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No CEL

CbJeepy

NAXJA Forum User
Location
Central Texas
I’m new so feel free to redirect me as needed. My 96 XJ cranks fine but no 12vdc to fuel pump and no CEL with key on. I have checked all fuses and relays including ASD relay, every relay gets power with key and closes as they should. Measured fuel pressure at rail is 0psi. I only drive this about once a week and it parked fine. FYI, no mods, changes, water or rodents since I last drove it a week ago. Everything points to pcm. Any help would be appreciated. Thanks.
 
Try banging on the fuel tank with a block of wood or rubber mallet.
Sounds like the fuel pump is "stuck" in it's off position. Sometimes
the vibration of a good rap on the tank will start it going again...
 
Is your 1996 OBD-I or OBD-II ?

When you write "no CEL with key on" does that mean the CEL does not illuminate with the self test, or that it is not ON and there are no stored trouble codes ?


…... My 96 XJ cranks fine but no 12vdc to fuel pump and no CEL with key on. I have checked all fuses and relays including ASD relay, every relay gets power with key and closes as they should. Measured fuel pressure at rail is 0psi.

Jumper the relay and test the fuel pump and fuel pressure. As suggested, smack the tank if necessary. Cranking and not starting is almost always a faulty Crankshaft Position Sensor.
 
Unplug the CPS then see if the CEL lights up. If not unplug the cam position sensor and see if the CEL lights up.
 
The Jeep is obdll, no CEL with self test and no voltage to fuel pump electrical connection. I’ll jump fuel relay tonight and see what happens, the lack of CEL has me stumped. I’ll try to force a CEL by disconnecting the CPS. Thanks all.
 
You may need to jump the ASD relay also to verify for sure your getting power.
 
No CEL can be a symptom of a faulty sensor or a sensor wire harness issue. As suggested, one at a time unplug each OBD engine sensor, cycle the ignition, and look for the CEL. At the same time try to get your Trouble Codes scanner to connect.
 
I jumped the fuel relay and the pump primed the fuel rail to 50psi. I’ll dig back into the ASD and disconnect sensor/s to try and force a CEL this afternoon. I bought the Jeep years ago from the original owner, I don’t remember there ever being a security system but I may have to poke under the dash to confirm. My scanner won’t play nice with the jeeps pcm so I have a friend bringing his over. We’ll see what it can tell us. Thanks for all the help.
 
Back to the xj. Friends scanner won’t see ecm, disconnected CPS to try and force a CEL, nothing. Jeep cranks, all lights and accessories work, including dash gauges. I’m beginning to believe the ecm died in it’s sleep. My friend is strong in auto electrical and he’s stumped too. None of my manuals give a clear path for troubleshooting the ecm, is there a manual or guide you could recommend? Thanks all.
 
Are the injectors pulsing?
I had a similar issue and finally realized it was the pcm fuse. Also on a 96. I know you said you checked them, but I didn't notice this blown fuse on the first check either ..

Sent from my SM-G950U using Tapatalk
 
Back to the xj. Friends scanner won’t see ecm, disconnected CPS to try and force a CEL, nothing. Jeep cranks, all lights and accessories work, including dash gauges. I’m beginning to believe the ecm died in it’s sleep. My friend is strong in auto electrical and he’s stumped too. None of my manuals give a clear path for troubleshooting the ecm, is there a manual or guide you could recommend? Thanks all.

Crank Position sensor, cam position sensor, and speed sensor share a power supply. Not sure of the voltage for a 96 it changes year to year, likely 7 or 8 volts. If a sensor shorts or has too low of resistance the power supply shuts down. A typical symptom is no CEL, fuel pump at startup etc.

Unplug the cam position sensor and see what happens.

Or you can volt test the orange wire going to the crank position sensor or the cam position sensor. Very low voltage indicates a short someplace, most likely in a sensor.
 
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