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Unread 04-14-2009, 10:27 PM   #1
ShmitHed
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4.0 will crank but won't turn

I recently swapped out my blown 4.0 with a junkyard 4.0 that was pulled out of a 1999 cherokee. I was having a problem with the new motor getting fuel but no spark. After I had checked and rechecked all the connections under the hood, I was able to get it to crank about 4-5 times, but now i'm back to square one, and everything seems to be connected right....any suggestions?

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Unread 04-15-2009, 09:34 AM   #2
CJ7-Tim
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The Crank Position Sensor (CKP) on the bell housing is easily damaged when you pull an engine. Try testing or replacing the CKP


The most likely cause of it cranks and cranks but won't start up is the Crank Position Sensor (CKP). CKP failure is very common. The CKP can stop working with no warning or symptoms and the engine will not run or the engine may randomly stall for no apparent reason.

Symptoms –
-Starter cranks and cranks but engine won't start up
-Fuel gauge and voltage gauges may not work or display properly.
-You sometimes will have No Bus on the odometer after 30-60 seconds.
-No spark at the spark plugs.
-Fuel pressure is OK at the fuel rail. There have been some instances where the fuel pump does not prime or run when the CPS is failed.

If the CKP is failed sometimes the OBDII code reader cannot make a connection to the computer or cannot read Check Engine Light/MIL codes because the CKP has failed.

Crank sensors can have intermittent “thermal failure”. This means that the sensor fails when engine gets hot, but works again when it cools back down.

Diagnostic steps to confirm the CKP is the cause of your no-start

You might be able to verify a bad CKP, by unplugging it, and turning the ignition key to on. If the voltage gauge and/or the fuel gauge now displays correctly, replace the CKP.

Exchange the fuel pump relay and the ASD relay with one of the other similar ones in the PDC to eliminate the relays as the cause of the no-start Confirm that the fuel pump to runs for 3-5 seconds when you turn the ignition key to ON.

Eliminate the NSS as a cause of no start. Wiggle the shift lever at the same time you try to start. Put the transmission in Neutral and do the same. Do the reverse lights come on when the shifter is in Reverse?

Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables and replace as needed. Do the same for the grounding wires from the battery and engine to the Cherokee's frame/body. Jeeps do not tolerate low voltage or poor grounds and the ECM/ECU will behave oddly until you remedy this.

CKP Testing

Crankshaft Position Sensor Connector



.



TESTING PROCEDURE 1991 – 2001 4.0L H.O. engines
1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C (See Image). Ohmmeter should be set to 1K-to-1OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.

TESTING PROCECURE for 1987 – 1990 4.0 L engines

Test # 1

· Get a volt/ohm meter and set it to read 0 - 500 ohms. Unplug the CKP and measure across the CKP connector's A & B leads. Your meter should show a CKP resistance of between 125 - 275 ohms. If the CKP is out of that range by much, replace it.


Test # 2

· You'll need a helper for this one. Set the volt/ohm meter to read 0 - 5 AC volts or the closest AC Volts scale your meter has to this range. Measure across the CKP leads for voltage generated as your helper cranks the engine. (The engine can't fire up without the CKP connected but watch for moving parts just the same!) The meter should show .5 - .8 VAC when cranking. (That's between 1/2 and 1 volt AC.) If it's below .5vac, replace it.
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Last edited by CJ7-Tim; 05-15-2010 at 08:53 PM..
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Unread 11-24-2009, 02:42 AM   #3
Jonny Jeep
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As far as the resistance goes when measuring pins b-c you might see about 8K ohms. Not open circuit by any means but the sensor would be good. I quoted that same section recently trying to help track down a no start and the OP tested and got about 8K ohms. Sensor was good. Turns out he had a wiring fault near the tank.
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Online factory service manuals (FSMs) and parts lists can be viewed at http://www.jeep4x4center.com/knowledge-base/index.htm
If the link doesn't work properly, look for the service manual link under Jeep Resources at the bottom of the page.
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Unread 02-23-2010, 09:56 AM   #4
Bbsalexaz
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I know I'm reviving an old thread but it's super importan I fix my nostart issue. I got fuel, but no spark. Only difference is I have a 2.5L i4, where will this sensor be located?

Thanks in advance guys, I have a 450mile drive home in a couple of days and I'm really worried. Any help is genuinely appreciated.
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Unread 02-23-2010, 02:37 PM   #5
CJ7-Tim
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Quote:
Originally Posted by Bbsalexaz View Post
... I got fuel, but no spark. Only difference is I have a 2.5L i4, where will this sensor be located? ....
What kind of Jeep ? What Year ?
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Unread 02-23-2010, 02:45 PM   #6
Bbsalexaz
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It's a YJ, 1990, 2.5L i4, I have replaced the coil, plugs, wires, cap, rotor, fuel pump, fuel filter. These were replaced in November. Coil was done last night. Idk what the problem
could be but I've been told crank angle sensor. I just was looking for a little more input.
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Unread 02-25-2010, 03:15 PM   #7
rain-gler
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I have a 2.5 TBI with a NO SPARK situation also.

I found that my Crank Position Sensor was damaged. A piece of the plastic housing was chipped off. So I removed it and tested it. I got back no ohm measurement whatsoever. (oops, did I need to leave it on the vehicle???)

But anyway, Im going to ground it and test again. If it comes up bad, I am on my way to A-zone for a new one.

I read a thread that said the ohms should be between 125 and 275 (?).

I will report back as soon as I get in this evening.
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