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HELP PLZ. Turns over but no start

TerraWrist

NAXJA Forum User
Location
Georgia
I have a 96 4.0L that doesnt want to start. It was running fine until i let my wife drive it to work :twak: she says it started up but when she was backing out of her parking space it cut off and wouldnt crank back up. she said she could feel it trying to die so tried to give it some gas and it cut out.

Im getting spark. its a strong blue arc. im pretty sure im getting fuel i can smell it on the plugs when i remove them. i cleaned my throttle body and tps. i cleaned my grounds but still no start. if my ground from the block to the fire wall was bad then the plugs wouldnt spark when in the head right? they spark just fine when grounded to the a/c compressor..this would explain why they stink like gas when i pull them..any thoughts?

thanks for any help
 
Could the plugs be gas fouled? Try starting with the petal to the metal to clear out the fouling. Or better yet, pull the plugs, clean them with spray start. Crank engine over a little to clear out excess gas, and put plugs back in.
 
I'll give it a try. You can smell the gas after trying to crank it a few times. The sensor by the block to fire wall ground, what is that? Mine needs replaced
 
If you have spark and gas, you might have too much gas. Check your fuel pressure.
 
After repeated attempts to start it is normal to have wet plugs or to smell fuel. Those would be symptoms of the problem, not causes.

If there are any known failed components, or other existing maintenance issues, fix them first.


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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Also check your cap and roter foe excessive wear or moisture. Press the shrader valve on the fuel rail for pressure.
 
Crank it over with the throttle fully depressed for a good five count. Then depress the pedal about an inch and crank it over and see if it doesn't fire. You may have to feather the pedal a little to help clear the cylinders of excess fuel until it gets to running well and you can hold a steady 2000 RPM.

I'm guessing your IAC stuck shut, which cuts off the air to the motor while you are trying to start.

It may be something else, but a stuck shut IAC is one of the first things to check.
 
I would highly recommend getting a pressure tester and checking your fuel pressure, as this is an easy check and once out of the way, it's out of the way you don't need to think about it again.

The Fuel pressure regulator (the little jobby on the end of the fuel rail) does go bad, and will bleed excess fuel into the intake manifold. When this happened to mine, the vehicle ran, but was sluggish, starting was often difficult, and I could see how the higher pressure fuel system on the HO engine could turn this into a flood/no-start problem.

Check:

1) Fuel Pressure regulator - pull off the vacuum connector look for signs that it's had gas in it (usually fuel drips out)
2) Check fuel rail pressure - open test port, screw on gauge, turn key to "run" position, you should see pressure spike to about 40-50PSI, and then crank it, if the engine starts it should drop to about 40PSI. If it measures any higher than this, you may have a problem with the fuel return system and excess fuel is blowing through your injectors.

Sensors are an obvious place to start, I know, I've been too quick to blame them for many of my running problems myself, however good trouble-shooting is the key to success.

Also, I should mention, if your vehicle has spark, you're CPS is probably fine, this usually manifests as a no-spark
 
Replaced the camshaft position sensor still no start. something is draining my battery though so I'll clean the grounds and see if that helps. How do you test a relay?
 
I'll check the fuel pressure to. I'm pretty sure I'm getting pressure but we shall see. I tried to spray starter fluid in the throttle body and it didn't fire...I have spark I've pulled all the plugs and tested them. It was out of gas when it died could that mess up the pump or regulator?
 
Jumped timing?

Based on what diagnostic procedure ?


What is the condition of your battery and alternator ? How about the battery/alternator/starter wires ?

The Jeep 4.0L does not tolerate low voltage, and poor ground connections. If you have starting issues the very first thing to do is inspect/clean/repair/firmly reconnect all the wires and grounds.
 
Ok so I found a loose ground on the starter ( the small wire ) the ring terminal slide right off. I'm waiting for a jump to see if this fixed the issue.
 
Got it to sputter but still won't fire. I replaced the fuel filter and IM getting fuel pressure. I cleaned the tps. I'm stumped.any suggestions?
 
Did you ever figure out a solution to this problem?

I'm having a similar issue. Jeep will turn over but no start. Tried starting fluid and no luck... Changed cps, and nothing. I have to prime my fuel pump to start but after prime ihave plenty of pressure... I'm thinking about changing the coil? Any suggestions?
 
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