2000 Cherokee - no spark

Hello - new member Steve here from North Bend, Wa. with a question about my wife's 2000 Cherokee Classic.

She was driving home the other night, when it dies - no sputter, nuthin - just died as if the ignition was switched off (it wasn't).

When I reached her, I took a quick look. I heard no fuel pump (fp) noise when I turned the ignition switch on, so after towing it home, I shotgunned it and replaced pump.

I replaced the battery at that time as well, as I had a new one on hand, and was intending to anyway when I got a moment.

Now, when I switch it on, I hear the pump run then turn off after a couple seconds which seems normal to me. It has fuel at the test port on the rail, s I'm figuring if the fp WAS a problem, I don't think it is now, so I checked for spark.

Took the coil pack rail (is that the correct term?) off and took a plug out, laid it up on the valve cover where I could see it from the drivers door, jumpers threads to ground and turned it over. No spark.

Hooked a code scanner to it, got no codes. Maybe they were lost when I replaced the battery?

I've done a bit of reading on the internet today looking for thoughts and information, but I've not been able to find any articles on the ignition system itself. Lots of references to the crank position sensor and cam sensor, but I'd rather try a better approach than just replacing parts until I get the right one.

A description of the ignition or even a troubleshooting chart would help.

Could one of you point me in the right direction?

Thanks in advance
Steve

sclark309d said:

... when I switch it on, I hear the pump run then turn off after a couple seconds which seems normal to me. It has fuel at the test port on the rail, s I'm figuring if the fp WAS a problem, I don't think it is now, so I checked for spark.....No spark.....Hooked a code scanner to it, got no codes.

Click to expand...

Welcome.

Did the code reader connect to the PCM ?





The most likely cause of it cranks and cranks but won't start up is the Crankshaft Position Sensor (CPS) located on the transmission bell housing. Often this part is also referred to as the CranKshaft Position Sensor (CKP) CPS/CKP failure is very common. The CPS/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.

Crank Position Sensors can have intermittent “thermal failure”. This means that the CPS/CKP fails when engine gets hot, but works again (and will test as “good”) when it cools back down.

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 or connectors and replace as needed. Do the same for the grounding wires from the starter to engine block, and from the battery and engine to the Jeep's frame/body. Jeeps do not tolerate low voltage or poor grounds and the ECM/ECU may behave oddly until you remedy this.



Symptoms –
- Starter cranks and cranks but engine won't start up and run.
- Fuel gauge and voltage gauge may not work or display properly.
- You sometimes will have No Bus on the odometer after 30-60 seconds.
- A failed CPS/CKP may or may not throw a CEL trouble code.
- No spark at the spark plugs.
- Fuel pump should run and prime for 3-5 seconds.

If the CPS/CKP is failed sometimes the OBD-II trouble code reader cannot make a connection to the ECU/computer or cannot read Check Engine Light/MIL codes because the CPS/CKP has failed. Disconnect the code reader, disconnect the CPS/CKP wire connector, and reconnect the code reader. If the code reader establishes contact with the ECU and scans, your CPS/CKP is failed and needs to be replaced.


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


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

Unplugging and reconnecting the CPS sensor where it connect to the main harness near the back of the intake manifold usually resets the ECU and if the jeep fires right up after doing this you can bet that the CPS is faulty and needs to be replaced.

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?

Inspect the wires and wire connectors at the O2 sensors on the exhausts pipe. A short circuit from melted insulation or from broken O2 sensor wires can blow a fuse and the ECU/ECM will loose communication. Don’t get tunnel vision and assume the sensor is bad (unless it tests bad with a meter). Damaged wiring or a dirty connector can inhibit the signal from making it to the computer. Inspect/test/clean/repair wiring or connectors as necessary.


CPS Testing


Crankshaft Position Sensor Connector (CPS/CKP)





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.


The 2000 and 2001 will have the CPS in the same location on the bell housing, but the wire connector may be on the passenger side, not as shown in the diagram below. Simply follow the wire from the sensor to the connector.

.

The steps from Tim_MN are very useful. You have already diagnosed enough to skip to the last step of actually testing the CKP with a meter.

Another nod to Tim's sticky on crankshaft position sensor troubleshooting. It is very comprehensive.

Your problem does sound like it could be crank sensor related. Time to get out the meter.

out to the garage I go...(actually the driveway in the rain - garage is full of other "treasures"...)

Thanks for the replies! Much appreciated.

Steve

How'd your testing go?

Testing - well, right after I headed to the garage, my buddy called and needed rescue, so I tralered his car back to his shop.

While I was in Schucks getting a new 2" ball, I asked them if they had a CPD.

"Yes" she said. "$34"

I figured for that much I'd just put a new one on for the hell of it.

Should be able to install tomorrow, if it isn't raining (and maybe if it is.

We'll see. Suspicious of the $34 sensor, but hey, mebbe prices have gotten better (or she sold me the wrong part)

Will report tomorrow.

Turns out she DID sell me the wrong part gotta love 'em...

I will say that I have seen more than antecdotal evidence of aftermarket crankshaft position sensors not lasting long. The crankshaft position sensor is one sensor that I always purchase directly from Jeep. My advice for sensors is generally to stay away from "el-cheapo". There is a pretty big difference in quality control and reliability testing on automotive sensors.

I worked in Test Engineering for 22 years for a company that mfg. certain sensors for the Big 3 auto manufacturers. There were quite a few DOA aftermarket sensors in our testing and lots of "infant mortality", where the sensors worked out of the box, but failed very early in their service life.

You want a CKP (crank position sensor). aka - CPS. There is another sensor that is the CMP (cam position sensor), that is not likely to be your problem. $75 at rockauto.com. http://www.rockauto.com/catalog/moreinfo.php?pk=498579

To all - thanks for all the help and advice. I do a lot better when I can think out loud as it were and get comments.

I managed to ge the right part, and installed on Sunday. Sure isn't easy to get to, but the next one will be much easier. The first time is always the hardest.

So - she fired right up, stumbled a bit, then seemed to run fine. Took her for a 10 mile spin successfully. Just had one small incident where she stumbled for probably a second, maybe two. I hit the gas, and it resumed running, and ran well. I wish my 96 Chevy pu with the 4.3 ran as well.

Anyway, the wifey drive it to town yesterday, and had two incidents where is seemed to die for a second, then ran fine.

The Jeep has about 30 minutes run time since replacing the battery, fuel pump, and CPS.

I'm thinking that either their might be a little air in the fuel system? or it's taking a bit for the computer to "optimize" settings. That's just speculation on my relatively uneducated part.

Do any of you have experience or advice? I'm thinking it might resolve itself with a bit more run time.

Thoughts?

Thanks
Steve

You might have something else going on. No optimizing necessary for an input signal to the computer (crank sensor replacement) and although there is a learning process that occurs after replacing the battery, that shouldn't result in the engine cutting out. Fuel system bleeds itself out.

Did you ever actually test the old crank sensor with a meter? Might be interesting to test both the old one and the new one and see what you get.

You could try flushing the two connectors for the crankshaft sensor with a spray can of electrical contact cleaner. The one connector is on the sensor itself and the other connector is inside the engine bay, near the firewall #6 injector. If there is any kind of debris in either of these connectors, that can equate to a resistance path for that crank signal.

If you do see any check engine light, no matter how momentarily, pull codes and post here for comment.

It could be the computer relearning as you suspect. Mine (2000) runs rough after a dead battery episode for a little while. Not over an hour though. And how old are your spark plugs?

To birchlakeXJ:
yes I did check the old sensor as well as the new. The old one was very low resistance across B&C (if I remember correctly - I can check again when I get home), but it was definitley bad compared to the new one.

No check engine light. 99% of the time it runs really good. Lots of power and pulls fine.

I'll pull codes tonight - good call.

To winterbeater:
I don't know how old the plugs are, the two I pulled out looked ok (They were light brown, no carbon), and it ran fine up to the moment the CPS crapped out. It's got 120K and she's had it for three years or so, so even if they were new when she bought the jeep, it's got 30 to 40K on them.

Check that the wire harness for the CPS/CKP sensor and the O2 sensors are not damaged from chafing on sharp edges or from melted insulation due to heat from, or contact, with the exhaust manifold.


The Cherokee owners manual and the Factory Service Manual both recommend replacing the spark plugs every 30,000 miles. With my 2000, I sometimes notice smoother running with fresh plugs.

Use basic Champion or Autolite plugs, the Jeep 4.0L does not run well with SplitFire type plugs or premium Platinum type plugs.

Clean the throttle body and add a can of injector cleaner to the nest 2 gas tank fill-ups.

If you want to re-boot the OBD-II ECM follow these steps -

Info from a JEEP Technician -

This very simple procedure will Erase the “Adaptive Memory” stored inside the PCM and allow a new “Adaptive Memory” to be developed.

After performing this procedure the PCM will re-learn and store into Adaptive Memory your engines performance characteristics.

Please perform these steps exactly as they are written, in the order they are written. This will cause the adaptive memory in the PCM to be erased and cause the PCM to go into Fast Learn Mode adaptive mode.

Disconnect the POSITIVE battery Terminal and touch it to ground ( not the battery negative terminal ) for 30 seconds. The engine block or the A/C compressor pump will work as a ground. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory.

Reconnect the Battery Cable
Turn Ignition Switch to the “On” position but DO NOT start the engine
Turn Headlight “On”
Turn Headlights “Off”
Turn Ignition Key “Off”


The PCM Adaptive memory has now been flashed, or erased from the PCM.

When you start the engine it will be running off a set of pre-programmed tables that come with the PCM from the factory.

When you get the engine up to operating temperature the PCM will start to collect data for the “Adaptive Memory”.

The PCM will collect data for Adaptive Memory for the first 50 Warm-up Cycles.

I have a similar problem. My jeep was acting like it was running out of gas, then it would stall. After it would cool off, it would start. I changed the CPS and now, it won't start at all. There is fuel in the EFI rail, but no spark (I removed the coil bar, took out a plug, put it back in the wire and...no spark.) If the CPS STILL isn't working (whether another bad one or the connection is not sound), shouldn't the "check engine" light stay on when i turn on the ignition? Because, it's not.

Did you hold the electrode of the spark plug to a ground like the head or block? It won't spark if you don't. Check out the CPS connection with a multimeter.

As it turns out, I grabbed and moved every wire i could get my hands on and...IT STARTED!! I have have no idea why. However, now it's doing the bucking bronco things after 20 minutes of driving. Occasionally, it stalls. It's sending the infamous code P1391. I've read every post on about this issue. I guess it's back to tracking down a grounding problem or a frayed or worn wire issue. Any other suggestions?

I just took it out to see if it was still going to have the "bucking" issue and it just plain stopped running not far from my house. It won't even start, although it tries and tries. I tried tugging on wires as i did before, but it got no better. I left it and walked home. I'll go back in an hour and try to start it again.