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Jeep 4.2L - Wont Idle!

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

Reply to
The Reverend Natural Light
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Reply to
Joe C

Whack it with a hammer....

Then swap in fuel injection :)

Reply to
Simon Juncal

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:

Reply to
The Reverend Natural Light

When only one is clogged, the computer will try and take an average of the two.

It doesn't surprise me to have a bad reman out of the box. Happens regularly, way more often that I'm happy with.

The Reverend Natural Light wrote:

Reply to
RoyJ

Those tubes are where the idle circuit 'picks up' it's fuel. If they're plugged, it's gonna run lean.

Reply to
bllsht

If you are going to run a carbed vehicle in 2006, you NEED to get some cores and tools and learn to rebuild your own. The reman places are all in hick towns and the average age in those places is going UP because they will not train new people. In fact, there are not that many young people (exceppt illiterate low IQ illegal immigrants if a packinghouse is nearby) around they could train if they wanted to. The workers are all gatting so old and they keep cranking up the piece rate, quality is plunging. That's true of carbs, distributors, starters, alternators.

Reply to
Bret Ludwig

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