Spark plug gaping
05-26-2011, 06:45 PM
#4
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Year: 1999
Model: Cherokee
Engine: 4.0
Spark + fuel (plus compression and air) = START.
You need to determine what part of the above equation you are missing. Assuming the engine has been running well recently, most people are missing spark or fuel.
Always verify spark first. Take out a plug, keep it attached to the plug wire, place the plug electrode near a good engine ground, have a buddy crank the engine while you watch. You are looking for a strong, blue, snapping spark. Yellow/orange/white indicates a weak spark, which may not be strong enough to start the engine.
If you have a STRONG spark (and only if), move onto fuel. Spray a small amount of starting fluid into the intake, or a small splash of gas. If the engine starts and runs for a short time with this technique, you have confirmed a "fuel delivery" problem.
The above tests go a long ways in isolating the root cause of a no-start.
Report back what you find.
You need to determine what part of the above equation you are missing. Assuming the engine has been running well recently, most people are missing spark or fuel.
Always verify spark first. Take out a plug, keep it attached to the plug wire, place the plug electrode near a good engine ground, have a buddy crank the engine while you watch. You are looking for a strong, blue, snapping spark. Yellow/orange/white indicates a weak spark, which may not be strong enough to start the engine.
If you have a STRONG spark (and only if), move onto fuel. Spray a small amount of starting fluid into the intake, or a small splash of gas. If the engine starts and runs for a short time with this technique, you have confirmed a "fuel delivery" problem.
The above tests go a long ways in isolating the root cause of a no-start.
Report back what you find.
05-26-2011, 09:39 PM
#6
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Year: 1995
Model: Cherokee
Engine: 4.0L I-6
Spark + fuel (plus compression and air) = START.
You need to determine what part of the above equation you are missing. Assuming the engine has been running well recently, most people are missing spark or fuel.
Always verify spark first. Take out a plug, keep it attached to the plug wire, place the plug electrode near a good engine ground, have a buddy crank the engine while you watch. You are looking for a strong, blue, snapping spark. Yellow/orange/white indicates a weak spark, which may not be strong enough to start the engine.
If you have a STRONG spark (and only if), move onto fuel. Spray a small amount of starting fluid into the intake, or a small splash of gas. If the engine starts and runs for a short time with this technique, you have confirmed a "fuel delivery" problem.
The above tests go a long ways in isolating the root cause of a no-start.
Report back what you find.
You need to determine what part of the above equation you are missing. Assuming the engine has been running well recently, most people are missing spark or fuel.
Always verify spark first. Take out a plug, keep it attached to the plug wire, place the plug electrode near a good engine ground, have a buddy crank the engine while you watch. You are looking for a strong, blue, snapping spark. Yellow/orange/white indicates a weak spark, which may not be strong enough to start the engine.
If you have a STRONG spark (and only if), move onto fuel. Spray a small amount of starting fluid into the intake, or a small splash of gas. If the engine starts and runs for a short time with this technique, you have confirmed a "fuel delivery" problem.
The above tests go a long ways in isolating the root cause of a no-start.
Report back what you find.
Thanks for all the help guys.
05-27-2011, 06:05 AM
#7
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Year: 1999
Model: Cherokee
Engine: 4.0
No coil pack on a 95. But you do have an ignition coil.
But now that you have verified there is no spark, the #1 cause is absolutely the crankshaft position sensor.
Everyone with a 4.0 needs to commit the above to memory!
But now that you have verified there is no spark, the #1 cause is absolutely the crankshaft position sensor.
Everyone with a 4.0 needs to commit the above to memory!
Last edited by tjwalker; 05-28-2011 at 05:42 AM.
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05-27-2011, 09:20 AM
#8
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Year: 1995
Model: Cherokee
Engine: 4.0L I-6
Yup def ment ignition coil not coil pack my bad. I was dead tired last night. Thanks for the help tj. So you sayin its most prob the csps?
05-27-2011, 10:59 AM
#10
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Year: 1995
Model: Cherokee
Engine: 4.0L I-6
No. it was running the nite before. Left it over night. When I came to get it she wouldnt crank. Since then I have checked my fuel pump, recently changed my fuel filter and regulator. So I checked for spark first. When I realized there was none I changed the cap rotor and plugs. Still, nothing. Im actually trying to get over to it now to change that coil.
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