cap and rotor (old plugs were worn
> but tan).
> 4. Verified functional vacuum advance function.
> 5. Verified electric choke function.
> 6. Tried various settings of the idle bleed screws. Currently 2 turns
> out.
>
> No help.
>
> Since it has an ECM controlling spark but no electronic carb, I figured
> the computer controlled spark could be an issue. So, I picked up a new
> spark control module for a non-ECM jeep and wired it up to the
> distributor following the wiring diagram for an older jeep. Now there
> is no computer control whatsoever.
>
> No help with idle, but the throttle response seems a bit crisper.
>
>
> It appears to be running lean at closed-throttle because it will idle
> if I manually close the choke flapper. This leads me to believe that
> the problem is not the common "idle tubes" issue which causes a rich
> condition. It really feels like a bad vacuum leak but I can't find it.
>
>
> I'm completely out of ideas. In all honesty, I'm a lot more
> comfortable working on fuel injection. A grizzled Jeep veteran could
> probably whack it with a hammer and it would purr like a kitten. Any
> advice?
>
> Thanks!
>
>
> -rev
>

Joe C

If it's the original Carter check out this site.
http://www.off-road.com/jeep/tech/engine/carter.html

"The Reverend Natural Light" <reverend@fourthgen.org> wrote in message
news:1152548720.923722.28230@s13g2000cwa.googlegro ups.com...
> Greetings.
>
> I'm working on a 1990 Jeep YJ, 4.2L I6, that won't idle. From 1200RPM
> up, everything's fine. It runs smooth under power. It won't idle at
> all.
>
> The previous owner replaced the carb with an older non-computer
> controlled unit. He made the decision to use the older carb because it
> was cheaper and simpler and someone knowledgeable (?) told him to. I
> believe it never ran right while he owned it.
>
> I have:
>
> 1. Checked for vacuum leaks.
> 2. Made sure the EGR valve is completely closed.
> 3. Replaced spark plugs and checked cap and rotor (old plugs were worn
> but tan).
> 4. Verified functional vacuum advance function.
> 5. Verified electric choke function.
> 6. Tried various settings of the idle bleed screws. Currently 2 turns
> out.
>
> No help.
>
> Since it has an ECM controlling spark but no electronic carb, I figured
> the computer controlled spark could be an issue. So, I picked up a new
> spark control module for a non-ECM jeep and wired it up to the
> distributor following the wiring diagram for an older jeep. Now there
> is no computer control whatsoever.
>
> No help with idle, but the throttle response seems a bit crisper.
>
>
> It appears to be running lean at closed-throttle because it will idle
> if I manually close the choke flapper. This leads me to believe that
> the problem is not the common "idle tubes" issue which causes a rich
> condition. It really feels like a bad vacuum leak but I can't find it.
>
>
> I'm completely out of ideas. In all honesty, I'm a lot more
> comfortable working on fuel injection. A grizzled Jeep veteran could
> probably whack it with a hammer and it would purr like a kitten. Any
> advice?
>
> Thanks!
>
>
> -rev
>

Simon Juncal

The Reverend Natural Light wrote:
> A grizzled Jeep veteran could
> probably whack it with a hammer and it would purr like a kitten. Any
> advice?

Whack it with a hammer....

Then swap in fuel injection :)



--
Simon
"I may be wrong, but I'm not uncertain." -- Robert A. Heinlein

Simon Juncal

The Reverend Natural Light wrote:
> A grizzled Jeep veteran could
> probably whack it with a hammer and it would purr like a kitten. Any
> advice?

Whack it with a hammer....

Then swap in fuel injection :)



--
Simon
"I may be wrong, but I'm not uncertain." -- Robert A. Heinlein

Simon Juncal

The Reverend Natural Light wrote:
> A grizzled Jeep veteran could
> probably whack it with a hammer and it would purr like a kitten. Any
> advice?

Whack it with a hammer....

Then swap in fuel injection :)



--
Simon
"I may be wrong, but I'm not uncertain." -- Robert A. Heinlein

The Reverend Natural Light

Joe C,

After all my dumbass troubleshooting, I went ahead and followed the
instructions to clear the idle tubes. Forget sludge in the tubes, one
of them had a huge chunk of metal stuck in it! I pulled the chunk out,
put the carb back together, and it runs great! This was a rebuilt carb
fresh from the parts store!!

Note to others: From all the notes I could find, clogged idle tubes
were supposed to look like a rich condition. Not in this case! It ran
like it had a horrible vacuum leak.

Thanks!

-rev


Oh, and apparantly someone already invented the old model ignition
module in the new model engine - it's called the "Nutter Bypass" and
there are far easier ways to do it.




The Reverend Natural Light wrote:
> Greetings.
>
> I'm working on a 1990 Jeep YJ, 4.2L I6, that won't idle. From 1200RPM
> up, everything's fine. It runs smooth under power. It won't idle at
> all.
>
> The previous owner replaced the carb with an older non-computer
> controlled unit. He made the decision to use the older carb because it
> was cheaper and simpler and someone knowledgeable (?) told him to. I
> believe it never ran right while he owned it.
>
> I have:
>
> 1. Checked for vacuum leaks.
> 2. Made sure the EGR valve is completely closed.
> 3. Replaced spark plugs and checked cap and rotor (old plugs were worn
> but tan).
> 4. Verified functional vacuum advance function.
> 5. Verified electric choke function.
> 6. Tried various settings of the idle bleed screws. Currently 2 turns
> out.
>
> No help.
>
> Since it has an ECM controlling spark but no electronic carb, I figured
> the computer controlled spark could be an issue. So, I picked up a new
> spark control module for a non-ECM jeep and wired it up to the
> distributor following the wiring diagram for an older jeep. Now there
> is no computer control whatsoever.
>
> No help with idle, but the throttle response seems a bit crisper.
>
>
> It appears to be running lean at closed-throttle because it will idle
> if I manually close the choke flapper. This leads me to believe that
> the problem is not the common "idle tubes" issue which causes a rich
> condition. It really feels like a bad vacuum leak but I can't find it.
>
>
> I'm completely out of ideas. In all honesty, I'm a lot more
> comfortable working on fuel injection. A grizzled Jeep veteran could
> probably whack it with a hammer and it would purr like a kitten. Any
> advice?
>
> Thanks!
>
>
> -rev

The Reverend Natural Light

Joe C,

After all my dumbass troubleshooting, I went ahead and followed the
instructions to clear the idle tubes. Forget sludge in the tubes, one
of them had a huge chunk of metal stuck in it! I pulled the chunk out,
put the carb back together, and it runs great! This was a rebuilt carb
fresh from the parts store!!

Note to others: From all the notes I could find, clogged idle tubes
were supposed to look like a rich condition. Not in this case! It ran
like it had a horrible vacuum leak.

Thanks!

-rev


Oh, and apparantly someone already invented the old model ignition
module in the new model engine - it's called the "Nutter Bypass" and
there are far easier ways to do it.




The Reverend Natural Light wrote:
> Greetings.
>
> I'm working on a 1990 Jeep YJ, 4.2L I6, that won't idle. From 1200RPM
> up, everything's fine. It runs smooth under power. It won't idle at
> all.
>
> The previous owner replaced the carb with an older non-computer
> controlled unit. He made the decision to use the older carb because it
> was cheaper and simpler and someone knowledgeable (?) told him to. I
> believe it never ran right while he owned it.
>
> I have:
>
> 1. Checked for vacuum leaks.
> 2. Made sure the EGR valve is completely closed.
> 3. Replaced spark plugs and checked cap and rotor (old plugs were worn
> but tan).
> 4. Verified functional vacuum advance function.
> 5. Verified electric choke function.
> 6. Tried various settings of the idle bleed screws. Currently 2 turns
> out.
>
> No help.
>
> Since it has an ECM controlling spark but no electronic carb, I figured
> the computer controlled spark could be an issue. So, I picked up a new
> spark control module for a non-ECM jeep and wired it up to the
> distributor following the wiring diagram for an older jeep. Now there
> is no computer control whatsoever.
>
> No help with idle, but the throttle response seems a bit crisper.
>
>
> It appears to be running lean at closed-throttle because it will idle
> if I manually close the choke flapper. This leads me to believe that
> the problem is not the common "idle tubes" issue which causes a rich
> condition. It really feels like a bad vacuum leak but I can't find it.
>
>
> I'm completely out of ideas. In all honesty, I'm a lot more
> comfortable working on fuel injection. A grizzled Jeep veteran could
> probably whack it with a hammer and it would purr like a kitten. Any
> advice?
>
> Thanks!
>
>
> -rev

The Reverend Natural Light

Joe C,

After all my dumbass troubleshooting, I went ahead and followed the
instructions to clear the idle tubes. Forget sludge in the tubes, one
of them had a huge chunk of metal stuck in it! I pulled the chunk out,
put the carb back together, and it runs great! This was a rebuilt carb
fresh from the parts store!!

Note to others: From all the notes I could find, clogged idle tubes
were supposed to look like a rich condition. Not in this case! It ran
like it had a horrible vacuum leak.

Thanks!

-rev


Oh, and apparantly someone already invented the old model ignition
module in the new model engine - it's called the "Nutter Bypass" and
there are far easier ways to do it.




The Reverend Natural Light wrote:
> Greetings.
>
> I'm working on a 1990 Jeep YJ, 4.2L I6, that won't idle. From 1200RPM
> up, everything's fine. It runs smooth under power. It won't idle at
> all.
>
> The previous owner replaced the carb with an older non-computer
> controlled unit. He made the decision to use the older carb because it
> was cheaper and simpler and someone knowledgeable (?) told him to. I
> believe it never ran right while he owned it.
>
> I have:
>
> 1. Checked for vacuum leaks.
> 2. Made sure the EGR valve is completely closed.
> 3. Replaced spark plugs and checked cap and rotor (old plugs were worn
> but tan).
> 4. Verified functional vacuum advance function.
> 5. Verified electric choke function.
> 6. Tried various settings of the idle bleed screws. Currently 2 turns
> out.
>
> No help.
>
> Since it has an ECM controlling spark but no electronic carb, I figured
> the computer controlled spark could be an issue. So, I picked up a new
> spark control module for a non-ECM jeep and wired it up to the
> distributor following the wiring diagram for an older jeep. Now there
> is no computer control whatsoever.
>
> No help with idle, but the throttle response seems a bit crisper.
>
>
> It appears to be running lean at closed-throttle because it will idle
> if I manually close the choke flapper. This leads me to believe that
> the problem is not the common "idle tubes" issue which causes a rich
> condition. It really feels like a bad vacuum leak but I can't find it.
>
>
> I'm completely out of ideas. In all honesty, I'm a lot more
> comfortable working on fuel injection. A grizzled Jeep veteran could
> probably whack it with a hammer and it would purr like a kitten. Any
> advice?
>
> Thanks!
>
>
> -rev