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10-15-2008, 08:49 PM
| | Stranger | | Join Date: Aug 2007
Posts: 12
| |  idle miss
My 97 GC 4.0 has develope a miss in the number one cylinder at idle only. I have checked wire (new), good solid sounds from the injector, cranking compression 120 psi. Hits every time at road speed, but sets a "number one cylinder misfre" code after about a minute of idle. Swapped plugs from different cylinder, both plugs looked great and are new. After changing plug, same problem.Never sets a code at road speed, only after a minute or two idling. Can't find a vacuum leak, don't know where else to look. Still gets 23 mpg at hiway speeds. Any ideas??
Thanks!
Last edited by gandalf0531; 10-15-2008 at 08:53 PM.
Reason: added info
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10-16-2008, 03:13 PM
|  | Keyboard Implanted | | Join Date: Mar 2003 Location: Holland
Posts: 2,743
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How does the thing start? Noticed any longer crancking than usual?
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Jamboree '94 stock 4.0 AX15 8.25
Cherokee Pioneer '88 i6 2-door 5 speed mostly stock put asleep
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10-18-2008, 11:09 AM
| | Stranger | | Join Date: Aug 2007
Posts: 12
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No, cranks up fine. Redid the compresion check, and it weird. Down to 65 or 70 at cranking, when running between 100 and 120. The cylinder leakdown is so slow you can hardly see the gauge move. Maybe a lifter leaking down at idle speed? The plug on the cylinder is perfect color. Maybe I will pull the valve cover and watch rocker arm movement at idle.
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10-18-2008, 03:25 PM
| | Aprentice | | Join Date: Oct 2008 Location: near Seattle
Posts: 95
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Check for a bent pushrod. If not, then a sticky or cracked valve guide is grabbing the valve, or a weak valve spring or (unlikely) cracked piston)
Chunk of carbon could be holding the valve open slightly or it may have a burnt valve (compression should be well over 120lbs with the throttle open)
A flattened out cam or bad lifter could cause an issue too.
Last edited by carnuck; 10-18-2008 at 03:27 PM.
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10-18-2008, 09:51 PM
| | Stranger | | Join Date: Aug 2007
Posts: 12
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Thanks for the input!! Did some reading, and will its not impossible, 4.0's dont seem to have had any cam issues. Cylinder leakdown has pretty much ruled out burnt valve or bad piston. Kinda thinking (hoping!) its a lifter issue. Engine is very quiet, oil pressure is 40+ hot, averaging 22-23 mpg rural driving. Think I will give it a dose of Seafoam then an oil change.
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10-19-2008, 12:39 PM
| | Aprentice | | Join Date: Oct 2008 Location: near Seattle
Posts: 95
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Injector may be clicking, but it could be clogging up.
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10-19-2008, 04:04 PM
| | Stranger | | Join Date: Aug 2007
Posts: 12
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Swapped injectors. Didn't help. Seafoam seems to be making a difference, will run a couple hundred miles and change oil.
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