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Unread 03-18-2010, 02:01 PM   #1
WPM
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1984 CJ7 
 
Join Date: Mar 2010
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258 I6 Trouble

New plugs, plug wires, coil, cap and rotor. New Weber carb. New fuel filter. Jeep starts but has a rough idle and violent shake. Can hear a noise in the carb that coincides with the shake. In trying to diagnose the issue, I pulled wires off the plugs one at a time beginning with No. 1. Problem stayed the same until I pulled the wire from No.3. Shake stopped and noise at carb went away. Engine ran smooth. I pulled the No. 3 plug and it was pretty badly fouled with black soot. I am going to put a new plug in this evening but I am not confident that will resolve the issue. If the rough idle/shake and noise at the carb remains even with the new plug, can someone tell me what may be the problem? Valve seals? Cylinder rings? My next thought was to pressure test that cylinder. Thanks.

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Unread 03-18-2010, 02:07 PM   #2
Mike Romain
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Yes, you need a compression test to tell more. You do one dry, then add a tablespoon or two of oil down the plug hole and do it wet. If the compression comes way up, it is bad rings, if not it is the intake valve that your symptoms imply is blown.

Mine was just missing and blowing massive blowby with only 25 psi in that cylinder. No popping out the carb or exhaust. Mine was rings.
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Unread 03-18-2010, 02:14 PM   #3
TDHofstetter
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Mike's got ya covered like paint on that one - dry compression test followed by wet compression test. Be prepared to yank that bad boy motor apart.

Oh, you might also take the valve cover off & verify that the whole valve train is moving uniformly, too - no significant rockers that don't seem to move nearly as much as the rest, that sort of thing. That'd indicate a warped valve, a bad lifter, or a camshaft with a lobe wiped off. A bad lifter or a gone camshaft lobe wouldn't go away when you pull off that plug wire, though.

If you were running MPFI, I'd clue ya that you needed to add a heat shield to #3 injector (a common issue), but you're not.
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Unread 03-18-2010, 02:42 PM   #4
Fatman
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Quote:
Originally Posted by TDHofstetter View Post
Be prepared to yank that bad boy motor apart.
Hold up there sparky !

Ok, WPM. Was this the same problem before you replaced the following: "New plugs, plug wires, coil, cap and rotor. New Weber carb. New fuel filter" ?

Did doing these replacements make a change in how the motor is running ?
Confirm that you have #3 and whatever other wire(s) plugged to the correct position, cap's on tight, timing set correctly

Did you replace the carb when you did these ignition upgrades ? Is the fuel filter clocked correctly ?

In the future (and this is not directed at you, the task is done) don't do ignition work AND carburetor work at the same time. It makes a beach of a time trouble shooting !
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Unread 03-18-2010, 06:42 PM   #5
JeepHammer
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Sounds like plug wires in the wrong place to me.
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Unread 03-18-2010, 11:34 PM   #6
WPM
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Checked the plug wires again just to make sure and they are all where they need to be.

As for the new parts, the Jeep had been laid up for over a year with no turn over. Before the time off I had bought the Weber and finally got around to installing it a few months back. When she would not turn over, I started diagnosing ignition problems and ultimately found a shot coil. Considering the time off, I gave her a whole new tune up (coil, cap, rotor, plugs, plug wires, etc.). I have adjusted timing according to the shop manual and she runs better but the miss/carb noise/shake is still there. I have obvious smoke coming out the exhaust. Tried a new plug in No. 3 this afternoon. Issues remain the same and there remains improvement when I pull the number three wire off the plug.

I guess this weekend I'll do the compression tests to determine rings versus seals. I'm open to any suggestions if someone believes something else could be causing these issues before I remove the head cover.

As always, thanks.
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Unread 03-19-2010, 05:11 AM   #7
CSCmrwizard
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sounds like a stuck valve
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Unread 03-19-2010, 08:21 AM   #8
TDHofstetter
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Quote:
Originally Posted by WPM View Post
Checked the plug wires again just to make sure and they are all where they need to be.

As for the new parts, the Jeep had been laid up for over a year with no turn over. Before the time off I had bought the Weber and finally got around to installing it a few months back. When she would not turn over, I started diagnosing ignition problems and ultimately found a shot coil. Considering the time off, I gave her a whole new tune up (coil, cap, rotor, plugs, plug wires, etc.). I have adjusted timing according to the shop manual and she runs better but the miss/carb noise/shake is still there. I have obvious smoke coming out the exhaust. Tried a new plug in No. 3 this afternoon. Issues remain the same and there remains improvement when I pull the number three wire off the plug.

I guess this weekend I'll do the compression tests to determine rings versus seals. I'm open to any suggestions if someone believes something else could be causing these issues before I remove the head cover.

As always, thanks.
A YEAR? This changes things a little. Was the gasoline fresh & stabilized back then? If not... that gasoline won't be fit for motor vehicle use now, and will need to be drained & replaced.
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Unread 03-19-2010, 02:26 PM   #9
WPM
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Quote:
Originally Posted by TDHofstetter View Post
A YEAR? This changes things a little. Was the gasoline fresh & stabilized back then? If not... that gasoline won't be fit for motor vehicle use now, and will need to be drained & replaced.
I added "fresh" gas to the gas that had been sitting in the tank for that year off and then before I started the diagnosis process I added some Iso Heat. Should I go ahead and drain it all?
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Unread 03-19-2010, 06:00 PM   #10
TDHofstetter
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If it's got at least three times as much fresh gas in it as old gas, it should be sufficient. Not GOOD, but sufficient to start, anyway. Anything less than about three good to one old, you better dump the whole tankful & start over. The Heet/DriGas stuff won't help much with old gasoline... most of the most volatile organics in the gas (which are necessary to use it as a motor fuel) will have evaporated off, and there's no reliable way to replace 'em.
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