98 XJ 6 cylinder sudden No Start -- strange symptoms

98 XJ had been running great; recent tuneup; over-maintained.

Suddenly won't start:
1) Starter cranks well; great battery; motor turns freely
2) No spark (tested at coil output)
3) No fuel pressure (no pump running); also tested at fuel rail & no pressure
4) No "check engine light"
5) ODB-II diagnostic tool which has previously worked on this XJ comes back with no error codes -- rather says "Link Failure"
6) All fuses in the master fuel box located passenger side in the engine compartment test OK.
7) When ignition key is first turned on all dash sensor indicator lights (such as "check engine") come on as per normal and stay on until key is turned one click further and starter engages; then they all go off and remain off as per normal.
8) None of the actual gauges themselves ever move at all.
9) Radio, dome lights, heater/blower motor, windshield wipers all work as normal.

I don't understand, but bet people here will know exactly what is wrong.

What am I missing? What do I do now? What should I check/repair next??

Help please -- and thanks .....

Could be the computer itself. You could try reseating electrical connections to it for starters....

Crank Position Sensor??????????????? Search threads or just replace! 85% Chance.

winterbeater said:

Crank Position Sensor??????????????? Search threads or just replace! 85% Chance.

Click to expand...

Actually just replaced the Crank Position Sensor (and a lot of other stuff) on another XJ last week -- where the problem eventually turned out to be the fuel pump return.

But isn't the fuel pump supposed to generate initial pressure the moment the key goes to the "run" position regardless of what the crank sensor does or does not see; without the engine even doing a rotation or the key going into the "start" position?

The one we just worked on was a 1988 and I realize these two XJ's are very different -- but that is how that works on the '88. Turn the key to just "on" and fuel pressure hits <> 39; fuel pump immediately shuts off and the pressure drops and holds at <> 31. Then turn the key to "start" to turn the motor over; pump again begins to run and maintains <> 31 from then on.

With this problem '98 XJ I need your help on here it appears the fuel pump never kicks on at all as I can tell by listening for the pump laying under the tank and by putting a gauge on the injector fuel rail; and watching the spark -- where it would normally take a few revs to appear due in part at least to that crank sensor design -- I see no spark at all regardless of the revs.

I get NO fuel pressure and NO spark no matter how long I crank the starter.

Appreciate the thoughts -- and not meaning to disagree in any way since I don't know what's wrong -- just trying to understand. Could a bad crank sensor or sensor connector cause the fuel pump to completely fail? Oh, and could there be a relationship to that and the ODB-II reader's failure to see codes?

Advice and suggestions most appreciated!!

Seems like you should have fuel pressure at the rail even befor the motor turns over...so I doubt it is the Crank position sensor....maybe a bad ASD relay...better get your meter out and start checking voltages at the PCM, Fuel Pump,and sensors...unless you want to throw parts at it. Maybe a bad ground somewhere...

A dead sensor can hose over the PCM...so you might want to unplug the CPS and other sensors to see if the fuel pump activates,,,

birchlakeXJ said:

Could be the computer itself. You could try reseating electrical connections to it for starters....

Click to expand...

Please let me demonstrate my ignorance here.

That sounds like a great idea -- couldn't hurt and doesn't even cost anything to try.

And if those connections (or the computer itself) are bad or failing would this possibly explain why the ODB-II reader that has worked on this vehicle before now fails to link up at all??

But my question, please -- where is this computer you are referencing located and where can I find those connectors?

And a followup-question: if working with the connectors does not solve the problem is there any way I can do diagnosis on the computer??

Thanks ..

Mike

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.

Computer is under the hood, mounted to driver side fender...3 connectors on it, White, Black, and Grey.

could be that the computer getting no power (no ground or no hot power as PCM suppose to control the igintion and the fuel pump request aka turn on the relay to energize the fuel pump)

you can use jump wire to bypass the relay to see if the fuel pump come on and make proper pressure. or even swap the relay to see if ther'es any change

as you say fail to connect with a scantool. id suspect the computer's failed to power on

nor can be simply a ignition switch problem

To answer you initial questions, the fuel pump should run whenever the key is in the crank position and for 3 seconds in the run position. I'd check out the ASD relay which controls the 12V to the fuel pump, injectors and spark.

winterbeater said:

To answer you initial questions, the fuel pump should run whenever the key is in the crank position and for 3 seconds in the run position. I'd check out the ASD relay which controls the 12V to the fuel pump, injectors and spark.

Click to expand...

but how can that explain on the fail of connetion to the scantool? this means the computer's not on or wiring problem

95, you make a good point. Power to the computer PCM needs to be verified. If you get power in and no signal out, PCM is dead. Not a usual XJ problem, but certainly possible.

pomerom -

What was the results of exchanging the ASD relay and the CPS diagnostics and testing ?

ECM/PCM problems can occur but should not be suspected until the ASD and CPS are confirmed to be functioning by testing or by exchanging with a known "good" part.

A bad CPS can and will cause the OBDII code reader to give error messages or to not connect at all.

Tim_MN said:

pomerom -

What was the results of exchanging the ASD relay and the CPS diagnostics and testing ?

ECM/PCM problems can occur but should not be suspected until the ASD and CPS are confirmed to be functioning by testing or by exchanging with a known "good" part.

A bad CPS can and will cause the OBDII code reader to give error messages or to not connect at all.

Click to expand...

Tim,

This vehicle actually belongs to a good friend; is driven by one of his family members (when it works, huh?).

He has been out of town; should return the middle to end of this week. So I've been trying to help out.

Work on it now will probably have to wait until he returns -- then I'll post solutions/results -- or more questions ....

Mike

Mike,
Just to confirm,
I had a bad CPS a couple months ago in my 98. The OBD tool "failed to connect"
and, The fuel pressure would only pressurize sometimes.
As I could tell the because the CPS was bad, it worked like a key stuck problem on a computer. it seemed like the CPU would post, but only until it got to the CPS and then it would just hang waiting for the sensor. (yeah I work on computers too much)
good luck when he gets back...

muduck18 said:

Mike,
Just to confirm,
I had a bad CPS a couple months ago in my 98. The OBD tool "failed to connect"
and, The fuel pressure would only pressurize sometimes.
As I could tell the because the CPS was bad, it worked like a key stuck problem on a computer. it seemed like the CPU would post, but only until it got to the CPS and then it would just hang waiting for the sensor. (yeah I work on computers too much)
good luck when he gets back...

Click to expand...

Tim,

I just went and pulled the connector modules from the Computer as has been suggested to "maybe reset it" .. no joy.

I am very familiar with that CPS where the problem is apparently sometimes the actual sensor and sometimes the connection into the wiring harness. As I understand it Jeep left very little room (i.e. resistance) for that circuit/sensor to deteriorate before it begins to give problems. And I don't know how the computer HW & SW actually deals with that in some failure mode. (I, too, am a life-long computer/IT person -- so I understand what you meant.)

If this '98 CPS system is similar to my '90 (I mistakenly called mine an '88' in an earlier post) -- it is possible to do basic tests on the CPS using a multimeter at the sensor/wiring harness interface. So I'll definitely keep everything you said in mind.

The owner just called a few minutes ago; he is also an experienced XJ person -- has three of them in the family and works on them all. Also familiar with the computer and had to replace one a couple of years ago. So when he returns to town we plan to take the suggestions we've received here, the XJ manual, and do some wire tracing. An earlier poster (might have been you) suggested starting with the basic "is the PCU getting power" so that will probably be the starting point. Makes sense to me.

BTW: Another maybe very important question depending upon what we find -- the owner remembers that computer as being a "Jeep Only" part; not available anywhere else -- therefore VERY EXPENSIVE. Anybody know if that is correct -- or are there other sources?? (I also have an '82 Jeep CJ8 who's computer failed and the Dealer tried to tell me the same thing. Turns out on the CJ's to be a common aftermarket item made by the original part manufacturer.)

Any additional thoughts and/or suggestions still very much appreciated.

Mike

pomerom said:

BTW: Another maybe very important question depending upon what we find -- the owner remembers that computer as being a "Jeep Only" part; not available anywhere else -- therefore VERY EXPENSIVE.

Click to expand...

A used computer can be model year specific depending on the model year. In most cases, swapping in a matching model year computer from a junkyard will be no problem. Re-flashing is recommended but not required. The 1997-2001 computers can be re-flashed based on just your VIN numbers by an aftermarket or eBay reseller, and/or by the dealership.

I'm having the same problems with my 97' . early symptoms: 2 wks prior I got gas, then the gas gauge went to empty, but the Jeep ran. came out of the store and everything was ok, a wk later I got gas and drove about 4 miles to home and then the gas went to empty again. next morning it started, ran for 2 seconds and stopped. I did the spray into the tb and it started for a second or 2, I also replaced the fuel pump relay, but not the ASD, have that yet to do. my question is the remedy is the Crank ps, from what I have read, is the 97' just like the 98' ? I will check that at the connect near the firewall. great site and thanks in advance for the help.

Bear

If it was the CKP (crank pos sensor), it wouldn't have spark. Running with spray into intake indicates you DO have spark. What about fuel pump ground? That affects both gage and pump.