no start issue

[TerraWrist]

I have a 96 with a 4.0 h.o. it is cranking but won't run. I'm getting spark, fuel, I've gone through the start and charge system everything checks out. I've cleaned all my grounds. Reset the ecu. I have compression. It has a new dizzy cap and rotor button, new Bosch plugs and fuel filter. Ive cleaned the tps. could a bad cps cause this? I have spark so I ruled that out at first but could it be firing at the wrong time? I've read a bad cps will result in no spark..any help is much appreciated thanks in advance.

 

[TerraWrist]

Forgot to mention relays and fuel pump are good. I believe it ran out of fuel and now won't start. When I changed my fuel filter it was very dirty. Could my injectors be clogged ?

 

[8Mud]

The only way to really check for spark is to open a used plug up to around 0.60 and watch the spark while you are grounding the plug. It should really crack and be a nice sharp spark. Using the spark plug cable end to ground isn't always a reliable test.

Hold a clean jar in front of the schrader valve on the fuel rail and have someone crank the motor over. When you get most of a cup, let it sit for awhile and see if dirt or water settles to the bottom.

Pull a plug and check to see if it is fuel fouled, soaking wet with fuel.

Best guess is you have a fuel pressure issue. Possible the fuel line and fuel rail is full of air, opening the schrader valve (just like a tire valve) should purge any air. Be careful, eye protection, if everything is working right, fuel should really squirt out of the valve. It takes a gentle touch to get it to come out of there slowly and/or trickle out.

Spark, air and fuel, then even in poor ratios something is bound to happen, even if it is an occasional pop. Something has to be really off to get nothing at all.

Loosen your gas cap, just in case something is screwy and the tank isn't venting.

Fuel pressure gauges aren't all that expensive (or rent one). You can even use an old (F-12) freon gauge, the same hose and schrader connection, for a pressure test.

Last on the list, but something to always keep in the back of your mind is water in the fuel. Sometimes it just happens, especially in the winter, the gas station lets it's tanks get way low then when they get a delivery the new gas churns up the dirt and water in the bottom of the tank. And/or the gas station owner pours twenty gallons of water in with the gas and a gallon of alcohol to keep the water in solution, then pockets some cash. I've seen numerous people pull there hair out, dump a bunch of cash into sensors and it eventually turned out to be bad gas. Not likely but a possibility.

 

[TerraWrist]

Thanks man! When I pull the plugs they are gas fouled. What does this mean?

 

[8Mud]

Often means weak spark. The plugs miss fire and the fuel builds up while you are trying to start. Usual cause of miss fire is the ignition high voltage cables, next is a weak coil, sometimes an iffy CPS (misses some beats fuel builds up) or a faulty MAP which defaults to full rich. Possible you are getting way to much fuel. Usually a sensor issue.

May also be bad fuel. If you have enough water in the fuel it can short out the plugs. I've been there done that, I've never been back to that gas station ever again.

I'm sure there are other reasons. I usually start out by cleaning the plugs and then trying to start with a squirt of quick start (Ether) down the TB throat (while holding the throttle plate open).

Try starting it with the gas pedal pushed about an inch or less.
Sometimes the IAC sticks shut and drowns the plugs (no air). Also possible to have low fuel pressure. To little fuel (vapor) for reliable ignition, the plugs foul and then you have too much fuel, it will usually pop when this happens, but may not start.

Cranking it for extended periods is to be avoided. If mine doesn't start (or at least pop) in say ten seconds, I go looking for a problem. Extended cranking rarely produces any good results (except when the air filter is water soaked, it may pop eventually).

I may not be the best guy to ask about this. My junk most always starts, it may run like cap, but it starts. Except when I've been puddle jumping or mudding. Then the cause is fairly obvious, I got water into someplace it shouldn't be.

 

[Tim_MN]

Numerous attempts to start will wet the spark plugs.

I would suspect the CPS.


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 when it cools back down.

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 displayed 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 code reader cannot make a connection to the computer or cannot read Check Engine Light/MIL codes because the CPS/CKP has failed.

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 these relays as the cause of the no-start. Confirm that the fuel pump 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 lose communication.

If you buy a new CPS, get a genuine Jeep CPS, or the premium one from NAPA. Cheap crappy “Lifetime Warranty” parts are often out of specification or even failed right out of the box. They usually also have a shorter service life than better quality parts. Buy good quality repair parts and genuine Jeep sensors for best results.

Also remember to perform 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.

Crankshaft Position Sensor Connector (CPS/CKP)
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CPS 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 the 10K-or-2OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.

TESTING PROCEDURE 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.

The 2000 and 2001 will have the CPS in the same location on the bell housing, but the wire connector is on the passenger side, near or on top of the Transfer case, not as shown in the diagram below. Simply follow the wire from the sensor to the wire connector.
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[TerraWrist]

It pops alittle so there is a good chance I'm having fuel issues. I play in the mud alot. I've sunk it a few times so it wouldn't surprise me if I have some dirty gas. I'm thinking my injectors are clogged. Thanks for the help I have it at a mechanic atm , they called yesterday and said mechanically everything is good they think its a sensor so I will hopefully have it back soon.

 

[jbmoose]

Hey Tim_MN, thanks a ton for the informative post!! My 2000 has been dying here and there while driving it, then she fires back up after about 10-15 minutes. I have also been getting the "No Bus" with the whole cluster crapping out. What brand of CPS would you recommend?? After a quick internet search, the BWD sensor seems to get ok reviews, but what gives with the Omix sensor costing 3 times as much or more than any other sensor? Any input? Thanks, JB

 

[heshhash]

Get your cps at a dealer only. Jeeps generally dont like aftermarket sensors.

 

[Tim_MN]

Buy genuine Jeep sensors. "Lifetime Warranty" sensors are often out of tolerance or even failed right out of the box.

Cheap parts are cheap for reason.

 

[jbmoose]

Just got done putting in a new CPS. Just to add to Tim_MN's writeup above: my 2000 4.0L/AW4 (9/99 manufacture date) had the wiring pigtail on the driver's side, right next the trans shift linkage, not on the passenger side. I have however seen others who gripe about the wires being too short on their new CPS, which would make sense for that. The bolts are 11 mm heads, with a torque spec of 14 ft./lbs, as per the 2000 XJ factory service manual. It also has specs for a 2 nut mounting setup, instead of the bolts, and uses the same 14 ft/lbs. torque spec. Also shown is a 1 bolt adjustable sensor, with a paper spacer that must be used. A new spacer (PN05252229) must be used when installing a used or previously installed sensor. That, and the fact that you need some good flex joints for your sockets. See how it works out. Special thanks to Tim_MN for that detailed post above