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  • zaken1 09/03/10 4:29 pm PST

    A question like this one is a classic example of why it is important to include accurate and complete information about a vehicle: You say the "camshaft was replaced." But I'd be willing to bet that the part that was replaced was the camshaft position sensor, and not the camshaft. However, you described the vehicle as a "Jeep Cherokee;" and neither of the two engines used in the Jeep Cherokee have a camshaft position sensor. But the 1999 Jeep Grand Cherokee comes with a choice of two engines; and one of those engines (the 287 cid SOHC V-8 with VIN code "N") does have a camshaft position sensor. So, if you have a Grand Cherokee, rather than a Cherokee, and that vehicle has the 287 V-8 motor; and it was the camshaft position sensor that was replaced; rather than the camshaft; then what you wrote would make sense to me. But most mechanics would be totally thrown off by such a report.

    The way to sort out a no start condition is to first test to see whether the motor has spark, fuel, and compression. It will be one of those areas that is causing the no start condition. If you blindly throw parts at the vehicle without first testing to see which system is bad; it usually will create a major waste of time and money.

    The way to check for spark is to pull the coil wire off the center of the distributor cap, and hold that end of the wire 1/4" from the engine block while someone cranks the starter with the ignition key. There should be a steady series of sparks from the wire while the starter runs.

    The easiest way to check for fuel is to buy a can of engine starting fluid, remove the air filter housing, hold the throttle partly open, and spray starting fluid into the throttle body air inlet for two seconds. Then quickly put the air filter assembly back on, and try to start the motor. If it starts, and soon dies; the starting problem is caused by lack of fuel.

    If the engine is getting fuel, and there is no spark; if an ignition system problem is not the cause; the starting problem is probably caused by a broken timing chain.

    If the engine is getting fuel, and there is a spark, but it will not start; this is probably caused by a timing chain that has stretched and jumped out of synch. This would cause the cylinder compression to be substantially reduced; and would also throw the ignition timing off by at least 10 degrees (and probably a lot more than that). So the way to confirm or disprove a blown timing chain is to check the cylinder compression and compare it to the manufacturers minimum limits. You could also pull the distributor cap, line up the timing marks on the crankshaft at 5 degrees BTDC, and confirm that the tip of the distributor rotor points directly at the cap terminal that feeds the plug wire for the # 1 cylinder. But if the camshaft had been replaced, and was installed properly; the timing chain would not be out of synch. So this is where the information in your post would have prevented a correct diagnosis.

  • tedd50 09/03/10 8:09 pm PST

    My daughter had what sounds like the same problem. Somebody pretty smart replaced what was called "The crankshaft sensor unit or timing sensor unit". This was several years ago, and the cost was under $60.00

  • 1024dp 09/03/10 11:19 pm PST

    if you vehicle uses a smart key (anti theft device) the chip in the key could be bad or the pick up sensor be bad, this would let it crank but not start. Had this happen to my PT one time and it was the key sensor not the key.

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