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post #1 of (permalink) Old 12-04-2007, 08:51 PM
Polarboy
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CJ Vacuum Question

I recently bought an '86 CJ with a 258 and an auto trans. It had a strong body but the engine was blown. I already had a '79 CJ with a 258 that ran strong but the frame and body were trash. So I swapped the engine out but used the intake, carb and exhaust from the '86. After the swap, as I was hooking up the vacuum I noticed the air tube from '86's Cat was plugged and the entire line (check valves and all) to the air cleaner was missing. So... I hooked a hose to the air cleaner and plugged it. I started the Jeep and it backfires and stalls at idle. Is this an effect of the airtube being plugged or does it sound like a Carb/timing issue to you guys? Do you think this will pass an emissions test with out the line to the Cat? Thanks for the help. This is probably the first of many.
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post #2 of (permalink) Old 12-05-2007, 05:45 AM
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Unless you have oxygen sensors in the exhaust down stream from the hose, I doubt that it could be your problem. It could be an ignition timing problem. I'd start there. What carb does it have? Did you swap everything that was on the '86 engine onto the replacement engine, including carb and distributor?

As for passing emission tests, it depends on what tests Pennsylvania has. If it's just a tailpipe sniffer, there's a good chance it will pass if the engine is in good condition and tune. Add a quart of alcohol to a full tank of fresh gas, put on a new air cleaner, spark plugs, oil and filter, and make sure the timing is at factory spec, even if the engine doesn't run as well that way.

Kalifornia and I think a few other places also do a visual inspection, and everything that was on there from the factory must still be in place and working. You wouldn't make that one.

Here in Illinois they recently dropped tests for all older vehicles without on-board diagnostics. The stated reason was that there aren't enough of them still on the road to be a significant contributor. The real reason was that it cost a lot to maintain, calibrate and certify all of the chassis dynos and gas analyzers, and the politicians wanted to waste the money in other ways. For newer vehicles they can just plug in a code reader to check for problems. If none show, you pass.

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Last edited by Jim_Lou; 12-05-2007 at 05:51 AM.
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post #3 of (permalink) Old 12-05-2007, 01:29 PM
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I switched everything from the '86, including the Carter carb and the distributer. That line to the Cat did not have an oxygen sensor in it, but it did have the pulse air valve that connected to a vacuum solenoid. I plugged the solenoid.

I will definitely check the timing. I don't know how long the '86 sat before I bought it. Do you think it could be a gummed up carb or old gas causing the problem? Thanks for the help.
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post #4 of (permalink) Old 12-05-2007, 03:35 PM
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That carb is a notorious trouble maker. There's a procedure called a "nutter bypass" that can correct it, but it may ruin your chances of passing an emission test. Do a search here. You will get dozens of references, and some old ones will describe the procedure.

Another popular modification is to swap it for a Motorcraft 2100 with 1.08" venturis. Those carbs work exceptionally well, but may also ruin your chances of passing emission tests.

The third option is to make the Carter run properly. That's not easy, but apparently it can be done. If RRich doesn't chime in here soon, send him a PM if that's what you want to try. I think he knows how to make them work.

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post #5 of (permalink) Old 12-05-2007, 04:24 PM
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There's another option, buy a Howell TBI fuel injection kit, 49 State Legal) for about $1000 and be done with it. Or, if your local emission laws permit, build your own TBI from junk yard parts. It's a cheap, but good alternative, depending on how brave you are.

Or if you want to fix the BBD carb, , buy this book, it's got 20 pages on fixing the BBD system RIGHT!


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post #6 of (permalink) Old 12-05-2007, 05:54 PM
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Smile Backfiring and stalling? Oversmog condition!

It isn't the carb and it isn't the timing; you are oversmogged. I just invented that term, but what I'm suggesting is that you have too much open area in the crankcase pcv. Try plugging that pvc hose for a minute and see if it runs better. The pcv valve in the engine block might be too big and too open for that intake and fuel setup. It could also be STUCK OPEN.

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post #7 of (permalink) Old 12-05-2007, 08:56 PM
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Thanks for the suggestions. I will try them all, starting with the easiest. If you think of anything else, let me know, I've got alot of spare time on my hands.
post #8 of (permalink) Old 12-05-2007, 11:03 PM
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If it were mine --
I'd get it running sweet first, then worry about smogging it -
Oversmogged? I like that.


BACK TO BASICS!
You connected the line to the air cleaner - then plugged it? Why? Make sure it's not leaking. Better yet, plug it somewhere else, not at the air cleaner.

That line is supposed to provide oxygen to the cat so it can burn the unburned fuel. The cat may be plugged by now - coked up - but don't worry about that yet!

First - get the initial timing set - set it to 8 degrees.
Then make sure the distributor vacuum is coming from PORTED vacuum, not manifold. Find the PORTED vacuum source - connect it direct - no solenoids or other switches.
PORTED has very little or no vacuum at idle, then slowly increases as the R's are increased. MANIFOLD vacuum is strong at idle - that's the wrong one.

See how it runs now - bet it's better,

Next - do a search here for "propane trick" - read it ALL! Make the device, use it to make sure there are no vacuum leaks - manifold, carb base, brake booster - pinch off the auto trans vacuum line too.
Fix any leaks.
Now test it for mixture - per instructions. Set the idle mixture screws.

Now you have a starting point.

Until you've got the basics set correctly, using prayer beads, praying to the east, using the wailing wall, killing a sheep at midnight, doing nutter butter bypass, swaping to FI, etc will NOT help at this point in time.

Once you have all that in order, let us know how it's doing.
Meanwhile - check your local smog laws - best way - go to a local smog station and ask them what the requirements are - leave the Jeep at home till you know what you'll need to do (avoids complications,) just describe it to them. Many of those guys will bend over backwards to help you.
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post #9 of (permalink) Old 12-06-2007, 03:58 PM
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Back to the basics? Sounds like a bunch of new age hooey. Killing a sheep at midnight sounds more scientific.

Will do. Thanks for the advice.

The metal air tube that comes off the Cat was already plugged. I just stuck a hose on the output of the aircleaner and plugged it so nothing could get in there. If you think that is bogging it down, I'll remove it.

I believe the guy that had this Jeep before me panicked when he blew the engine and tore out all of the vacuum lines. I've used the diagrams off the internet (which had the vacuum advance off the manifold, so they were obviously inaccurate) to hook it back up. I don't know where the vacuum goes into the trans or where the vacuum comes from.

Last edited by Polarboy; 12-06-2007 at 04:03 PM.
post #10 of (permalink) Old 12-06-2007, 05:08 PM
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Using manifold vacuum is correct - stock configuration - but it HAS to go through the 2 solenoids that you said were gone. They inhibit the advance except for when it's in high gear and totally warmed up, and you are not accelerating. It's a smog thing.
They used manifold vacuum simply as a power source to pull the diaphragm - like some vehicles use vacuum to operate heater controls, headlight doors, windshield wipers, even power windows! (Old Mercedes.)

Using straight ported advance will make it run better than it ever has before.
Once it's running good, we'll address any smog issues.
As long as that hose is totally plugged off, it's OK.

Yes, back to basics - not bull. Kids just don't realize that before you can build something you need a foundation.
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