98 XJ 6 cylinder sudden No Start -- strange symptoms

[Sand-Dog]

And the answer is....it was a bad CPS. Mike was doin' the research on this forum while I was on the road on a business trip. We had just replaced the CPS on his '90 XJ a few weeks ago and the symptoms didn't seem the same. No gas to the fuel rail was throwing us off the diagnosis of a bad CPS. Tonight we first tried swapping relays. Nothing. But, following the advice in this thread, we unplugged the CPS and the gas gauge worked and the fuel rail pressurized. We also tested the resistance on terminals B & C of the CPS connector and did not get the right reading (should have read open circuit). So a quick trip to NAPA, dropped the front drive shaft, replaced the CPS, and twenty minutes later my daughter's '99 XJ started right up. Moral: Don't let the lack of fuel pressure on the keep you from testing the Crank Position Sensor. No spark, no gas = bad CPS in this case.

 

[Sand-Dog]

BTW...thanks to all who responded. Great advice... it put us on the right track. Gotta love the OEM forum for this kind of help.

 

[4x4bear]

when I unplugged the crank pos. sens. I got my gas and volt gauges back. so that means it is the CPS, correct? I don't want to spend 85 duggots if it isn't.

Bear

 

[muduck18]

The only thing that is odd is the lack of fuel pump function.

.

The most likely cause of it cranks and cranks but won't start up is the Crank Position Sensor (CPS). CPS failure is very common. The CPS 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.

If the CPS is failed sometimes the OBDII code reader cannot make a connection to the computer or cannot read Check Engine Light/MIL codes because the CPS 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 CPS is the cause of your no-start

You might 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.

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.

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 will behave oddly until you remedy this.

CPS 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 CPS and measure across the CPS connector's A & B leads. Your meter should show a CPS resistance of between 125 - 275 ohms. If the CPS 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 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. (That's between 1/2 and 1 volt AC.) If it's below .5vac, replace it.

when I unplugged the crank pos. sens. I got my gas and volt gauges back. so that means it is the CPS, correct? I don't want to spend 85 duggots if it isn't.

Bear

There is one way to test it.
more than likely Yes. It is your Crank Position sensor.

 

[4x4bear]

what size nut/bolt holds the cps into the bellhousing?

Bear

 

[muduck18]

There are two bolts on either side of it,
I can't remember what size.. 12? 13? MM maybe?

 

[4x4bear]

it was a 11 mm. Morgantown,Pa. Hmmm I used to live in Sinking Spring and travel to Coatesville to work.

Bear

 

[muduck18]

I actually live in Geigertown, and travel to Worcester for work...
and I was 1 mm off
sorry bout that...

 

[4x4bear]

thanks for the help everyone. it was indeed the crank sensor, patient is doing well.

Bear

 

[XJ Geek]

Fusible link?

 

[winterbeater]

Fusible link?

Don't forget the second page!:cheers:

 

[gradon]

My CPS just went out Friday night. Same symtoms: cranks, no start, no spark, sometimes fuel(prob from disco'ing the cps), and no connectivity to the pcm. 4.6megaohms between two adjacent pins and infinite between the other two(I'll recheck to make sure of A, B, and C). I have a ZJ I'm working on for a co-worker and my pcm works fine in it, so I ruled that out. I broke out and highlighted the Diagnostic fsm last night and will go through that if the replacement doesn't work. Now where did I put that spare. . .?

 

[gradon]

Took out cps and it measured .4 ohms(shorted) b/t b&c, swapped in used one (6.4megaohm b/t b&c) and she fired up after charging the battery for a while. I knew it was good before it started because the scan-tool could now connect to the pcm.

 

[liljoe71]

Ok so I woke this AM to the sound of my wife's XJ just turning over and not starting. Started to check the usual as follows;
-move shifter to neutral and try to start.
-place back in park try to start.
-did all but 5 from Pomeron's original post.
80+ dollars later, turned out to be the CPS on mine as well. Winterbeater, should we change the percentage from 85% to 99%, lol.
and Tim_MN thanks to your and all you other guys technical troubleshooting all is well here again.

Lil Joe

 

[Redsnake]

Another one here...

Yesterday I go out to my 96 XJ and getting ready to leave and No start... just continuous cranking over and over. So I took my wife's Libby where I needed to go.

Got on here and did some searching and checking and it led me to a potential CPS malfunction. So I tested it as per recommendations here and it appeared to be bad. Swapped out one w/a new part f/ AZone and it fired right up. Had a little trouble trying to get my big@ss hands up in there to start the bolts on the new CPS, but once I got them going it was no biggie. Dropped the front of the front driveshaft and that really helped give some room to move around.

A BIG thanks to all those here who share information and give such great advice. It has saved me a TON of $$ and time getting direction here.

 

[jackate]

That happened on my 99, would not start, but turned over fine.
It was my CPS crank positioning sensor.

I saw a "nobus" message at my odometer.

I changed the sensor and it started right up. it's on the bell housing, kind of hard to get to, but not bad if you have the right tools.

 

[Benzilla]

I am having similar symptoms, but when I unplug the CPS the fuel and voltage meters don't do
squat but i get the same "no buS" off of the odometer. Checked the resistance between pins
B and C at 2K it reads 0.51 but I don't really know how to read a multimeter. I also don't hear
the fuel pump come on when I click on the ignition...

Jeep specs:
'99 XJ sport
Manual
189k

 

[Benzilla]

Turned out to be the Cam Position Sensor...