tried it all, not a cracked head! 2000 xj intermittant rough idle
11-24-2012, 09:12 PM
#1
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tried it all, not a cracked head! 2000 xj intermittant rough idle
Hey everyone this is my first post but i am a longtime jeeper and am quite familiar with them. Heres my problem;it throws a po305 code randomly. doesnt happen at any temp or condition specifically,runs amazing and pulls hard but will idle in a bucking manner at stop lights. Starts out minor and eventually gets worse at every light.have swapped injectors around.new plugs, checked the voltage at injectors with power probe,refreshed grounds,swapped IAC,TPS,MAP,IAT, new 02's(cal emissions) has 4,sprayed for leaks around intake.checked pins for injector pulse. One thing i have found is the harness for c1 and c2 the wires are stuck but not melted through so i replaced parts that were stuck.re indexed cam sensor.if someone is familiar with power probes,when i put it on the ground of any sensor or the ground strap directly,it turns green but cuts out every couple of seconds.but i have all new ground straps from firewall to motor,battery to engine and extra batt to frame.compression test showed 120-135 across the board.vacuum is 16-17 hg slight fluctuating which leads me to belive i have either a burned or stuck exhaust valve.any ideas anyone?
11-25-2012, 12:35 AM
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Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
Start simple:
plug wires?
dizzy cap?
cracked rotor?
sorry yours is a 2000....
bad coil?
bad plug boot?
dizzy sending unit?
plug wires?
dizzy cap?
cracked rotor?
sorry yours is a 2000....
bad coil?
bad plug boot?
dizzy sending unit?
Last edited by highmileage; 11-25-2012 at 12:46 AM.
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11-25-2012, 02:34 AM
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Year: 1989 xj sport 2dr
Model: Cherokee
Engine: 12 hole bosch Injectors
Hey everyone this is my first post but i am a longtime jeeper and am quite familiar with them. Heres my problem;it throws a po305 code randomly. doesnt happen at any temp or condition specifically,runs amazing and pulls hard but will idle in a bucking manner at stop lights. Starts out minor and eventually gets worse at every light.have swapped injectors around.new plugs, checked the voltage at injectors with power probe,refreshed grounds,swapped IAC,TPS,MAP,IAT, new 02's(cal emissions) has 4,sprayed for leaks around intake.checked pins for injector pulse. One thing i have found is the harness for c1 and c2 the wires are stuck but not melted through so i replaced parts that were stuck.re indexed cam sensor.if someone is familiar with power probes,when i put it on the ground of any sensor or the ground strap directly,it turns green but cuts out every couple of seconds.but i have all new ground straps from firewall to motor,battery to engine and extra batt to frame.compression test showed 120-135 across the board.vacuum is 16-17 hg slight fluctuating which leads me to belive i have either a burned or stuck exhaust valve.any ideas anyone?
11-25-2012, 03:52 AM
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Like maybe a dead cell? Alt puts out 13.7 and radio lights dim when i turn on headlights.the intermittant-ness of it suggests it might be electrical, but vacuum points to internal engine problems
11-25-2012, 03:55 AM
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Year: 1989 xj sport 2dr
Model: Cherokee
Engine: 12 hole bosch Injectors
One issue at a time if enging stumbles vacuum will be affected trydisconneting battery cables then check battery with meter see if voltage remains steady then connect cables try again then start xj test again is what id do .
11-25-2012, 10:51 AM
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Year: 1999
Model: Cherokee
Engine: 4.0
Generally, a fluctuating needle at idle will indicate bad valve guides but if
when revving the engine, as rpm increases, a wider variation occurs in needle movement it could mean a weak valve spring.
When you've exhausted all electrical and visual diagnosis, you may want to pull the valve cover and look at the #5 valve springs. Move #5 to TDC and see if you can move the valve springs around with your fingers and look for cracked spring.
Do a compression loss test on that cylinder. A burnt valve may show up. With the cylinder pressurized to about 90 psi; listen for air escaping in the intake (TB), and/or in the exhaust manifold/tail pipe. If no air is heard escaping, but the pressure drops off, it could be a bad head gasket.
Good luck.
11-25-2012, 01:37 PM
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I assume the vacuum reading you mention is at idle. What does the needle do when you advance the throttle to around 2,000 RPM? Does the needle fluctuate more radidly or does it smooth out?
Generally, a fluctuating needle at idle will indicate bad valve guides but if
when revving the engine, as rpm increases, a wider variation occurs in needle movement it could mean a weak valve spring.
When you've exhausted all electrical and visual diagnosis, you may want to pull the valve cover and look at the #5 valve springs. Move #5 to TDC and see if you can move the valve springs around with your fingers and look for cracked spring.
Do a compression loss test on that cylinder. A burnt valve may show up. With the cylinder pressurized to about 90 psi; listen for air escaping in the intake (TB), and/or in the exhaust manifold/tail pipe. If no air is heard escaping, but the pressure drops off, it could be a bad head gasket.
Good luck.
Generally, a fluctuating needle at idle will indicate bad valve guides but if
when revving the engine, as rpm increases, a wider variation occurs in needle movement it could mean a weak valve spring.
When you've exhausted all electrical and visual diagnosis, you may want to pull the valve cover and look at the #5 valve springs. Move #5 to TDC and see if you can move the valve springs around with your fingers and look for cracked spring.
Do a compression loss test on that cylinder. A burnt valve may show up. With the cylinder pressurized to about 90 psi; listen for air escaping in the intake (TB), and/or in the exhaust manifold/tail pipe. If no air is heard escaping, but the pressure drops off, it could be a bad head gasket.
Good luck.