Strange no start condition

2jeepdrivers · **Joined:** Thu Apr 10, 2008 10:07 pm **Posts:** 9

I have an 03' libby 4x4 w/ a 3.7 and 5-speed. The clutch switch went out some time ago and I just jumped it and know not to crank it in gear. Recently though it has started not cranking at random, the first time it done this the ignition fuse was bad I put a new one in and it started right up. Now it is still doing the no cranking thing. I have checked all of the wires going to and from the ignition switch checked the battery cables and all connections, it has a new battery and I can't ever get it to keep doing it long enough to check and see if there is power going to the starter solenoid when it won't crank. This is just a random problem you never know when it is going to do it and if you keep trying to start it, it will eventually start. If anyone knows what might be causing this any input would be great I am at a dead end.

Li-bah-tee_13x · **Posted:** Fri Apr 11, 2008 8:47 pm

hey i think i might be having the same problem... ive got an 02' limited but it died on me today...and im trying to figure out why... when yours wont start...does it prevent you from putting it in nuetral?...or can you shift it?

WoodysKJ · **Posted:** Sat Apr 12, 2008 12:33 pm

Pull your alternators and have them tested. they may be failing and not charging when called upon by the PCM all the time.

You said new battery. Is it the correct one for your KJ? 02's used a Group 25 battery which is L-9 5/16 in.; W-6 13/16 in.; H-7 5/8 in in size.

other years use a group 34 battery which is:L-10 in.; W-6 7/8 in.; H-7 13/16 in. in size. You see the difference. You can use a g34 in an 02 but you will need to trim the tray so the temp sensor can work with the different sized battery. I THINK you trim the side nearest the fender and a g34 will work. Ask Troy (tjkj2002) he has done this.

Located near the battery, is a temp sensor. this is what tells the PCM to allow the alt/gen to start charging the battery as it is drained. Not the same way we are used to charging systems. IF the temp sensor is failing or not close enough to the wrong battery or what ever then it can not tell the PCM that the battery has reached the temp for charging and you may be running it dead. But later it decides to charge it and you are ok.

The KJ does not run off the alternator like most people think it does. it needs the battery to be near a certian level of charge to power the computer correctly. It runs off the battery because it can control the voltage and current better and not allowing spikes from the alt/gen to fry the PCM. SO when the battery is down all kinds of weird things happen, like what you are discribing and then some.

It is important to have a good fitting battery so it can comunicate with the temp sensor and alloow the PCM to make the correct instructions to the alt/gen.

Rush345 · **Posted:** Sat Apr 12, 2008 10:21 pm

I have an '02 and a few months back had a simular problem. After sitting 2 days I stepped out one night to make a short trip and the Jeep would hardly turn over , much less start. After several attempts it started and took at least 15 minutes of my foot on the pedal to keep it running. Drove about 5 blocks stepped on the brakes and died. So started the procedure all over again. Once running this time go on the highway and drove for at least an hour with cruise at different speeds. The next day it started right up on it's own. But not to be fooled twice went out and bought a new battery that day. No hiccups since, but I'm sure it had the original factory battery and was ready for a change.

2jeepdrivers · **Joined:** Thu Apr 10, 2008 10:07 pm **Posts:** 9

I have a group 34 battery in it and had the alternator checked. When it does this all of the lights and everything light up like you had just turned the key to run but not cranked it over, but when you turn it to crank it doesn't do anything. I can keep trying a few times and sometimes it will go ahead a crank sometimes it won't. When it does crank it fires right up and runs fine and may not do it again for a few days or it might do it the next time you go to start it. I pulled the fuse panel out of the engine compartment and cleaned all of the connections and soldered a few of them and it seems like it might have fixed it. It hasn't done it in a week now.

Rush345 · **Posted:** Sun Apr 20, 2008 4:46 pm

If you have a Checker Auto Parts or Part America Store in your area they can test alternators and starters.

2jeepdrivers · **Joined:** Thu Apr 10, 2008 10:07 pm **Posts:** 9

Finally figured it out. Mainly because it completely quit starting so I had to. I started out checking all the relays and fuses and they were fine, then I checked the battery and alternator and they checked out great. Then I went throught the hassle of pulling the starter ( exhaust bolts suck) and it was fine. Also put in an ignition switch since thery are only twelve bucks mainly just hoping it would work, which it didn't. So I got out the mulitmeter and a wiring diagram and went to town on it, it turns out that the wire going from the starter relay to the starter had a break in it and if I wiggled it I could get a connection. So after hours of work it turned out to be a bad wire. Now I have to put it all back together. Just thought I would share maybe I can help out somebody else with a not start condition.

tjkoen01 · **Posted:** Tue Jun 03, 2008 9:10 am

Description and Operation

CHARGING SYSTEM
The charging system consists of:

* Generator
* Electronic Voltage Regulator (EVR) circuitry within the Powertrain Control Module (PCM)
* Ignition switch
* Battery (refer to Battery for information)
* Battery temperature sensor
* Generator Lamp (if equipped)
* Check Gauges Lamp (if equipped)
* Wiring harness and connections (refer to Wiring for information)

The charging system is turned on and off with the ignition switch. The system is ON when the engine is running and the ASD relay is energized. When the ASD relay is ON, voltage is supplied to the ASD relay sense circuit at the PCM. This voltage is connected through the PCM and supplied to one of the generator field terminals (Gen. Source +) at the back of the generator.

The amount of DC current produced by the generator is controlled by the EVR (field control) circuitry contained within the PCM. This circuitry is connected in series with the second rotor field terminal and ground.

A battery temperature sensor, located in the battery tray housing, is used to sense battery temperature. This temperature data, along with data from monitored line voltage, is used by the PCM to vary the battery charging rate. This is done by cycling the ground path to control the strength of the rotor magnetic field. The PCM then compensates and regulates generator current output accordingly.

All vehicles are equipped with On-Board Diagnostics (OBD) . All OBD-sensed systems, including EVR (field control) circuitry, are monitored by the PCM. Each monitored circuit is assigned a Diagnostic Trouble Code (DTC) . The PCM will store a DTC in electronic memory for certain failures it detects. Refer to Diagnostic Trouble Codes in; Powertrain Control Module; Electronic Control Modules for more DTC information.

The Check Gauges Lamp (if equipped) monitors: charging system voltage, engine coolant temperature and engine oil pressure. If an extreme condition is indicated, the lamp will be illuminated. This is done as reminder to check the three gauges. The signal to activate the lamp is sent via the CCD bus circuits. The lamp is located on the instrument panel. Refer to Instrument Cluster for additional information.

BATTERY TEMPERATURE SENSOR
The Battery Temperature Sensor (BTS) is attached to the battery tray located under the battery.

The BTS is used to determine the battery temperature and control battery charging rate. This temperature data, along with data from monitored line voltage, is used by the PCM to vary the battery charging rate. System voltage will be higher at colder temperatures and is gradually reduced at warmer temperatures.

The PCM sends 5 volts to the sensor and is grounded through the sensor return line. As temperature increases, resistance in the sensor decreases and the detection voltage at the PCM increases.

The BTS is also used for OBD II diagnostics. Certain faults and OBD II monitors are either enabled or disabled, depending upon BTS input (for example, disable purge and enable Leak Detection Pump (LDP) and O2 sensor heater tests). Most OBD II monitors are disabled below 20 degrees F .

GENERATOR
The generator is belt driven by the engine using a serpentine type drive belt It is serviced only as a complete assembly. If the generator fails for any reason, the entire assembly must be replaced.

As the energized rotor begins to rotate within the generator, the spinning magnetic field induces a current into the windings of the stator coil. Once the generator begins producing sufficient current, it also provides the current needed to energize the rotor.

The stator winding connections deliver the induced AC current to 3 positive and 3 negative diodes for rectification. From the diodes, rectified DC current is delivered to the vehicle electrical system through the generator battery terminal.

Although the generators appear the same externally, different generators with different output ratings are used on this vehicle. Be certain that the replacement generator has the same output rating and part number as the original unit. Refer to Specifications and see Generator Ratings for amperage ratings and part numbers.

Noise emitting from the generator may be caused by: worn, loose or defective bearings; a loose or defective drive pulley; incorrect, worn, damaged or misadjusted fan drive belt; loose mounting bolts; a misaligned drive pulley or a defective stator or diode.

Fig.5 Generator Decoupler Pulley (Typical)

GENERATOR DECOUPLER PULLEY
The generator decoupler is used only with certain engines. The decoupler is used in place of the standard generator drive pulley (Fig. 5).

The generator decoupler is used only with certain engines. The decoupler (Fig. 5). is a one- way clutch designed to help reduce belt tension fluctuation, vibration, reduce fatigue loads, improve belt life, reduce hubloads on components, and reduce noise. Dry operation is used (no grease or lubricants). The decoupler is not temperature sensitive and also has a low sensitivity to electrical load. The decoupler is a non-serviceable item and is to be replaced as an assembly

VOLTAGE REGULATOR
The Electronic Voltage Regulator (EVR) is not a separate component It is actually a voltage regulating circuit located within the Powertrain Control Module (PCM) . The EVR is not serviced separately. If replacement is necessary, the PCM must be replaced.

The amount of DC current produced by the generator is controlled by EVR circuitry contained within the Powertrain Control Module (PCM). This circuitry is connected in series with the generators second rotor field terminal and its ground.

Voltage is regulated by cycling the ground path to control the strength of the rotor magnetic field. The EVR circuitry monitors system line voltage (B+) and battery temperature (refer to Battery Temperature Sensor for more information). It then determines a target charging voltage. If sensed battery voltage is 0.5 volts or lower than the target voltage, the PCM grounds the field winding until sensed battery voltage is 0.5 volts above target voltage. A circuit in the PCM cycles the ground side of the generator field up to 100 times per second (100Hz) , but has the capability to ground the field control wire 100% of the time (full field) to achieve the target voltage. If the charging rate cannot be monitored (limp-in), a duty cycle of 25% is used by the PCM in order to have some generator output. Also refer to Charging Operation for additional information.

Strange no start condition

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