MCObray

Jeep just wants to crank and crank... and crank. I have no means of testing the CPS and such right now. On the dash I have really low volts, and "check gauges" is on. When I have the keys one click before starting the radio, lights, aux. lights all work. My Jeep just doesn't want to start. The battery terminals were recently replaced.

Any help or suggestions are welcomed. Thanks.

Check out the video I took:
http://youtu.be/fa2VmoVyXkM

XJ Mulisha

Anyone you know have a scan tool? Looks like it wants to start, maybe a fuel problem. Not sure if it will try to start with a bad CPS, I thought it will just turn over and not try to start. Have to search and see what the CPS should read if its good or bad.

MCObray

This is only one of the reasons why I suspect a bad CPS:

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

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.

XJ Mulisha

That is what I was talking about testing it. Have you tried to OHM it out?

tjwalker

If you buy one, buy it directly from Jeep.

Aftermarket crank sensors are hit and miss. With a LOT of miss.

The extra $25 or so spent on an OEM Jeep crank sensor is the best money you will ever spend. That is, unless you like doing things twice............

rrich

The Crank Position Sensor (CPS) only provides a sync pulse to the ECM.
Without a pulse, the ECM does not know when to fire the injectors or the spark.

It will NOT AFFECT the gauges, or anything else.

The fuel pump will still run, pressurizing the fuel rail.

A code will rarely set - a failed CPS shuts down before it can set a code.
A good scan tool can see there aren't any pulses.

Sounds like a bad battery or bad battery connections. Check connections in the fuse/relay box.

Whoever told you otherwise doesn't know anything about what a CPS is or does.

MCObray

Yeah i'm kind of leaning towards the battery. We used a battery charger for 3 hours and to my avail, it wouldn't start. It cranked the same as I tried before for the first, but the second and third time the cranks were very faint and it wouldn't even crank anymore... Battery?

tjwalker

Actually, a failing crank sensor can affect the gauges. I've personally seen it affect the voltage and fuel gauges. And I've answered a few threads of others having the problem. It certainly doesn't always accompany a failing crank sensor, but it definitely can happen. When it happens, usually both the voltage and fuel gauge won't work at all.

BUT, the original poster has a "low" voltage reading and a check gauges light. That's different. That indicates low available battery voltage.

1. Get that battery load tested and or replaced. Load testing is the only accurate way of determining battery condition. Any parts store will do this for you for free. See if that resolves. If it doesn't, proceed to step #2.

2. TEST FOR SPARK. You really need to know if you have quality spark or not. Remove a plug, keep it attached to the plug wire, place the plug electrode near a good engine ground, have a buddy crank the engine while you watch. You are looking for a strong, blue, snapping spark. Yellow/orange/white indicates a weak spark which may not be strong enough to start the engine (suspect ignition coil for a weak spark)

You need to do some basic testing here (battery/spark) to narrow down ANY no-start.

rrich

Look at the wiring diagrams - CPS has nothing to do with the fuel gauge or voltmeter. TOTALLY UNRELATED.

But a low voltage to the ECM or the dash can.

Just because it cranks doesn't mean the other circuits are getting proper voltage.

sweeper

My (cps) just went out last week and it didn't effect my gauges. It just died and would crank over but it wouldn't start. Did you run your battery down cranking it by any chance ,and that is effect the gauges? If it wasn't for this forum I wouldn't have known about the (CPS) so there is alot of good help on here.

tjwalker

Sorry Rich, but I disagree with you and have the experience with this exact fail to back up my position. I agree that it doesn't sound logical, but it absolutely happens. Wiring diagrams are certainly valuable and I'm the first to refer to them, (I'm an electrical technician by trade) but circuits can have strange things like feedback loops, etc.

Here are but a few threads illustrating the relationship of the crank sensor to fuel/voltage gauges.

http://timlaqua.com/2011/07/troubles...fuel-no-spark/

http://www.justanswer.com/jeep/4yjuy...not-start.html

http://www.jeepforum.com/forum/f11/c...ailing-639123/

I've seen it personally and I'll bet I've seen it at least a dozen times on this and other XJ forums. Gauge issues don't happen the majority of the time with a failing crank sensor, but they absolutely can happen. You probably just haven't run into it yet..........

You should be able to verify a bad crank sensor by unplugging it, and turning the ignition key to on. If the voltage gauge and/or the fuel gauge now displays correctly and/or the NO-BUS message that you also may see on the dash is gone, replace the crank sensor.

But I digress....the original poster most likely does NOT have a crank sensor issue. This is a voltage issue almost certainly. Battery most likely.

rrich

Thinking about it - it possibly could IF the CPS was a dead short. Never seen it - diagnosed and fixed probably 30 CPS failures.

A popular problem - not the CPS itself, but the connector to it.
It's right under the hood/cowl joint. When water leaks through, it goes right on that connector. The corrosion kills the weak signal = no start.

Unplug, dielectric grease, plug - good to go.

MCObray

It's got to be a battery problem.

Used a "battery charger" all night last night and when I woke up I thought I would give it a shot to see if it would work. To my surprise it cranked, very sluggish start, gave it a little gas and it was running.

I drove over 120 miles today, stopped and started more than 3 times and it's back to normal: One crank and she starts.

My buddy and I inspected all electrical connections and everything appeared to be good. Turned the Jeep on and the voltage was at 14.1. Blasted the heat/high beams/stereo and volts dropped significantly. I believe the battery is on it's last leg.

tjwalker

Don't screw around any longer.

Get a new battery in there. Go at least with a mid-line as it is worth the few extra bucks.

MCObray

Yeeah, i'm leaning towards a Optima Yellow-Top only because I can get $50 off, where as I would pay $220 for DieHard Platinum.

$150>$220.