it cranks, has fuel, no spark

First time poster with Naxja! Thanks for reading folks. I've searched and searched. But can't seem to find an answer. Sorry for the long post.

I have this same issue on a 2000 Cherokee sport 4.0L. It cranks (engine spins) but it won't actually start.

Got the "no bus" error on the dash the first time we tried to start it and found that there was a heavy ground right behind the alternator that wasn't connected. We disco'd the ground on the battery, reconnected the ground to one of the two studs right behind the alt on the block and reconnected the battery. It then started cranking just fine, but no spark.

Just put a new long block in after the old one chewed up a piston. Everything worked fine before the engine went. Now it just refuses to start. Battery was dead as a door nail, so got a fresh one and put that in. Read about a possible security disable feature where you have to unlock the drivers door with the physical key this morning... havent had a chance to try it yet. I have fuel pressure, but no spark. Here's what I've done:

* I've swapped the ASD relay
* Checked for fuel pressure, the fender got sprayed so I think I'm ok there
* I've swapped cam position sensor out
* I unlocked the car using the remote entry fob
* Checked the crank sensor (ohm test between 1k-10k) checks fine
* Checked the internals on the PCM, looks fine connections are AOK
* Checked fuses, found 1 10A fuse dead (4th from the top on the right) and replaced it
* Pulled the coil pack off the engine and checked for spark and its got nothing

I just put a new long block in after the old one chewed up a piston. Everything worked fine before the engine went. Now it just refuses to start. Battery was dead as a door nail, so got a fresh one and put that in. Read a lot about a possible security disable feature where you have to unlock the drivers door with the physical key this morning... havent had a chance to try it yet.

I don't think the truck has the chip in the key... this key was working fine before the engine went...

Any other ideas?

Grab your meter and check for voltage going into the coil.

Thanks for the reply, I'll give that a shot.

Can anyone confirm that you can test the crank position sensor by ohming out pins B & C on the sensor itself?

Quote from BirchlakeXJ earlier post (thanks):

Crankshaft Position Sensor: (CPS/CKP) Failure Symptoms / Testing

*Both the fuel gauge and or voltage gauge may not work/display

*It is possible that you may see a No Bus on the odometer (on newer models only)

*You will have no spark. Fuel pressure may check out okay at the fuel rail, but fuel won’t get to the fuel injectors

*For 96 + newer, sometimes the OBDII code reader has trouble connecting to /reading codes. Crankshaft position sensor failure may or may not result in a check engine light/fault code.

*Crankshaft position sensors can be intermittent resulting in an abrupt misfire. "Thermal failure" is common. Thermal fail means that the sensor fails when engine gets hot, but works again when engine cools down. Be aware of this when testing, as if you have a sensor that suffers from thermal failure, it’s possible that it may test GOOD as soon as it cools down.

*Don’t get tunnel vision and assume the sensor is bad (unless it checks out as bad with a meter) Damaged wiring or a dirty connector can inhibit the signal from making it to the computer. Check/clean/repair as necessary.
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CRANKSHAFT SENSOR 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. The terminals are identified as A-B-C looking into connector from left to right with the "notch" in the middle of the connector on your right. Ohmmeter should be set to 1K-to-10K scale for this test.

3. The meter reading should be open (infinite resistance). Replace sensor if LOW RESISTANCE

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CRANKSHAFT SENSOR TESTING PROCECURE: 1987 – 1990 4.0 L engines

Test # 1

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


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 CPS leads for voltage generated as your helper cranks the engine. (The engine can't fire up without the CPS connected but watch for moving parts just the same!) The meter should show .5 - .8 VAC when cranking. If it's below
.5 VAC, replace sensor.

Swapped out the crank sensor today, now I have a constant "no bus" on the dash, even after leaving the battery disconnected. I'm gonna push this POS off a cliff.

Have you checked the orange wire coming in to the CKP to see if it's getting 5 volts? This should work to ground and to the brown/yelllow wire which grounds in the PCM.

checking now... gotta put the PCM back too... thinking thats all I have left to replace...

Put the PCM back in... and I only get 1.9v or 2.1v DC on either side of the crank position sensor plug's ground (center wire seems to be ground).

This is holding the plug with the clip up:

A/B/C
1.9/0.0/2.1

^ just like that...

Looking at getting a replacement PCM... hooked up a scanner and get no data. SO...

The computer in the Jeep says PN 634AE, found another on ebay from the same year with the PN 635AF. Can anyone confirm that this PCM will work?

In your first post said you saif you found a bad fuse and replaced it..a 10 amp fuse..
I think that fuse is for the Sentry Key Immobilizer module....( thats the only 10A fuse in my 2001)...
So, was this immobilizer disabled when the fuse was blown and now it's working?

Another thought..+5volt supply from PCM goes to the Crank Position Sensor, Camshaft Posistion Sensor, Map Sensor, and Throttle Position Sensor...any of those sensors or the circuit wiring shorting out can draw the +5volt supply down...

Try disconecting those sensors to see if the +5volt comes back at the CKP connector.

You could also check the orange wire right at the PCM.

On my renix, I had to actually disconnect the PCM after the new Crank position sensor went in, before it would actually reset and fire up.

i got very irritated aswell! my rig was down for 3 months before i actually got it figured out.

Now, anytime i have a problem, i just disconnect the plug from sensor, but that one time it wouldn't do anything until i disconnected the computer!

Just went through all this no spark condition had to replace the computer all is good now

Thanks for all the replies guys. The new ECM is on order from ebay, should be here by the weekend. I am not near the truck right now to check the 5v supply, but I"ll give it a shot when I see it next. It better work with a new PCM...