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Unread 03-20-2013, 08:10 AM   #1
wesleyj06
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1999 cherokee xj cranks no start????

Please help? I have a 1999 jeep cherokee xj.
I was driving down the hwy at 65mph an it just died like u cut it off. We thats been a week ago an I haven't been getting for to the plugs. I have changed the crankshaft position sensor, coil, distributor cap, rotary button,the battery is good. I hooked it up to a scanner an no codes shows up all gauges work? Any help please?????

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Unread 03-20-2013, 09:00 AM   #2
tjwalker
It's the crank sensor!
 
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You need to determine if you are missing fuel, spark or both.

Spark: 12 volts from ignition switch to the ASD relay; when the key is first turned on the PCM provides a ground to the ASD relay to energize it, then the ASD relay passes 12 volts to the coil primary side. If no crank sensor signal is generated after a couple of seconds the PCM cuts the ground to the ASD relay (and fuel pump relay too) and that cuts power to the coil (and fuel pump). Key to START and once again the PCM energizes the ASD relay. Now, a critical element is the crank sensor--no signal from the crank sensor and the PCM won't trigger the coil to provide spark.

**Have you actually checked for spark? Spark is easily verified by pulling a plug, keeping it attached to the plug wire, place the plug electrode near a good engine ground and 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 don't have spark, I would try is to swap the ASD relay (located inside of the power distribution center/black box under the hood) with another non-critical relay, like the cooling fan to see if that allows the engine to start. These relays are all the same part number, so swapping is not a problem.

**By design, the fuel pump should energize and run for about 2 seconds when you turn the key to the ON position (not start). Do you hear the fuel pump? If you do not, you have a problem with either fuel pump or the control electronics for the fuel pump.

**A quick and dirty test for fuel delivery (do this only if you have good spark) is to introduce a little gas or starting fluid into the throttle body. If the engine starts and runs for a short time with this technique, you have confirmed that you have a fuel delivery problem.

You need to adopt a "testing based strategy" at this point. Don't throw any more parts at it. Good luck and let us know what you find out with your testing!
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Unread 03-20-2013, 09:08 AM   #3
wesleyj06
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Ok I will try switching the relays thanks but I did check an replaced the plugs an nothing. So gonna check the relays on my lunch brake thanks ill let u know
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Unread 03-20-2013, 10:16 AM   #4
wesleyj06
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Well I put new relays in it an nothing still. The fuel pump works an is pumping
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Unread 03-20-2013, 10:20 AM   #5
tjwalker
It's the crank sensor!
 
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Testing for spark is next. Only takes a few minutes and although you likely don't have spark, it really should be verified.

And it's good that your fuel pump runs, but that is no guarantee that it is working properly and building the necessary pressure at the fuel rail. That can only be verified with a fuel pressure gauge. For a 99, you need approximately 49 psi to start the engine.
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Unread 03-20-2013, 10:23 AM   #6
CCKen
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Quote:
Originally Posted by wesleyj06 View Post
Well I put new relays in it an nothing still. The fuel pump works an is pumping
What relay(s) did you replace?
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Unread 03-20-2013, 10:30 AM   #7
CCKen
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Check the fuse marked "ASD" and the fuse marked "Fuel Injectors/Coil" in the PDC.



And fuse #11 in the Junction Block (in the passenger footwell fuse panel).

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Unread 03-20-2013, 10:31 AM   #8
wesleyj06
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Well I put new relays in it an nothing still. The fuel pump works an is pumping
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