Hey everyone, I need some help with my TJ. It dosn't want to start...it turns over fine but not start. I know fuel & spark but I don't here my fuel pump run when I turn on the ignition. Also my idiot lights on my dash come on but the gauges don't move. I checked my fuses under the hood and behind the glove box...all good. Another weird thing is that I can't communicate with my onboard computer...any idea's?
03 TJ won't start
- Thread starter timst3r
- Start date
sweetpeet
New member
wow, that is really weird. my first thought would be a short somewhere but that would mess up everything. from what your saying sounds like everything works except the engine's not moving. try checking the spark plug wires for and disconnects or any type of damage. also check the voltage on the battery (just in case). as fat as the computer goes, I got nothing right now. sry. but let me know how the other stuff goes.
SteelHeadz
Super Moderator
Check the CKP sensor connections and wirings. Even if the fuel pump runs with the key on, the injectors will not pulse and the COP will not fire if the CKP is faulty since there will be no refference on the ignition timing.
ok well I did some more reading and checking. It seems that the CPK does not come into play until you turn the key to the start position. I don't even get the fuel pump prime when you turn the key to on. I traced the power going to the PCM and I get 12.4vdc between term 22 and 31(gnd) so I know there is power going to the PCM....I think the PCM is bad
SteelHeadz
Super Moderator
Very true, however, if the PCM see's a short to ground, short to voltage or open short, it will command the ASD relay to shut the circuits down. The PCM will be an expensive guess. CKP sensors are also known to cause a "NoBus" message on the cluster as well as various anomally's on the circuit.
SteelHeadz
Super Moderator
With the use of a volt meter, test the voltage signal from the sensor during cranking.
The CMP sensor contains a hall effect device called a sync signal generator to generate a fuel sync signal. This sync signal generator detects a rotating pulse ring (shutter) on the oil pump drive shaft . The pulse ring rotates 180 degrees through the sync signal generator. Its signal is used in conjunction with the crankshaft position sensor to differentiate between fuel injection and spark events. It is also used to synchronize the fuel injectors with their respective cylinders.
When the leading edge of the pulse ring (shutter) enters the sync signal generator, the following occurs: The interruption of magnetic field causes the voltage to switch high resulting in a sync signal of approximately 5 volts.
When the trailing edge of the pulse ring (shutter) leaves the sync signal generator, the following occurs: The change of the magnetic field causes the sync signal voltage to switch low to 0 volts. If there is NO change in the voltage while cranking, the sensor is bad.
The CMP sensor contains a hall effect device called a sync signal generator to generate a fuel sync signal. This sync signal generator detects a rotating pulse ring (shutter) on the oil pump drive shaft . The pulse ring rotates 180 degrees through the sync signal generator. Its signal is used in conjunction with the crankshaft position sensor to differentiate between fuel injection and spark events. It is also used to synchronize the fuel injectors with their respective cylinders.
When the leading edge of the pulse ring (shutter) enters the sync signal generator, the following occurs: The interruption of magnetic field causes the voltage to switch high resulting in a sync signal of approximately 5 volts.
When the trailing edge of the pulse ring (shutter) leaves the sync signal generator, the following occurs: The change of the magnetic field causes the sync signal voltage to switch low to 0 volts. If there is NO change in the voltage while cranking, the sensor is bad.
ok I see, makes sense now. So which terminals should I be reading the 5v-0v on? Is the center common?
Thanks...yeah first thing I did....lol
SteelHeadz
Super Moderator
Manual transmission 4.0 Cav.circuit function 1k24 18gy/bk crankshaft position sensor signal 2k4 20bk/lb sensor ground 3k7 20 orange 5 volt supply.
Auto trans. 4.0. 20 Orange (4.0L)5V SUPPLY 18GY/BK (2.4L)CRANKSHAFT POSITION SENSOR SIGNAL , 18BK/LB (2.4L)SENSOR GROUND, 20BK/LB SENSOR GROUND, 18GY/BK (4.0L)CRANKSHAFT POSITION SENSOR SIGNAL, 18OR (2.4L)5V SUPPLY.
Auto trans. 4.0. 20 Orange (4.0L)5V SUPPLY 18GY/BK (2.4L)CRANKSHAFT POSITION SENSOR SIGNAL , 18BK/LB (2.4L)SENSOR GROUND, 20BK/LB SENSOR GROUND, 18GY/BK (4.0L)CRANKSHAFT POSITION SENSOR SIGNAL, 18OR (2.4L)5V SUPPLY.
Thanks man, ok that worked...well kinda. Now it starts but but my relays for the fuel pump and ASD keep clicking and it starts hard and doesn't idle. If I pump the gas it stays running long enough for me to drive it, then its fine. Could it be that I have fuel pump issues? This has got to be the weirdest car problem I have ever had.....
SteelHeadz
Super Moderator
Bench clean the t.body and IAC.
Hey everyone...well I found the problem. We were all wrong...well actually I didn't find the problem, a mechanic did. But he worked hard for it...apparently a wire from the PDC to the PCM was the cause of the problems. It had corroded to the point of only a couple strands were holding on, just enough to give the impression of a connection but when under load it was cutting off. A simple wire crimp did the job. Anyway thanks for your help and hopefully this will help someone else.
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